Object under investigation: process of cathodic hydrogen evolution from an alkaline solution at metal (Ni, Co, Ti, steel) electrodes, including electrodes whose surface is modified by electrolytic metal alloys with low electrode overpotential, and anodic oxygen evolution at gas-diffusion nickel electrodes.
Methods of investigation: potentiometry, including ac pulse potentiometry, method of polarization curves, including that with rotating disk electrode, cyclic voltammetry, electron microscopy, quantitative electron probe microanalysis and atomic absorption analysis.
The advantageousness of the reduction of cathodic and anodic overpotential, which constitutes a considerable part of electrolyzer terminal voltage, for the development of highly efficient and competitive technologies for hydrogen production by the low-temperature electrolysis of alkaline solution has been theoretically substantiated and experimentally confirmed. To reduce cathodic hydrogen evolution overpotential, it is proposed to modify the cathode surface. It has been shown that the deposition of a small amount of electrolytic alloys of iron-group metals with molybdenum and tungsten on nickel, cobalt, titanium and steel electrodes reduces greatly (by 40-50%) the overpotential of cathodic hydrogen evolution at them from alkaline solution. Therefore, the kinetics and mechanism of hydrogen evolution at the cathodes obtained have been studied in detail.
The reduce the overpotential of anodic oxygen evolution from alkaline solution, it is proposed to use gas-diffusion anodes, through which gases-depolarizers with reducing properties were passed. Carbon monoxide, natural gas and hydrogen were tried as such gases. To generate hydrogen directly on the anode surface, ac pulse electrolysis was used. The depolarizing effect of these gases on anodic oxygen evolution is achieved by their oxidation at an overpotential that is lower than oxygen evolution overpotential.
A pilot laboratory three-section electrolyzer with bipolar bimetallic electrodes for high-purity hydrogen production by low-temperature electrolysis of alkaline solution has been developed and made. A thin layer of electrolytic Co-W alloy was deposited on the cathode sides of the steel electrodes. The anode side of the electrodes was nickel. An asbestos cloth was used as diaphragm. Laboratory tests showed that the terminal voltage of this electrolyzer is lower by 9% than that of electrolyzer with steel electrodes.
Keywords: hydrogen, oxygen, water electrolysis, electrode overpotential, depolarization, pulse electrolysis, expenditure of electrical energy.