Biochar/Zinc Oxide Composites as Effective Catalysts for Electrochemical CO2 Reduction

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.

Automated summary

Novel electrocatalysts based on zinc oxide and biochars were prepared through a simple and scalable route for the electrocatalytic reduction of CO2. The study found that pyrolyzed chitosan with pyridinic- and pyridone-N species outperformed pyrolyzed brewed waste coffee in terms of CO selectivity and current density. The composite with 40.6 wt % of biochar showed the best performance, with high CO selectivity and electrode activity retention during long-term CO2 electrolysis.