Enhanced Production of Formic Acid in Electrochemical CO₂ Reduction over Pd-Doped BiOCl Nanosheets

Bismuth oxyhalides (BiOX, X = F, Cl, Br, I) are emerging energy materials because of their remarkable catalytic activity. The BiOX compounds usually have a tetragonal type crystal structure with unique layered morphology consisting of [X-Bi-O-Bi-X] sheets. Although the BiOX nanosheets exposed with {001} facets perform superior photoactivity, there is lack of understanding about their capability in the electrochemical CO₂ reduction reaction (CO₂RR). Herein, we adopt wet-chemical syntheses to make 2D BiOCl and Pd-doped BiOCl nanosheets for CO₂RR. In the results, formic acid is the only one kind of product converted from CO₂ along with H₂ gas from water reduction over both BiOCl and Pd-doped BiOCl nanosheets. By thorough analyses with ex situ and in situ spectroscopy, the results reflect that (1) metallic Bi⁰ atoms generated by the applied negative potentials serve as the catalytic sites for the hydrogen evolution reaction (HER) and CO₂RR and (2) the existence of doped Pd ions in the BiOCl structure reduces the barrier of charge transfer over the nanosheets, which enhances HER and CO₂RR activities. We believe that the observations are important references for making catalysts toward CO₂RR performance.