Mechanistic Insights into Enhanced Hydrogen Evolution of CrO /Rh Nanoparticles for Photocatalytic Water Splitting.

The hydrogen evolution reaction (HER) of Rh nanoparticles (RhNP) coated with an ultrathin layer of Cr-oxides (CrO ) was investigated as a model electrode for the Cr O /Rh-metal core-shell-type cocatalyst system for photocatalytic water splitting. The CrO layer was electrodeposited over RhNP on a transparent conductive fluorine-doped tin oxide (FTO) substrate. The CrO layer on RhNP facilitates the electron transfer process at the CrO /RhNP interface, leading to the increased current density for the HER. Impedance spectroscopic analysis revealed that the CrO layer transferred protons via the hopping mechanism to the RhNP surface for HER. In addition, CrO restricted electron transfer from the FTO to the electrolyte and/or RhNP and suppressed the backward reaction by limiting oxygen migration. This study clarifies the crucial role of the ultrathin CrO layer on nanoparticulate cocatalysts and provides a cocatalyst design strategy for realizing efficient photocatalytic water splitting.