CATALYTIC NANOMATERIAL, ITS PREPARATION AND USE IN APROTIC ALKALI METAL-GAS BATTERIES
20250293269 ยท 2025-09-18
Inventors
Cpc classification
H01M12/08
ELECTRICITY
International classification
H01M12/08
ELECTRICITY
Abstract
A catalytic nanomaterial includes a Janus hollow nanostructure of a heterophase noble metal and a heterophase non-precious metal. The method for synthesizing the catalytic nanomaterial and the use of the catalytic nanomaterial are also addressed.
Claims
1. A catalytic nanomaterial comprising a Janus hollow nanostructure of a heterophase noble metal and a heterophase non-precious metal.
2. The catalytic nanomaterial as claimed in claim 1, wherein the Janus hollow nanostructure includes a tubular structure with one or more protrusions.
3. The catalytic nanomaterial as claimed in claim 2, wherein the tubular structure and the protrusion each being a formation of the heterophase noble metal and the heterophase non-precious metal.
4. The catalytic nanomaterial as claimed in claim 3, wherein the protrusion includes a heterophase non-precious metal section deposited on a heterophase noble metal section.
5. The catalytic nanomaterial as claimed in claim 3, wherein the tubular structure includes a heterophase noble metal tubular formation with scattered heterophase non-precious metal crystal formations.
6. The catalytic nanomaterial as claimed in claim 3, wherein the protrusion axially extends from the tubular structure.
7. The catalytic nanomaterial as claimed in claim 4, wherein an interface is defined between the heterophase non-precious metal section and the heterophase noble metal section.
8. The catalytic nanomaterial as claimed in claim 5, wherein the heterophase noble metal tubular formation is porous.
9. The catalytic nanomaterial as claimed in claim 1, wherein the heterophase noble metal comprises a 4H/fcc noble metal and the heterophase non-precious metal comprises a 4H/fcc non-precious metal.
10. The catalytic nanomaterial as claimed in claim 1, wherein the heterophase noble metal is selected from the group consisting of Ru, Rh, Ir, Pd, and Pt.
11. The catalytic nanomaterial as claimed in claim 1, wherein the heterophase non-precious metal is selected from the group consisting of Ni, Co, Fe, and Zn.
12. The catalytic nanomaterial as claimed in claim 9, wherein the heterophase noble metal comprises 4H/fcc Ru and the heterophase non-precious metal comprises 4H/fcc Ni.
13. The catalytic nanomaterial as claimed in claim 2, wherein the tubular structure is a porous 4H/fcc Ru nanotube scattered with 4H/fcc Ni crystals and the one or more protrusions are dendritic structures axially protruding from the nanotube.
14. The catalytic nanomaterial as claimed in claim 13, wherein the 4H/fcc Ni crystals are epitaxially deposited on the porous 4H/fcc Ru nanotube.
15. The catalytic nanomaterial as claimed in claim 13, wherein the heterophase non-precious metal section comprises epitaxial deposition of 4H/fcc Ni crystals on the heterophase noble metal section of 4H/fcc Ru, thereby defining a RuNi interface.
16. The catalytic nanomaterial as claimed in claim 13, wherein the porous 4H/fcc Ru nanotube comprises a wall formed with a plurality of nanoholes.
17. The catalytic nanomaterial as claimed in claim 13, wherein Ru and Ni have an atomic ratio of about 72.5:27.5.
18. The catalytic nanomaterial as claimed in claim 13 is in powder form.
19. The catalytic nanomaterial as claimed in claim 13, wherein the 4H/fcc Ru provides a carbon dioxide reduction reaction active site and the 4H/fcc Ni provides a carbon dioxide evolution reaction active site, thereby acting as a bifunctional catalyst.
20. A method for synthesizing the catalytic nanomaterial as claimed in claim 1, comprising the steps of: epitaxially growing a 4H/fcc noble metal on a 4H/fcc Au nanorod; selectively etching the 4H/fcc Au nanorod to obtain a hollow 4H/fcc noble metal nanotube with a plurality of dendritic structures; quasi-epitaxially growing a 4H/fcc non-precious metal on the hollow 4H/fcc noble metal nanotube to obtain a Janus hollow nanostructure of the 4H/fcc noble metal and the 4H/fcc non-precious metal.
21. The method as claimed in claim 20, wherein the noble metal is selected from the group consisting of Ru, Rh, Ir, Pd, and Pt, and the non-precious metal is selected from the group consisting of Ni, Co, Fe, and Zn.
22. The method as claimed in claim 20, wherein the noble metal is Ru and the non-precious metal is Ni.
23. The method as claimed in claim 22, comprising the steps of: epitaxially growing 4H/fcc Ru on the 4H/fcc Au nanorod in the presence of 1, 2-hexadecanediol and oleylamine under heat treatment; selectively etching the 4H/fcc Au nanorod in a solution mixture of 0.1 M CuCl.sub.2 and DMF under heat treatment to obtain a hollow 4H/fcc Ru nanotube with a plurality of 4H/fcc Ru dendritic structures; quasi-epitaxially growing 4H/fcc Ni on the hollow 4H/fcc Ru nanotube with a plurality of 4H/fcc Ru dendritic structures in the presence of 1,2-hexadecanediol and oleylamine under heat treatment to obtain a 4H/fcc RuNi Janus hollow nanostructure.
24. An aprotic alkali metal-gas battery comprising the catalytic nanomaterial as claimed in claim 1, wherein the battery is selected from the group consisting of aprotic LiCO.sub.2 battery, aprotic Li-air battery, aprotic NaCO.sub.2 battery, aprotic Na-air battery, aprotic KCO.sub.2 battery and aprotic K-air battery.
25. The aprotic alkali metal-gas battery as claimed in claim 24 comprising a cathode having the catalytic nanomaterial, the cathode being positioned in an aprotic electrolyte along with an alkali metal anode.
26. The aprotic alkali metal-gas battery as claimed in claim 25 wherein the battery is selected from the group consisting of an aprotic LiCO.sub.2 battery and an aprotic Li-air battery.
27. The aprotic alkali metal-gas battery as claimed in claim 26 comprising: a Li-based aprotic electrolyte; a Li metal anode; a cathode including a 4H/fcc RuNi Janus hollow nanostructure including a heterophase noble metal comprising 4H/fcc Ru and a heterophase non-precious metal comprising 4H/fcc Ni; and a separator disposed between the Li metal anode and the cathode.
28. The aprotic alkali metal-gas battery as claimed in claim 27, wherein the Li-based aprotic electrolyte includes a DMSO solution of a Li salt, and an ionic liquid.
29. The aprotic alkali metal-gas battery as claimed in claim 28, wherein the Li salt is selected from the group consisting of lithium hexafluorophosphate (LiPF.sub.6), lithium perchlorate (LiClO.sub.4), lithium nitrate (LiNO.sub.3), lithium tetrafluoroborate (LiBF.sub.4), lithium bistrifluoromethane sulfonimide (LiTFSI), lithium difluorosulfonimide (LiFSI), lithium triflate (LiCF.sub.3SO.sub.3) and a combination thereof.
30. The aprotic alkali metal-gas battery as claimed in claim 28, wherein the Li salt has a concentration of about 0.1 M to about 4 M.
