Constructing Hydrangea‐Like Iron‐Cobalt Phosphides via Boron‐Assisted Strategy as an Efficient Catalyst for Water Splitting at High Current Density

Abstract Finding suitable bifunctional catalysts for industrial hydrogen production is the key to fully building a hydrogen energy society. In this study, we present a novel approach to modifying the surface morphology of electrodeposited cobalt phosphide (CoP). Specifically, we have developed a method to create a hydrangea‐like structure of bimetallic cobalt‐iron phosphide (B‐CoFeP@CoP) through ion‐exchange and NaBH4‐assisted strategies. This catalyst exhibited excellent bifunctional catalytic capability at high current densities, achieving a current density of 500 mA cm −2 at a small overpotential (387 mV for OER and 252 mV for HER). When assembled into an OWS electrolyzer, this catalyst showed a fairly low cell voltage (≈1.88 V) at 500 mA cm −2 current density., Furthermore, B‐CoFeP@CoP shows ceaseless durability over 120 h in both freshwater and seawater with almost no change in the cell voltage. A combined experimental and theoretical study identified that the unique hydrangea‐like structure provided a larger electrochemically active surface area and more effective active sites. Further analysis indicates that during the OER process, phosphides ensure that bimetallic active sites adsorb more OOH * intermediates and further DFT calculations showed that B‐Fe 2 P and B‐Co 2 P acted as active centers for dissociation of H 2 O and desorption of H 2 , respectively, to synergistically catalyze the HER process.