Enabling Pt-free photocatalytic hydrogen evolution on polymeric melon: Role of amorphization for overcoming the limiting factors

Abstract

Polymeric melon shows real promise to be a next generation photocatalyst material for solar hydrogen production. Because it is earth abundant, and highly stable in photoredox reactions. However, a long-standing problem with polymeric melon is that it is inactive for photocatalytic hydrogen evolution without a metal cocatalyst, such as Pt. Sluggish charge transfer kinetics and a high activation energy for proton reduction makes pristine melon overly dependent on a high loading of precious Pt-cocatalyst for hydrogen evolution. While Pt-assisted hydrogen evolution is not considered economic for scale-up, a modulation of intrinsic photophysical and physicochemical properties of melon is therefore crucial to overcome the Pt dependency. However, to our knowledge, no systematic study has been reported to date to make melon independent of Pt for solar hydrogen evolution. Here we show that the limiting factors of Pt-dependent hydrogen production can be overcome by amorphization. The amorphization lowers the band gap, shifts the proton reduction potential close to the origin, and enhances the light harvesting and charge transport. Therefore, it results in a Pt-free hydrogen evolution under visible light irradiation. We here also present a mechanistic understanding of the origin of this cocatalyst-free hydrogen evolution.