31. The aprotic alkali metal-gas battery as claimed in claim 28, wherein the ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazole tetrafluoroborate ([Emim]BF.sub.4), 1-ethyl-3-methylimidazole bistrifluoromethosulfonimide ([Emim]TFSI), 1-ethyl-3-methylimidazole difluorosulfonimide ([Emim]FSI), 1-Ethyl-3-methylimidazolium chloride ([Emim]Cl) and a combination thereof.
32. The aprotic alkali metal-gas battery as claimed in claim 28, wherein the Li-based aprotic electrolyte includes about 5% to about 50% by volume of the ionic liquid.
33. The aprotic alkali metal-gas battery as claimed in claim 27, wherein the cathode further includes a conductive carbon material and a binder.
34. The aprotic alkali metal-gas battery as claimed in claim 33, wherein the conductive carbon material is selected from the group consisting of graphene, carbon nanotubes (CNTs), carbon blacks, carbon paper, carbon cloth and a combination thereof.
35. The aprotic alkali metal-gas battery as claimed in claim 33, wherein the binder includes Nafion.
36. The aprotic alkali metal-gas battery as claimed in claim 33, wherein the cathode has a weight ratio of 4H/fcc RuNi Janus hollow nanostructure:conductive carbon material:binder of about 2.7:0.9:0.4.
37. The aprotic alkali metal-gas battery as claimed in claim 33, wherein the cathode has a mass loading of a mixture of the 4H/fcc RuNi Janus hollow nanostructure and the conductive carbon material of about 0.2 mg cm.sup.3 to about 0.3 mg cm.sup.3.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0042] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
[0043] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:
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DETAILED DESCRIPTION OF OPTIONAL EMBODIMENT
[0210] As used herein, the forms a, an, and the are intended to include the singular and plural forms unless the context clearly indicates otherwise.
[0211] The words example or exemplary used in this invention are intended to serve as an example, instance, or illustration. Any aspect or design described in this disclosure as exemplary is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the words example or exemplary is intended to present concepts in a concrete fashion. As used in this application, the term or is intended to mean an inclusive or rather than an exclusive or. That is, unless specified otherwise or clear from context, X employs A or B is intended to mean any of the natural inclusive permutations. That is, if X employs A, X employs B, or X employs both A and B, then X employs A or B is satisfied under any of the foregoing instances.
[0212] As used herein, the phrase about is intended to refer to a value that is slightly deviated from the value stated herein. Examples have been described throughout the present disclosure.
[0213] One of the possible solutions to mitigate the aforementioned shortcomings suffered by the current alkali metal-gas batteries such as LiCO.sub.2 and LiO.sub.2/air batteries might be using appropriate redox mediators dissolved in electrolytes. Another possible solution might be using carbon materials such as super P, Ketjen blacks, carbon nanotubes (CNTs) and graphenes as cathode catalysts. However, it is believed that these materials may suffer from low catalytic activities, leading to high charge potential (usually >4.2 V) which enables the decomposition of Li.sub.2CO.sub.3 even at low current densities. There are also some reports on hybridizing the carbon materials with metals/alloys such as Ru, Ir, Ni, Fe, Co, Cu, RuCo, RuRh, etc., and/or metal compounds such as Mo.sub.2C, VN, IrO.sub.2, etc. to promote the reaction kinetics and reversibility of LiCO.sub.2 electrochemistry.
[0214] Without wishing to be bound by theory, the inventors have, through their own researches, trials, and experiments, devised that the kinetics and reversibility of carbon redox reactions (carbon reduction reaction (CO.sub.2RR) and carbon dioxide evolution reaction (CO.sub.2ER)) of the alkali metal-gas batteries may be enhanced/catalyzed by an unconventional heterophase metal-metal Janus nanostructure, particularly an unconventional 4H/face centered cubic (fcc) noble metal-non-precious metal (also known as base metal) Janus nanostructure. As illustrated in the present disclosure, the unconventional 4H/fcc noble metal-non-precious metal Janus nanostructure may act as a bifunctional cathode catalyst to facilitate the reversibility and decomposition kinetics of discharge products in, for example, aprotic LiCO.sub.2 and Li-air batteries. It is believed that the noble metal of the Janus nanostructure may act as electrophilic sites for CO.sub.2RR and at the same time the non-precious metal of the Janus nanostructure may act as nucleophilic sites for CO.sub.2ER. In other words, the Janus nanostructure may include different sites for CO.sub.2RR and CO.sub.2ER (i.e., decoupled CO.sub.2RR and CO.sub.2ER sites). It is also believed that the unconventional 4H/fcc noble metal-non-precious metal Janus nanostructure may be capable of reducing the leakage of corrosive .sup.1O.sub.2 and O.sub.2.sup..Math. species upon charging at high rates. Accordingly, as illustrated in some example embodiments of the present disclosure, the aprotic LiCO.sub.2 and Li-air batteries with cathode containing the unconventional 4H/fcc noble metal-non-precious metal Janus nanostructure may have a high-rate discharge-charge electrochemical behavior, ultra-small minimum overpotential gap of, e.g., 0.65 V, and long-term cycling stability of at least 150 cycles at least 250 mA g.sup.1.
[0215] In a first aspect of the present invention, there is provided a catalytic nanomaterial comprising a Janus hollow nanostructure of a heterophase noble metal and a heterophase non-precious metal. The catalytic nanomaterial in accordance with various embodiments of the present invention may have a Janus nanostructure as exemplified in
[0216] In some embodiments, the tubular structure 108 may include a heterophase noble metal tubular formation 112 with scattered heterophase non-precious metal crystal formations 114. In particular, the heterophase noble metal tubular formation may include a wall formed with one or more pores/holes, particularly nanopores/nanoholes 116. In other words, the heterophase noble metal tubular formation may be porous.
[0217] The one or more protrusions 110 may axially extend from the tubular structure. In particular, the one or more protrusions may include a heterophase non-precious metal section 118 deposited on a heterophase noble metal section 120, thereby defining an interface 122 between the heterophase non-precious metal section and the heterophase noble metal section.
[0218] In some embodiments, the heterophase noble metal may comprise a 4H/face centered cubic (fcc) noble metal and the heterophase non-precious metal comprises a 4H/fcc non-precious metal. In some particular embodiments, the heterophase noble metal may be selected from the group consisting of Ru, Rh, Ir, Pd, and Pt. In some particular embodiments, the heterophase non-precious metal may be selected from the group consisting of Ni, Co, Fe, and Zn.
[0219] In an exemplary embodiment, the heterophase noble metal may comprise 4H/fcc Ru and the heterophase non-precious metal may comprise 4H/fcc Ni. Referring to
[0220] The porous 4H/fcc Ru nanotube 112 may have a diameter ranging from about 20 nm to about 40 nm, such as 18 nm . . . 18.2 nm . . . 18.6 nm . . . 20.1 nm . . . 22 nm . . . 22.8 nm . . . 23 nm . . . 26 nm . . . 26.4 nm . . . 27 nm . . . 31 nm . . . 35 nm . . . 38 nm . . . 40 nm . . . 40.5 nm . . . 41 nm . . . 42 nm and the like. The nanotube wall of the porous 4H/fcc Ru nanotube may be of about 2 nm thick such as about 1.7 nm, 1.75 nm, 1.8 nm, 1.82 nm, 1.86 nm, 1.9 nm, 1.99 nm, 2 nm, 2.01 nm, 2.1 nm and the like.
[0221] The dendritic structures may have an average diameter from about 8 nm to about 10 nm, such as 7 nm . . . 7.5 nm . . . 7.8 nm . . . 8 nm . . . 8.3 nm . . . 8.7 nm . . . 9 nm . . . 9.6 nm . . . 10 nm . . . 10.2 nm . . . 10.4 nm . . . 11 nm and the like.
