Bi-metallic MOFs possessing hierarchical synergistic effects as high performance electrocatalysts for overall water splitting at high current densities

Abstract

Bi-metallic metal organic framework (MOF) compounds, FeNi(BDC)(DMF,F), adequately modulated through alloying of Ni and Fe, were demonstrated outstanding electrocatalysts for overall water splitting. It was composed of two well mixed bi-metallic MOF phases, Fe-rich FeNi(BDC)(DMF,F) and Ni-rich FeNi(BDC)(F), each containing two molecularly well mixed metallic clusters, to give pronounced hierarchical synergistic effects toward overall water splitting, delivering current densities of 10 and 400 mA cm−2 at ultralow cell voltages of 1.58 and 1.90 V, respectively, outperforming the pairing of benchmark electrodes, Pt-C//IrO2. The stability of the electrodes was also excellent, experiencing only minor chronoamperometric decay after a continuous operation at 400 mA cm−2 for 30 h. The success may be attributed to the MOF/substrate synergistic effects between the FeNi(BDC)(DMF,F) and the conductive macroporous nickel foam, the inter-molecular synergistic effects between the two constituent MOF phases, and the intra-molecular synergistic effects between the FeO6 and NiO6 clusters of the Fe-rich FeNi(BDC)(DMF,F).