Theoretical and Experimental Framework for the Synthesis of Nitrogen and Sulphur Co-doped Carbon Nanomaterials as Electrocatalysts for the Hydrogen Evolution Reaction

The hydrogen evolution reaction from water splitting is a critical enabling reaction for green hydrogen production, which is increasingly positioned as central to Nigeria's long-term energy transition agenda, yet effective non-precious metal electrocatalysts for hydrogen evolution that can be produced from locally available precursors remain to be developed through systematic scientific investigation. This study established an original theoretical and experimental framework for the rational synthesis of nitrogen and sulphur co-doped carbon nanomaterials as electrocatalysts for the hydrogen evolution reaction. The theoretical component employed periodic density functional theory calculations to screen a series of hypothetical nitrogen-sulphur co-doped graphene and carbon nanotube structures for hydrogen evolution activity, using the hydrogen adsorption free energy as the primary activity descriptor aligned with the Sabatier principle. The effects of co-dopant concentration, spatial arrangement, and local bonding geometry on electrocatalytic activity were systematically evaluated. Optimal dopant configurations were predicted for thermally stable nitrogen-sulphur co-doped graphene with adjacent N-S pairs exhibiting hydrogen adsorption free energy of minus 0.11 electron volts, close to the thermoneutral ideal. These computationally optimised structures were realised experimentally by high-temperature pyrolysis of chitosan-thiourea-graphene oxide precursor mixtures prepared from locally sourced shrimp shell chitosan. The synthesised materials were characterised by X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and electrochemical methods. Experimental overpotentials for hydrogen evolution at 10 mA/cm2 as low as 187 mV in acid were achieved, consistent with computational activity predictions. This original theoretical-experimental framework provides a template for the systematic development of earth-abundant electrocatalysts for green hydrogen production.

Keywords: carbon nanomaterials, nitrogen-sulphur co-doping, hydrogen evolution reaction, density functional theory, green hydrogen