[0222] The atomic ratio of the heterophase noble metal and the heterophase non-precious metal may be tunable in various embodiments of the present invention. In this exemplary embodiment, the Ru and Ni may have an atomic ratio of about 72.5:27.5, such as 72:27.3, 72:27.4, 72.4:27.4, 72.5:27.5, 72.6:27.6 and the like.
[0223] The catalytic nanomaterial 100 is preferably to be in powder form. It is believed that with such a physical form, it may be beneficial for the preparation of flexible cathode.
[0224] Without wishing to be bound by theory, it is believed that the 4H/fcc Ru may provide a carbon dioxide reduction reaction (CO.sub.2RR) active site and the 4H/fcc Ni may provide a carbon dioxide evolution reaction (CO.sub.2ER) active site, thereby the catalytic nanomaterial 100 may act as a bifunctional catalyst. In particular, it is believed that the unusual 4H phases of Ru/Ni may effectively lower the energy barriers and promote the intermediate steps of CO.sub.2 redox reactions. It is also believed that the co-existence of these decoupled CO.sub.2RR/CO.sub.2ER sites (i.e., CO.sub.2RR and CO.sub.2ER do not occur on the same metal site but on different sites) may facilitate the reduction of the release of corrosive oxygen species generated during the operation of alkali metal-gas batteries. Thus, it is believed that the catalytic nanomaterial may enable fast recharging, high energy efficiency and long cycle life of the alkali metal-gas batteries. Accordingly, it is believed that the catalytic nanomaterial is particularly suitable for cathodic application in alkali metal-gas batteries.
[0225] The method for synthesizing the catalytic nanomaterial as described herein will now be disclosed.
[0226] The method may comprise the steps of: epitaxially growing a 4H/fcc noble metal on a 4H/fcc Au nanorod; selectively etching the 4H/fcc Au nanorod to obtain a hollow 4H/fcc noble metal nanotube with a plurality of dendritic structures; and quasi-epitaxially growing a 4H/fcc non-precious metal on the hollow 4H/fcc noble metal nanotube to obtain a Janus hollow nanostructure of the 4H/fcc noble metal and the 4H/fcc non-precious metal.
[0227] The epitaxial growing step may include the steps of providing a first reaction mixture containing 4H/fcc Au nanorod, a noble metal precursor, a reductant, and a surfactant; optionally carrying out a first heat treatment to remove low-boiling impurities from the first reaction mixture; and carrying out a second heat treatment for the epitaxial growth of the 4H/fcc noble metal on a 4H/fcc Au nanorod to obtain a 4H/fcc Au@noble metal nanorod.
[0228] The noble metal precursor may be in form of a coordination compound of the noble metal. Examples of coordination ligands for the noble metal may include halides, sulfate, carbonyl, ammine, oxalate, acetate, formate, phosphine, diamine, cyclopentadienyl, arenes, etc.
[0229] The reductant may be selected from the group consisting of 1,2-hexadecanediol and 1,4-butanediol. In some particular embodiments, the reductant may be 1,2-hexadecanediol. The surfactant may be selected from the group consisting of oleylamine and hexadecylamine. In some particular embodiments, the surfactant may be oleylamine.
[0230] The first heat treatment may be carried out under reduced pressure such as under vacuum at a temperature from about 100 C. to about 120 C., about 95 C. to about 120 C., about 98 C. to about 125 C., about 98 C. to about 118 C., about 105 C. to about 120 C., about 105 C. to about 115 C., particularly at about 110 C. In some embodiments, the first heat treatment may be carried out for from about 20 mins to about 30 mins, about 18 mins to about 30 mins, about 20 mins to about 28 mins, about 22 mins to about 30 mins, about 22 mins to about 28 mins, particularly for about 25 mins.
[0231] The second heat treatment may be carried out under an inert atmosphere such as under argon or nitrogen, at a temperature from about 215 C. to about 230 C., about 215 C. to about 232 C., about 213 C. to about 230 C., about 218 C. to about 230 C., about 218 C. to about 228 C., about 220 C. to about 230 C., about 222 C. to about 228 C. particularly at about 225 CC.
[0232] After the second heat treatment, the 4H/fcc Au@noble metal nanorod may be isolated from the first reaction mixture by way of, for example centrifugation and/or washing with a suitable solvent or solvent mixture.
[0233] The selective etching step may be carried out by heat treating a second reaction mixture containing the 4H/fcc Au@noble metal nanorod and an etching agent such as CuCl.sub.2 at a temperature from about 70 C. to about 100 C., about 72 C. to about 100 C., about 70 C. to about 98 C., about 75 C. to about 90 C., about 70 C. to about 90 C., about 75 C. to about 85 C., particularly at about 80 C., for at least 24 hours such as for about 36 hours. After that a hollow 4H/fcc noble metal nanotube with a plurality of dendritic structures may be obtained and may be isolated from the second reaction mixture by way of, for example centrifugation and/or washing with a suitable solvent or solvent mixture.
[0234] The quasi-epitaxial growing step may be similar to the epitaxial growing step as described herein. In particular, the quasi-epitaxial growing step may include the steps of providing a third reaction mixture containing the hollow 4H/fcc noble metal nanotube, a non-precious metal precursor, a reductant such as 1,2-hexadecanediol, a surfactant such as oleylamine, and a capping agent-releasing compound such as Mo(CO).sub.6, W(CO).sub.6, Cr(CO).sub.6 and the like for releasing CO as capping agent; optionally carrying out a third heat treatment to remove low-boiling impurities from the third reaction mixture; and carrying out a fourth heat treatment for the quasi-epitaxial growth of the 4H/fcc non-precious metal on the hollow 4H/fcc noble metal nanotube to obtain the Janus hollow nanostructure of the 4H/fcc noble metal and the 4H/fcc non-precious metal (i.e., 4H/fcc noble metal-non-precious metal Janus hollow nanostructure).
[0235] The non-precious metal precursor may be in form of a coordination compound of the non-precious metal. Examples of coordination ligands for the non-precious metal may include halides, sulfate, carbonyl, ammine, oxalate, acetate, formate, phosphine, diamine, cyclopentadienyl, arenes, etc.
[0236] The capping agent-releasing compound may be dissolved and in solution form in the third reaction mixture. It is appreciated that the capping agent-releasing compound will remain (chemically) stable during the third heat treatment, and will only decompose to release the capping agent (e.g., CO) during the fourth heat treatment.
[0237] The third heat treatment may be carried out under reduced pressure such as under vacuum at a temperature from about 70 C. to about 100 C., about 72 C. to about 100 C., about 70 C. to about 98 C., about 75 C. to about 90 C., about 70 C. to about 90 C., about 75 C. to about 85 C., particularly at about 80 C. In some embodiments, the third heat treatment may be carried out for from about 20 mins to about 30 mins, about 18 mins to about 30 mins, about 20 mins to about 28 mins, about 22 mins to about 30 mins, about 22 mins to about 28 mins, particularly for about 25 mins.
[0238] The fourth heat treatment may be carried out under an inert atmosphere such as under argon or nitrogen, at a temperature from about 140 C. to about 180 C., about 138 C. to about 180 C., about 140 C. to about 182 C., about 143 C. to about 178 C., about 145 C. to about 180 C., about 148 C. to about 170 C., about 150 C. to about 170 C., about 155 C. to about 180 C., about 155 C. to about 168 C., particularly at about 160 C., for at least 10 mins, such as for 15 mins.
