Abstract
Novel electrocatalysts based on zinc oxide (ZnO) and biochars are prepared through a simple and scalable route and are proposed for the electrocatalytic reduction of CO₂ (CO₂RR). Materials with different weight ratios of ZnO to biochars, namely, pyrolyzed chitosan (CTO) and pyrolyzed brewed waste coffee (CBC), are synthesized and thoroughly characterized. The physicochemical properties of the materials are correlated with the CO₂RR to CO performance in a comprehensive study. Both the type and weight percentage of biochar significantly influence the catalytic performance of the composite. CTO, which has pyridinic- and pyridone-N species in its structure, outperforms CBC as a carbon matrix for ZnO particles, as evidenced by a higher CO selectivity and an enhanced current density at the ZnO_CTO electrode under the same conditions. The study on various ZnO to CTO weight ratios shows that the composite with 40.6 wt % of biochar shows the best performance, with the CO selectivity peaked at 85.8% at −1.1 V versus the reversible hydrogen electrode (RHE) and a CO partial current density of 75.6 mA cm–² at −1.3 V versus RHE. It also demonstrates good stability during the long-term CO₂ electrolysis, showing high retention in both CO selectivity and electrode activity.
Highlights
The electrochemical conversion of carbon dioxide (CO2) to valuable fuels and chemicals using renewable electricity while reducing CO2 emissions is of high economic and environmental interest.[1,2] Among many products from the electrochemical CO2 reduction reaction (CO2RR), carbon monoxide (CO) is considered the most important one as it has high relevance for the chemical industry.[3−6] It is a versatile C1-building block and is intensively used in large-scale industrial processes such as the Fischer−Tropsch synthesis of hydrocarbons[7] and Monsanto/Cativa acetic acid synthesis.[8]
Monometallic Zn-based electrocatalysts can be obtained with different particle shapes and porosities, showing good performance for converting CO2 to CO.[16−20] Zn metal can be combined with other metals, for example, copper (Cu),[21,22] to obtain enhanced efficacy and selectivity
The carbon weight percentage incorporated into zinc oxide (ZnO)-based samples was determined by TG analyses
Summary
Building block and is intensively used in large-scale industrial processes such as the Fischer−Tropsch synthesis of hydrocarbons[7] and Monsanto/Cativa acetic acid synthesis.[8] Despite the CO2RR being an appealing technology, it presents some drawbacks associated with high kinetic barriers, multistep reactions, and competitive hydrogen evolution reaction (HER), leading to a high overpotential, a poor conversion rate, and low selectivity.[2] To overcome these issues, sustainable, cost-efficient, and high-performance electrocatalysts capable of efficiently converting CO2 into CO must be developed.[9,10] For this purpose, different metal electrodes such as gold (Au),[11−13] silver (Ag),[14] palladium (Pd),[15] and zinc (Zn)[16−18] have been suggested. Zn/ rGO electrodes were prepared and tested in the CO2RR, with a CO Faradaic efficiency of 85% at −0.84 V versus reversible
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