Fe-doped NiCoP nanosheet arrays rich in phosphorus vacancies for highly efficient electrochemical water splitting

Transition metal phosphides (TMPs) have emerged as highly active bifunctional electrocatalysts, owing to their excellent conductivity and tunable electronic structure. However, a major bottleneck for TMP-based catalysts is their limited active-site accessibility and insufficient operational durability, which together impede their practical adoption. In this work, V_p-Fe-NiCoP (Fe-doped NiCoP nanosheet arrays with abundant phosphorus vacancies) was prepared via a metal-organic-framework (MOF)-to-MOF strategy followed by phosphorization and H₂ reduction. MOF-derived nanosheets offer an extensively exposed active surface along with shortened pathways for charge transport, thereby enhancing reaction kinetics. The synergistic combination of Fe doping and P vacancies fine-tunes the electronic structure of the electrocatalyst, resulting in improved intrinsic conductivity and a higher density of active sites. Consequently, V_p-Fe-NiCoP exhibits outstanding activity in 1.0 M KOH, requiring overpotentials of only 240 mV for the oxygen evolution reaction (OER) and 164 mV for the hydrogen evolution reaction (HER) at 100 mA cm^-2. Moreover, it maintains excellent stability, showing negligible potential variation after 250 h of OER and 140 h of HER operation at the same current density. The integrated two-electrode cell achieves a current density of 100 mA cm^-2 at a cell voltage of only 1.7 V. The exceptional activity and robust stability demonstrated here validate the designed material as a high-performance bifunctional electrocatalyst suitable for efficient water splitting.