[0239] After the fourth heat treatment, the 4H/fcc noble metal-non-precious metal Janus hollow nanostructure may be isolated from the third reaction mixture by way of, for example centrifugation and/or washing with a suitable solvent or solvent mixture.
[0240] As described herein, in some embodiments, the noble metal may be selected from the group consisting of Ru, Rh, Ir, Pd, and Pt, and the non-precious metal may be selected from the group consisting of Ni, Co, Fe, and Zn.
[0241] In an exemplary embodiment, the noble metal may be Ru and the non-precious metal may be Ni. In this embodiment, the method may be used to preparing the 4H/fcc RuNi Janus hollow nanostructure as described herein. The method may comprise the steps of: epitaxially growing 4H/fcc Ru on the 4H/fcc Au nanorod in the presence of 1, 2-hexadecanediol and oleylamine under heat treatment; selectively etching the 4H/fcc Au nanorod in a solution mixture of 0.1 M CuCl.sub.2 and DMF under heat treatment to obtain a hollow 4H/fcc Ru nanotube with a plurality of 4H/fcc Ru dendritic structures; and quasi-epitaxially growing 4H/fcc Ni on the hollow 4H/fcc Ru nanotube with a plurality of 4H/fcc Ru dendritic structures in the presence of 1, 2-hexadecanediol and oleylamine under heat treatment to obtain the 4H/fcc RuNi Janus hollow nanostructure.
[0242] Also pertain to the present invention is an aprotic alkali metal-gas battery comprising the catalytic nanomaterial as described herein, wherein the battery is selected from the group consisting of aprotic LiCO.sub.2 battery, aprotic Li-air battery, aprotic NaCO.sub.2 battery, aprotic Na-air battery, aprotic KCO.sub.2 battery and aprotic K-air battery.
[0243] In some embodiments, the aprotic alkali metal-gas battery may comprise a cathode having the catalytic nanomaterial as described herein, and the cathode may be positioned in an aprotic electrolyte along with an alkali metal anode.
[0244] The cathode may further include a conductive carbon material and a binder. In some embodiments, the conductive carbon material may be selected from the group consisting of graphene, carbon nanotubes (CNTs), carbon blacks, carbon paper, carbon cloth and a combination thereof. In some particular embodiments, the cathode may further include a support selected from the group consisting of carbon paper, carbon cloth and a combination thereof.
[0245] The binder may include Nafion. It is appreciated that any other suitable binder may be used in accordance with practical needs.
[0246] In some embodiments, the cathode may have a weight ratio of the catalytic nanomaterial:conductive carbon material:binder may be of about 50-90:10-30:1-20, such as about 2.7:0.9:0.4. In some embodiments, the cathode may also have a mass loading of a mixture of the catalytic nanomaterial and the conductive carbon material of about 0.2 mg cm.sup.3 to about 0.3 mg cm.sup.3.
[0247] The alkali metal anode may vary in accordance with practical needs. For example, it is appreciated that a Li metal anode will be used in a Li-gas battery, a Na metal anode will be used in a Na-gas battery, a K metal anode will be used in a K-gas battery, etc. It is also appreciated that the alkali metal anode may be of various shapes and/or dimensions in accordance with practical needs. For example, the alkali metal anode may be in form of a foil, a plate, a rod, a disk, etc.
[0248] The aprotic electrolyte may include an alkali metal salt and an ionic liquid. In particular, the alkali metal salt may vary in accordance with practical needs. For example, a Li salt may be used in a Li-gas battery, a Na salt may be used in a Na-gas battery, a K salt may be used in a K-gas battery and the like. The alkali metal salt may include any one of the following anions: hexafluorophosphate, perchlorate, nitrate, tetrafluoroborate, bistrifluoromethane sulfonimide, difluorosulfonimide, and triflate.
[0249] In some embodiments where the aprotic alkali metal-gas battery is a Li-gas battery, the alkali metal salt may be a Li salt selected from the group consisting of lithium hexafluorophosphate (LiPF.sub.6), lithium perchlorate (LiClO.sub.4), lithium nitrate (LiNO.sub.3), lithium tetrafluoroborate (LiBF.sub.4), lithium bistrifluoromethane sulfonimide (LiTFSI), lithium difluorosulfonimide (LiFSI), lithium triflate (LiCF.sub.3SO.sub.3) and a combination thereof.
[0250] In some embodiments where the aprotic alkali metal-gas battery is a Na-gas battery, the alkali metal salt may be a Na salt selected from the group consisting of sodium hexafluorophosphate (NaPF.sub.6), sodium perchlorate (NaClO.sub.4), sodium nitrate (NaNO.sub.3), sodium tetrafluoroborate (NaBF.sub.4), sodium bistrifluoromethane sulfonimide (NaTFSI), sodium difluorosulfonimide (NaFSI), sodium triflate (NaCF.sub.3SO.sub.3) and a combination thereof.
[0251] In some embodiments where the aprotic alkali metal-gas battery is a K-gas battery, the alkali metal salt may be a K salt selected from the group consisting of potassium hexafluorophosphate (KPF.sub.6), potassium perchlorate (KClO.sub.4), potassium nitrate (KNO.sub.3), potassium tetrafluoroborate (KBF.sub.4), potassium bistrifluoromethane sulfonimide (KTFSI), potassium difluorosulfonimide (KFSI), potassium triflate (KCF.sub.3SO.sub.3) and a combination thereof.
[0252] The alkali metal salt may have a concentration of about 0.1 M to about 4 M, such as 0.1 M . . . 0.12 M . . . 0.2 M . . . 0.35 M . . . 0.4 M . . . 1 M . . . 1.1 M . . . 1.5 M . . . 2 M . . . 2.6 M . . . 3 M . . . 3.3 M . . . 4 M and the like. In some particular embodiments, the alkali metal salt may have a concentration of about 3 M.
[0253] The ionic liquid may be an imidazolium-based such as a 1-ethyl-3-methylimidazolium-based ionic liquid. In some embodiments, the ionic liquid may be selected from the group consisting of 1-ethyl-3-methylimidazole tetrafluoroborate ([Emim]BF.sub.4), 1-ethyl-3-methylimidazole bistrifluoromethosulfonimide ([Emim]TFSI), 1-ethyl-3-methylimidazole difluorosulfonimide ([Emim]FSI), 1-Ethyl-3-methylimidazolium chloride ([Emim]Cl) and a combination thereof.
[0254] In some embodiments, the aprotic electrolyte may include about 5% to about 50%, about 4.5% to about 50%, about 5% to about 51%, about 5% to about 50.5%, about 8% to about 49%, about 10% to about 50%, about 5% to about 45%, about 15% to about 45%, about 20% to about 50%, about 20% to about 35%, about 20% to about 30%, particularly about 25% by volume of the ionic liquid.
[0255] In some exemplary embodiments, the aprotic alkali metal-gas battery may be an aprotic LiCO.sub.2 battery or an aprotic Li-air battery. In these embodiments, these batteries may share a substantially the same configuration, except that each of these batteries is operated under different gaseous environments, i.e., CO.sub.2 for the aprotic LiCO.sub.2 battery whereas ambient air or compressed air for the aprotic Li-air battery. The aprotic LiCO.sub.2 or the protic Li-air battery may comprise a Li-based aprotic electrolyte; a Li metal anode such as a Li metal foil; a cathode including the 4H/fcc RuNi Janus hollow nanostructure as described herein; and a separator such as a glass fiber disposed between the Li metal anode and the cathode.
