Showing papers on "Photoelectrolysis published in 1984"

The characterization of doped iron oxide electrodes for the photodissociation of water: stability, optical, and electronic properties

Abstract: A characterization of optical and electronic properties is presented for p-type (Mg-doped) and n-type (Si-doped) iron oxides used in the photoelectrolysis of water. Photocurrent vs. wavelength spectra for these electrodes indicate that ..cap alpha..-Fe/sub 2/O/sub 3/ is the active optical component for both p-type and n-type materials. Band-edge locations for p-type and n-type iron oxides in sodium hydroxide aqueous solution are determined from differential capacitance measurements. The thermodynamic feasibility of the catalytic photodissociation of water without external potential is demonstrated for a short-circuited p/n diode assembly on an energy level diagram of the electrode/electrolyte interfaces. The open-circuit voltage (V/sub oc/) and short-circuit current (I/sub sc/) generated by the p/n assembly as a function of the intensity of laser irradiation indicate that these doped iron oxides are low mobility, high carrier density semiconductors. Photo-oxidation of water at the n-type anode is verified through oxygen detection. Gas evolution is monitored from an operating diode assembly using mass spectrometry and isotopically labeled water (H/sub 2//sup 18/O). Photocurrent from these p/n assemblies show excellent long-term stability in aqueous solution and Auger analysis of the semiconductor surfaces indicates no evidence of electrode dissolution.

The generation of hydrogen peroxide during water photoelectrolysis at n-titanium dioxide

Abstract: The rotating ring-disk electrode (RRDE) technique has been used to investigate the photoproduction of H/sub 2/O during water photoelectrolysis on n-TiO/sub 2/. In spite of the fact that hydrogen peroxide is a real intermediate product of water photoelectrolysis, it cannot be detected at the ring electrode under different working conditions of illumination intensity and disk potential. Part of the photogenerated H/sub 2/O/sub 2/ is believed to be photooxidized before diffusing away from the electrode. Probably a very small amount of H/sub 2/O/sub 2/, which is under the detection limit of the RRDE technique, is able to dissolve into the electrolyte. Mechanisms describing O/sub 2/ evolution via the photogeneration of H/sub 2/O/sub 2/, which are consistent with the observed RRDE results, are postulated.

On the generation of H2O2 during water photoelectrolysis at n-TiO2

Abstract: Utilisation de la methode de l'electrode a disque et anneau tournant pour etudier la photoproduction de H 2 O 2 au cours de la photoelectrolyse de l'eau sur TiO 2 -n

Hydrogen evolution and iodine reduction on an illuminated n-p junction silicon electrode and its application to efficient solar photoelectrolysis of hydrogen iodide

Abstract: A p-type silicon electrode, highly doped with phosphorus from the surface (hereafter abbreviated as an n/sup +//p-Si electrode), generated a photocurrent corresponding to iodine (or triiodide) reduction in a hydrogen iodide/iodine solution at potentials much more positive than those at platinum and p-Si electrodes. The photocurrent-potential curve did not change when the electrode was illuminated for 60 h at a sufficiently cathodic potential, but changed due to the formation of a thin silicon oxide layer at the surface when illuminated near the onset potential of the photocurrent. The kinetics of the photoevolution of hydrogen on the n/sup +//p-Si electrode in acid solutions were improved by depositing a 0.5-3 nm thick platinum layer on the surface. The hydrogen-evolution photocurrent at the Pt-coated n/sup +//p-Si electrode gradually decayed under prolonged illumination, but was restored to the initial value by keeping the electrode in an oxidative condition. This suggests that the decay is due to the formation of a reduced surface species. Photoelectrochemical cells constructed with a Pt-deposited n/sup +//p-Si electrode and a Pt counterelectrode separated by a commercial cation-exchange membrane electrolyzed hydrogen iodide into hydrogen and triiodide ions under no externally applied voltage with an encouragingly high solar-to-chemical energy conversion efficiency (phi/submore » chem//sup s/) of 7.8% under simulated solar AM 1 radiation. 30 references, 8 figures.« less

Liquid junction photoelectrodes using amorphous silicon-based thin film semiconductor

Abstract: An amorphous silicon semiconductor alloy having multiple layers is used to form a photoelectrode (either a photoanode or a photocathode) for use in a photoelectrochemical cell for the photoelectrolysis of water to produce hydrogen or the conversion of solar energy into electrical energy Each layer of the semiconductor alloy has a different dopant concentration ranging from no dopant to a heavy dopant concentration The photoelectrochemical cell can utilize a photocathode and a conventional metal anode, a photoanode or both a photocathode and a photoanode according to the present invention The semiconductor alloy of the photoelectrode is a-Si:F:H or a-Si:H x deposited on a reflective layer of aluminum or molybdenum which is deposited on a substrate of glass or stainless steel A tunnelable oxide layer can be deposited or intrinsically formed to cover and protect the top surface of the semiconductor alloy body The photoanode is of an n-type configuration while the photocathodes can be either a p-type or a P-I-N type configuration

Influence of Mechanical Polishing on the Photoelectrochemical Properties of SrTiO3 Polycrystalline Anodes

Abstract: Etude de l'influence des defauts de reseau produits par polissage mecanique de la surface sur les proprietes photo-electrochimiques des anodes polycristallines de SrTiO 3

Passive hydrogel fuel generator

Abstract: A passive hydrogen oxygen generator in which the long wavelength infrared portion of the sun's spectrum heats water to provide circulation of the water within the generator. The shorter wavelength portion of the spectrum to which water is transparent is used in splitting water into hydrogen and oxygen by photoelectrolysis.

