Copper-doped nickel oxide supported on carbon black for highly active oxygen reduction/evolution electrocatalysis

Zinc-air batteries (ZABs) are increasingly recognized as promising candidates for advanced energy storage due to their high theoretical energy density, environmental friendliness, operation safety and low cost. In this paper, we synthesized an ORR/OER bifunctional catalyst of copper doped nickel oxide on carbon black (Cux-NiOSC) by co-precipitation. By optimizing the Cu/Ni molar ratio, the as-synthesized Cu0.2-NiOSC exhibits large specific surface area and mixed-valence states of Ni and Cu elements. In ORR process, the Cu0.2-NiOSC shows the best ORR catalytic activity among the NiOSC, CuOSC, Cu0.15-NiOSC and Cu0.25-NiOSC, with the Tafel slope of 57.8 mV dec−1 and the electron transfer number of ca. 3.6, together with excellent cycling stability. In OER process, the Cu0.2-NiOSC exhibits the minimum overpotential of 510 mV at 10 mA cm−2, and its ∆E value indexing the ORR/OER bifunctional catalytic performance is also the smallest (0.93 V) among the examined samples. By using the Cu0.2-NiOSC as catalyst at the cathode, the cycle life of ZABs is significantly extended to over 120 h at 5 mA cm−2, and the rate performance and full-discharge capacity are also substantially enhanced. The specific capacity and power density of the ZAB have also reached 612 mAh gZn−1 and 96 mW cm−2, respectively. The results demonstrate that the copper doping leads to the synergistic enhancement on the catalytic performance of nickel oxide supported on carbon black, which paves a new pathway to the rational design of bifunctional catalysts for ZABs at low cost.