Electrolytic cell equipped with microelectrodes

Abstract

The invention relates to an electrolytic cell equipped with microelectrodes for the generation of un-separated products and the method for obtaining it. The cell and the microelectrodes of the present invention are obtained using a technology for the production of microelectromechanical systems (MEMS). The anodic and cathodic microelectrodes have an electrocatalytic coating and are mutually intercalated at an interelectrodic gap lower than 300 micrometres.

Claims

1. Electrolytic cell for generation of oxidizing radical species consisting of: a lithographically patterned substrate consisting of a surface, a multiplicity of finger shaped anodic and cathodic microelectrodes embedded into said surface, said anodic and cathodic microelectrodes being mutually intercalated at an inter-anodic-cathodic gap lower than 100 micrometres and said anodic and cathodic microelectrodes having an average surface roughness R.sub.a lower than 0.05 μm, and an electrolytic solution, wherein the multiplicity of finger shaped anodic and cathodic microelectrodes embedded on said surface are boron-doped diamond, and wherein the electrolytic cell generates oxidizing radical species.

2. Electrolytic cell according to claim 1 wherein said average surface roughness R.sub.a of the anodic and cathodic microelectrodes is lower than 0.01 μm.

3. Electrolytic cell according to claim 1 wherein said lithographically-patternable substrate is made of a semiconductor material.

4. Electrolytic cell according to claim 1, wherein the boron-doped diamond contains at least 5000 ppm of boron doping.

5. Electrolytic cell for generation of oxidizing radical species consisting of: a lithographically patterned substrate consisting of an interdigitated surface; a multiplicity of finger shaped anodic and cathodic microelectrodes formed surrounding each digit of said interdigitated surface, said anodic and cathodic microelectrodes being mutually intercalated at an inter-anodic-cathodic gap lower than 100 micrometres and said anodic and cathodic microelectrodes having an average surface roughness R.sub.a lower than 0.05 μm, and an electrolytic solution, wherein the electrolytic cell generates oxidizing radical species.

6. Electrolytic cell according to claim 5, wherein said average surface roughness R.sub.a of the anodic and cathodic microelectrodes is lower than 0.01 μm.

7. Electrolytic cell according to claim 5, wherein at least said anodic microelectrodes comprise an external layer consisting of a vacuum-deposited boron-doped diamond film.

8. Electrolytic cell according to claim 5, wherein said microelectrodes comprise an external layer made of a material containing at least one element selected from the group consisting of Pt, Pd, Ir, Ru, Rh, Nb and Ti.

9. Electrolytic cell according to claim 5, wherein said lithographically-patternable substrate is made of a semiconductor material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a sectional view of a plurality of anodic and cathodic microelectrodes embedded in the same substrate according to an embodiment of the invention.

(2) FIG. 2 shows a top view of a plurality of anodic and cathodic microelectrodes embedded in the same lithographically-patterned substrate with interdigitated geometry and corresponding interelectrodic gaps according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(3) In FIG. 1 there is shown a sectional view of an embodiment of the invention which consists of a multiplicity of microelectrodes 1, which can be anodic microelectrodes and cathodic microelectrodes embedded in the same substrate lithographically-patterned with interdigitated geometry 2 at an interelectrodic gap 3. Anodic and cathodic microelectrodes 1 are deposited on the walls of fingers 4 which are formed as a result of the lithographic patterning. The area 5 that separates the anodic microelectrodes from the cathodic microelectrodes is suitably made of insulating material.

(4) In FIG. 2 there is shown a top view of an embodiment of the invention consisting of a multiplicity of microelectrodes 1 embedded in a lithographically-patterned substrate with interdigitated geometry at an interelectrodic gap 3.

(5) The following examples are included to demonstrate particular embodiments of the invention, whose practicability has been largely verified in the claimed range of values. It should be appreciated by those of skill in the art that the compositions and techniques disclosed in the examples which follow represent compositions and techniques discovered by the inventors to function well in the practice of the invention; however, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the scope of the invention.

EXAMPLE 1

(6) On a silicon wafer of circular shape having a diameter of 200 mm and a thickness of 2 mm and provided with a 1 μm thick SiO.sub.2 top layer, an interdigitated pattern was transferred via MEMS photolithography. The surface of the wafer was then subjected to etching with 30% KOH for 15 minutes at room temperature. On the wafer thus obtained, suitably provided with an insulating screen according to the selected microelectrode pattern, a layer of titanium was deposited by means of physical vapour deposition (PVD). Subsequently an electrocatalytic layer of platinum was deposited, again by physical vapour deposition, in two instances: a first deposition maintaining the main axis of the substrate (target) tilted 45 degrees from the plane, so as to deposit the electrocatalyst on a first face of the fingers patterned on the substrate, and a second instance maintaining the substrate tilted 45 degrees from the plane in the opposite direction so as to deposit the electrocatalyst on the second face of the patterned fingers. A post-production heat treatment of the microcell was carried out in argon-purged atmosphere at 500° C. for 1 hour with a 5° C./min temperature ramp. Other kinds of inert or reducing environments, such as a hydrogen-purged atmosphere, may be suitable for the heat treatment step. An interelectrodic gap of 100 micrometres and an average electrode surface roughness Ra of 0.01 μm were determined by laser techniques.

(7) In the cell thus obtained, tested with an aqueous solution of KOH at 60 ppm concentration, at a current density of 40 mA/cm.sup.2 and cell voltage of 5 V, a current efficiency for the production of ozone of 5% was measured.

EXAMPLE 2

(8) On a silicon wafer of circular shape having a diameter of 200 mm and a thickness of 2 mm and provided with a 1 μm thick SiO.sub.2 top layer, a boron-doped diamond film was grown directly on the SiO.sub.2 using microwave-assisted chemical vapour deposition (CVD) and laser etching resulting in approximately 6 μm thick electrodes with a boron doping level of 6000 ppm. An interelectrodic gap of 86 micrometres and an average electrode surface roughness Ra of 0.02 μm were determined by laser techniques.

(9) In the cell thus obtained, tested with an aqueous solution of KOH at 60 ppm concentration, at a current density of 40 mA/cm.sup.2 and cell voltage of 5 V, a current efficiency for the production of ozone of 4% was measured.

EXAMPLE 3

(10) The cell described in Example 2 was tested for electrochemical oxidant production and EOD (Electrochemical Oxygen Demand) treatment using a methyl orange solution in tap water at 5, 10 and 25° C.

(11) 125 ml of quiescent tap water containing 10.sup.−5 M methyl orange were treated at 9 kA/m.sup.2 for one hour. The UV absorption of the solution was measured before and after the treatment, showing an 80 to 85% reduction at the three temperatures. Besides the magnitude of the result, the fact that the efficiency of EOD treatment is not temperature-dependent in such conditions is surprising and indicates that the cell is not merely producing ozone. The tests were in fact repeated while measuring the rate of ozone production, which was several times higher at 5° C. as expected (about 1.2 mg/l vs. 0.2 at 25° C.). The above results indicate that an oxidant species more active than ozone is produced by the cell in these conditions, much likely a short-lived oxygen radical species, not detectable with available techniques.

(12) The previous description shall not be intended as limiting the invention, which may be used according to different embodiments without departing from the scopes thereof, and whose extent is solely defined by the appended claims.

(13) Throughout the description and claims of the present application, the term “comprise” and variations thereof such as “comprising” and “comprises” are not intended to exclude the presence of other elements, components or additional process steps.

(14) The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention before the priority date of each claim of this application.