Novel Microporous Iron-Embedded Cobalt Phosphonates Feasible for Electrochemical Overall Water Splitting

Developing a low-cost effective, readily available, highly efficient electrocatalyst is essential to produce clean and sustainable energy. We report the synthesis of microporous iron-anchored cobalt phosphonate materials, i.e., FeCoPIm-6, FeCoPIm-12, FeCoPIm-24, and FeCoPIm-48, using iminodi(methylphosphonic acid) as a ligand, by varying the reaction time under hydrothermal condition and post-grafting synthetic pathway. The FeCoPIm-12 catalyst exhibits excellent electrocatalytic activity for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), acquiring low overpotentials of 117 and 249 mV vs. reversible hydrogen electrode (RHE), respectively, at the current density of 10 mA cm–2 with outstanding long-term durability up to 100 h in a 1.0 M KOH electrolyte solution. Also, the bifunctionalized electrocatalyst FeCoPIm-12 requires a cell voltage of 1.53 V at 10 mA cm–2 for overall water splitting in an alkaline medium and displays long-term stability. The superior electrochemical performance of the FeCoPIm-12 catalyst over the as-synthesized catalyst is due to its higher surface area with microporous channel throughout the catalyst and the synergistic effect of the highly active metal oxyhydroxide (FeOOH and CoOOH) components on the pore wall.