Hierachical Aerogel-Supported Cu–Sn–Ox Solid Solutions for Highly Selective CO2 Electroreduction and Zn–CO2 Batteries

The electrochemical CO₂ reduction reaction (CO₂RR) into high-value carbon compounds such as CO and HCOOH is a promising strategy for the utilization and conversion of emitted CO₂. However, the selectivity of the CO₂RR for HCOOH is typically less than 90% and operates within a narrow voltage range, which limits its practical application. Herein, we propose a novel heterostructural aerogel as a highly efficient electrocatalyst for CO₂RR to HCOOH. This catalyst consists of Cu-Sn-O_x solid solutions embedded in a reduced graphene oxide matrix (Cu-Sn-O_x/rGO). The incorporation of Cu²⁺ into the SnO₂ matrix enhances HCOOH production by improving the adsorption of the *OCHO intermediate and inhibiting H₂ evolution, as confirmed by in situ measurements and computational studies. As a result, Cu-Sn-O_x/rGO achieves a remarkable Faradaic efficiency (FE) of up to 91.4% for HCOOH and maintains high selectivity over a broad operating voltage range (-0.8 to -1.1 V). Additionally, the assembled Zn-CO₂ batteries demonstrated an excellent power density of 1.14 mW/cm² and exceptional stability for over 25 h.