Efficient Electroreduction of CO₂ to CO on Porous ZnO Nanosheets with Hydroxyl Groups in Ionic Liquid‐based Electrolytes

Abstract

Electrochemical reduction of CO2 is a very promising route to realize carbon cycle and alleviate energy shortage. Herein, the porous zinc oxide nanosheets with hydroxyl groups on carbon paper substrates (ZnO(OH)/CP‐x,×represents the deposition time) were proved to be excellent catalysts for CO2 electroreduction to CO. As far as we know, the hydroxyl groups were first introduced into ZnO catalysts for this reaction, which can enhance the surface areas and improve the capacity of binding CO2 by the formation of hydrogen bond. Especially, the total current density could reach 44.3 mA cm−2 with 97.8 % Faradaic efficiency (FE) of CO over ZnO(OH)/CP‐600 catalysts with moderate hydroxyl groups in 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([Bmim]PF6, 30 wt%)/acetonitrile/H2O (5 wt%) ternary electrolytes at −2.0 V versus Ag/Ag+, although the self‐reduction of the catalysts could be occurred simultaneously during electrolysis. Besides, the composition of the electrolytes also can significantly modulate the catalytic activity and selectivity of CO. The outstanding performance of ZnO(OH)/CP‐600 catalyst resulted mainly from the introduction of hydroxyl groups, high surface area, good contact with the substrate, and synergy effect between the catalyst and the electrolyte.

Photoelectrochemical CO2 Reduction Products Over Sandwiched Hybrid Ga2O3:ZnO/Indium/ZnO Nanorods

“…This process became pronounced when the thickness of GZO was increased. The surface HOOC ad is then transformed into formate or changed into surface O≡C ad via HOOC ad + H + + e − → O≡C ad + H 2 O ( Lu et al, 2018 ; Qin et al, 2018 ; Zhang et al, 2018 ; Liu et al, 2019 ; Daiyan et al, 2020 ; Luo et al, 2020 ; Wang et al, 2021 ). The formate production was only observed when In and GZO (Ga 2 O 3 :ZnO) were present.…”

“…Several reasons were plausibly proposed. In the present study, we used a 2 mm thick Zn plate different from those (e.g., powder in carbon paste) in the literature (Sekimoto et al, 2016;Tatsumi et al, 2017;Kikkawa et al, 2018;Lu et al, 2018;Qin et al, 2018;Yamamoto et al, 2018;Zhang et al, 2018;Liu et al, 2019;Ma et al, 2019;Murali et al, 2019;Zhang et al, 2019;Akatsuka et al, 2020;Daiyan et al, 2020;Hou et al, 2020;Luo et al, 2020;Tan et al, 2020;Yang et al, 2020;Deng et al, 2021;Li et al, 2021;Liang et al, 2021;Ma et al, 2021;Teng et al, 2021;Wang et al, 2021;Wei et al, 2021;Wu et al, 2021;Xiao et al, 2021;Yoon et al, 2021). Therefore, non-Faradaic current such as capacitive current might be significantly involved.…”

“…Electrochemical CO 2 reduction is a promising method, and the development of electrodes is a major goal for approaching practical application in the industry. Among many materials such as pure metals and metal oxides, ZnO, indium (In), and Ga 2 O 3 show very unique CO 2 reduction products after electrochemical reaction (Sekimoto et al, 2016;Tatsumi et al, 2017;Kikkawa et al, 2018;Lu et al, 2018;Qin et al, 2018;Yamamoto et al, 2018;Zhang et al, 2018;Liu et al, 2019;Ma et al, 2019;Murali et al, 2019;Zhang et al, 2019;Akatsuka et al, 2020;Daiyan et al, 2020;Hou et al, 2020;Luo et al, 2020;Tan et al, 2020;Yang et al, 2020;Deng et al, 2021;Li et al, 2021;Liang et al, 2021;Ma et al, 2021;Teng et al, 2021;Wang et al, 2021;Wei et al, 2021;Wu et al, 2021;Xiao et al, 2021;Yoon et al, 2021).…”

“…ZnO (and metallic Zn) is known to predominantly produce CO with a high Faradaic efficiency by electrochemical CO 2 reduction ( Lu et al, 2018 ; Qin et al, 2018 ; Zhang et al, 2018 ; Liu et al, 2019 ; Daiyan et al, 2020 ; Luo et al, 2020 ; Tan et al, 2020 ; Deng et al, 2021 ; Wang et al, 2021 ). Thereby, Zn-based materials have been chosen for CO and syngas (CO and H 2 ) production.…”

Electrochemical conversion of CO2 to syngas with a stable H2/CO ratio in a wide potential range over ligand-engineered metal–organic frameworks

“…33 This enhanced adsorption effect might be accomplished by the construction of hydrogen bonds between -COOH and CO 2 c À at the interface, leading to the augmented adsorption of CO 2 , by which the signicantly improved current density and selectivity of CO 2 conversion could be explained. 41,42 In situ spectroscopy characterization…”