Bandgap engineering of melon using highly reduced graphene oxide for enhanced photoelectrochemical hHydrogen evolution

Abstract

The uncondensed form of polymeric carbon nitrides (PCN), generally known as melon, is a stacked two-dimensional structure of poly(aminoimino)heptazine. Melon is used as a photocatalyst in solar energy conversion applications, but suffers from a poor photoconversion efficiency due to weak optical absorption in the visible spectrum, high activation energy, and inefficient separation of photoexcited charge carriers. We report experimental and theoretical studies to engineer the bandgap of melon with highly reduced graphene oxide (HRG). Three HRG@melon nanocomposites with different HRG:melon ratios (0.5%, 1%, and 2%) were prepared. The 1% HRG@melon nanocomposite showed a higher photocurrent density (71 μA cm−2) than melon (24 μA cm−2) in alkaline conditions. The addition of a hole scavenger further increased the photocurrent density to 630 μA cm−2 relative to the reversible hydrogen electrode (RHE). These experimental results were validated by calculations using density functional theory (DFT), which revealed that HRG results in a significant charge redistribution and an improved photocatalytic hydrogen evolution reaction (HER).