Sequential biligand engineering of gold nanoparticles for near-unity selectivity and long-term stability in electrochemical CO2 reduction.

Electrochemical reduction of CO2 into CO is a promising technique to close the carbon cycle and provide chemical feedstocks sustainably, but achieving high selectivity at industrially relevant current densities remains challenging, often accompanied by catalyst poisoning from residual synthesis ligands. This work employs sequential biligand engineering using oleylamine (OAm) and 1-dodecanethiol (DDT) to synthesize gold nanoparticles (Au@OAm/DDT) under an inert atmosphere, yielding uniformly well-dispersed spherical 6.5 ± 0.03 nm nanoparticles, highly selective for CO production. This biligand shell is hypothesized to create a synergic nanoenvironment in which the OAm domains could potentially act as local CO2 concentrators, while the hydrophobic ligand matrix impedes water access, thereby promoting CO production and suppressing the HER. When integrated with a carbon substrate at loadings of 30-60 wt%, the 30 wt% loading notably exhibits an exceptional CO faradaic efficiency (FECO% = 99% ± 1.2%) at -0.7 V vs. RHE and chronoamperometric stability over 160 h (FECO% = 93% ± 2.1% retention). Additional chronopotentiometric stability tests across industrially relevant current densities of -10 to -100 mA cm-2 reveal extended operation for tens of hours up to -20 mA cm-2 and a sharp operational ceiling between -20 and -40 mA cm-2 for this catalyst/cell configuration. Au@OAm/DDT significantly outperforms the other Au catalysts (Au@OAm FECO% = 83% ± 1.5%, Au@DDT FECO% = 37% ± 1.2%) at the same -0.7 V vs. RHE, which suffer from aggregation-induced site blockage and surface poisoning, respectively. This study demonstrates that a pre-synthetic ligand scheme is as crucial as post-synthetic activation for developing superior, highly selective electrocatalysts, paving the way for next-generation electrochemical applications.