Operational Spectroelectrochemical Investigation on the Interfacial Charge Dynamics of Copper Bismuth Oxide Based Photocathode.

Copper bismuth oxide (CBO) is an emerging photocathode in photoelectrochemical (PEC) water splitting but exhibits limited performance due to the severe recombination of photogenerated charges at the semiconductor-liquid junction (SCLJ). For the first time, a set of operational spectroelectrochemical experiments including electrochemical impedance spectroscopy (EIS), transient photocurrent spectroscopy (TPS), and intensity-modulated photocurrent/voltage spectroscopy (IMVS, IMPS) are designed to investigate the charge dynamics at the SCLJ. It is indicated that there are dense surface states above the valence band of CBO, inducing the "Fermi level pinning" (FLP) effect at the SCLJ. The kinetic parameters speculated by IMVS and IMPS indicate the charge transfer efficiency of below 10% with even a bias of ∼0.7 V applied. TPS confirms the sluggish dynamics because of the charging behavior of the surface states. It is expected that this work would provide new connotations of charge dynamics at the SCLJ for the further optimization of CBO-based PEC systems.