Regulation of electron delocalization between flower-like (Co, Ni)-MOF array and WO₃/W photoanode for effective photoelectrochemical water splitting

A stable heterometallic (Co, Ni)-MOF array with a 3D hierarchical flower-like morphology was coated onto the coral-like WO3/W thin film. The optimal (Co, Ni)-MOF/WO3/W photoanode exhibits a high photocurrent density of 2.96 mA cm(-2) at 1.23 V in the 0.5 M Na2SO4 solution and the photoelectrochemical (PEC) cell displays an excellent solar-to-hydrogen (STH) efficiency (2.17 %) under AM 1.5 G solar light. Moreover, the separation behavior and spatial distribution of photogenerated charges have been demonstrated by photo-assisted Kelvin probe force microscopy (KPFM). Furthermore, the shift of the d-band center and the change of Gibbs free energy for oxygen evolution reaction (OER) are realized by density functional theory (DFT) calculations. Overall, the coupling effect of these ions of Co2+, O2-, Ni2+, and W6+ could result in an electron delocalization in the (Co, Ni)-MOF/WO3/W photoanode, boosting the OER activity and finally improving the PEC water splitting performance.