Laser modification-induced NiCo2O4-δ with high exterior Ni3+/Ni2+ ratio and substantial oxygen vacancies for electrocatalysis

Abstract To explore the surface state of electrocatalysts, herein we developed a surface laser modification (pulsed laser ablation, PLA) approach for the fabrication of NiCo 2 O 4-δ with substantial inner oxygen vacancies (Vo ·· ) and higher exterior Ni 3+ /Ni 2+ ratio. The separated NiCo 2 O 4 nanoplates were transformed to cross-linked NiCo 2 O 4-δ nanostructure through PLA strategy. As compare with the primordial NiCo 2 O 4 produce, the laser-modificated NiCo 2 O 4-δ exhibits higher capacitance, lower overpotential and better electrocatalytic performance. The first-principles calculation proves that the additional energy level is introduced between the valence band and conduction band of L-NiCo 2 O 4-δ . The additional energy level not only benefits the hopping of electrons, but also inhibits the recombination of electron-hole pairs. The X-ray photoelectron spectrum (XPS) confirms that the active sites of the electrocatalytic reaction are Vo ·· , suggesting that the electron structure of catalyst could be adjusted by PLA. The high electrocatalytic activity of laser-modificated NiCo 2 O 4-δ could be ascribed to the synergistic effect of increased number of inner Vo ·· , higher electrochemically active surface area, and dominated Ni oct . Our findings might inspire new thoughts on the tuning the surface state and electronic structure of electrocatalyst.