Abstract
A class of metal-doped polyanilines (PANIs) was synthesized and investigated as electrocatalysts for the carbon dioxide reduction reaction (CO2RR). These materials show good affinity for the electrode substrate and allow to obtain stable binder-free electrodes, avoiding the utilization of expensive ionomer and additives. The emeraldine-base polyaniline (EB-PANI), in absence of metal dopant, shows negligible electrocatalytic activity and selectivity toward the CO2RR. Such behavior significantly improves once EB-PANI is doped with an appropriate cationic metal (Mn, Cu or Sn). In particular, the Sn-PANI outperforms other metal-doped samples, showing a good turnover frequency of 72.2 h−1 for the CO2RR at − 0.99 V vs the reversible hydrogen electrode and thus satisfactory activity of metal single atoms. Moreover, the Sn-PANI also displays impressive stability with a 100% retention of the CO2RR selectivity and an enhanced current density of 4.0 mA cm−2 in a 10-h test. PANI, a relatively low-cost substrate, demonstrates to be easily complexed with different metal cations and thus shows high tailorability. Complexing metal with conductive polymer represents an emerging strategy to realize active and stable metal single-atom catalysts, allowing efficient utilization of metals, especially the raw and precious ones.Graphic abstract
Highlights
Energy consumption rapidly grows all around the world, from emerging countries with conventional industries to western society with more and more sophisticated technologies, demanding fast increase in the fossil fuels combustion and boosting the CO2 emission
A typical absorption pattern of polyaniline is observed for the ES-PANI (Figure S1) and it is preserved for the emeraldine-base polyaniline (EB-PANI) and metaldoped samples (Fig. 1)
EB-PANI shows the characteristic νN–H at 3172 cm−1 stretching of secondary amines, the νC–H at 3031 cm−1 stretching of aromatic rings, the νC–N at 1597 cm−1 of the benzenoid ring and the νC–C at 1495 cm−1 stretching of the quinoid ring of the polymer chain, the νC–N at 1312 cm−1 stretching of aromatic amines, the quinoid ring stretching at 1151 cm−1, and the out of plane bending of para-disubstituted benzene at 819 cm−1
Summary
Energy consumption rapidly grows all around the world, from emerging countries with conventional industries to western society with more and more sophisticated technologies, demanding fast increase in the fossil fuels combustion and boosting the CO2 emission. A general limit of metallic electrodes is the high price and the scarce availability of many chemical species These materials, even in the form of nanostructures, have low active sites-to-mass ratios. In order to enhance the metal utilization, an ideal strategy is to constrain each single metal atom to act as active site for the reaction [14,15,16,17] From this perspective, organometallic complexes are the best example, in which each metal cation/atom coordinates different ligands, being stabilized and enriched in electron density [18]. Organometallic complexes are the best example, in which each metal cation/atom coordinates different ligands, being stabilized and enriched in electron density [18] Those molecules are commonly used in homogeneous catalysis systems that require the catalyst dissolution in a proper solvent without being immobilized onto the working electrode. High overpotentials could be required to form the active catalytic species and to overcome the low conductivity
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