Deposition of Bismuth Nanoplatelets onto Graphene Foam for Electrocatalytic CO₂ Reduction

Bismuth nanoplatelets are efficient electrocatalysts for reducing carbon dioxide to formate─a promising renewable energy storage media. Yet, while various promising catalyst supports are acid-sensitive, deposition of Bi on these supports is hindered by the Bi3+ ions’ solubility, which is limited to low pH values (<2). Here, we used monometallic and bimetallic Bi thiolate precursors to electrodeposit metallic Bi nanoplatelets from a pH-neutral solution. Analysis of the electrochemical deposition mechanism revealed an intricate kinetic balance between the electron transfer and precursor dissociation steps and a stronger tendency toward instantaneous nucleation and growth when the bimetallic precursor was used. In continuance, the nanoplatelets electrodeposited from the bimetallic precursor were thinner than the nanoplatelets electrodeposited from the monometallic precursor. They exhibited an ∼120 mV lower overpotential at 5 mA/cm2 for reduction of CO2 to formate. Both electrocatalysts yielded high faradaic efficiency (∼95%) for formate generation when deposited on a flat support. Finally, a highly conformal coating of graphene foam with Bi nanoplatelets was obtained, which yielded a low onset potential (∼350 mV vs RHE) for CO2 reduction to formate. This work establishes a facile route for coating acid-sensitive supports with functional coatings using thiolate-based precursors for the first time. It also lays out the reaction mechanism and correlation between the precursor structure–electrodeposit structure and functionality.