A New Doped Graphene-Based Catalyst for Hydrogen Evolution Reaction Under Low-Electrolyte Concentration and Biomass-Rich Environments

Abstract

Graphene-based catalysts are emerging as promising alternatives to reduce reliance on metal-based catalysts in the hydrogen evolution reaction (HER). This study introduces a novel family of metal-free graphene-based materials codoped with nitrogen and phosphorus (GNP). These materials were synthesized, characterized, and evaluated for HER performance as glucose-tolerant cathodes for biomass electrolysis in a soft alkaline medium, referred to as Mixed Electrolyte (ME): 0.1 M NaOH + 1.0 M Na₂SO₄. It was found that the calcination time directly affects the catalytic properties of the final catalysts, with longer calcination times enhancing HER activity. This was attributed to the effective incorporation of nitrogen (N pyrrolic, N quaternary) and phosphorus (P graphitic) into the graphitic network, along with increased catalyst mesoporosity, which significantly improves mass and electron transfer. Furthermore, chronopotentiometry tests revealed substantial electrochemical activation of HER catalytic performance, stemming from the removal of heteroatoms from the carbon framework. This process, confirmed by XPS and Raman Spectroscopy, led to the formation of topological 5- and 7-membered carbon rings, which serve as the main active sites for the reaction. This significantly accelerates the water dissociation activity, leading to improved catalytic performance with a final overpotential (η₁₀) of −0.386 V in ME. Notably, the exceptional stability and electrochemical activity under various alkaline media, along with its tolerance in the presence of glucose, make this new cathodic catalyst a suitable candidate for a membrane-less biomass electrolyzer.