Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
  • H01G9/20—Light-sensitive devices
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/50—Processes
  • C25B1/55—Photoelectrolysis
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M14/00—Electrochemical current or voltage generators not provided for in groups H01M6/00 - H01M12/00; Manufacture thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M14/00—Electrochemical current or voltage generators not provided for in groups H01M6/00 - H01M12/00; Manufacture thereof
  • H01M14/005—Photoelectrochemical storage cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S204/00—Chemistry: electrical and wave energy
  • Y10S204/03—Auxiliary internally generated electrical energy

Definitions

• a photochemical electrode will exhibit, in electrolyte, a potential difference relative to a reference electrode, this potential difference varying with the intensity and wavelength of illumination.
• light energy can be converted into electrical energy, for example by putting a photo ⁇ chemical electrode and an inert counterelectrode into electrolyte, making an electrical circuit between the electrodes, and illuminating the photochemical electrode while keeping the other dark.
• Known photochemical electrodes are usually either stable towards light, but responsive only to wavelengths in the ultra ⁇ violet, or responsive to visible light but decompose under its action.
• the ultraviolet-responsive type may be sensitized to visible light -by expedients such as adsorbed dyes, dopants or dissolved sensitizers, and the light-decomposable type may be protected by coating with metal or stable semiconductor or by adding redox couples which will compete with the decomposition reaction, but these efforts are troublesome.
• a photochemical electrode would thus be desirably stable towards visible light and photochemically responsive to it.
• the present invention is a photochemical electrode comprising a conductive member contacting initially-red mercuric sulphide, which need not be a single crystal.
• the member may be a mesh
• OMPI (which may be woven or expanded), for example of metal such as platinum or titanium or of carbon fibres, and the mercuric sulphide may form a coating on the member.
• the mercuric sulphide may be in some such form as a slurry or suspension or fluidised bed.
• the coating may be applied by dipping the conductive member (carrier) in a suspension of red mercuric sulphide and drying the conductive member in air (preferably blown hot air), and repeating the dipping and drying as necessary.
• the mercuric sulphide coated on the electrode may be pretreated by using the electrode in a reducing electrolyte until the mercuric sulphide is blackened; the electrode is then preferably washed clean of reductant.
• the atomic % of mercury in the blackened mercuric sulphide is preferably at least 48.9%.
• the blackening is preferably performed while irradiating the mercuric sulphide.
• the reductant is preferably from 0.05M to 1.0M.
• the duration of this pretreatment may be from ⁇ 0 to 2-0 minutes, preferably from 45 to l8 ⁇ minutes, more preferably up to 120 minutes, preferably at a potential in the reductant of within 0.2V of the standard calomel electrode.
• the reductant may be a halide (especially iodide) or thiocyanate for example.
• the invention in another aspect is converting visible light into electricity using the photochemical electrode set forth above, whereto no biassing potential need be applied.
• a cell comprising the photochemical electrode
• an inert counterelectrode and an electrolyte, such as aqueous sodium nitrate solution, optionally including a reducing agent, and allowing visible light to be absorbed by the mercuric sulphide, a circuit being provided connecting the photochemical electrode and the counterelectrode, in which circuit electricity flows depending on the light.
• an electrolyte such as aqueous sodium nitrate solution, optionally including a reducing agent
• Some reducing agents such as iodide ion may increase the photocurrent but may _lso solubilise the mercuric sulphide.
• This cell need not be driven by an applied potential, but it may be if desired.
• the invention in a further aspect is photoassisted electrolysis of water using the photochemical electrode set forth above, applying, between the photochemical electrode and a counterelectrode both in the same body of water, a biassing potential (which may be O.OV) less than the thermodynamic potential for electrolysing the water, allowing visible light to be absorbed by the mercuric sulphide, and collecting any product from the counterelectrode and/or • photochemical electrode.
• a biassing potential which may be O.OV
• biassing potential appears to be pH-dependent, and to depend on the duration of the blackening pretreatment. Where that was from 120 to 240 minutes, a O.OV bias can deliver good photocurrent.
• a preferred biassing potential vs. the standard calomel electrode for a reasonable rate of electrolysis is +0.2 to +1.0V, preferably +0.3 to +0.6V.
• Red (non-preblackened) mercuric sulphide in some circumstances goes black in use. In this form it still does not always dissolve and furthermore it absorbs longer wavelengths, which is advantageous. Red cinnabar from different sources can give rise to photopotentials of different magnitude. After blackening, however, all samples behave consistently.
• Figure 1 shows a cell including a photochemical electrode according to the invention
• Figure 2 is a circuit diagram of the cell of Figure 1. PREPARATION OF PHOTOCHEMICAL ELECTRODE
• Analytical grade red mercuric sulphide HgS (2g) is placed in 30 ml of de-oxygenated de-ionized water, which is boiled until the volume is 25 ⁇ - . thus ensuring a dispersed suspension of the mercuric sulphide. The suspension is further dispersed by an ultrasonic probe.
