Selective Electrocatalytic Reduction of CO₂ into CO at Small, Thiol-Capped Au/Cu Nanoparticles

Abstract

The electrochemical CO2 reduction reaction (CO2RR) is a promising approach for converting fossil fuel emissions into environmentally sustainable chemicals and fuels. The ability to control the surface structure of CO2RR nanocatalysts provides an opportunity to tune product selectivity. Bimetallic gold–copper catalysts have been identified as emerging electrocatalyst candidates, but Cu incorporation typically lowers product selectivity compared with pure Au. Here we show sustained CO selectivity and activity up to 49% Cu content in small (<2 nm), thiol-capped Au/Cu nanoparticles (NPs). Bimetallic NPs containing 49% Cu selectivity converted CO2 into CO with 100 ± 6% CO Faradaic efficiency and average mass activity of ∼500 mA/mg during a 12 h electrolysis experiment at −0.8 V vs RHE. Au/Cu NPs synthesized without thiol ligands selectively produced H2, whereas larger (>10 nm), thermally dethiolated Au/Cu NPs produced a wider product distribution including H2, CO, and C2H4. Density functional theory (DFT) modeling of CO2RR and H2 evolution at realistic, thiol-capped Au/Cu NP structures indicated that copper–thiol surface structures sustained CO selectivity by stabilizing key *CO intermediates while making *H binding less favorable. Calculations also predicted that removing a significant fraction of the thiol ligands would increase *CO binding strength such that desorption of CO product molecules could become the most thermodynamically challenging step. This result, coupled with increased *H stability on dethiolated nanoclusters, points to decreased CO2RR selectivity for small, ligand-free catalysts, which is in line with experimental observations from our group and others. Our results demonstrate that thiol-ligand surface structures can sustain the CO selectivity of bimetallic Au/Cu NPs and reduce precious metal requirements for CO2RR.

Galvanic Replacement of Electrochemically Restructured Copper Electrodes with Gold and Its Electrocatalytic Activity for Nitrate Ion Reduction

“…The gold coverage estimated from EDX analysis for the 3 min of galvanic replacement gave a value of 9 wt %. This synergistic effect between Cu 2 O and Au, as well as the bimetallic Cu/Au system has been reported previously for heterogeneous catalysis reactions [ 33 , 46 , 47 , 68 , 69 ], as well as electrocatalytic reactions [ 33 , 70 , 71 , 72 ]. To ensure that the electrocatalytic response was not due to the reduction of residual oxides on the surface the same linear sweep voltammetry experiments were performed in the absence of nitrate ions ( Figure 6 c).…”

Surface Modification for Promoting Durable, Efficient, and Selective Electrocatalysts

“…A small number of examples concerning the activation of other fuel molecules can be found in the literature. Recently, Kauffman and coworkers have reported the electrocatalytic activity of small thiol‐capped AuCu nanoparticles toward CO 2 RR . When capped with thiols, small (2 nm) bimetallic AuCu (49 at % Cu) nanoparticles convert selectively CO 2 to CO with nearly 100 % FE with a cathodic E onset shift of 120 mV.…”

Noble Metal Nanostructured Materials for Chemical and Biosensing Systems

“…Due to the strong passivation of thiol substances, the obtained AuNPs have relatively small particle size and good stability (no aggregation and decomposition), though the particle size distribution range is relatively wide [30,31]. Furthermore, using a thiol compound such as 5-phenylthiocarbazole or cysteine as stabilizer and a large molecular polymer such as polyhexamethylene glycol, silk fibroin or polyaniline as reducing agent, the prepared AuNPs were with a uniform particle size and suitable for the construction of sensing systems with high performance [32,33]. Reverse micelle or microemulsion method refers to a heterogeneous liquid phase synthesis method for forming micelles or reverse micelle droplets between a surfactant and a solution for restraining the size or morphology of NPs [34].…”