Sequential Engineering of Ternary CuFeNi with a Vertically Layered Structure for Efficient and Bifunctional Catalysis of the Oxygen and Hydrogen Evolution Reactions.

Developing efficient and earth-abundant electrocatalysts for electrochemical water splitting is greatly desired due to growing energy demands. Herein, we develop a promising hierarchical nickel-iron-copper nitride electrode that is fabricated via a three-step process, starting with a hydrothermal synthesis of nickel-iron hydroxide on nickel foam and followed by the direct growth of copper metal-organic frameworks and, finally, low temperature ammonization. This approach yields a material that is an efficient catalyst for both the oxygen evolution reaction and the hydrogen evolution reaction. The as-fabricated heterostructured nickel-iron-copper nitride electrode exhibits an excellent activity with an overpotential of only 121 mV for the oxygen evolution reaction and an even a lower overpotential of 33 mV for the hydrogen evolution reaction. Additionally, this structure displays strong long-term stability with only a negligible increase in potential after 500 cycles of uninterrupted cyclic voltammetry testing. To the best of our knowledge, this as-prepared hierarchical nickel-iron-copper nitride is one of the most promising alternatives for the electrochemical oxygen and hydrogen evolution reactions.