Electronic Structure Engineering of Bimetallic Wolframites: Synergistic Ni-Doped and Ag-Decorated Cobalt Tungstate Nanoparticles for Bifunctional Oxygen Electrocatalysis

Mixed transition-metal oxides (MTMOs) have attracted significant attention as nonprecious alternatives to expensive noble-metal electrocatalysts, facilitating the development of sustainable energy conversion and storage devices. This work demonstrates the bifunctionality of dilute Ni-incorporated bimetallic tungstate (NiCoWO 4 ) for oxygen electrocatalysis, which is fundamental to the performance of energy conversion and storage devices. Synthesized via a facile and scalable wet-chemical route, with optimized bimetallic ratios, NiCoWO 4 exhibits excellent oxygen evolution reaction (OER) activity, with a current density of up to 343 mA/cm 2, surpassing the parent tungstate and a low overpotential of 360 mV at 10 mA/cm 2, positioning it as a highly active material for oxygen production. A reduced Tafel slope of 66.5 mV/dec and a high turnover frequency (TOF) value of 5 s –1, along with enhanced intrinsic activity, arise from low-level incorporation of Ni, which modifies the Co–O covalency and facilitates oxygen activation. Dilute incorporation of Ni into the nanoscale wolframite framework results in Co-rich bimetallic tungstate without phase segregation. Although NiCoWO 4 exhibits oxygen reduction reaction (ORR) activity, the incorporation of Ag nanoparticles further augmented the electrochemical ORR. The microwave-assisted polyol synthesis generated Ag nanoparticles with a size range of 4–5 nm, promoted abundant active interfacial sites, and enhanced charge transfer. The as-synthesized Ag/NiCoWO 4 exhibits a high ORR current density of −5 mA/cm 2 at 2600 rpm, with an onset potential of 0.73 V and excellent durability with a slight reduction in current density potential in alkaline media over 12 h of chronoamperometry. Rechargeable zinc–air coin cells employing NiCoWO 4 and Ag/NiCoWO 4 as air-cathode electrocatalysts delivered peak power densities of 69 and 52 mW/cm 2, respectively, demonstrating their practical applicability toward energy conversion systems. This work establishes NiCoWO 4 as an economically viable, highly efficient bifunctional oxygen electrocatalyst, marking a significant step toward the development of high-performance, cost-effective devices for sustainable energy applications.