Abstract
CO2 and steam/CO2 electroreduction to CO and methane in solid oxide electrolytic cells (SOEC) has gained major attention in the past few years. This work evaluates, for the very first time, the performance of two different ZnO–Ag cathodes: one where ZnO nanopowder was mixed with Ag powder for preparing the cathode ink (ZnOmix–Ag cathode) and the other one where Ag cathode was infiltrated with a zinc nitrate solution (ZnOinf –Ag cathode). ZnOmix–Ag cathode had a better distribution of ZnO particles throughout the cathode, resulting in almost double CO generation while electrolysing both dry CO2 and H2/CO2 (4:1 v/v). A maximum overall CO2 conversion of 48% (in H2/CO2) at 1.7 V and 700 °C clearly indicated that as low as 5 wt% zinc loading is capable of CO2 electroreduction. It was further revealed that for ZnOinf –Ag cathode, most of CO generation took place through RWGS reaction, but for ZnOmix–Ag cathode, it was the synergistic effect of both RWGS reaction and CO2 electrolysis. Although ZnOinf –Ag cathode produced trace amount of methane at higher voltages, with ZnOmix–Ag cathode, there was absolutely no methane. This seems to be due to strong electronic interaction between Zn and Ag that might have suppressed the catalytic activity of the cathode towards methanation.
Highlights
Issues related to the over-exploitation of fossil fuels coupled with the alarming emission of greenhouse gases have made a compelling case for atmospheric CO2 recycling via conversion to valuable fuels and chemicals
Many such approaches are being explored that allow effective valorisation of C O2, one of the most promising ones being electrolytic routes where CO2 captured from air undergoes electrochemical reduction along with water into chemical feedstocks and fuels [1,2,3,4]
Electrochemical CO2 reduction in an aqueous environment at lower temperatures is a complex process that involves multielectron/proton transfer processes coupled with numerous possible reaction intermediates and products [7,8,9]. CO2 electroreduction in solid oxide electrolytic cells (SOEC) involves a less complicated reaction pathway and has been a topic of great interest in the past many years [3, 4, 10, 11]
Summary
Issues related to the over-exploitation of fossil fuels coupled with the alarming emission of greenhouse gases have made a compelling case for atmospheric CO2 recycling via conversion to valuable fuels and chemicals. Many such approaches are being explored that allow effective valorisation of C O2, one of the most promising ones being electrolytic routes where CO2 captured from air undergoes electrochemical reduction along with water into chemical feedstocks and fuels [1,2,3,4]. The cathode electrode where electroreduction of CO2 occurs is key component that needs further development and optimisation to achieve target selectivity and conversion rates using minimal energy
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