Engineering Ru–N4 single atom catalysts on Ni-MOF-derived porous graphitic carbon for pH universal water electrolysis

Abstract

The rational development of highly active and robust single-atom electrocatalysts for pH-universal overall water splitting is imperative for large-scale green hydrogen production. However, unsatisfactory electrocatalytic activity due to sluggish reaction kinetics, along with the challenge of balancing activity and stability, remains a significant hurdle. In this report, we synthesized an electrocatalyst (Ru₁/Ni-NPGC), in which Ru single atoms and Ni nanoparticles are firmly anchored onto a porous graphitic carbon support via controlled pyrolysis of Ni-MOF. Unique coordination features, along with the synergistic combination of Ru–N₄ single-atom sites and Ni nanoparticles stabilized on the support through strong metal–support interactions, provide not only excellent electrocatalytic activity over a broad pH range, but also show remarkable stability during long-term operation. Outstandingly, the Ru₁/Ni-NPGC electrocatalyst requires a minimal overpotential of ∼195 mV for the oxygen evolution reaction (OER) and ∼54 mV for the hydrogen evolution reaction (HER) to achieve a current density of 10 mA cm⁻² in an alkaline medium. The fabricated electrolytic cell (Ru₁/Ni-NPGC‖Ru₁/Ni-NPGC) demonstrated excellent overall water electrolysis performance in acidic (pH 1), neutral (pH 7.4) and alkaline (pH 14) media by requiring only 1.5 V, 1.55 V and 1.48 V cell potentials, respectively, to achieve a current density of 10 mA cm⁻². Moreover, the cell exhibited excellent long-term electrocatalytic stability over extended periods at low (10 mA cm⁻²) and high (100 mA cm⁻²) current densities. This work opens a new perspective for the synergistic design of pH-universal bifunctional electrocatalysts for electrochemical hydrogen production.