Deposition of Tin Catalysts from Thiolated Precursor Organic Solutions for CO2 Reduction to Formate: A Potential-Dependent Mechanism Study.

The production of efficient catalysts is mandatory to attain superior catalytic performance. Once the catalyst deposition mechanism is clear, one can define the optimal physical and chemical conditions of the deposition process, such as electrolyte composition, reduction potential, current operation mode, the result chemical composition of the catalyst, its structure, and morphology. Here, the electrodeposition mechanism of tin catalysts in dimethyformamide of a thiolated tin complex under potential control for CO2 reduction to formate is investigated. First, a new synthesis route is presented for a tin thiolate precursor, Bis(1,2-ethanedihiolate)Sn(IV). Second, a potential-controlled deposition process of tin from dimethylformamide solutions of this precursor is discussed, with the intention of deposition of tin catalysts on acid-sensitive substrates, such as carbon-composed gas-diffusion-layers. Scan-rate cyclic-voltammetry, scan rate mass-potential, and chronoamperometry measurements expose irregular current-potential and mass change phenomena along electrodeposition, which reflect a complicated potential-dependent mechanism composed of redox and chemical reactions. Disproportionation and comproportionation reactions of tin are indicated by the holistic picture of the potential and time-dependent mass measurements and complementary structure and morphology analysis, suggested as playing an important role in the deposition mechanism of tin. The complex mechanism is untied and the deposition conditions are defined accordingly, in order to deposit tin catalysts with high faradaic efficiency (FEformate = ≈100% with Sn-coated Cu coupons). In practice, tin is electrodeposited potentiostatically from the thiolated tin complex-DMF solution on carbon-based gas-diffusion-layer electrodes. Chronoamperometry measurements of electrochemical reduction of CO2 to formate in the gas-diffusion-electrode cell configuration presented FEformate > 92% and over 170 mA cm-2 along 1 h continuous CO2 gas flow reduction.