(Invited) Lead-Free Halide Perovskites for Hydrogen Evolution

Abstract

Metal halide perovskites (MHPs) semiconductors possess unique optical properties, such as high optical absorption in the visible region, tunable band-gap and long carrier lifetime, which have been extensively exploited in photovoltaics and optoelectronic applications.[1] More recently there has been a growing interests towards novel applications of MHPs, in particular in the field of solar-driven photocatalysis.[2] However, some of the most interesting photocatalytic reactions such as H2O splitting, CO2 and N2 reduction, dye degradation, require the use of water or alternative polar solvents, this represent a conundrum foreseeing MHPs utilization. In this talk we report clear evidence of water stability for two lead-free metal halide perovskites, namely dimethylammonium (DMA) DMASnBr3 and phenylethylammonium (PEA) PEA2SnBr4 obtained by means of diffraction, optical and x-ray photoelectron spectroscopy. The water stability for the 2D material is somehow expected due to the water-repulsive nature of the symmetry breaking organic cation, some computational work is addressing such improved water stability, showing also that the same mechanism is thought to protect tin from +2 to +4 oxidation. The stability in water of the 3D analogous represent instead an important innovation of the field. Such unprecedented water-stability has been applied to promote photocatalysis in aqueous medium, in particular by devising a novel composite material by coupling DMASnBr3 to g-C3N4, taking advantage from the combination of their optimal photophysical properties. The prepared composites provide an impressive hydrogen evolution rate >1700 μmol g-1 h-1 generated by the synergistic activity of the two composite constituents. DFT calculations provide insight into this enhancement deriving it from the favorable alignment of interfacial energy levels of DMASnBr3 and g-C3N4. The demonstration of an efficient photocatalytic activity for lead-free metal halide perovskites in water paves the way to a new class of light-driven catalysts working in aqueous environments.