Octahedral SnO2 Single Crystals for Selective CO2 Electroreduction

Abstract

CO2 electrochemical reduction is one of the effective ways to close the global anthropogenic carbon cycle. However, CO2 reduction is a sluggish process involving multi-electrons and multi-protons transfer and needs to compete with hydrogen evolution reaction (HER)1. According to the pioneering studies by Hori et al., metal catalysts can be classified into four categories in terms of main products, where formic acid/formate as an ideal hydrogen storage carrier is an attractive product. Indeed, a recent technoeconomic analysis shows that the 2e- products (formate and CO) are more desirable. The p-block transition metals (such as In, Sn, Pb, Tl, Bi) have been found to be able to selectively convert CO2 to formate. In particular, tin-based catalysts have been intensively investigated owing to its inexpensive price and low toxicity.Our previous work has explored the size effect of SnO2 nanoparticles and carbon support effect on the catalytic activity for CO2 electroreduction2. Kanan’s group has also investigated bulk tin oxide layer for the CO2 electroreduction3. Unfortunately, all the aforementioned tin catalysts display volcano-type formate selectivity against potential plots, since too positive or too negative potentials favor competitive hydrogen evolution reaction, which limits their applications in practical CO2 electrolyzers.Herein, we have synthesized octahedral SnO2 single crystals exposed with facets denoted (332) and (111). Interestingly, those high-energy facets exhibit remarkably high CO2 catalytic activity and high formate selectivity of over 80% within a ~500 mV potential window. Density function theory (DFT) calculations and In situ Raman spectroscopic studies demonstrate that the strong adsorption energies for *OCHO species and weak binding strength to HCOOH* favor formate production in a broad potential range. We believe this work will advance the development of practical CO2 electrolyzers.Reference1 Zhang, S.; Fan, Q.; Xia, R.; Meyer, T. J. Acc. Chem. Res. 2020, 53 (1), 255-264.2 Zhang, S.; Kang, P.; Meyer, T. J. J. Am. Chem. Soc. 2014, 136 (5), 1734-1737.3 Chen, Y.; Kanan, M. W. J. Am. Chem. Soc. 2012, 134 (4), 1986-1989.