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

Finding suitable bifunctional catalysts for industrial hydrogen production is the key to fully building a hydrogen energy society. Here we report a modulation of the surface morphology of electrodeposited CoP to form hydrangea-like Cobalt-Iron bimetallic phosphide (B-CoFeP@CoP) via ion-exchange and NaBH4-assisted methods. 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-Fe2P and B-Co2P acted as active centers for dissociation of H2O and desorption of H2, respectively, to synergistically catalyze the HER process.