Achieving visible light-driven hydrogen evolution at positive bias with a hybrid copper-iron oxide|TiO2-cobaloxime photocathode

H-2 is an environmentally-friendly fuel that would allow for a circular economy but its sustainable production, e.g. from solar energy and water, remains a challenge. A hybrid CuFexOy|TiO2-CoHEC (CoHEC = chloro([4,4 '-bipyridine]-2,6-dicarboxylic acid)bis(dimethylglyoximato)cobalt(iii)) photocathode for hydrogen evolution reaction (HER), with faradaic efficiencies of 54-88%, is described, the preparation of which uses only non-toxic and Earth-abundant elements, avoids etching treatments and limits the use of organic solvents. The semi-conducting CuFexOy light absorber is obtained by sol-gel synthesis followed by calcination at moderate temperature. Grafting the CoHEC cobaloxime catalyst at its surface results in H-2 evolution with an onset photocurrent potential of +860 mV; this process being stabilized by the presence of a thin layer of amorphous TiO2 deposited onto CuFexOy.