Trimetallic Phosphide Nanostructures Derived from In Situ Coated ZIF-L Film for Overall Water Splitting

Transition metal phosphides (TMPs) have attracted extensive attention as efficient catalysts with excellent conductivity for overall water splitting. However, most of the TMPs exhibit electrochemical instability under the OER catalytic oxidation potential. In this work, the microscopic morphology of the CoNiFe-CH nanoneedle precursor is regulated by in situ introduction of a ZIF-L film to modify its nanostructure and avoid the destruction of its structure during the phosphating process, which leads to the improvement of stability and catalytic activity. The as-prepared ternary metal phosphide catalyst, CoNiFeP-Z, exhibits excellent performance in 1.0 M KOH for the OER and HER, and it only requires 236 and 168 mV to achieve a current density of 100 mA cm–2, respectively. Furthermore, after 500 h of the OER reaction at 100 mA cm–2 and 100 h of the HER reaction at 20 mA cm–2, there is no apparent change in overpotential, demonstrating the superb activity and outstanding stability. Such remarkable OER and HER performance of CoNiFeP-Z is attributed to the synergistic effect between Co, Ni, and Fe and the structural stability resulting from the modification of the ZIF-L film. As a bifunctional catalyst, CoNiFeP-Z served as the anode and cathode in an electrolysis cell, exhibiting a voltage of only 1.549 V at 10 mA cm–2, surpassing the Pt/C||IrO2, and maintaining stability for over 100 h at 20 mA cm–2. In addition, CoNiFeP-Z exhibits a relatively favorable alkaline seawater splitting performance. This work furnishes an idea for the application of ZIF in catalysts to regulate the nanostructure and microscopic morphology to enhance the stability and activity.