Photoelectrochemical Behavior and Computational Insights for Pristine and Doped NdFeO Thin-Film Photocathodes.

Among the different strategies that are being developed to solve the current energy challenge, harvesting energy directly from sunlight through a tandem photoelectrochemical cell (water splitting) is most attractive. Its implementation requires the development of stable and efficient photocathodes, NdFeO being a suitable candidate among ternary oxides. In this study, transparent NdFeO thin-film photocathodes have been successfully prepared by a citric acid-based sol-gel procedure, followed by thermal treatment in air at 640 °C. These electrodes show photocurrents for both the hydrogen evolution and oxygen reduction reactions. Doping with Mg and Zn has been observed to significantly enhance the photoelectrocatalytic performance of NdFeO toward oxygen reduction. Magnesium is slightly more efficient as a dopant than Zn, leading to a multiplication of the photocurrent by a factor of 4-5 for a doping level of 5 at % (with respect to iron atoms). This same trend is observed for hydrogen evolution. The beneficial effect of doping is primarily attributed to an increase in the density and a change in the nature of the majority charge carriers. DFT calculations help to rationalize the behavior of NdFeO by pointing to the importance of nanostructuring and doping. All in all, NdFeO has the potential to be used as a photocathode in photoelectrochemical applications, although efforts should be directed to limit surface recombination.