Optimizing the electronic spin state and delocalized electron of NiCo2(OH)x/MXene composite by interface engineering and plasma boosting oxygen evolution reaction

Abstract

The electrocatalytic activity of transition-metal-based compounds is closely related to the electronic configuration. However, optimizing the surface electron spin state of catalysts remains a challenge. Here, we developed a spin-state and delocalized electron regulation method to optimize oxygen evolution reaction (OER) performance by in-situ growth of NiCo2(OH)x using Oswald ripening and coordinating etching process on MXene and plasma treatment. X-ray absorption spectroscopy, magnetic tests and electron paramagnetic resonance reveal that the coupling of NiCo2(OH)x and MXene can induce remarkable spin-state transition of Co3+ and transition metal ions electron delocalization, plasma treatment further optimizes the 3d orbital structure and delocalized electron density. The unique Jahn-Teller phenomenon can be brought by the intermediate spin state (t2g5eg1) of Co3+, which benefits from the partial electron occupied eg orbitals. This distinct electron configuration (t2g5eg1) with unpaired electrons leads to orbital degeneracy, that the adsorption free energy of intermediate species and conductivity were further optimized. The optimized electrocatalyst exhibits excellent OER activity with an overpotential of 268 mV at 10 mA cm−2. DFT calculations show that plasma treatment can effectively regulate the d-band center of TMs to optimize the adsorption and improve the OER activity. This approach could guide the rational design and discovery of electrocatalysts with ideal electron configurations in the future.