Ion Irradiation Inducing Oxygen Vacancy‐Rich NiO/NiFe₂O₄ Heterostructure for Enhanced Electrocatalytic Water Splitting

Abstract

Oxygen evolution reaction (OER) is an obstacle to the electrocatalytic water splitting due to its unique four‐proton‐and‐electron‐transfer reaction process. Many methods, such as engineering heterostructure and introducing oxygen vacancy, have been used to improve the catalytic performance of electrocatalysts for OER. Herein, the above two kinds of regulation are simultaneously realized in a catalyst by using unique ion irradiation technology. A nanosheet structured NiO/NiFe2O4 heterostructure with rich oxygen vacancies converted from nickel–iron layered double hydroxides by Ar+ ions irradiation shows significant enhancement in both OER and hydrogen evolution reaction performance. Density functional theory (DFT) calculations reveal that the construction of NiO/NiFe2O4 can optimize the free energy of O* to OOH* process during OER reaction. The oxygen vacancy‐rich NiO/NiFe2O4 nanosheets have an overpotential of 279 mV at 10 mA cm−2 and a low Tafel slope of 42 mV dec−1. Moreover, this NiO/NiFe2O4 electrode shows an excellent long‐term stability at 100 mA cm−2 for 450 h. The synergetic effects between NiO and NiFe2O4 make NiO/NiFe2O4 heterostructure have high conductivity and fast charge transfer, abundant active sites, and high catalytic reactivity, contributing to its excellent performance.

Interface coupling induced built-in electric fields boost electrochemical nitrate reduction to ammonia over CuO@MnO2 core–shell hierarchical nanoarrays

“…47 Forming a heterostructure, as a type of interfacial structure, is a favorable strategy to enhance the catalytic performance of materials, which not only overcomes the inherent disadvantages of each material but also generates new properties due to interfacial effects. 48–52 In particular, heterogeneous nanointerfaces with a built-in electric field have demonstrated outstanding electrocatalytic activities because they can boost the interfacial charge transfer during electrocatalytic processes and effectively influence the adsorption of the corresponding reactants and intermediates. 53–55 Therefore, the construction of Cu-based materials/MnO 2 heterostructures with well-designed built-in electric fields is advantageous for enhancing the activity of electrochemical nitrate reduction to ammonia.…”

Construction of Ru/FeCoP heterointerface to drive dual active site mechanism for efficient overall water splitting

“…Overall, this catalysis mechanism of constructing an Ru/FeCoP heterointerface to drive dual active site overcomes the problems of the high cost and low water-decomposition efficiency of noble metal-based catalysts. 48,49…”

NiCo2O4 nanoparticles rich in oxygen vacancies: Salt-Assisted preparation and boosted water splitting

“…When NiCo 2 O 4 is gradually formed during annealing, a large number of O v will be generated. Many studies have shown that O v has been proven to exert favorable roles in promoting HER ( Zhang et al, 2018b ; Li et al, 2021b ; Lu et al, 2021 ) and OER ( Liu et al, 2019 ; Xiao et al, 2020 ; Zhong et al, 2021 ) activity in alkaline conditions, mainly because the O v lowers the coordination numbers of active metal ions, and thus modifies their electronic structures and further tunes the adsorption strength of HER and OER intermediates (*H for HER, and *OH, *O and *OOH for OER) on them and the O v also can decrease the energy barriers during HER or OER processes ( Zhu et al, 2020b ; Badreldin et al, 2021 ; Wu et al, 2021 ). Together plus the effects of the smaller sizes, NiCo 2 O 4 -2KCl with the more O v can expose more active sites on its surface and achieves the higher EASAs ( Figure 6A ) as compared with NiCo 2 O 4 .…”