High crystallinity Sn crystals on Ni foam: an ideal bimetallic catalyst for the electroreduction of carbon dioxide to syngas

Abstract

The investigation of highly efficient catalysts for the electrochemical reduction of carbon dioxide (ER-CO₂) is the most critical challenge to commercialize conversion and utilization of CO₂. Herein we propose a new and very promising catalyst, high crystallinity Sn crystals on Ni foam (Sn@f-Ni), for the electroreduction reaction of CO₂ in potassium bicarbonate aqueous solution. The catalyst is fabricated in situ on a pretreated Ni foam substrate through a galvanostatic electrodeposition strategy. SEM and XRD demonstrate that high crystallinity Sn crystals, with an average size of 2–3 μm, evenly dispersed on the Ni foam support can be reproducibly obtained. Electrochemical measurements demonstrate that the Sn@f-Ni electrode at the deposition current of 15 mA exhibits superior performance in promoting the ER-CO₂. Tafel measurements show that except for electrodes with a deposition current of 5 mA, the Tafel slopes of the other four electrodes are all above 100 mV dec⁻¹, which is consistent with a rate-determining initial electron transfer to CO₂ to form a surface adsorbed intermediate, a mechanism that is commonly invoked for metal electrodes. A stable composition of syngas can be obtained by electrolysis at −1.7 V potential (vs. Ag/AgCl), indicating that the Sn surface with high crystallinity conforms to the Heyrovsky–Volmer mechanism at a potential of −1.7 V. The ratio of CO and H₂ generation was about 1 : 2, meaning it could be used as syngas for preparing some valuable fuels. This work provided an efficient method to convert the surplus CO₂ to valuable syngas.