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

To explore the surface state of electrocatalysts, herein we developed a surface laser modification (pulsed laser ablation, PLA) approach for the fabrication of NiCo2O4-delta with substantial inner oxygen vacancies (Vo(center dot center dot)) and higher exterior Ni3+/Ni2+ ratio. The separated NiCo2O4 nanoplates were transformed to crosslinked NiCo2O4-delta nanostructure through PLA strategy. As compare with the primordial NiCo2O4 produce, the laser-modificated NiCo2O4-delta 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-NiCo2O4-delta. The additional energy level not only benefits the hopping of electrons, but also inhibits the recombination of electron-hole pairs. The Xray photoelectron spectrum (XPS) confirms that the active sites of the electrocatalytic reaction are Vo(center dot center dot), suggesting that the electron structure of catalyst could be adjusted by PLA. The high electrocatalytic activity of laser-modificated NiCo2O4-delta could be ascribed to the synergistic effect of increased number of inner Vo(center dot center dot), 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. (C) 2018 Published by Elsevier Ltd.