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

The hydrogen evolution reaction (HER) of Rh nanoparticles (RhNP) coated with an ultrathin layer of Cr-oxides (CrO x ) was investigated as a model electrode for the Cr 2 O 3 /Rh-metal core-shell-type cocatalyst system for photocatalytic water splitting. The CrO x layer was electrodeposited over RhNP on a transparent conductive fluorine-doped tin oxide (FTO) substrate. The CrO x layer on RhNP facilitates the electron transfer process at the CrO x /RhNP interface, leading to the increased current density for the HER. Impedance spectroscopic analysis revealed that the CrO x layer transferred protons via the hopping mechanism to the RhNP surface for HER. In addition, CrO x 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 x layer on nanoparticulate cocatalysts and provides a cocatalyst design strategy for realizing efficient photocatalytic water splitting.