Copper (Cu) has unique features for electrochemically converting CO2 to a range of chemicals including hydrocarbons [2], but its selectivity for specific products is low. Especially, at a low or intermediate overpotential, the hydrogen evolution reaction (HER) dominates the overall process on polycrystalline Cu in aqueous solutions [3]. However, the selectivity of Cu can be tuned by introducing a secondary metal. Tin-modified nanostructured Cu (CuSn) electrocatalysts have been developed for electrochemically converting CO2 to carbon monoxide (CO). The doped Sn atoms in the topmost layer alloy with Cu, form a CuSn shell, and efficiently suppress the HER. By optimizing the Sn content in the CuSn layer and the nanostructure, the faradaic efficiency for CO reaches > 90 % at -0.7 V vs. RHE, and remains above 85 % in a wide potential range from -0.7 to -1.0 V [4]. However, the excellent selectivity for CO can be only observed at CuSn dendrites. When the CuSn catalyst has a particulate morphology, the selectivity for CO becomes much worse, even though the surface composition has the optimal Cu/Sn ratio. The CuSn particles are active for the HER at a low overpotential. Although the HER can be efficiently suppressed to a faradaic efficiency of less than 15 % at a high overpotential, the major products for CO2 reduction are both CO and formate (COOH-) [5]. This work highlights the importance of nanostructure and surface composition of CuSn catalysts for active and selective CO2 reduction.
Electrodes consisting of a three-dimensional porous architecture are prepared for a large active surface per unit geometric area. The CO production achieves a high partial current density of 4.9 mA·cm-2 at -0.8 V [4].
[1] Centi, G., et al. Energy Environ. Sci. 2013, 6, 1711-1731 [2] Qiao, J., et al., Chem. Soc. Rev. 2014, 43, 631-675 [3] Li, C., et al., J. Am. Chem. Soc. 2012, 134, 7231-4 [4] Zeng, J., et al., submitted [5] Ju, W., et al., in preparation