Mn–Sn co-doped NiO nanostructures with boosted activity for integrated energy conversion and storage

Abstract

Mn and Sn co-doped nickel oxide (NiO) nanostructures were synthesized with controlled compositions using the formula Ni_0.9(Mn_1−xSn_x)_0.1O (x = 0.00, 0.25, 0.50, and 0.75), corresponding to pristine NiO, NMS 2, NMS 5, and NMS 7. Their structural, electrochemical, and catalytic properties were systematically investigated. Among the series, the NMS 5 composition (5% co-doping) exhibited the best overall performance, delivering a high specific capacitance of 1339.09 F g⁻¹ at 1 mV s⁻¹ and 1467.91 F g⁻¹ at 13 mA cm⁻², along with an energy density of 50.96 Wh kg⁻¹ at a power density of 677.08 W kg⁻¹, highlighting its suitability for high-performance supercapacitor applications. In addition, NMS 5 demonstrated excellent bifunctional electrocatalytic activity toward overall water splitting, achieving low overpotentials of 208 mV for the hydrogen evolution reaction and 126 mV for the oxygen evolution reaction at 10 mA cm⁻², accompanied by favourable Tafel slopes of 194 and 162 mV dec⁻¹, indicating improved reaction kinetics and charge-transfer efficiency. The enhanced performance was further supported by its highest double-layer capacitance (1.782 mF) and electrochemically active surface area (16.2 cm²), confirming an increased density of accessible redox-active sites. These results demonstrate that synergistic Mn and Sn co-doping effectively tailors the electronic structure and interfacial properties of NiO, establishing it as a promising multifunctional electrode material for advanced energy storage and water-splitting applications.