Method of making n-silicon electrodes

Abstract: The photoelectrolysis of water by solar radiation to produce hydrogen and oxygen is achieved using semiconductor electrodes The cell comprises a p-silicon wafer treated with catalyst as photocathode and metal doped n-silicon wafer as photoanode The cell is operated at a small bias potential

Hydrogen evolution and iodine reduction on an illuminated n-p junction silicon electrode and its application to efficient solar photoelectrolysis of hydrogen iodide

Abstract: A p-type silicon electrode, highly doped with phosphorus from the surface (hereafter abbreviated as an n/sup +//p-Si electrode), generated a photocurrent corresponding to iodine (or triiodide) reduction in a hydrogen iodide/iodine solution at potentials much more positive than those at platinum and p-Si electrodes. The photocurrent-potential curve did not change when the electrode was illuminated for 60 h at a sufficiently cathodic potential, but changed due to the formation of a thin silicon oxide layer at the surface when illuminated near the onset potential of the photocurrent. The kinetics of the photoevolution of hydrogen on the n/sup +//p-Si electrode in acid solutions were improved by depositing a 0.5-3 nm thick platinum layer on the surface. The hydrogen-evolution photocurrent at the Pt-coated n/sup +//p-Si electrode gradually decayed under prolonged illumination, but was restored to the initial value by keeping the electrode in an oxidative condition. This suggests that the decay is due to the formation of a reduced surface species. Photoelectrochemical cells constructed with a Pt-deposited n/sup +//p-Si electrode and a Pt counterelectrode separated by a commercial cation-exchange membrane electrolyzed hydrogen iodide into hydrogen and triiodide ions under no externally applied voltage with an encouragingly high solar-to-chemical energy conversion efficiency (phi/submore » chem//sup s/) of 7.8% under simulated solar AM 1 radiation. 30 references, 8 figures.« less

Photoelectrode and photochemical cell

Abstract: An amorphous silicon semiconductor alloy (32 and 34) having multiple layers (38 and 58) (42 and 60) is used to form a photoelectrode (either a photoanode (14) or a photocathode (16) for use in a photoelectrochemical cell (10) for the photoelectrolysis of water to produce hydrogen or the conversion of solar energy into electrical energy. Each layer of the semiconductor alloy has a different dopant concentration ranging from no dopant to a heavy dopant concentration. The semi-conductor alloy of the photoelectrode is a -Si:F:H or a-Si:Hx deposited on a reflective layer (28 and 30) of aluminum of molybdenum which is deposited on a substrate (24 and 28) of glass or stainless steel. A tunnelable oxide layer (62) can be deposited or intrinsically formed to cover and protect the top surface (60) of the semiconductor alloy body. The photoanode is of an n-type configuration while the photocathodes can be either a p-type or a P-I-N type configuration.

Metal Sulfides in Photovoltaic, Photoelectrochemical and Solar Biological Energy Conversion

Abstract: Crystallized metal compounds of sulfur are gaining increasing importance in various rapidly developing areas of solar energy conversion. One reason is that many metal sulfides form semiconductors with energy gaps well suited for the capture of solar energy. Several photovoltaic and photoelectrochemical solar cells with good energy conversion efficiencies have already been tested using CdS, Cu 2 S, CuInS 2 , MoS 2 and other sulfides. For the photoelectrolysis of water into hydrogen and oxygen semiconducting materials are being developed which permit light-induced hole reactions via valence energy bands derived from transition metal d-states. Sulfur compounds of transition metals (PtS 2 , RuS 2 , Ru 1-x Fe x S 2 ) constitute the first useful materials for oxygen evolution from water using low energy photons. In this case advantage is taken of the favourable property of sulfur as a metal ligand which permits efficient d-d interaction resulting in adequate d-d splitting and reasonably broad d-state energy bands. A third property of metal sulfides interesting for solar energy conversion is their ability to store chemical energy and to serve as an energy source for autotrophic bacteria (Thiobacilli). When metal sulfides are generated from their oxidation products (metal sulfates) by means of solar power using high pressure thermal and photoelectrochemical techniques, they can be used to grow bacterial biomass. Experimental and theoretical studies suggest that such an artificial solar biomass production could be far more energy-efficient than natural photosynthesis, besides of permitting the use of infertile and arid land on which compact and largely automatic installations would generate proteins, carbohydrates and lipids for energy and food with a remarkable economy of water consumption. Several aspects of sulfur chemistry with respect to mechanism of solar energy conversion are still unexplored and deserve detailed investigations.

The characterization of doped iron oxide electrodes for the photodissociation of water. stability, optical, and electronic properties

Abstract: A characterization of optical and electronic properties is presented for p-type (Mg-doped) and n-type (Si-doped) iron oxides used in the photoelectrolysis of water. Photocurrent vs. wavelength spectra for these electrodes indicate that ..cap alpha..-Fe/sub 2/O/sub 3/ is the active optical component for both p-type and n-type materials. Band-edge locations for p-type and n-type iron oxides in sodium hydroxide aqueous solution are determined from differential capacitance measurements. The thermodynamic feasibility of the catalytic photodissociation of water without external potential is demonstrated for a short-circuited p/n diode assembly on an energy level diagram of the electrode/electrolyte interfaces. The open-circuit voltage (V/sub oc/) and short-circuit current (I/sub sc/) generated by the p/n assembly as a function of the intensity of laser irradiation indicate that these doped iron oxides are low mobility, high carrier density semiconductors. Photo-oxidation of water at the n-type anode is verified through oxygen detection. Gas evolution is monitored from an operating diode assembly using mass spectrometry and isotopically labeled water (H/sub 2//sup 18/O). Photocurrent from these p/n assemblies show excellent long-term stability in aqueous solution and Auger analysis of the semiconductor surfaces indicates no evidence of electrode dissolution.