Joost Manassen

Photoelectrochemical energy conversion and storage using polycrystalline chalcogenide electrodes

WE report here on a major improvement in the conversion efficiency of corrosion-free photoelectrochemical cells (PECs) and on a novel extension of such cells which allows the storage of part or all of the converted energy in situ for subsequent use.

Electrocatalytic Electrodes for the Polysulfide Redox System

Porous electrocatalytic electrodes for the polysulfide redox system, containing one of various metallic sulfides (especially of Co, Cu, Pb) are described. Emphasis is placed on their use as counterelectrodes in photoelectrochemical cells employing polysulfide electrolytes. Their activity is measured as a function of electrolyte temperature and composition. The ratio of S to S2−, and through it the local redox potential of the solution, is shown to be an important factor controlling electrode activity. The short and long term stability of the electrodes, as cathodes, is discussed, and it is shown that, when used in conjunction with photoanodes, and may poison the photoelectrode surface, thereby reducing total cell efficiency.

Electrochemical measurement on the photoelectrochemical reduction of aqueous carbon dioxide on p-Gallium phosphide and p-Gallium arsenide semiconductor electrodes

Abstract The photoelectrochemical reduction of aqueous carbon dioxide was carried out using single crystal p-gallium phosphide and p-gallium arsenide as photocathodes. The organic products measured were mainly formic acid, but also formaldehyde and methanol. The effect of carbon dioxide pressure on the current-potential relationships and on yields of organic reduction products was studied using a photoelectrochemical autoclave, fitted with a quartz window. Highest Faradaic yield of reduction products, 80%, was obtained with a p-GaP cathode at a cathodic bias of -1.00 V (vs. a standard silver electrode), in a medium initially 0.5 M Na2CO3, under 8.5 atm pressure of CO2, a cation exchange diaphragm and a platinum counterelectrode, under illumination with a 150 W Xe lamp.

The Mechanism of Dehydration of Alcohols over Alumina Catalysts

Publisher Summary The mechanism of dehydration of alcohols over “acidic” and “nonacidic” alumina is the same. In the presence of the “acidic” alumina, the readsorption of the dehydrated product can occur, leading to either double bond migration or skeletal isomerization, depending on the strength of the acid sites, the structure of the olefins produced, and the experimental conditions. The dehydration of tertiary alcohols over aluminas can be interpreted by a carbonium ion mechanism. Experimental evidence demonstrates that secondary and primary alcohols are dehydrated by a concerted mechanism, whereby both the intrinsic acid and base sites of the alumina participate. The steric course of the reaction proves that the dehydration of alkylcyclohexanols proceeds via a trans elimination. There is a strong parallel between elimination reactions in solution and the dehydration of alcohols over alumina. The trans elimination reactions and the anchimeric assistance of alcohols over aluminas suggest that the dehydration must occur within either the submicroscopical pores, or crevices, or channels of the aluminas. The aluminas therefore, must surround the alcohol molecules providing acid sites to act as proton donors or electron acceptors and basic sites to act as proton acceptors or electron donors.

Photoelectrochemical Energy Conversion and Storage The Polycrystalline Cell with Different Storage Modes

The photoelectrochemical cell (PEC) furnishes an alternative to the commercially available photovoltaic cells for the direct conversion of sunlight into electrical energy. It has the distinct advantage over a photovoltaic cell in that storage of the converted energy is possible in situ. Some general principles connected with storage in a PEC are discussed, and experimental evidence is given that, after due development, this mode may be able to compete with the combination photovoltaic cell/storage battery.

Electroplated cadmium chalcogenide layers: Characterization and use in photoelectrochemical solar cells

Abstract CdSe and Cd(Se, Te) alloy layers were electroplated onto titanium substrates from both acid and alkaline baths. When annealed, these layers show good photoelectrode behaviour in a polysulphide electrolyte with high quantum efficiencies and stability. Donor densities are found to be in the range of 10 14 –10 15 cm -3 . Scanning electron microscopy studies show the layers to have a very irregular morphology and generally to be composed of elongated spherical particles. Annealing conditions can be chosen such that the layers are of cubic or hexagonal structure.

High efficiency n‐Cd(Se,Te)/S=photoelectrochemical cell resulting from solution chemistry control

High efficiency (12.7%) CdSe0.68Te0.32/cesium polysulfide photoelectrochemical cells are demonstrated in this work. Crystals of the ternary alloy Cd(Se, Te) of type n type were synthesized by the traveling heater method. The nature of the polysulfide electrolyte, based on Cs polysulfide without excess hydroxide and containing small amounts of copper ions, is shown to be of particular importance in determining the cell efficiency. Reasonable output stability of the cell was obtained under accelerated tests.

Metal complexes of phthalocyanine and α,β,γ,δ-tetraphenyl porphyrin as heterogeneous catalysts in oxidative dehydrogenation. Correlation between catalytic activity and redox potential

Abstract The catalytic activity of tetraphenyl porphyrin and phthalocyanine complexes for the heterogeneous dehydrogenation of cyclohexadiene in the gas phase, using nitro-benzene as the oxidizing agent, was measured. A general correlation of catalytic activity with polarographically measured first oxidation potentials was found. By controlled potential electrolysis, coulometry and EPR measurements, the mode of oxidation of these complexes in solution was ascertained. The first oxidation of Fe 2+ and Co 2+ tetraphenyl porphyrin appeared to be at the central metal atom, while the Zn 2+ and Cu 2+ complexes gave ligand oxidation. For the Ni 2+ complex the potentials for central metal atom oxidation and ligand oxidation were very close together. Therefore, these complexes were capable of two kinds of redox processes, either valency change of the central metal atom (Fe 2+ , Co 2+ ) or ligand oxidation/reduction (Cu 2+ , Zn 2+ ) or both (Ni 2+ ). By comparing these principles with results obtained earlier on the catalytic activity of these complexes for cumene oxidation, this difference in redox mechanism could be correlated with the catalytic activity of the complexes in question.

Photo-electrochemical energy conversion: electrocatalytic sulphur electrodes

Electrodes for the sulphide/sulphur (polysulphide) redox system are described which show low polarization when operated under conditions to be expected in a practical photo-electrochemical cell (P. E. C.)-These electrodes are composed of Teflon-bonded high surface area carbon, loaded with electrocatalysts, the best results having been obtained using cobalt as electrocatalyst.

RADICAL GENERATION DURING THE ILLUMINATION OF AQUEOUS SUSPENSIONS OF TUNGSTEN OXIDE IN THE PRESENCE OF METHANOL, SODIUM FORMATE and SODIUM BICARBONATE. DETECTION BY SPIN TRAPPING

Abstract— Free radical intermediates appearing during illumination of aqueous suspensions of tungsten oxide were detected by electron spin resonance using the technique of spin trapping. Solutions irradiated contained methanol, formaldehyde, sodium formate and sodium hydrogen carbonate. Signals assigned to the spin adducts of the •H, •OH, •CO2‐ and •CH2OH radicals were found.