Crystalline metal phosphide-coated amorphous iron oxide-hydroxide (FeOOH) with oxygen vacancies as highly active and stable oxygen evolution catalyst in alkaline seawater at high current density.

In this study, we employed a straightforward phosphorylation approach to achieve a dual objective: constructing c-a heterostructures consisting of crystalline NiP and amorphous FeOOH, while simultaneously enhancing oxygen vacancies. The resulting oxygen evolution reaction (OER) catalyst, NiP/FeOOH/NF, exhibited remarkable performance with current densities of 500 mA cm in both 1 M KOH and 1 M KOH + seawater, requiring low overpotentials of only 288 and 365 mV, respectively. Furthermore, NiP/FeOOH/NF exhibited only a slight increase in overpotential, with increments of 18 mV and 70 mV in 1 M KOH after 15 and 150 h, and 32 mV and 108 mV in 1 M KOH + seawater at 500 mA cm after 15 and 150 h, respectively. This minimal change can be attributed to the stabilized c-a structure, the protective coating of NiP, and superhydrophilic. Through in-situ Raman and ex-situ XPS analysis, we discovered that NiP/FeOOH/NF can undergo a reconfiguration into an oxygen vacancy-rich (Fe/Ni)OOH phase during OER process. The elevated OER activity is mainly due to the contribution of the oxygen vacancy-rich (Fe/Ni)OOH phase from the reconfigure of the NiP/FeOOH/NF. This finding emphasizes the critical role of oxygen vacancies in facilitating the production of OO species and overcoming the limitations associated with OOH formation, ultimately enhancing the kinetics of the OER.