Tuning the Composition of Bimetallic Electrodeposited Sn-Pb Catalysts for Enhanced Activity and Durability in CO2 Electroreduction to Formate
Authors: Moore Colin Edward , Gyenge Elod L. 
Published: February 2022

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 This newly formed Sn0 surface is no longer active for CO2 reduction to formate but instead preferentially produces parasitic H2.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.

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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.

Figure 1