Enhanced photoelectrochemical water splitting performance of a molten-salt carbon nitride photoanode with morphology and defect regulation induced by hydrochloric acid treatment

Abstract

The utilization of polymeric carbon nitride (PCN) photoanodes in photoelectrochemical (PEC) water splitting has garnered significant attention, although challenges such as charge recombination and sluggish oxygen evolution kinetics remain critical barriers. In this work, a post-treatment strategy involving HCl etching is employed to optimize the performance of the molten-salt carbon nitride photoanode (MCN). Detailed characterizations reveal that HCl treatment induces the partial detachment of the PCN framework in MCN, generating favorable defects while reducing the content of K ions. Under the condition of AM 1.5G illumination, the optimal HCl-treated MCN photoanode (HMCN) exhibits a remarkable photocurrent density of ca. 233 μA cm⁻² at a potential of 1.23 V vs. RHE, indicating a 2.3-fold enhancement with respect to the pristine MCN. This enhancement can be attributed to the improved accessibility of the active sites, increased charge carrier density, and reduced charge transfer resistance. This work establishes acid post-treatment as a facile route for regulating the morphology, defects, and electronic properties of PCN photoanodes, thereby advancing their applicability in solar-driven water splitting.