Multifunctional Role of Ag‐Substitution in Enhancing the Photoelectrochemical Properties of LaFeO3 Photocathodes

Earth‐abundant LaFeO3 is a promising p‐type semiconductor for photoelectrochemical cells due to its stable photoresponses, high photovoltages and appropriate band alignments, but the photoelectrochemical properties of LaFeO3, especially the incident‐photon‐to‐current conversion efficiency, need to be further improved. Herein, we propose to partially substitute La3+ of LaFeO3 with Ag+ to enhance the photoelectrochemical performance of LaFeO3. The combined experimental and computational studies show that Ag‐substitution improves surface charge transfer kinetics through introducing active electronic states and increasing electrochemically active surface areas. Furthermore, Ag‐substitution decreases grain boundary number and increases majority carrier density, which promotes bulk charge transports. Ag‐substitution also reduces the bandgap energy, increasing the flux of carriers involved in photoelectrochemical reactions. As a result, after 8 % Ag‐substitution, the photocurrent density of LaFeO3 is enhanced by more than 6 times (−0.64 mA cm−2 at 0.5 V vs RHE) in the presence of oxygen, which is the highest photocurrent gain compared with other cation substitution or doping. The corresponding photocurrent onset potential also demonstrates a positive shift of 30 mV. This work highlights the versatile effects of Ag‐substitution on the photoelectrochemical properties of LaFeO3, which can provide useful insights into the mechanism of enhanced photoelectrochemical performance by doping or substitution. Ag‐substitution improves the entire physicochemical process of LaFeO3 (LFO) participating in photoelectrochemical (PEC) reactions, including light absorption, bulk charge transport, and surface charge injection. 8 % Ag‐substituted LFO exhibits an over 6‐fold increase in photocurrents, which is the benchmark performance for enhancing the PEC properties of LFO by cation substitution or doping.