• a platinum mesh is taken. This mesh consists of a plain weave of 0.25* ⁇ * ⁇ diameter platinum wire at 0.7-*- centres .(Other weaves, such as twill and hollander, may also be used.) A rectangle of mesh 15mm x 30mm is mounted on a platinum strap - ⁇ _m x 15mm, the long direction of the strap being parallel to the shorter side of the rectangle and midway along the longer side. The strap has a 1mm diameter platinum wire about 6 ⁇ mm long for electrical connection purposes. - 5 - The mesh is swirled around the suspension, removed and dried in a blown hot air stream.
• the darkened material includes cinnabar, metacinnabar and unidentified material.
• the atomic % of mercury in the HgS was 50.0%, giving a reflectance at 700nm of 78%.
• iodide-treatment,of cinnabar we exploit the favourable features of reducing-agent-treatment, in this example iodide-treatment,of cinnabar.
• the electrode is used in an irradiated iodide (0.1- «f KI) electrolyte at O.OV with respect to a standard calomel electrode for 6 ⁇ minutes (until blackened), then removed and washed well with distilled water.
• the coated mesh which is the desired photochemical electrode, is conditioned by storing for at least 15 hours in de-oxygenated decimolar aqueous sodium nitrate.
• an experimental cell according to the invention for converting visible light into electricity, comprise an electrode 1 which is the photochemical electrode prepared as described above.
• the photochemical electrode 1 has, as already described, a platinum wire for electrical connection purposes, and this wire is connected to a brass screw 2, and the screw 2 to a lead 3 "to an external circuit.
• the electrode 1 is mounted in a (nominal quarter-litre) flask 6 closed by a tightly clamped lid 8.
• the flask 6 contains 250ml of decimolar aqueous sodium nitrate solution 9 which has been de-oxygenated and which, to keep it that way, is continuously purged with nitrogen which enters at a modest rate by an inlet 12.
• the sodium nitrate solution 9 is the electrolyte.
• the inlet 12 feeds to an 'air-stone' l4 arranged to deliver the nitrogen as streams of fine bubbles.
• a black plastics barrier plate l6 protects the photochemical electrode 1 from the bubbles. Nitrogen is vented from the flask 6 through an outlet l8 in the lid 8.
• a counter electrode 20 is mounted dipping into the solution 9 ⁇ similarly to the photochemical electrode 1, by way of a platinum wire connected to a brass screw 22 held, just as the screw 2, in the lid 8, and connected to a lead 23 to the external circuit.
• the counter electrode 20 is identical to the photochemical electrode 1, except that it is not coated with any mercuric sulphi
• a reference electrode 24 (a saturated calomel electrode) is mounted through the lid 8 dipping into the solution 9 and has a reference lead 26 for voltage measurement purposes. CONVERTING VISIBLE LIGHT INTO ELECTRICITY
• the cell just described is set on a bench with the photochemical electrode 1 to the right-hand side (for ease of description) of the black plate l6. Further to the right along the bench are a first lens 30a and a second lens 0b (lOcm and l ⁇ cm respectively from the photochemical electrode l), the lenses being convergent with focal lengths of 5cm and 13cm respectively and defining a light path directed on to the photochemical electrode 1.
• a glass tank 32 acts as a light filter, containing a 0.28M aqueous ' solution, held at 5 C, of cupric chloride CuCl offering a path length of 11cm to light
• the light filter tank ⁇ ⁇ transmits (maximum) 40% at 515 m and 3% a 400nm, and is kept cool by continuously circulating the contents through the pipes shown to a refrigerator.
• a high-impedance voltmeter V is connected across the photochemical and reference electrodes, and an ammeter A (or any circuit capable of doing useful work when> current flows in it) connects the photochemical and counter electrodes.
• the preferred pH of the electrolyte solution 9 is 2 to 13, as both at too low pH (such as 1. M nitric acid) and at too high pH (such as 2M potassium hydroxide), non-repeatable potentials are obtained, and also, even in the dark, the photochemical electrode 1 and the counter electrode 20 can pass a current through A of 200 microamps (positive or negative depending on whether acid or alkaline).
• too low pH such as 1. M nitric acid
• 2M potassium hydroxide such as 2M potassium hydroxide
• the cell of Figure 1 was now applied to the photoassisted electrolysis of water of pH 4.
• the potentiostat (P in Figure 2) was set so as to provide a potential difference between the photochemical electrode and the counterelectrode 20 of 0.6V. In the dark, almost nothing happened. With the xenon lamp ⁇ k on, after a period of time, bubbles began to be evolved at the counterelectrode 20, and are believed to be hydrogen.. This indicates that the water was being electrolysed.
• the thermodynamic potential for electrolysing the water under these conditions would have been 1.23V, which with overvoltage demands about 1.6V.
• a product might also be collectable from the photochemical electrode 1.
• the relative photocurrent under these conditions was 28 microamps.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Engineering & Computer Science (AREA)
• General Chemical & Material Sciences (AREA)
• Power Engineering (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Inorganic Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Hybrid Cells (AREA)
• Battery Electrode And Active Subsutance (AREA)

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• 1979
  • 1979-04-18 JP JP50063179A patent/JPS55500237A/ja active Pending
  • 1979-04-18 WO PCT/GB1979/000062 patent/WO1979000992A1/en unknown
  • 1979-04-18 DE DE7979900399T patent/DE2965090D1/de not_active Expired
  • 1979-04-26 AU AU46478/79A patent/AU524627B2/en not_active Ceased
  • 1979-12-04 EP EP79900399A patent/EP0015949B1/en not_active Expired
  • 1979-12-19 US US06/178,463 patent/US4305794A/en not_active Expired - Lifetime

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