Surfactant Doping Effect on the Performance of Gold Nanocluster-Modified Electrodes for CO2 Electroreduction

Electrochemical reduction of carbon dioxide (CO2RR) is a promising approach for converting CO2 into useful chemical products while helping to reduce atmospheric CO2 levels. However, advancing this technology requires developing efficient electrocatalysts and precise surface engineering strategies to improve reaction selectivity, suppress competing reactions, and maximize active-site utilization. In this work, we modified highly oriented pyrolytic graphite (HOPG) electrodes with atomically precise Au25(SC4)18 nanoclusters (AuNCs) mixed with didodecyldimethylammonium bromide (DDAB) surfactant using the Langmuir–Schaefer (LS) technique. This approach allowed us to control the arrangement of nanoclusters on the electrode surface by tuning the deposition surface pressure and the component ratios in the film. Adding DDAB to the AuNCs film: (i) improves the spreading of the AuNCs at the air–water and electrode–solution interfaces, enhancing the exposed active sites to the reactant, and (ii) provides a suitable hydrophobic microenvironment to increase local CO2 concentration near the electrode. The electrode modified with an AuNCs film doped with 5% DDAB, in which AuNCs exposure and the hydrophobic effect of DDAB were optimally balanced, exhibited the best electrocatalytic activity toward CO2. The maximum turnover frequency (TOFCO) of 49.45 s–1 at –1.50 V vs Ag|AgCl, achieved with the AuNCs/DDAB 95/5% electrode, was significantly higher than that of the electrode modified with AuNCs alone. These findings demonstrate that combining Au25(SC4)18 nanoclusters with the positively charged DDAB surfactant provides an effective way to tune surface hydrophobicity, manipulate the microenvironment, and enhance nanocluster dispersion on the electrode.