Air- and water-stable halide perovskite nanocrystals protected with nearly-monolayer carbon nitride for CO2 photoreduction and water splitting

• Air-stable and water-stable halide perovskite photocatalysts. • Core-shell CsPbBr3@monolayer carbon nitride heterojunction. • Visible light harvesting photoanode for water-splitting. • CO2 reduction photocatalyst. • Unusual 30 nm redshift after wrapping CsPbBr3 QDs with CN nanosheets. Halide perovskites are exciting candidates for broad-spectrum photocatalysts but have the problem of ambient stability. Protective shells of oxides and polymers around halide perovskite nano- and micro-crystals provide a measure of chemical and photochemical resilience but the photocatalytic performance of perovskites is compromised due to low electron mobility in amorphous oxide or polymer shells and rapid charge carrier recombination on the surface. Herein an in situ surface passivation and stabilization of CsPbBr 3 nanocrystals was achieved using monolayered graphenic carbon nitride (CNM). Extensive characterization of carbon nitride protected CsPbBr 3 nanocrystals (CNMBr) indicated spherical CsPbBr 3 nanoparticles encased in a few nm thick g-C 3 N 4 sheets facilitating better charge separation via percolation/tunneling of charges on conductive 2D nanosheets. The CNMBr core-shell nanocrystals demonstrated enhanced photoelectrochemical water splitting performance and photocurrent reaching up to 1.55 mA cm −2 . The CNMBr catalyst was successfully deployed for CO 2 photoreduction giving carbon monoxide and methane as the reaction products.