Heteroatom doping-engineered cobalt manganese selenides with tunable lattice and electronic structure for sustainable energy storage and electrocatalysis

The precise control over heteroatom cation doping is a key parameter yet poorly investigated in modulating crystal structure, reaction kinetics, and charge transport in multi-metal selenides for bifunctional electrochemical applications. Here, we systematically demonstrate the Ni doping level in cobalt manganese selenide to illustrate the concentration-dependent phase modulation, lattice modifications, and electrochemical functionality for advanced supercapacitors and the alkaline hydrogen evolution reaction. These nanostructures are synthesised via a scalable co-precipitation route followed by low temperature calcination. The structural investigations revealed that the incorporation of nickel concentration introduces controlled lattice expansion, defect regulation, and crystallinity, thereby promoting faster charge transfer and ion transport. An optimal nickel concentration of 10% maximises redox-active sites while maintaining structural stability, leading to significant enhancement in pseudocapacitive behaviour. The resulting electrode shows specific capacitance of 311 F g −1 at 0.5 A g −1 , substantially surpassing the pristine cobalt manganese selenide. Apart from energy storage, dopant concentration strongly influences the hydrogen evolution activity in an alkaline electrolyte, overpotential of 197 mV at 10 mA cm −2 with Tafel slope of 107 mV dec −1 . Therefore, this work establishes dopant concentration as a critical parameter in bimetal selenides and provides a unified strategy for enhancing the electrochemical behaviour.