Mixed Halide Formation in Lead‐Free Antimony‐Based Halide Perovskite for Boosted CO₂ Photoreduction: Beyond Band Gap Tuning

Abstract

Photocatalytic conversion of carbon dioxide (CO2) into value‐added fuels is a vastly promising anthropogenic chemical carbon cycle to combat the greenhouse effect while meeting the ever‐increasing energy demand. Recently, lead‐based halide perovskites have demonstrated great potential in various applications including photochemical reduction of CO2. However, in view of lead toxicity, the exploration of a lead‐free alternative is crucial for long term application. Herein, a series of lead‐free mixed halide perovskites Cs3Sb2ClxBr9−x (0 ≤ x ≤ 9) is prepared via a facile antisolvent recrystallization technique, where the incorporation of a secondary halide enhances the charge transfer and separation while allowing precise tuning of bandgap between 2.59 and 2.90 eV. Theoretical calculations further reveal that the formation of mixed Cl/Br halides engenders favorable charge redistribution due to lower octahedral distortion, which in turn strengthens CO2 adsorption and activation. Under visible light illumination, the optimal dual halide perovskite, Cs3Sb2Cl4Br5 manifests substantial twofold and fourfold enhancements of CH4 yield over the single halide perovskite, Cs3Sb2Br9 and Cs3Sb2Cl9, respectively. In brief, this study provides a compelling demonstration of lead‐free mixed halide perovskites for photocatalytic CO2 reduction, and it is anticipated to drive further application of perovskite‐based photocatalysts toward a diverse range of artificial photoredox reactions.

Perovskite Paradigm Shift: A Green Revolution with Lead-Free Alternatives in Photocatalytic CO2 Reduction

“…The mixed halide strategy was employed for the synthesis of Sb-based halide perovskites, forming Cs 3 Sb 2 Cl x Br 9−x (0 ≤ x ≤ 9). 132 Intriguingly, the electronic band structure as illustrated in Figure 16g−i shows that the bandgap type transforms from indirect to direct as Br substitutes Cl. Apart from bandgap tuning, it was discovered that the formation of Cl/Br halides led to a lower octahedral distortion and favorable charge redistribution, which in turn resulted in strengthened CO 2 adsorption and activation as depicted in Figure 16j Encapsulation.…”

“…The ligand-free anti-solvent recrystallization technique is generally used for the preparation of microscale halide perovskites. 132,146,180,181 The procedure is analogous to ligand-assisted reprecipitation, except that ligands are not utilized in the anti-solvent recrystallization method. For example, ligand-free Cs 3 Sb 2 Br 9 can be synthesized by adding a small amount (500 μL) of the DMSO solution comprising dissolved precursor salts in stoichiometric ratios into 25 mL of methyl acetate.…”

“…LFHPs are endowed with tunable bandgap, long carrier lifetime, and unique optoelectronic properties. Based on the reported projected density of states (PDOS) from DFT calculations, the CB edge is typically dominated by the antibonding hybrid state from the x orbitals of B-site metallic atoms ( x depends on the type of metal atoms) with little contribution from the p orbitals of X-site halogen atoms. − Meanwhile, the p orbitals of halogen atoms dictate the VB edge, whereas the hybridization of the p orbital of the halogen and the x orbital of the B-site metal determines the composition of the VB. Classically, the A-site atoms have minimal to no participation in the CB nor the VB; hence, the A-site cations hardly influence the optoelectronic properties of LFHPs.…”

“…Conduction and valence band positions of several reported all-inorganic LFHP photocatalysts with the relative potential in photocatalytic CO 2 reduction. The band levels are acquired from published results. ,,− …”

“…Despite being capable of maintaining structural stability, organic ligands with long carbon chains can bind tightly to perovskite surfaces, which may block active sites and hamper charge migration to result in lower photocatalytic activity. ,, Therefore, researchers have also explored the synthesis of halide perovskite materials without the use of organic ligands. The ligand-free anti-solvent recrystallization technique is generally used for the preparation of microscale halide perovskites. ,,, The procedure is analogous to ligand-assisted reprecipitation, except that ligands are not utilized in the anti-solvent recrystallization method. For example, ligand-free Cs 3 Sb 2 Br 9 can be synthesized by adding a small amount (500 μL) of the DMSO solution comprising dissolved precursor salts in stoichiometric ratios into 25 mL of methyl acetate.…”