[0256] In particular, the Li-based aprotic electrolyte may include a DMSO solution of a Li salt as described herein, and about 5% to about 50% by volume, such as about 25% by volume of an ionic liquid as described herein.
[0257] The cathode of the aprotic LiCO.sub.2 or the aprotic Li-air battery may further include a conductive carbon material as described herein and a binder as described herein. In particular, the cathode may have a weight ratio of 4H/fcc RuNi Janus hollow nanostructure:conductive carbon material:binder of about 2.7:0.9:0.4. The cathode may also have a mass loading of a mixture of the 4H/fcc RuNi Janus hollow nanostructure and the conductive carbon material of about 0.2 mg cm.sup.3 to about 0.3 mg cm.sup.3.
[0258] As mentioned, the catalytic nanomaterial may act as a bifunctional catalyst to facilitate the reversibility and decomposition kinetics of discharge products in aprotic alkali metal-gas batteries such as LiCO.sub.2 and Li-air batteries. Thus, it is believed that the aprotic alkali metal-gas batteries as described herein may exhibit a higher-rate discharge-charge electrochemical behavior, ultra-small minimum overpotential gap, and long-term cycling stability as discussed in the later part of the present disclosure.
[0259] Hereinafter, the present invention is described more specifically by way of examples, but the present invention is not limited thereto.
EXAMPLES
Materials
[0260] Gold(III) chloride hydrate (HAuCl.sub.4.Math.xH.sub.2O, 52% Au basis), triruthenium dodecacarbonyl (Ru.sub.3(CO).sub.12, AR), ruthenium acetylacetonate (Ru(acac).sub.3, ACS reagent, 99.0%), nickel formate dihydrate (Ni(HCOO).sub.2.Math.2H.sub.2O, 99.0%), copper chloride dihydrate (CuCl.sub.2.Math.2H.sub.2O, 99.0%), 1,2-hexadecanediol (1,2-HDD, AR), ascorbic acid (L-AA, 99.0%), n-heptane (anhydrous, 99%), oleylamine (OAm, 70%, technical grade), N-ethylcyclohexylamine (AR, 99.9%), n-hexane (anhydrous, 99.5%), ethanol (99.9%), Nafion solution (5%), lithium bis-trifluoromethanesulfonimide (LiTFSI, ACS reagent, 99.0%), dimethylsulfoxide (DMSO, anhydrous, 99.0%), 1-ethyl-3-methylimidazole tetrafluoroborate ([Emim]BF.sub.4, 99% for electrochemistry), N, N-dimethylformamide (DMF, anhydrous, 99.0%) and the other chemicals without special mention were purchased from Sigma-Aldrich. Carbon paper (Toray TGP-H-060) and multi-walled carbon nanotubes (CNTs) were purchased from Fuel Cell Earth. Ultrapure Milli-Q water (Milli-Q System, Millipore) was used in the experiments. All the chemicals were used as received without any further purification.
Characterization
[0261] XRD measurements were conducted on a Rigaku SmartLab SE X-ray diffractometer using Cu K.sub. radiation at a wavelength of 1.5406 . SEM and EDS data were acquired by a Thermo Fisher Scientific (TFS) Quattro S scanning electron microscope operated at 15 kV. TEM images and EELS results were collected on a field emission JEM-2100F (JEOL, Japan) operated at 200 kV. The HAADF-STEM images and EDS elemental mapping were obtained on a double aberration-corrected Spectra 300 TEM/STEM (TFS, USA) operated at 300 kV and equipped with a Super-X EDS spectrometer (TFS, USA). Raman spectra were recorded on the LabRAM HR Raman spectrometer with laser excitation at 514.5 nm from an Ar ion laser source. XPS analysis was based on a ESCALAB 220i-XL electron spectrometer from VG Scientific using 300 W Al KR radiation (base pressure <10.sup.5 mbar). The detection of .sup.1O.sub.2 in electrolyte was carried out using the nuclear magnetic resonance spectroscopy (NMR 300 MHz, Bruker AVANCE III BBO Probe). The XAS data were collected in total fluorescence mode, which was conducted at beamline 12B of Taiwan beamline at Spring-8 of National Synchrotron Radiation Research Center (NSRRC). The electron storage ring was operated at 8.0 GeV with a constant current of 400 mA. The incident beam energy was monochromatized by a Si(111) double crystal monochromator..sup.[6] The XAS-related data processing was conducted using Athena and Artemis software packages.
Electrochemical Measurements
[0262] The electrochemical performance of LiCO.sub.2 batteries was evaluated using CR2032 coin-type cells with several holes on the cathode side to allow CO.sub.2 permeation. A slice of Toray carbon paper (H-060) coated with the obtained metal catalysts was used as the cathode, while a piece of commercial lithium chip acted as the counter and reference electrodes. The glass fiber (Whatman, GF/D) was used as the separator. The electrolyte is 3 M LiTFSI dissolved in DMSO added with 25%.sub.vol. EmimBF.sub.4. Note that 120 L of the electrolyte were utilized in every LiCO.sub.2 cell. The assembly of LiCO.sub.2 battery cells was conducted in an Ar-filled glove box with the H.sub.2O and O.sub.2 concentrations less than 1 ppm. The assembled LiCO.sub.2 batteries were tested in a dried and sealed chamber which was pumped with pure CO.sub.2 gas at 80 sccm for at least 15 min to ensure the gas purity inside. To ensure the sufficient diffusion of CO.sub.2, it required a rest period of 18 h for stabilization before tests.
[0263] Cyclic voltammetry (CV) measurement was conducted on the electrochemical workstation (Ivium-n-Stat, Netherlands) at a scan rate of 0.2 mV s.sup.1 over the potential window of 2.0-4.5 V (vs. Li.sup.+/Li). The galvanostatic discharge/charge measurements of these LiCO.sub.2 batteries were carried out on the electrochemical workstation (LAND CT2001 ) under different experimental parameters at room temperature.
[0264] The Li-air cells were assembled and measured along the same process with that of LiCO.sub.2 cells except for replacing CO.sub.2 gas with commercial compressed air to fill the test chambers.
[0265] When conducting long-term cycling stability tests for Li-air batteries, Li anodes protected by artificial solid electrolyte interface (SEI) layers were utilized rather than fresh Li disks to assemble the cells. The artificial SEI layers on Li anodes were generated after the LiCO.sub.2 cells with CNT cathodes operated at 500 mA g.sup.1 and 500 mAh g.sup.1 for 10 cycles.
[0266] In-situ differential electrochemical mass spectrometry (DEMS) test for gas evolution was performed on a Linglu DEMS analysis system, where the coin-type cells using nanometal cathodes with the mass loading of 1 mg were firstly discharged at 250 A for 4 h in the commercial gas containers filled with CO.sub.2 and then transferred into the Swagelok cells for recharging at 250 A with an Ar carrier gas flow of 0.8 sccm. By monitoring the changes of O.sub.2, CO and CO.sub.2 concentrations, the corresponding gas evolution rates can be obtained.
