Efficient and durable catalysts are needed to convert CO₂ to value added products. In recent years, extensive research has been done on tin (Sn) because of its high faradaic efficiency for producing formate (HCOO^-) from CO₂ [1–5] and lead (Pb) because of its high hydrogen evolution (HER) overpotential [4, 6]. In our recent study [7], bimetallic Sn-Pb catalysts with five different Sn/Pb atomic ratios were electrodeposited on Teflonated carbon paper and non-Teflonated carbon cloth using both metal fluoroborate- and metal oxide-containing deposition media to produce catalysts for electrochemical reduction of CO₂ (ERC) to HCOO^-. The interaction between catalyst composition, morphology, substrate and deposition media was investigated by cyclic voltammetry followed by chronoamperometry at -2.0 V vs. Ag/AgCl for 2 h in 0.5 M KHCO₃. Sn majority catalysts with 15 to 35 atomic % Pb generated faradaic efficiencies up to 95% with stable performance. Pure Sn catalysts on the other hand, in spite of high initial stage formate production rates, experienced extensive (up to 30%) decrease of the faradaic efficiency. The decrease in faradaic efficiency is most likely due to the reduction of the SnO₂ layer to metallic Sn⁰ during formate production. This newly formed Sn⁰ surface is no longer active for CO₂ reduction to formate but instead preferentially produces parasitic H₂. XRD results demonstrated the presence of polycrystalline SnO₂ after electrolysis using Sn-Pb catalysts with 35 atomic % Pb and its absence in case of pure Sn. It is proposed that the presence of Pb (15 to 35 at %) in Sn majority catalysts stabilized SnO₂, which is responsible for the enhanced faradaic efficiency and catalytic durability in ERC. Our results point to a promising strategy for increasing the durability of Sn based catalyst materials for ERC.

1. Oloman C, Li H (2008) Electrochemical Processing of Carbon Dioxide. ChemSusChem 1:385–391. doi: 10.1002/cssc.200800015
2. Li H, Oloman C (2005) The Electro-Reduction of Carbon Dioxide in a Continuous Reactor. J Appl Electrochem 35:955–965. doi: 10.1007/s10800-005-7173-4
3. Bumroongsakulsawat P, Kelsall GH (2015) Tinned graphite felt cathodes for scale-up of electrochemical reduction of aqueous CO₂. Electrochimica Acta 159:242–251. doi: 10.1016/j.electacta.2015.01.209
4. Alvarez-Guerra M, Del Castillo A, Irabien A (2014) Continuous electrochemical reduction of carbon dioxide into formate using a tin cathode: Comparison with lead cathode. Chem Eng Res Des 92:692–701. doi: 10.1016/j.cherd.2013.11.002
5. Chen Y, Kanan MW (2012) Tin Oxide Dependence of the CO₂ Reduction Efficiency on Tin Electrodes and Enhanced Activity for Tin/Tin Oxide Thin-Film Catalysts. J Am Chem Soc 134:1986–1989. doi: 10.1021/ja2108799
6. Innocent B, Liaigre D, Pasquier D, Ropital F, Léger J-M, Kokoh KB (2009) Electro-reduction of carbon dioxide to formate on lead electrode in aqueous medium. J Appl Electrochem 39:227–232. doi: 10.1007/s10800-008-9658-4
7. Gyenge EL, Moore CE (2017) Tuning the Composition of Bimetallic Electrodeposited Sn-Pb Catalysts for Enhanced Activity and Durability in CO₂ Electroreduction to Formate. ChemSusChem 17:3512-3519 . doi: 10.1002/cssc.201700761

Figure 1. Cumulative formate production faradaic efficiency (FE) (a, c) and total moles of formate synthesized (b, d) for catalysts produced by electrodeposition using the fluoroborate bath. Chronoamperometry at -2.0 V vs Ag/AgCl in 0.5 M KHCO₃ at 293 K for 2 hours. Substrates: (a, b) teflonated carbon paper and (c, d) carbon cloth.