Stability of Ni-Mo Electrocatalysts Employed in Water Splitting

Abstract

The stability of Ni-Mo electro-catalysts, electro-deposited on a titanium surface, during electro-catalytic water splitting was researched. An optimum in efficiency was observed during the first hours of catalysis using chronopotentiometry and linear sweep voltammetry. This optimum was caused by changes at the catalyst surface that occurred during contact with the electrolyte. Using XPS depth profiling, SEM-EDX and ICP-AES molybdenum was shown to leach into the electrolyte and sodium or potassium from the electrolyte were shown to be incorporated. This led to roughening of the catalyst surface as determined with SEM, AFM and DLC measurements. As a result there was an increase in active surface sites causing the optimum in overpotential. The subsequent increase of overpotential was caused by corrosion of the material. The hydrogen production per minute that was measured with GC was higher than could be accounted for by the HER. The excess in production is likely related to conversion of molybdenum to molybdate which leaches into the electrolyte. Increased leaching was observed for increased current densities. Leaching was shown to be higher for catalysis in TBAOH and KOH electrolyte than for catalysis in NaOH electrolyte.