In-situ tracking of phase conversion reaction induced metal/metal oxides for efficient oxygen evolution
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Published online 28 August 2020 | https://doi.org/10.1007/s40843-020-1424-2
In-situ tracking of phase conversion reaction induced metal/metal oxides for efficient oxygen evolution 1†
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Shahid Khan , Chao Wang , Haoliang Lu , Yufeng Cao , Zeyang Mao , Chenglin Yan and 2* Xianfu Wang ABSTRACT Due to the unique interface and electronic structure, metal/metal oxide composite electrocatalysts have been designed and exploited for electrocatalytic oxygen evolution reaction (OER) in alkaline solution. However, how to fabricate metal/metal oxides with abundant interfaces and well-dispersed metal phases is a challenge, and the synergistic effect between metal and metal oxides on boosting the electrocatalytic activities is still ambiguous. Herein, by controlling the lithium-induced conversion reaction of metal oxides, metal/metal oxide composites with plentiful interfaces and excellent electrical interconnection are fabricated, which can enhance the active sites, and accelerate the mass transfer during the electrocatalytic reaction. As a result, the electrocatalytic oxygen evolution activities of the as-fabricated metal/ metal oxide composite catalysts including NiCo/NiCo2O4, NiMn/NiMn2O4 and CoMn/CoMn2O4 are greatly improved. The catalytic mechanism is also explored using the in-situ Xray and Raman spectroscopic tracking to uncover the real active centers and the synergistic effect between the metal and metal oxides during water oxidation. Density functional theory plus U (DFT + U) calculation confirms the metal in the composite can optimize the catalytic reaction path and reduce the reaction barrier, thus boosting the electrocatalytic kinetics. Keywords: in-situ tracking, electrochemical conversion reaction, metal/metal oxide interfaces, electrocatalytic mechanism, oxygen evolution
INTRODUCTION Electrochemical water splitting is widely considered to be a critical way for the clean and renewable energy pro-
duction, storage and usage such as sustainable hydrogen production, rechargeable metal-air batteries and fuel cells [1–4]. However, owing to the multistep four-electron − − redox process (4OH → 2H2O + 4e + O2), oxygen evolution reaction (OER) often requires a relatively high overpotential, which leads to the sluggish kinetics and obvious energy loss [5–7]. Though the state-of-the-art precious-metal-based catalysts including IrO2 and RuO2 show impressive OER activities, the scarcity and high cost hinder their scale-up deployment [8–10]. Therefore, it is of great significance to develop earth-abundant transition metals (especially Fe, Co, and Ni) and their derivatives as highly efficient electrocatalysts for oxygen evolution [11– 22]. Among the non-noble metal-based electrocatalysts, transition metal oxides (TMOs) and layered doublehydroxides (LDHs) have been well designed with satisfying OER activities [23–27]. However, their activity and stability require to be further improved, and in-depth research into the catalytic mechanism of non-noble metal-based electrocatalysts is still lacking. Rational desi
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