METHOD OF FABRICATING A CATALYST ON A SUBSTRATE

Abstract

A method of fabricating a catalyst on a substrate comprising: providing a substrate having a layer of metal thereon; and contacting the layer of metal with a corrosive solution to form the catalyst.

Claims

1-75. (canceled)

76. A method of fabricating a catalyst on a substrate comprising: providing the substrate; applying a seed layer to the substrate; forming a layer of metal on the seed layer, the layer of metal comprising one or more metals selected from Ni, Mo, Co, Fe, Cu, Mn and Zn; and contacting the layer of metal with a corrosive metal halide solution to form the catalyst.

77. The method of claim 76, wherein the seed layer has a minimum thickness of approximately 50 nm.

78. The method of claim 76, wherein the seed layer has a thickness of approximately 100 nm.

79. The method of claim 76, wherein the seed layer comprises Ti and/or Ni.

80. The method of claim 79, wherein the seed layer comprises at least one of a layer of Ti and a layer of Ni.

81. The method of claim 76, wherein applying the seed layer to the substrate comprises depositing the seed layer by electron beam evaporation.

82. The method of claim 76, wherein applying the seed layer to the substrate comprises depositing the seed layer by thermal evaporation.

83. The method of claim 76, wherein applying the seed layer to the substrate comprises depositing the seed layer by sputter deposition.

84. The method of claim 76, wherein forming the layer of metal on the seed layer comprises electroplating the metal on the seed layer.

85. The method of claim 76, wherein the layer of metal has a thickness of 0.5 m to 10 m.

86. The method of claim 76, wherein the layer of metal is applied on the seed layer by electroplating the seed layer with a Ni(II) chloride solution as the electrolyte, to thereby form a layer of Ni on the seed layer.

87. The method claim 76, wherein the layer of metal comprises two or more metals.

88. The method of claim 76, wherein forming the layer of metal on the seed layer comprises applying a metal plate or foil on the seed layer.

89. The method of claim 76, wherein the substrate is an electrode.

90. The method of claim 76, wherein the substrate is a photovoltaic cell.

91. The method of claim 90, wherein substrate is a GaAs photovoltaic cell.

92. The method of claim 76, wherein the catalyst comprises one or more metal hydroxides.

93. The method of claim 76, wherein the corrosive metal halide solution is a transition metal halide solution.

94. The method of claim 93, wherein the corrosive metal halide solution comprises one or more transition metal chlorides.

95. The method of claim 94, wherein the corrosive metal halide solution comprises a mixture of Ni(II) and Fe(III) chlorides.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Embodiments will now be described by way of example only, with reference to the accompanying drawings in which:

[0081] FIG. 1 is a schematic diagram showing embodiments of the fabrication process disclosed herein.

[0082] FIG. 2 shows photographs of electroplated Ni on various substrates before and after the formation of NiFe LDH.

[0083] FIG. 3(a) is an EDS mapping image of a cross-section region of NiFe LDH formed on a Ni surface. Reference EDS mapping images of Ni, Fe and O are shown on the right.

[0084] FIG. 3(b)-(c) are SEM images of (b) Ni electroplated on a Si surface and (c) NiFe LDH formed on a Ni surface.

[0085] FIGS. 4(a)-(c) are graphs showing performance comparisons between Ni electroplated Si with and without NiFe LDH catalyst: (a) Forward LSV scans at 0.01 V/s and (b) EIS Nyquist spectra at 1.49 V vs RHE. (c) Chronopotentiometric results for NiFe LDH catalyst formed on Ni deposited on various substrates at 10 mA cm.sup.2.

[0086] FIGS. 4(d)-(e) Overpotential measurements of NiFe LDH: (d) at 10 and 50 mA cm.sup.2 deposited on various substrates and (e) at 10 mA cm.sup.2 after various deposition and etch times in 0.1 M HCl (Si substrate).

[0087] FIG. 5(a) is a schematic illustration of a GaAs PV-assisted photoanode with rear-deposited NiFe LDH.

[0088] FIG. 5(b)-(d) are graphs showing the current-voltage and the chronoamperometric characteristics of the photoanode of FIG. 4(a). (b) J-V curve of photoanode with respective Applied bias photon-to-current efficiency (ABPE) in 1.0 M KOH measured under AM 1.5 G 1 sun illumination, (c) Incident Photon-to-current Conversion efficiency (IPCE) of GaAs PV-assisted photoelectrode with NiFe LDH catalyst measured in relation to AM 1.5 G solar spectrum and (d) Chronoamperometric results at 1.3 V vs RHE.

DETAILED DESCRIPTION

[0089] In the following detailed description, reference is made to the accompanying drawings which form a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawings and defined in the claims, are not intended to be limiting. Other embodiments may be utilised and other changes may be made without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

[0090] The present disclosure provides a method of fabricating a catalyst on a variety of substrates and/or support materials. The method comprises the steps of (i) applying a layer of metal on the substrate to form a metalized substrate; and (ii) contacting the layer of metal to a corrosive solution to form a layer of the catalyst.

