CO2 photoreduction using encapsulated potassium bismuth iodide (K3Bi2I9) perovskite in porous supports

Lead-free halide perovskites (LFHP) are one of the most promising materials for CO₂ photoreduction; however, their stability is an issue that must be solved to scale up the manufacturing. To overcome this limitation, this work proposes the encapsulation of LFHP of K₃Bi₂I₉ in three inorganic supports based on aluminosilicates such as (i) geopolymer, (ii) tobermorite, and other based on (iii) magnesium oxychloride. These supports provide a porous structure and active sites to host the perovskite particles, which favor enhanced light absorption, stability, and their activity for CO₂ reduction under visible light. The encapsulated perovskites exhibited activity to photoconvert CO₂ into formic acid (HCOOH) with efficiencies up to 2500 μmol h⁻¹ using the K₃Bi₂I₉ host in geopolymer. This support provides stable polysialate-diloxo chains to encapsulate the perovskite, delayed the degradation in aqueous medium, and its activity was demonstrated during 16 h of continuous visible light irradiation. The good stability and efficiency for CO₂ reduction was associated to the formation of K₃Bi₂I₉/BiOI heterojunction that prevent the degradation of the structure and enhance the charge transfer between both semiconductors.