Pulse electrodeposition of CoP nanostructures on TiO2 nanotube arrays and their charge-transfer mechanism via EIS and DRT analyses.

Efficient and stable self-supported electrocatalysts as well as the charge-transfer mechanism of overall water splitting remain a critical challenge for sustainable hydrogen production. Herein, we study a pulse electrodeposition strategy for the controlled dispersion of cobalt phosphide (CoP) nanoparticles onto TiO2 nanotube arrays (TNAs), forming a well-defined CoP/TNA bifunctional electrode. Precise pulse parameter regulation enabled uniform CoP nucleation throughout the TNA framework, establishing nanoscale heterojunctions with significant interactions at the CoP/TiO2 interface. The optimized 200-CoP/TNA electrode achieved overpotentials of 156 mV and 370 mV for the HER and OER, respectively, while the two-electrode 200-CoP/TNA∥200-CoP/TNA electrolyzer operated at a cell voltage of 2.3 V at 1 A cm-2 with stable performance over 200 hours. In particular, operando electrochemical impedance spectroscopy (EIS) coupled with distribution of relaxation time (DRT) analysis revealed enhanced mass transport and electron transfer kinetics and confirmed that interfacial CoP/TiO2 interactions induce favorable modifications to the reaction pathway, reducing overall energy consumption. These results establish pulse electrodeposition as an effective nanoengineering strategy for fabricating high-performance self-supported electrodes toward practical water electrolysis.