Insights into in situ one-step synthesis of carbon-supported nano-particulate gold-based catalysts for efficient electrocatalytic CO2 reduction

Abstract

Gold materials are typical catalysts for electroreduction of CO₂ into CO. However, a conventional two-step method involving pre-forming gold nanoparticles and their subsequent deposition on carbon is inconvenient and uneconomical. Herein, carbon supported gold/gold sulfide nanoparticles (ca. 4.2 nm) and gold/gold(III) compound nanoparticles (ca. 4.1 nm) were synthesized via an in situ one-step procedure using sodium sulfide (SS) and urea (UR) as precipitating agents, respectively. Preliminary electroreduction at −0.78 V versus the reversible hydrogen electrode (RHE) in CO₂-saturated KHCO₃ could reduce and reconstruct the two freshly prepared catalysts, i.e., Au–SS/C and Au–UR/C, into carbon-supported metallic gold nanoparticles with a somewhat larger size and result in a substantial removal of residual CTAC ligands. Detectable amounts of mono- and poly-sulfides remained on the Au surface of the reduced Au–SS/C. Studies on electrocatalytic CO₂ reduction revealed that the electrochemically reduced forms of Au–SS/C and Au–UR/C deliver 1.7-fold and 2-fold enhanced maximum CO current densities at around −0.96 V versus RHE compared with polycrystalline Au foil, respectively. Besides, they exhibit CO faradaic efficiencies as high as 91.8% and 94.2%, respectively, and show good long-term stability. Argon-annealing of the two freshly prepared catalysts could also transform the gold sulfide and gold(III) compound into metallic gold, but decreased the number and/or accessibility of active sites, being proved as a counterproductive strategy for electroreduction of CO₂ to CO.