[0267] To detect the release of .sup.1O.sub.2 from discharge products when charging, 30 mM DMA and 3 M LiTFSI dissolved in DMSO added with 25%.sub.vol. EmimBF.sub.4 was utilized as the electrolyte to assemble coin-type cells with different catalytic cathodes. After cycles, the coin-type cells were disassembled in glove box, of which the battery components were washed carefully by DMSO-d.sub.6. The obtained solutions were then subjected to .sup.1H NMR characterizations.
DFT Calculations
[0268] To obtain the geometric structures of 4H solid phase of Ru and Ni, the structure prediction was performed using Crystal Structure Analysis by Particle Swarm Optimization (CALYPSO). Based on the analysis of more than 3000 structural phases generated, the common 2H Ru, unusual 4H Ru and 4H Ni modes were found. The mainly-exposed (004) and (110) surfaces of 4H Ru/Ni nanodendrites were established. For comparison, the thermodynamically abundant (002) surface of traditional 2H Ru was considered in the simulations. All the computational simulations were performed on basis of DFT calculations with plane-wave technique which is implemented in the Vienna ab initio simulation package (VASP). Gradient corrected exchange-correlation functional of Perdew, Burke, and Emzerhof (PBE) models was used under the projector augmented wave (PAW) method, with a cut-off kinetic energy of 500 eV for plane wave basis. The convergence criterion of the total energy was set up to be within 110.sup.5 eV, while all the atoms and geometries were optimized until the residual forces became less than 110.sup.2 eV/. For 4H Ru and 4H Ni crystals, these optimized energetically most favourable structures after the full geometry relaxation were implemented within a K-point 993 grid.
[0269] For the adsorption energy simulations, the DFT-D3 method with Beck-Jonson damping was used to include the physical Van der Waals interaction. For all the surface-related calculations including the adsorption/dissociation of atoms and molecules on Ru/Ni (004).sub.4H, (110).sub.4H and (002).sub.2H surfaces, they were carried out within a K-point 221 grid. In the vertical direction, a vacuum layer of 15 thick was introduced for all of the surfaces. The adsorption energy of various discharge products and intermediates was defined as E.sub.ads=E.sub.T(E.sub.A+E.sub.S), where E.sub.A and E.sub.S represent the energy of the specified atoms or molecules and the pristine system, respectively, and E.sub.T is the total energy of the corresponding system with specified atoms or molecules adsorbed.
Example 1
Synthesis of Unusual 4H/fcc Au Nanorods
[0270] The unusual 4H/fcc Au nanorods were synthesized by a modified wet-chemical synthetic strategy. Firstly, 15 mg of HAuCl.sub.4.Math.xH.sub.2O were added into 10 mL of the mixture of OAm and n-heptane with a volume ratio of 1/1, followed by a short sonication for several seconds to get a homogenous transparent solution. After 1000 L of N-ethylcyclohexylamine were dropped into the aforementioned solution, the obtained solution was rapidly transferred into a 20 mL glass vial. Then the glass bottle containing the growth solution was put in an oil bath and kept at 68 C. for 48 h. Thereafter, the suspension was taken out from the reaction bottle, washed with n-hexane and centrifuged at 4000 rpm for several times until the supernatant liquid became colourless. The obtained unusual 4H/fcc Au nanorods were redispersed into 2 mL of toluene for further use.
Example 2
Synthesis of Unconventional 4H/fcc Ru Dendrites on Au Template
[0271] 4H/fcc Au nanorods were used as hard templates for the epitaxial growth of 4H/fcc Ru dendrites. Specifically, 4 mL of 4H/fcc Au stock solution, 3 mg of Ru.sub.3(CO).sub.12, 50 mg of 1,2-HDD and 10 mL of OAm were successively added into a 25 mL two-neck flask. After that, the flask was connected with the double-bank pipe system for sealing. Before reaction, the mixed solution was stirred under vacuum at 110 C. for 25 min to remove the low-boiling impurities. Next, the flask was purged with nitrogen and heated to 225 C. rapidly under the protection of nitrogen. The solution was kept for 15 min at 225 C. under stirring for the epitaxial growth of 4H/fcc Ru dendrites on Au seeds. When the flask cooled down to room temperature, all the mixed solution was taken out and then added with 20 mL of n-hexane. The sediments were collected by centrifugation at 4000 rpm for 3 min and the supernatant liquid was discarded. The obtained precipitates were washed and purified with 10 mL of pure n-hexane for several times until the supernatant liquid became colourless (centrifugation at 4000 rpm for 1 min every time). The final products were 4H/fcc Au@Ru nanorods.
Example 3
Synthesis of Hollow 4H/fcc Ru Nanotubes
[0272] The hollow 4H/fcc Ru nanotubes are prepared by selective etching the Au templates. Specifically, the obtained 4H/fcc Au@Ru nanorods were successively washed with the mixtures of chloroform/DMF (v/v=1/1) once, chloroform/DMF (v/v=1/2) twice, and pure DMF once, and then redispersed in 2 mL of DMF. The obtained slurry was transferred into a 20 mL glass bottle, after which 2 mL of 0.1 M CuCl.sub.2-DMF solution and 10 mL of pure DMF were added into the bottle. Thereafter, the bottle was sealed and sonicated for 5 min, followed by heat-treatment at 80 C. for 36 h under stirring. After that, the mixed solution was centrifuged at 10000 rpm for 10 min to collect the sediments, which were then washed with the mixture of n-hexane/ethanol (v/v=1/1) for three times. The obtained 4H/fcc Ru hollow nanotubes were redispersed in 2 mL of toluene for further use.
Example 4
Synthesis of 4H/fcc RuNi Heteronanostructures
[0273] The 4H/fcc RuNi heteronanostructures are prepared by an orientated growth of 4H/fcc Ni dendrites on 4H/fcc Ru. Specifically, 4 mL of 4H/fcc Ru stock solution, 1 mL of Ni(HCOO).sub.2 solution (1 mg mL.sup.1, in OAm), 50 mg of 1,2-HDD, 20 mg of Mo(CO).sub.6 and 9 mL of OAm were successively added into a 25 mL two-neck flask, which was then connected with the double-bank pipe system for sealing. The solution was stirred under vacuum at 80 C. for 25 min to remove the low-boiling impurities. Next, the flask was purged with nitrogen and heated to 160 C. slowly and then kept for 15 min without stirring under the protection of nitrogen. After the reaction, the mixed solution was taken out and then added with 5 mL of n-hexane and 25 mL of ethanol. The products were collected by centrifugation at 10000 rpm for 10 min. After washing with 10 mL of pure degassed ethanol for several times, 4H/fcc RuNi heteronanostructures were obtained.
Example 5
Synthesis of the Comparative 2H Ru Nanosheets
[0274] The 2H Ru nanosheets are synthesized for comparative studies. The synthesis of the 2H Ru nanosheets involves a one-pot synthesis process. Specifically, 2 mg of Ru(acac).sub.3 were firstly dissolved in 2 mL of the mixture of benzyl alcohol/OAm (v/v=3/1) through sonication for 30 min. The obtained dark red solution was added into a 4 mL glass bottle, which was then transferred into a sealed 30 mL autoclave for solvothermal growth. After heating at 200 C. for 12 h, the obtained solution was centrifuged at 10000 rpm for 10 min to collect the sediments. A mixture of n-hexane/ethanol (v/v=1/1) was utilized to wash the products for several times. Finally, the obtained black sediments are traditional 2H Ru nanosheets.
