Photoelectrochemically Induced CO2 Reduction Using Halide-Tunable Lead-Free Perovskites

We report on a series of ambient processed, all-inorganic, lead-free nanocrystalline perovskites, viz. Cs<inf>3</inf>Bi<inf>2</inf>Cl<inf>9-x</inf>Br<inf>x</inf>, which are halide-tunable and demonstrate photocatalytic CO<inf>2</inf> reduction. The conversion yield of CO<inf>2</inf> to CO could be tuned by meticulously regulating the Cl-to-Br ratio within the perovskite material. While all of the samples demonstrated CO<inf>2</inf> reduction purely under photoillumination (i.e., illumination with an applied bias of 0 V vs Ag/AgCl), it was remarkable that the conversion yield almost doubled for all samples on applying a negative potential of −0.5 V vs Ag/AgCl to the photocatalyst in addition to the illumination. This display of synergistic enhancement in yield under simultaneous application of light and electrical stimulus was maximized for the Cs<inf>3</inf>Bi<inf>2</inf>Br<inf>3</inf>Cl<inf>6</inf> nanocrystal variant, which registered a maximum yield of ∼105 μmol/g after 3 h of continuous illumination together with an applied bias of −0.5 V vs Ag/AgCl. The sample demonstrated decent stability over 10 h with a collective CO yield of 239.02 μmol/g. Such a competent CO yield is ascribed to the efficient charge carrier separation and migration to the reactive sites, further corroborated by a quantitative assessment of the electrochemical impedance spectroscopy (EIS) Nyquist plots of the nanocrystal variants. This study strives to provide new avenues and crucial insights into innovative designs, synthesis, and fabrication of competent, lead-free halide perovskite materials for CO<inf>2</inf> reduction using photocatalysis.