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Catalysis; Oxygen reduction reaction; Mechanism; Zinc oxide
Abstract:
The electrochemical oxygen reduction reaction (ORR) along a two-electron transfer pathway has been considered as an eco-friendly route for producing hydrogen peroxide (H2O2). However, large-scale industrial application of this ORR technology calls for ultrafast and effective generation of H2O2 under operating conditions (current densities >1 A/cm2 and Faradaic efficiency ≈ 100%). This imposes strict criteria for exploring innovative strategies for enhancing the adsorption and activation of O2 under vigorous reaction condition, which represents a significant challenge thus far. Here, we report an ‘oxygen-vacancy-type’ Mars–van Krevelen mechanism for promoting ORR. Our theoretical calculations show that the structural oxygen vacancies of zinc oxide catalysts effectively alter the electron densities of nearby metal active sites, producing a more electron-deficient Zn center, which, in turn, assists the adsorption and activation of O2. A catalyst electrode designed as that exhibits superior ORR activities with a Faradaic efficiency of 98.1% at a current density of 1 A/cm2 (H2O2 yield rate of 621.88 mg/h/cm2). Further mechanism study has been performed through in situ Raman spectroscopy to monitor the adsorption and activation of oxygen intermediate (∗O2) of ORR, providing additional experimental evidence for the Mars–van Krevelen mechanism.
