Boosting water oxidation kinetics of BiVO4 through a metal-organic co-catalyst enriched with phosphate groups (Co,Fe-NTMP): Insights from LMCT mechanism and DFT study

The primary challenges of BiVO4 include its poor stability and inefficient electron-hole pair separation. To enhance BiVO4 photoanode oxygen evolution reaction (OER), a Co,Fe- nitrilotris (methylene phosphonic acid) (Co,Fe-NTMP) metal-organic co-catalyst was developed and applied to the BiVO4 photoelectrode surface using the SILAR technique. The proposed approach significantly improved charge separation and transfer. The optimized BiVO4/Co,Fe-NTMP photoanode exhibited a current density of 2.6 mA cm-2 at 1.23 V vs. RHE, representing more than a fivefold increase compared to bare BiVO4 (0.5 mA cm-2 at 1.23 V vs. RHE) under illumination of AM 1.5 G without a sacrificial agent. Additionally, the applied bias photon-to-current efficiency (ABPE) of BiVO4/Co,Fe-NTMP reached 0.58 % at 0.83 V vs. RHE. The Delta OCP measurements indicated improved band bending and enhanced charge separation following the Co,Fe-NTMP coating. The BiVO4/Co,Fe-NTMP photoanode also demonstrated remarkable stability for 9000 s, which can attributed to the formation of ligandto-metal charge transfer (LMCT), which facilitates efficient electron transport. This mechanism was substantiated by XPS and DFT analyses.