[0091] The method for fabricating a catalyst on a substrate will now be described by way of example and with reference to the figures.

[0092] According to the embodiment schematically shown in FIG. 1, the method includes applying a seed layer to the substrate prior to applying the layer of metal, such that the seed layer facilitates the adhesion of the layer of metal to the substrate.

[0093] In the described embodiment, the seed layer is deposited on one side of the substrate using electron beam evaporation. However, any other suitable deposition technique can be used. For example, in some embodiments the seed layer is applied by chemical bath deposition.

[0094] In the described embodiment, the composition of the seed layer includes Ti and Ni. In particular, the seed layer is composed by a 50 nm layer of Ti and a 50 nm layer of Ni. In the described embodiment, the layer of Ti is deposited on the substrate and the Ni layer is deposited on top of the Ti layer.

[0095] The seed layer improves or provides conductivity to the underlying substrate. Additionally, the Ti layer helps to improve the adhesion of the metal layer (in this case Ni layer) during the subsequent plating process.

[0096] However, the composition and the thickness of the seed layer can be selected as desired and tailored to the specific use of the catalyst in catalytic processes.

[0097] The substrate shown in FIG. 1 has an approximate geometric area of 1 cm.sup.2. However, the method is scalable and can be applied to much larger areas.

[0098] According to the described embodiment, after the deposition of the seed layer, a layer of metal is applied to the substrate by electroplating. It should be noted that the deposition of the seed layer is optional, and, in some embodiments, the layer of metal is applied directly on the substrate.

[0099] In the described embodiment, a layer of Ni is applied by electroplating. In particular, a Ni(II) chloride solution is used as the electrolyte to deposit the layer of Ni on the substrate.

[0100] The electrodeposition is performed at 20 mA/cm.sup.2 using a 0.36 M Ni(II) chloride solution.

[0101] Although not apparent from the schematic shown in FIG. 1, the thickness of the metal layer according to the described embodiment is approximately 2-3 micron. However, the thickness of the layer of metal can be tailored as desired and/or according to specific requirements of a catalyst reaction.

[0102] Referring to FIG. 1, after the Ni electroplating of the substrate, the layer of deposited metal is contacted with a corrosive solution by dipping the substrate in the corrosive solution. The corrosive reaction converts part of deposited metal into a catalytic material as described in more detailed below with reference to the described embodiment.

[0103] In the described embodiment, the substrate is dipped for 1 minute into a 15 mM solution mixture of Ni(II) and Fe(III) chloride at 1:1 molar ratio. The chloride ions in the solution initiate the corrosion process of the electroplated Ni layer to form NiFe double hydroxides at the film surface. The substrate is then dried at 70 C. for 1 hour.

EXAMPLE

[0104] Substrates made of different materials, including semiconductors (Si and GaAs), metals (Cu mesh, Cu plate, stainless steel) and a polymer (PET), were coated using the method described in FIG. 1. In particular, one side of the substrates (approximate geometric area: 1 cm.sup.2) was coated with a layer of Ti/Ni (50 nm/50 nm) using electron beam evaporation to function as a conductive seed layer.

[0105] The substrates were then electroplated at 20 mA/cm.sup.2 with Ni using 0.36 M Ni(II) chloride solution as the electrolyte.

[0106] After the Ni electroplating, the substrate was dipped for 1 minute into a 15 mM solution mixture of Ni(II) and Fe(III) chloride at 1:1 molar ratio. The chloride ions in the solution initiated the corrosion process of the electroplated Ni film thereby forming NiFe double hydroxides at the film surface.

[0107] The substrates were finally dried at 70 C. for 1 hour.

[0108] FIG. 2, shows photographs of Ni electroplated substrates before and after the formation of NiFe LDH. After the electroplating process, all the substrates showed uniform Ni film thickness across the substrate with good substrate-film adhesion. While the catalyst formation requires a degree of corrosion of the Ni film, the film integrity remains uncompromised by this process as shown in FIG. 3(a). FIG. 3(a) is an energy-dispersive spectroscopy (EDS) image of a cross-section region of a Ni electroplated substrate dipped in a solution mixture of Ni(II) and Fe(III) showing the NiFe LDH formed on a Ni surface. The EDS image shows a bottom layer (10-20 nm thick) comprised of Ni and a distinctive Fe/O layer (10-20 nm thick) on top of the Ni layer. The layer of Fe/O is indicative of the successful formation of the catalyst on the Ni surface through the corrosion process. As shown in FIG. 3(a) the layer of Fe/O does not permeate through the entire Ni metal layer, thereby safeguarding the integrity and the reusability thereof.

[0109] Once the chloride-solution dipping process is completed, it was possible to observe a visible change in the Ni film appearance in all substrates, whereby a brown rust-like appearance was noticed in contrast to the metallic grey appearance commonly seen in untreated Ni films.

