In this paper we present an easy, quick and scalable route, based on anodic oxidation, for the preparation of mesoporous SnO₂ as an efficient electrocatalyst for the CO₂ reduction reaction (CO₂RR). Crystallographically interconnected SnO₂ nanocrystals with abundant grain boundaries, high specific surface area and easily accessible porosity result to be active and selective for the CO₂RR. This electrocatalyst shows faradaic efficiency (FE) of about 95% at -0.97 V and -1.06 V vs. reversible hydrogen electrode (RHE) towards the formation of predominant HCOOH and minor CO. A peak FE value of 82 % for the HCOOH production is obtained at -1.06 V vs. RHE. High HCOOH partial current densities of 10.2 mA cm^-2 and 15.3 mA cm^-2 are observed at -0.97 V and -1.15 V vs. RHE, respectively. Thorough electrochemical characterizations demonstrate that the synthesized SnO₂-based gas diffusion electrode allows efficient diffusion of CO₂ even at high kinetics, due to the highly open porous structure. The good understanding of the catalyst behavior is achieved also after the electrode testing and it shows that the proposed preparation route results in a stable and durable material. The here reported promising results can be exploited for developing high-performance and sustainable electrocatalysts with a high potentiality to be implemented in real CO₂ conversion devices.

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.