Efficient electrocatalytic CO2 reduction to ethanol through the proton coupled electron transfer process of PVnMo(12-n) (n = 1, 2, 3) over indium electrode

Abstract

The multistep proton-coupled electron transfer (PCET) processes are beneficial for products distribution and selectivity of the electrocatalytic CO₂ reduction reaction (CO₂RR), which are affected by the nature of the catalyst and electrolyte at electrode–electrolyte interface. Polyoxometalates (POMs) are electron regulators of PCET processes, which can catalyze CO₂RR effectively. Accordingly, the commercial indium electrodes are combined in this work with a series of Keggin-type POMs (PV_nMo_(12-n)O₄₀)⁽ⁿ⁺³⁾⁻, n = 1, 2, 3) to process CO₂RR with Faradaic efficiency toward ethanol reaching 93.4% at −0.3 V (vs. RHE). The cyclic voltammetry and X-ray photoelectron spectroscopy results reveal the activation of CO₂ molecules by the first PCET process of the V^Ⅴ/Ⅳ in POM. Subsequently, the PCET process of Mo^Ⅵ/Ⅴ results the oxidation of the electrode, causing the loss of In⁰ active sites. Electrochemical in-situ infrared spectroscopy confirms the weak adsorption of *CO at the later stage of electrolysis due to the oxidation of the In⁰ active sites. The indium electrode in PV₃Mo₉ system retains more In⁰ active sites owing to the highest V-substitution ratio, thereby ensuring a high adsorption ratio of *CO and CC coupling. In sum, the regulation of the interface microenvironment by POM electrolyte additives can be used to boost the performance of CO₂RR.