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.