Copper–nickel embedded into a nitrogen-doped carbon octahedron as an effective bifunctional electrocatalyst

Abstract

The development of inexpensive and effective electrocatalysts is significant for large-scale application of renewable and clean energy. Herein, a sequence of bifunctional catalysts are successfully synthesized by the direct pyrolysis reaction of copper–nickel coexisting metal–organic framework precursors (CuNi-BTC, BTC = 1,3,5-benzenetricarboxylic acid). The as-obtained catalysts consisting of nitrogen-doped carbon with embedded copper–nickel alloy nanoparticles (CuNi-NC) are developed for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. We demonstrate that the introduction of nickel in appropriate proportion is in favor of improving the degree of graphitization, enlarging the electrochemical active surface area, and accelerating charge transport. As a result, the optimized CuNi-NC-2 sample exhibits an overpotential of 390 mV at 10 mA cm⁻² and a Tafel slope of 76 mV dec⁻¹ in the OER process, while all CuNi-NC samples have better performance (lower overpotential and smaller Tafel slope) compared to the Cu-NC in the HER process, and their acceptable durability is also confirmed. In view of convenient preparation, satisfactory activity, reliable durability, and low cost, such transition metal carbon-based catalysts could provide significant guidance for the rational design of bifunctional catalysts for overall water splitting.