Efficient Electrochemical Reduction of CO₂ to HCOOH over Sub‐2 nm SnO₂ Quantum Wires with Exposed Grain Boundaries

Electrochemical reduction of CO₂ could mitigate environmental problems originating from CO₂ emission. Although grain boundaries (GBs) have been tailored to tune binding energies of reaction intermediates and consequently accelerate the CO₂ reduction reaction (CO₂ RR), it is challenging to exclusively clarify the correlation between GBs and enhanced reactivity in nanostructured materials with small dimension (<10 nm). Now, sub-2 nm SnO₂ quantum wires (QWs) composed of individual quantum dots (QDs) and numerous GBs on the surface were synthesized and examined for CO₂ RR toward HCOOH formation. In contrast to SnO₂ nanoparticles (NPs) with a larger electrochemically active surface area (ECSA), the ultrathin SnO₂ QWs with exposed GBs show enhanced current density (j), an improved Faradaic efficiency (FE) of over 80 % for HCOOH and ca. 90 % for C1 products as well as energy efficiency (EE) of over 50 % in a wide potential window; maximum values of FE (87.3 %) and EE (52.7 %) are achieved.