Polyethylenimine-assisted Synthesis of Au Nanoparticles for Efficient Syngas Production

The ability to capture, store, and use CO₂ is important for remediating greenhouse-gas emissions and combatting global warming. Herein, Au nanoparticles (Au-NPs) are synthesized for effective electrochemical CO₂ reduction and syngas production, using polyethylenimine (PEI) as a ligand molecule. The PEI-assisted synthesis provides uniformly sized 3-nm Au NPs, whereas larger irregularly shaped NPs are formed in the absence of PEI in the synthesis solution. The Au-NPs synthesized with PEI (PEI−Au/C, average PEI Mw=2000) exhibit improved CO₂ reduction activities compared to Au-NPs formed in the absence of PEI (bare Au NPs/C). PEI−Au/C displays a 34 % higher activity toward CO₂ reduction than bare Au NPs/C; for example, PEI−Au/C exhibits a CO partial current density (j_CO) of 28.6 mA cm⁻² at −1.13 V_RHE, while the value for bare Au NPs/C is 21.7 mA cm⁻²; the enhanced j_CO is mainly due to the larger surface area of PEI−Au/C. Furthermore, the PEI−Au/C electrode exhibits stable performance over 64 h, with an hourly current degradation rate of 0.25 %. The developed PEI−Au/C is employed in a CO₂-reduction device coupled with an IrO₂ water-oxidation catalyst and a proton-conducting perfluorinated membrane to form a PEI−Au/C|Nafion|IrO₂ membrane-electrode assembly. The device using PEI−Au/C as the CO₂-reduction catalyst exhibits a j_CO of 4.47 mA/cm² at 2.0 V_cell. Importantly, the resulted PEI−Au/C is appropriate for efficient syngas production with a CO ratio of around 30–50 %.