Multi-walled carbon nanotube integrated Ni–Co hydroxide/Cu₂(OH)₃NO₃ heterostructures for efficient oxygen evolution in alkaline media

The development of sustainable and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is essential for efficient hydrogen (H₂) production. In this study, Cu₂(OH)₃NO₃ (CuHN) and Ni-Co hydroxide/Cu₂(OH)₃NO₃ (CuNiCo) electrocatalysts were synthesized using the reflux method. To further enhance the electrocatalytic properties, multi-walled carbon nanotubes (CNT) were integrated into CuNiCo with various weight fractions ( x = 1.5, 2.5, 3.5 wt.%) to create composites (denoted as CuNiCo@CNT-1, 2, 3). Among these, CuNiCo@CNT-2 supported on nickel foam (NF) exhibited efficient OER activity, achieving low overpotentials (η) of 280 mV and 350 mV at current densities (J) of 50 and 100 mA/cm² in 1M KOH. This enhanced performance is attributed to improved conductivity, increased active sites, and strong electronic coupling between CuNiCo and CNT. Moreover, the CuNiCo@CNT-2ǀǀPt/C@NF electrolyzer exhibited a low cell voltage of 1.49 V at 10 mA/cm² and demonstrated excellent durability over 50 h at different current densities. These results highlight the strong potential of the CuNiCo@CNT composite as a cost-effective and robust electrocatalyst for practical water-splitting applications.