[0110] The top-view scanning electron microscope (SEM) images in FIGS. 3(b) and (c) show a substantially corroded appearance on the previously pristine textured Ni film surface, indicating a thin catalyst layer formation on the surface.

[0111] Voltammetric measurements of a Ni-electroplated Si substrate with and without the catalyst were performed to determine the catalytic improvement provided by the NiFe LDH. In particular, the OER performance of the Ni-electroplated Si substrate with and without the catalyst, respectively, were compared by connecting the substrate as a working electrode in a three-electrode cell with Pt plate and Ag/AgCl as counter and reference electrodes, respectively, at 1.0 M KOH solution (pH 13). The linear sweep voltammetry (LSV) curves of electroplated Ni on Si with and without NiFe LDH (FIG. 4(a)) shows demonstrably lower overpotential at 10 mA cm.sup.2 (308 mV) when the bimetallic hydroxide catalyst is present as compared to the pure Ni layer (630 mV).

[0112] Additionally, according to the Nyquist plot obtained from the electrochemical impedance spectroscopy (EIS) of the Ni-electroplated Si substrate with and without the catalyst (FIG. 4(b)), the catalyst supporting Si substrate shows greater OER reaction kinetics than the untreated Ni electroplated Si due to lower charge transfer resistance.

[0113] In terms of stability, the NiFe LDH catalyst was able to sustain OER activity at 10 mA cm.sup.2 for 24 hours without any major deviation in overpotential required (FIG. 4(c)), with similar behaviour observed for Ni plated S-steel and GaAs substrates.

[0114] The OER performance test was extended to all the assessed substrates of FIG. 2(a) and showed relatively consistent overpotential values at 10 and 50 mA cm.sup.2 (FIG. 4(d)), thereby demonstrating that the catalyst performance is substrate agnostic.

[0115] To demonstrate the reusability of the layer of metal applied to the substrate for multiple catalyst regeneration processes, the NiFe LDH catalyst was removed from the catalyst supporting Si substrate by treating the substrate with an etchant (hydrochloric acid (HCl) 0.1 M) for 10 minutes. The cleaned metal surface was then dipped in the 15 mM solution mixture of Ni(II) and Fe(III) chloride using the same dipping conditions of the first dipping process. The etching-corrosion process is repeated for four times. The overpotential was measured after each cycle to monitor changes in the catalyst performance.

[0116] FIG. 3(e) shows the overpotential measurements of the NiFe LDH catalyst on Si substrate before and after multiple cycles of etching the catalyst in 0.1 M of hydrochloric acid (HCl) for 10 minutes followed by regeneration of NiFe LDH using the same dipping conditions as the first dipping process. After each of the subsequent four etch-corrosion cycles, the catalyst performance remained relatively similar with no noticeable deterioration in performance. This demonstrates that the layer of Ni deposited on a substrate may be reused multiple times to form a layer of catalyst without the need of applying a fresh layer of metal on the substrate each time.

[0117] The method according to the present disclosure can also be used to stabilize catalysts for III-V semiconductor-based photoelectrode devices. III-V semiconductors exhibit good efficiency in (photovoltaic) PV and water splitting cells, but they can be sensitive to photo-corrosion in harsh electrolyte environments.

[0118] As schematically shown in FIG. 5(a), a commercial single-junction GaAs PV cell was electroplated with Ni at the rear contacts and dipped in the corrosive solution to form the catalyst layer as described above.

[0119] As shown in FIG. 5(b), at AM 1.5 G 1 sun illumination, the photoanode device achieved a saturated photocurrent density of approximately 27 mA/cm.sup.2 (FIG. 5(b)), which is within the expected range for single junction GaAs PV cells. The device also exhibited a good photo-response throughout the measured potential range based on the generated photocurrent under illumination as compared to that in dark conditions. From the obtained JV curve, the ABPE was calculated to be approximately 11.7% at 0.52 V vs RHE (see FIG. 5(b)) which is an excellent ABPE value for the photoanode. Additionally, about 80% incident photon-to-current efficiency (IPCE) was achieved for this photoelectrode design in the spectral region of 500-800 nm (FIG. 5(c)). This demonstrates an overall good conversion efficiency of the photoelectrode, with some losses expected due to the absorbance and reflection by the encapsulating glass at the irradiation area of the PV cell. The stability of the photoanode device was assessed at the onset potential of saturated photocurrent density (1.3 V vs RHE), in which the device performance is sustained for 100 hours (FIG. 5(d)).

[0120] The experimental results discussed above and illustrated in the accompanying Figures demonstrate that the method according to the present disclosure can be used to construct and stabilise semiconductor electrodes for solar water splitting, achieving record levels of photoanode efficiency.

[0121] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

[0122] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word comprise or variations such as comprises or comprising is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.