Example 6
Preparation of Working Electrodes
[0275] Before the preparation of cathode electrodes, all of the as-synthesized metal nanomaterials were mixed with commercial CNT powders at a weight ratio of 3/1. After that, the obtained active material mixtures were redispersed in 15 mL of degassed ethanol added with 8 mg of L-AA and stirred overnight at 80 C. to remove the surface ligands. The pre-treated catalysts were collected by centrifugation, washed with ethanol for several times, and then dried at 50 C. in vacuum oven. Next, the obtained catalysts were directly mixed with Nafion (5% wt. in ethanol) at a weight ratio of 9/1. A proper amount of isopropanol was utilized as the solvent to make a homogenous slurry through sonication. The obtained catalyst ink was dropped onto the carbon paper (Toray, H060) disks slowly and homogenously. After dried at 30 C. in vacuum oven over 48 h, the cathode electrodes corresponding to the different Ru/Ni nanostructures were obtained for further use. Without specified or otherwise, the mass loading of active materials was controlled at 0.2 to 0.3 mg per cathode.
Example 7
Design of the Catalysts
[0276] First-principle calculations was used in the design of the catalysts of the present invention. Five representative noble metals including Ru, Ir, Pd, Pt and Rh, coupled with four non-precious metals including Fe, Co, Ni and Zn, and taking Li.sub.2CO.sub.3+C and Li.sub.2C.sub.2O.sub.4 as the two types of discharge products of LiCO.sub.2 batteries, are studied.
[0277] Given that nucleophilic and electrophilic sites are both necessary to stimulate LiCO.sub.2 electrochemistry, the interactions between proposed metals and reactants/products were firstly investigated, with the calculation results shown in
[0278] It is observed that noble metals exhibit stronger adsorption energies of Li (E.sub.ads(Li)) and CO.sub.2 (E.sub.ads(CO.sub.2)) than non-precious metals, on average. Thus, it is believed that noble metals would be more preferable to play as the CO.sub.2RR sites. Besides the better wettability towards Li, the significant difference is observed at CO.sub.2 capture evaluation where the E.sub.ads(CO.sub.2) for Ru (0.32 eV) and Pt (0.24 eV) outperform the others. In view of the higher difficulty on enhancing electrophilicity, it is believed that Ru may be a better choice to enrich reactants on catalyst surface. Meanwhile, Ru demonstrates the best wettability towards Li.sub.2CO.sub.3 (E.sub.ads(Li.sub.2CO.sub.3)=2.85 eV), C (E.sub.ads(C)=0.08 eV) and Li.sub.2C.sub.2O.sub.4 (E.sub.ads(Li.sub.2CO.sub.3)=3.39 eV) among all the considered metals, suggesting that it is also beneficial for the uniform nucleation and distribution of discharge products (
[0279] On the contrary, CO.sub.2ER is a process related to the electrochemical degradation of Li.sub.2CO.sub.3 and the release of Li and CO.sub.2. Therefore, ideal CO.sub.2ER centers should have weak affinity towards Li and CO.sub.2, but a moderate adsorption towards Li.sub.2CO.sub.3 is necessary to ensure good interfacial contacts with discharge products to catalyze its decomposition. Compared to noble metals, non-precious metals have such features according to the calculation results (
[0280] Furthermore, from the viewpoint of kinetics, a climbing-image nudged elastic band (CI-NEB) method was used to simulate the dynamic degradation processes of Li.sub.2CO.sub.3 and Li.sub.2C.sub.2O.sub.4. The CO.sub.2 evolution process from discharge products mainly involves two steps: the fracture of the weakest LiO bond (Stage I) and the delithiation of the generated Li ion (Stage II). Because the crystallinity difference between these two species (commonly seen in practical cases) is not considered here for simulations, these two degradation processes should be analyzed individually. From
[0281] After selecting Ru and Ni as the components of desirable dual-site electrocatalysts, the CO.sub.2RR and CO.sub.2ER behaviors on the thermodynamically stable and metastable Ru/Ni crystals were simulated for designing the phase of the electrocatalyst. 2H, unconventional fcc and 4H phases were selected for Ru, and usual fcc and unconventional 4H phases were selected for Ni. The commonly exposed (002) facet for 2H phase, (111) facet for fcc phase and (004)/(110) facets for 4H phase are considered. Due to the lack of systematic understanding on 4H phases, phonon spectra were simulated to check the dynamic stability of 4H Ni and 4H Ru crystals obtained by CALYPSO. The lack of imaginary frequency certificates that both of them possess good dynamical stability theoretically (
[0282] For the CO.sub.2RR side, the wettability of different Ru/Ni crystal phases towards reactive materials and possible discharge products was investigated. As shown in
[0283] Five representative unconventional and common Ru/Ni facets were picked out to explore the possible CO.sub.2RR pathways. In general, it is believed that 4H Ru/Ni crystals demonstrate better wettability towards key intermediates of LiCO.sub.2 electrochemistry when compared with 2H Ru (
[0284] Simultaneously, the introduction of 4H Ni crystal is in favor of metal-oxygen couplings between the metal catalysts and the detected discharge products, according to the partial electronic density of states (PDOS) displayed in
(i.e., Li ions may be firstly seized by (004) surfaces of 4H Ru/Ni crystals and then quickly immigrate to their (110) surfaces (CO.sub.2-rich regions) to participate in the subsequent CO.sub.2 electroreduction process. Similarly, an inverse order of delithiation and Li.sup.+ migration happens on the corresponding surfaces to proceed with CO.sub.2 evolution when charging).
[0285] Based on the above, it is believed that these simulation results highlight the significance of RuNi dual sites and unconventional 4H phases in promoting the round-trip CO.sub.2RR and CO.sub.2ER kinetics. Combining with the desired feature of high atomic utilization efficiency for catalysts towards aprotic metal-gas electrochemistry, a hollow and ultrathin RuNi heteronanostructures with unconventional 4H phases as efficient bifunctional catalysts for LiCO.sub.2 batteries is thus designed.
Example 8
Synthesis and Characterization of the Catalyst
[0286] It is believed that it may be difficult to avoid the formation of concomitant fcc domains during practical preparation of 4H phases, the synthesized hollow and ultrathin RuNi heteronanostructures thus adopted a 4H/fcc heterophase (denoted as 4H/fcc RuNi).
