Oxygen Vacancy‐induced Electron Density Tuning of Fe₃O₄ for Enhanced Oxygen Evolution Catalysis

Abstract

Despite the tremendous efforts devoted to enhancing the activity of oxygen evolution reaction (OER) catalysts, there is still a huge challenge to deeply understand the electronic structure characteristics of transition metal oxide to guide the design of more active catalysts. Herein, Fe3O4 with oxygen vacancies (Fe3O4‐Vac) was synthesized via Ar ion irradiation method and its OER activity was greatly improved by properly modulating the electron density around Fe atoms. The electron density of Fe3O4‐Vac around Fe atoms increased compared to that of Fe3O4 according to the characterization of synchrotron‐based X‐ray absorption near‐edge structure (XANES), extended X‐ray absorption fine structure (EXAFS) spectra, and density functional theory (DFT) calculation. Moreover, the DFT results indicate the enhancement of the desorption of HOO* groups which significantly reduced the OER reaction barrier. Fe3O4‐Vac catalyst shows an overpotential of 353 mV, lower than that of FeOOH (853 mV) and Fe3O4 (415 mV) at 10 mA cm−2, and a low Tafel slope of 50 mV dec−1 in 1 M KOH, which was even better than commercial RuO2 at high potential. This modulation approach provides us with valuable insights for exploring efficient and robust water‐splitting electrocatalysts.

Steering Hole Transfer from the Light Absorber to Oxygen Evolution Sites for Photocatalytic Overall Water Splitting

“…However, rGO cannot serve as an efficient cocatalyst to oxidize H 2 O into O 2 , so that the overall water splitting still cannot be proceeded with. In contrast, in the case of Pt/2D g‐CN/FeO x comprised of appropriate semiconductor photocatalyst, H 2 ‐evolving cocatalyst (Pt), and O 2 ‐evolving cocatalyst (FeO x ), [ 53 ] can realize the overall water splitting, generating H 2 and O 2 in about 2:1 stoichiometric (Figure 3c). The hydrogen evolution rate arrives at ≈3.9 µmol h −1 in the initial 5 h, but decreases to ≈1.5 µmol h −1 in the 4th cycle after the 15 h reaction.…”

Efficient Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc–Air Battery: Fe3O4/N−C Nanoflowers Derived from Aromatic Polyamide

“…This is a common feature of the formation of oxygen vacancy in metal oxides crystals because the electron left in oxygen vacancy partially reduces high valence ions to low valence ones. [51,52] Further, the ideal atomic ratio of Fe 3 + / Fe 2 + in Fe 3 O 4 is known to be 2 : 1; however, this ratio will fall below 2 once a high concentration of oxygen vacancy exists, because some surface Fe 3 + can be reduced to Fe 2 + . Therefore, the Fe 2p2/3 XPS spectrum was fitted and is deconvoluted into two peaks at 712.7 and 711.2 eV, corresponding to Fe 3 + and Fe 2 + , respectively (Figure S5).…”

“…[21] Fe 3 O 4 nanowire array with oxygen vacancies showed much higher OER activity than a Fe 3 O 4 nanowire without oxygen vacancies, because of the modulating effect of oxygen vacancy on the electron density around Fe atom. [22] Inspired by these researches, we decided to investigate deeply the feasibility of increasing both the ORR and OER activity of Fe 3 O 4 by incorporating oxygen vacancies into its crystal structure, in order to develop low-cost, efficient bifunctional oxygen electrocatalysts for the rechargeable zincair batteries.…”

Anchoring stable FeS2 nanoparticles on MXene nanosheets via interface engineering for efficient water splitting

“…[1][2][3] Electrochemical production of hydrogen from water splitting is considered to be one of the most efficient ways to acquire green energy. [4][5][6] However, the sluggish kinetics of the oxygen evolution reaction (OER) keeps electrochemical water splitting from being practical. The OER involves a complex four-electron-proton coupling reaction while the hydrogen evolution reaction (HER) is only a two-electron-transfer reaction, and hence the OER is regarded as the rate-determining step during the water-splitting process.…”