Hierarchical tri-functional electrocatalysts derived from bimetallic–imidazolate framework for overall water splitting and rechargeable zinc–air batteries

Abstract

There is a growing need for an efficient multi-functional electrocatalyst that can produce industry-level high currents at low overpotentials. Herein, we report a highly efficient, robust tri-functional catalytic electrode that simultaneously catalyzes three different electrochemical reactions: the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR). The catalytic electrodes with a hierarchical structure are converted from a hierarchical nickel-rich, nickel–cobalt bimetallic–imidazolate framework directly grown onto a nickel foam. Catalytic electrodes composed of bimetallic phosphides exhibit excellent OER and HER catalytic activity (an overpotential of 201/250 mV at 20/100 mA cm⁻² for OER and an overpotential of 67/110 mV at 20/100 mA cm⁻² for HER), as well as ORR activity with a half-wave potential at 0.82 V vs. RHE. Furthermore, the bimetal–nitrogen–carbon (M–N–C) catalytic electrode also exhibits tunable tri-functional catalytic activity, including excellent ORR activity with a half-wave potential at 0.88 V vs. RHE. The high potential of these multi-functional electrocatalysts from single nickel-rich bimetallic–organic complexes is demonstrated by employing them as robust alkaline water electrolyzers, as well as decoupled air electrodes for rechargeable zinc–air batteries (ZABs).