Oxygen Vacancy-Determined Highly Efficient Oxygen Reduction in NiCo₂O₄/Hollow Carbon Spheres

Abstract

Rationally generating oxygen vacancies in electrocatalysts is an important approach to modulate the electrochemical activity of a catalyst. Herein, we report a remarkable enhancement in oxygen reduction reaction (ORR) activity of NiCoO supported on hollow carbon spheres (HCS) achieved through generating abundant oxygen vacancies within the surface lattice. This catalyst exhibits enhanced ORR activity (larger limiting current density of ∼-5.8 mA cm) and higher stability (∼90% retention after 40 000 s) compared with those of NiCoO/HCS and NiCoO. The results of X-ray photoelectron spectroscopy (XPS) characterizations suggest that the introduction of oxygen vacancies optimizes the valence state of active sites. Furthermore, we carried out density functional theory (DFT) calculations to further confirm the mechanism of oxygen vacancies, and results show that oxygen vacancies enhance the density of states (DOS) near the Fermi level, decrease work function, and lower the calculated overpotential of NiCoO.

Defect‐Enriched Nitrogen Doped–Graphene Quantum Dots Engineered NiCo2S4 Nanoarray as High‐Efficiency Bifunctional Catalyst for Flexible Zn‐Air Battery

“…Based on the above characterizations, the NiCo 2 S 4 (311) crystal plane appears to have the highest exposure to the reaction and thus this plane was selected as the active surface for simulation because it is the highest exposure plane. In this study, the most likely ORR mechanism on the N‐GQDs/NiCo 2 S 4 /CC catalyst is considered as a four‐electron predominant pathway, in which the intermediate product of OOH* is first produced and simultaneously reduced into OH* at the interface between NiCo 2 S 4 and N‐GQDs . Based on the DFT calculations, the relative Gibbs free energy and the optimized structural configuration of NiCo 2 S 4 /CC and N‐GQDs/NiCo 2 S 4 /CC catalysts interacting with oxygen intermediates are depicted in Figure .…”

“…Moreover, it is noted that the rate limiting reaction for NiCo 2 S 4 /CC catalyst changes from O 2 → OOH* to OOH* → O* after the introduction of N‐GQDs ( U = 1.23 V). The latter implies that the engineering of NiCo 2 S 4 with N‐GQDs favors the adsorption of O 2 and affects the interactions between oxygen intermediates and NiCo 2 S 4 by modifying charge density and chemical activity . This point is strongly supported by the adsorption configurations and the adsorption energies of oxygen intermediates on these two catalysts, respectively.…”

Experimental and Theoretical Investigation of the Effect of Oxygen Vacancies on the Electronic Structure and Pseudocapacitance of MnO2

“…For example, Lei and co‐workers reported O‐vacancy‐enriched NiO electrodes with a hexagonal platelets structure with extraordinary specific capacitance and high capacitance retention . Mai and co‐workers illustrated the effect of oxygen vacancies on the electrical conductivity, surface area and edge sites of an electrode . Figueiredo and co‐workers demonstrated that the key to determining the activity of manganese oxide was the reducibility and reactivity of the lattice oxygen .…”

“…[34] Mai and co-workers illustrated the effect of oxygen vacancies on the electrical conductivity,s urface area and edge sites of an electrode. [35] Figueiredo and co-workersd emonstrated that the key to determining the activity of manganese oxide was the reducibility and reactivity of the lattice oxygen. [36] Despite this progress, the relationship between the electronic structure caused by oxygen vacancies and pseudocapacitance needs to be further systematically studied.…”

Synthesis and Progress of New Oxygen‐Vacant Electrode Materials for High‐Energy Rechargeable Battery Applications

“…Recently, researchers have also invested a lot of interest in Zn–air batteries and Li–S batteries . Oxygen‐vacant materials were prepared and applied to enhance ORR and OER activity in Zn–air batteries.…”