Boosting Interface Dynamics via Axial Coordination Engineering to Enhance Photoelectrochemical Water Splitting Performance

Efficient charge separation and robust surface catalytic activity at the semiconductor/transition-metal oxyhydroxide/electrolyte (SC/TMOOH/ELC) interface are pivotal for high-performance photoelectrodes. However, these two processes occur over a wide time scale ranging from 10^–6 to 100 s, meaning achieving matched and ideal active interfaces simultaneously remains a significant challenge. Here, we report a cobalt porphyrin (CoPy) coordinated out-of-plane with imidazole-2-carbaldehyde (denoted as CoPy@I-2-C) loaded between SC and TMOOH via axial coordination engineering. This CoPy@I-2-C can concurrently regulate interfacial charge transfer and surface catalytic reaction dynamics. As expected, the optimized BiVO₄/CoPy@I-2-C/FeNiOOH photoanode displays an impressive photocurrent density of 6.40 mA/cm² at 1.23 V_RHE, along with excellent stability. In situ scanning photoelectrochemical microscopy and density functional theory calculations reveal that CoPy@I-2-C, acting as an "interface activator", influences the SC/TMOOH and TMOOH/ELC interfaces through an electron-rich porphyrin ring and downward shifted d-band center of Co sites. Furthermore, this engineering can be applied to the TiO₂/CoPy@I-2-C/FeNiOOH photoanode system, demonstrating universality. This work offers a perspective on active interface modulation for constructing highly efficient photoanodes for water splitting.