Cobalt-Doped Bismuth Nanosheet Catalyst for Enhanced Electrochemical CO 2 Reduction to Electrolyte-Free Formic Acid.

Electrochemical carbon dioxide (CO ₂ ) reduction reaction (CO ₂ RR) to valuable liquid fuels, such as formic acid/formate (HCOOH/HCOO ^- ) is a promising strategy for carbon neutrality. Enhancing CO ₂ RR activity while retaining high selectivity is critical for commercialization. To address this, we developed metal-doped bismuth (Bi) nanosheets via a facile hydrolysis method. These doped nanosheets efficiently generated high-purity HCOOH using a porous solid electrolyte (PSE) layer. Among the evaluated metal-doped Bi catalysts, Co-doped Bi demonstrated improved CO ₂ RR performance compared to pristine Bi, achieving ~90 % HCOO ^- selectivity and boosted activity with a low overpotential of ~1.0 V at a current density of 200 mA cm ^-2 . In a solid electrolyte reactor, Co-doped Bi maintained HCOOH Faradaic efficiency of ~72 % after a 100-hour operation under a current density of 100 mA cm ^-2 , generating 0.1 M HCOOH at 3.2 V. Density functional theory (DFT) results revealed that Co-doped Bi required a lower applied potential for HCOOH generation from CO ₂ , due to stronger binding energy to the key intermediates OCHO* compared to pure Bi. This study shows that metal doping in Bi nanosheets modifies the chemical composition, element distribution, and morphology, improving CO ₂ RR catalytic activity performance by tuning surface adsorption affinity and reactivity.
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