Sol-gel copper chromium delafossite thin films as stable oxide photocathodes for water splittingElectronic supplementary information (ESI) available: Experimental details, the UV-vis absorbance spectrum for an FTO/CuCrO2 electrode, an additional SEM image, linear scan voltammograms under transient 1 sun illumination and photocurrent transients under 1 sun illumination in 0.1 M HClO4, linear scan voltammograms under transient illumination in 0.1 M NaOH, and long-term chronoamperometric experiment

Significant effort is being devoted to the study of photoactive electrode materials for artificial photosynthesis devices. In this context, photocathodes promoting water reduction, based on earth-abundant elements and possessing stability under illumination, should be developed. Here, the photoelectrochemical behavior of CuCrO 2 sol-gel thin film electrodes prepared on conducting glass is presented. The material, whose direct band gap is 3.15 eV, apparently presents a remarkable stability in both alkaline and acidic media. In 0.1 M HClO 4 the material is significantly photoactive, with IPCE values at 350 nm and 0.36 V vs. RHE of over 6% for proton reduction and 23% for oxygen reduction. This response was obtained in the absence of charge extraction layers or co-catalysts, suggesting substantial room for optimization. The photocurrent onset potential is equal to 1.06 V vs. RHE in both alkaline and acidic media, which guarantees the combination of the material with different photoanodes such as Fe 2 O 3 or WO 3 , potentially yielding bias-free water splitting devices. Sol-gel prepared copper chromium delafossite electrodes behave as stable and efficient photocathodes for water reduction without the need for co-catalysts.