Charge Trapping in Terminal States in Polymeric Carbon Nitride for Photocatalytic Reduction Reaction

Abstract

Charge trap states play a key role in the photocatalytic activity of polymeric carbon nitride. Favorable shallow trap states prolong the lifetime of photogenerated charges in photocatalysis while unfavorable deep trap states deactivate the photogenerated charges. It is imperative to identify the origins and functions of shallow trap states in polymeric carbon nitride. We found that intrinsic NH2 terminals are not efficient active sites for photocatalytic reduction reactions such as hydrogen evolution or CO2 reduction in polymeric carbon nitride due to short trapped electron lifetimes. Rational terminal group design introduced shallow charge trap states with extended charge lifetime into the nanosecond timescale, positively contributing to hydrogen evolution reaction and CO2 reduction. Manipulating terminal shallow trap states enabled a 1.6 time improvement in hydrogen evolution activity and enhanced CO2 conversion to CO and CH4, with a yield of 8.4 and 3.6 μmol/g/h, respectively, under one sun condition (AM 1.5G).