CO₂ Reduction to Formate on Amine Modified Pb Electrodes

The electrochemical conversion of CO2 into high value-added chemicals and fuels using renewable energy sources is of considerable interest. Lead is among the best electrode materials for the reduction of CO2 to formic acid (or formate). However, the Faradic efficiency and energy efficiency of this process are hindered by the competing hydrogen evolution reaction (HER) at high reduction potentials. Strategies to improve the performance of Pb electrodes include the formation of metastable Pb oxide layers [1], the formation of 3D porous structures [2], and the growth of active Pb (100) surfaces on a dendrite-like secondary structure [3]. In this work, the growth of islands-like aryl-aliphatic, aminophenyl and nitrophenyl amines on Pb surfaces is proposed as an effective way to improve toward the Faradic efficiency of the reduction of CO2 to formate [4]. The aryl-aliphatic amines and aminophenyl porous layers were grafted on the surface of Pb surfaces using diazonium chemistry. The grafting of the amines results in a lower Pb electroactive sites which in turn hinders the HER but without blocking the active sites for the CO2 reduction, Figure 1.a. In fact, the porous organic film lowers the overpotential for the CO2 reduction reaction. Because of these combined effects, the Faradic efficiency for formate increases from 8% for the bare Pb to 94% for modified Pb electrodes, Figure 1.b. The present study offers a new route to decouple CO2 reduction from the HER, thus allowing the development of highly efficient and selective electrodes for the electroreduction of CO2 into value added products. Figure 1. (a) Current densities recorded at -1.09 V vs RHE in Ar- and CO2- saturated electrolyte and their difference (Δ(CO2-Ar)) and normalized to Pb electrochemical surface area as a function of the extent of grafting (t) of Pb – modified electrodes with 4-ABA (4-aminomethylbenzene); (b) Faradic efficiency for formate as a function of the (N/Pb) atomic ratio determined by XPS for various Pb – modified electrodes: 4-ABA (4-aminomethylbenzene), 3-ABA (3-aminomethylbenzene), AEA (4-(2-aminoethyl)benzene), 4-NB (nitrobenzene). Acknowledgments This work was financially supported by NSERC (Canada). N. Z. acknowledges the Tunisian government for the INRS-Tunisia agreement scholarship. M.F. acknowledges the FRQNT (Quebec, Canada) for the PBEEE scholarship. References [1] C.H. Lee, M.W. Kanan, ACS Catalysis 2015, 5, 465-469. [2] Z. He, J. Shen, Z. Ni, J. Tang, S. Song, J. Chen, L. Zhao, Catalysis Communications 2015 , 72, 38-42. [3] M. Fan, S. Garbarino, G.A. Botton, A.C. Tavares, D. Guay, Journal of Materials Chemistry A 2017, 5, 20747-20756. [4] N. Zouaoui, B. Ossonon, M. Fan, S. Garbarino, G. de Silveira, G. A. Botton, D. Guay, A. C. Tavares, Journal of Materials Chemistry A 2019 , 7, 11272-11281. Figure 1

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