Dimeric Ni Co single-atom anchored on ultrathin N-doped 2D molybdenum carbide boosted performance in solid-state supercapacitor

Tuning the electronic structure of single-atom catalysts through dimeric single-atom formation could be an innovative approach to increasing their energy storage activity, but the process of achieving this is challenging. In this study, we designed a simple technique to obtain NiCo single atom dimers (SADs) anchored on N-doped molybdenum carbide (N-Mo2C) through in-situ encapsulation of NiCo into molybdenum polydopamine, followed by annealing with optimal tuning of nitrogen dopant. The NiCo atomic level coordination was confirmed with X-ray absorption spectroscopy. When used as energy storage supercapacitor, The NiCo-SADs showed enhanced specific capacity (1004.8 F g−1 at 1 A g−1), enhanced rate capability (75 %), and exceptional cycling stability (93.6 % with 98.5 % coulombic efficiency) via a dominant capacitive charge storage. The augmented charge storage characteristics are attributed to the collaborative features of the active NiCo constituents acting as electron reservoir for effective adsorption of HO− ion during the electrochemical process. The DFT study showed thermodynamically favorable OH− adsorption between the three metal bridges that promoted redox reaction kinetics and enhanced conductivity for the NiCo-SADs. When using N-Mo2C as the anode to fabricate hybrid supercapacitors, the device exhibits high energy density of 69.69 Wh kg−1 at power density of 8200 W kg−1, respectively and shows excellent long-term cycling stability (93.42 % after 3000 cycles), which affirms the potential of the assembled device for applications in solid state supercapacitors.