Oxygen Vacancies in ZnO Nanosheets Enhance CO₂ Electrochemical Reduction to CO

Abstract

As electron transfer to CO 2 is generally considered to be the critical step during the activation of CO 2 ,itisimportant to develop approaches to engineer the electronic properties of catalysts to improve their performance in CO 2 electrochemical reduction. Herein, we developed an efficient strategy to facilitate CO 2 activation by introducing oxygen vacancies into electrocatalysts with electronic-richs urface.Z nO nanosheets rich in oxygen vacancies exhibited ac urrent density of À16.1 mA cm À2 with aF aradaic efficiency of 83 %f or CO production. Based on density functional theory (DFT) calculations,t he introduction of oxygen vacancies increased the charge density of ZnO around the valence band maximum, resulting in the enhanced activation of CO 2 .M echanistic studies further revealed that the enhancement of CO production by introducing oxygen vacancies into ZnO nanosheets originated from the increased binding strength of CO 2 and the eased CO 2 activation.AsCO 2 is an abundant and inexpensive carbon resource in the chemical industry,recyclingCO 2 into fuels and high valueadded chemical stocks via an electrochemical process represents apromising path to mitigate the energy crisis. [1,2] Owing to the high thermodynamic stability of CO 2 , [3] the standard potential of CO 2 /CO 2 À couple is as negative as À1.9 Vversus reversible hydrogen electrode (RHE) in water for the formation of highly energetic CO 2 anion radicals. [4] As such, the effective activation of CO 2 plays ak ey role in CO 2 electrochemical reduction. [5] From both theoretical and experimental perspectives,t he electron transfer to CO 2 is generally considered as the critical step during the activation of CO 2 . [6,7] To overcome this bottleneck, it is especially important to rationally design ah ighly active and robust electrocatalyst which has electron-donation centers to capture CO 2 molecules and activate the stable C=On on-polar bonds.Recently,t he introduction of oxygen vacancies has provided ap owerful method to enhance the performance of CO 2 conversion in heterogenous catalysis by promoting CO 2 adsorption and activation. Fori nstance,t he introduction of oxygen vacancy defects into TiO 2 surface gives rise to highly stable adsorption configurations with astronger activation of the C=Obonds,which leads to the exothermic dissociation of CO 2 with barriers up to 22.2 kcal mol À1 . [8] In addition, oxygen vacancies decorated on BiOCl nanoplates made the surface electronic-rich, and served as electron trap centers to transform CO 2 into CO 2 À by ao ne-electron transfer process.[9] Moreover,p revious studies have theoretically shown that engineering the surface vacancies of electrochemical catalysts also provides away to regulate the catalytic performance for ammonia synthesis and oxygen reduction by modifying their electronic structures. [10] However,t oour knowledge,i mplementing this strategy in the electrochemical reduction of CO 2 is still at the rudimentary state.Herein, we developed an efficient strategy to facilitate CO 2 activatio...

Direct probing of atomically dispersed Ru species over multi-edged TiO 2 for highly efficient photocatalytic hydrogen evolution

“…Compared with the pure TiO 2 , an increased total density of states (TDOS) is observed at the valence band maximum after Ru decoration, leading to an easier excitation and transfer of photogenerated electrons from TiO 2 to Ru centers (Fig. 5, C and D) (28). These occupied states of Ru largely turn into "electron trap" for TiO 2 and lift the Fermi level to the position close to the conduction band minimum of TiO 2 .…”

Progress in development of electrocatalyst for CO2 conversion to selective CO production

“…The Cuenya group further revealed that unlike OD‐Au, Zn cations were shown to be stable during electrolysis by in‐situ XANES and EXAFS results (Figure E) . In a study using ZnO nanosheets, it was suggested that the selectivity increase observed on OD‐Zn originated from the lower ∆ G for *COOH formation on the ZnO slab with oxygen vacancy, activating CO 2 and leading to the favorable kinetics for CO production . Nevertheless, most of above‐mentioned electrocatalysts achieved the maximum CO FE from approximately 78% to 85% in the KHCO 3 electrolyte at potential range from –0.9 to –1.1 V RHE , which remained a relatively lower CO FE and higher overpotential compared to Au‐ or Ag‐based catalysts.…”

“…E, EXAFS spectrum of 3.9 nm NPs during CO 2 RR (Dashed vertical lines show the limits of the fit) (Reproduced with permission: Copyright 2018, American Chemical Society). F, CO partial current densities on three ZnO nanosheets showing highest current density for CO production on V o ‐rich ZnO (Reproduced with permission: Copyright 2018, Wiley). G, Proposed mechanism for effect of Cl – accelerating the reduction of CO 2 on nanostructured Zn surface in Cl – electrolyte (Reproduced with permission: Copyright 2015, Royal Society of Chemistry).…”

Core@shell structured Au@SnO2 nanoparticles with improved N2 adsorption/activation and electrical conductivity for efficient N2 fixation

“…As a critical subject in the research field of oxide semiconductors, oxygen (O) vacancy has been extensively studied for many years [26]. The presence of O vacancies in oxide semiconductors can trap the metastable-state electrons to change the adsorption and activation of reactive substrate during the catalysis, which profoundly affect the catalytic performance [27][28][29][30]. For example, the existed O vacancies in ZnO affected the adsorption of CO 2 , resulting in different products selectivity for electrochemical CO 2 reduction [28].…”