[0287] Transmission electron microscopy (TEM) and aberration-corrected high-angle annular dark-field scanning TEM (HAADF-STEM) show that the as-synthesized 4H/fcc RuNi exist as hollow nanotubes, of which the majority possesses a diameter ranging from 20 to 40 nm (
[0288] Importantly, the corresponding fast Fourier transform (FFT) patterns reveal the formation of 4H phases in both Ru and Ni regions (
[0289] The energy dispersive X-ray spectroscopy (EDS) result elucidates the Ru/Ni atomic ratio of 72.5/27.5 in the 4H/fcc RuNi heteronanostructures (
[0290] The chemical state and coordination environment of 4H/fcc RuNi heteronanostructures were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). In the high-resolution Ru 3p XPS spectra (
[0291] The above results are well consistent with subsequent XAS analysis. The Ru K-edge X-ray absorption near-edge structure (XANES) of 4H/fcc RuNi, 4H/fcc Ru and 2H Ru shows the near-edge absorption energy approaching Ru foil rather than RuO.sub.2, but 4H/fcc RuNi exhibits a white line position at the slightly lower energy region than 4H/fcc Ru (
[0292] Based on the corresponding Fourier transformed (FT) k.sup.2-weighted extended X-ray absorption fine structure (EXAFS) spectra (
Example 9
Electrochemical Performance of the Catalyst in Aprotic LiCO.SUB.2 .Battery/Cell
[0293] Without specified or otherwise, all the aprotic LiCO.sub.2 cells in this work were assembled using coin-type rather than Swagelok configuration. Benefitting from the high atomic utilization efficiency of 4H/fcc RuNi, all the applied current densities and capacities were normalized to the total weight of metal nanostructures and carbon nanotube (CNT) additives (i.e., mA g.sup.1.sub.metal+CNT, mAh g.sup.1.sub.metal+CNT) loaded on cathodes. Before measurements, it was confirmed that there is negligible capacity contribution by Li intercalation and pseudo-capacitance (
[0294] Galvanostatic discharge was first applied to evaluate the electrochemical performances of as-assembled aprotic LiCO.sub.2 cells. Upon fully discharged to 2 V, 4H/fcc RuNi delivers a large specific capacity of 17360.1 mAh g.sup.1 at 50 mA g.sup.1, which is about 2.94, 1.84 and 2.30 times those of 4H/fcc Ru, 2H Ru and bare CNT, respectively (
[0295] Subsequently, rate capability measurements were conducted to unravel the electroactivity of as-synthesized Ru-based catalysts at various rates. From
[0296] Benefitting from the lower energy barriers of CO.sub.2RR and CO.sub.2ER, 4H/fcc RuNi demonstrates an ultrasmall discharge-charge voltage difference of 0.65 V at 50 mA g.sup.1, while this value for common 2H Ru is as high as 1.13 V at the same conditions and its voltage polarization is much more rapid with cycles (
[0297] As a reflection of the aforementioned favorable indexes, the LiCO.sub.2 cells with 4H/fcc RuNi exhibit a small decline on energy efficiency from 80.0% at 50 mA g.sup.1 to 63.1% at 500 mA g.sup.1, surpassing all the other cells with bare Ru nanostructures and commercial CNTs (
[0298] It is believed that long-term cycling stability is an important indicator to assess the reversibility of LiCO.sub.2 electrochemistry. As shown in
[0299] Failure analysis reveals that the lithium anode corrosion (attacked by CO.sub.2 and free electrolyte solvent) would be the main factor resulting in the battery collapse (
[0300] Based on the above, it is believed that the unconventional phase metal-metal heteronanostructures of the present invention is able to boost the redox reaction kinetics of LiCO.sub.2 batteries.
Example 10
Analysis of the Discharge Products from the Aprotic LiCO.sub.2 Battery/Cell
[0301] Discharge product analysis was conducted to reveal the mechanism differences of LiCO.sub.2 electrochemistry modulated by unconventional 4H/fcc RuNi and common 2H Ru nanostructures. Different from the clean surface of fresh electrodes (
[0302] TEM and selected-area electron diffraction (SAED) characterizations indicate that amorphous and low-crystalline Li.sub.2CO.sub.3/carbon agglomerates associated with Li.sub.2C.sub.2O.sub.4 constitute the discharge products (
[0303] The properties of discharge products at different discharge depths at 500 mA g.sup.1 were examined. After the cells were discharged to 500 mAh g.sup.1, discharge products on 4H/fcc RuNi cathodes exist as waved gels anchored with submicron-sized islands (
[0304] According to the Raman and XRD results (
[0305] The in-situ Raman was utilized to investigate the product evolution on 4H/fcc RuNi cathodes with a larger mass loading during cycling at 500 mA g.sup.1 within 1000 mAh g.sup.1, in light of the absence of signals in above ex-situ characterizations for standard cathodes (
[0306] For comparison, the Li.sub.2CO.sub.3 signal, a characteristic peak at 1085 cm.sup.1 (marked by R1), shows a weak intensity variation. It means that the LiCO.sub.2 electrochemistry happening on 4H/fcc RuNi cathode does not only depend on usual Li.sub.2CO.sub.3+C as the main discharge products within the initial high-rate discharge stage, which is in good agreement with the predictions by DFT calculations. This is further evident by XPS analysis. From the high-resolution C is spectra in
[0307] When further exploring the chemical states of metal elements, it reveals a lower proportion of zero-valent Ni at the discharged state than that at the recharged state (
[0308] The morphology evolution of 4H/fcc RuNi cathodes has been further checked at the 30.sup.th and 60.sup.th cycle (
[0309] To further understand the underlying CO.sub.2ER mechanisms, in-situ differential electrochemical mass spectrometry (DEMS) measurements during charging were carried out. At the present stage, it is believed that there are three possible decomposition ways of discharge products when charging. It is believed that the completely reversible oxidation is the most ideal pathway via equation (1), but there are reports suggesting that that the synergistic degradation of Li.sub.2CO.sub.3C mixture seems not to be an elementary reaction with proper stoichiometric numbers.
It is believed that a multiple-step process composed of the preliminary decomposition of Li.sub.2CO.sub.3 should be involved, via electrochemical reactions of equation (2) and equation (3) and the following oxidation of concomitant C into CO and CO.sub.2 by singlet oxygen (.sup.1O.sub.2) or superoxide radicals (O.sub.2.sup..Math.) via spontaneous chemical reactions of equation (4) (Note that it is an illustration rather than a stoichiometric reaction).
[0310] When cells are operated at high rates, it is believed that O.sub.2.sup..Math. and .sup.1O.sub.2 easily overflow from discharge products and attack carbon additives/electrolyte, leading to rapid collapse or even sudden death of batteries. Nevertheless, if discharge behavior can be tuned towards the Li.sub.2C.sub.2O.sub.4 path, there are not similar concerns, because the Li.sub.2C.sub.2O.sub.4 decomposition occurs at a lower overpotential and only produces moderate species via equation (5).
[0311] From
[0312] The overall charge-to-mass ratios are calculated to be 1.43 e.sup./CO.sub.2 for 4H/fcc RuNi and 2.01 e.sup./CO.sub.2 for 2H Ru, implying that more efficient CO.sub.2 evolution is electrochemically driven by 4H/fcc RuNi cathodes. Besides, there is less .sup.1O.sub.2 leakage into the electrolyte of the cells with 4H/fcc RuNi compared to the one with 2H Ru, according to the results of NMR tests using 9,10-dimethylanthracene (DMA) as the molecular trap (
Example 11
Electrochemical Performance of the Catalyst in Aprotic Li-Air Battery/Cell
[0313] The capability of bifunctionality of the 4H/fcc RuNi in Li-air batteries was also investigated. Li-air batteries were therefore assembled to check whether it is able to facilitate LiO.sub.2 electrochemistry in real air atmosphere with CO.sub.2 and moisture as the main contaminations.
[0314] When the current density increases to 500 mA g.sup.1, 4H/fcc RuNi can still deliver a high discharge plateau of 2.61 V, resulting in a low voltage gap of 1.47 V. In sharp contrast, the voltage gap for 2H Ru is as large as 2.13 V (
Example 12
Application of the Catalyst in Flexible Aprotic Li-Air Battery/Cell
[0315] To demonstrate the application potentials, flexible Li-air pouch cells have been constructed using carbon cloth-supported 4H/fcc RuNi as the flexible cathodes. According to the start-up powers of electronics, flexible Li-air pouch cells can be easily fabricated at appropriate mass loadings of catalysts. Here, a mini-type Li-air pouch loaded with ca. 1 mg of active materials is able to run a desk lamp toy (
[0316] The invention has been given by way of example only, and various other modifications of and/or alterations to the described embodiment may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.