Enhanced electrocatalytic performance and thermodynamic insights of gCN, Cu-doped gCN nanocomposites for efficient overall water splitting

This study comparatively investigates the electrocatalytic and thermodynamic performance of pristine graphitic carbon nitride (gCN), copper-doped gCN (Cu/gCN), and copper oxide–decorated gCN (CuO/gCN) for overall water splitting. Two synthesis strategies were employed to incorporate copper species into the gCN framework, enabling the assessment of their influence on electrochemical activity. The first approach involved direct Cu doping, while the second produced CuO nanoparticles supported on the gCN matrix. X-ray photoelectron spectroscopy revealed distinct copper chemical states, with Cu⁰/Cu⁺ species in Cu/gCN and Cu²⁺ species with characteristic satellite features in CuO/gCN, indicating strong metal–support interactions that contribute to improved catalytic performance. Pristine gCN exhibited limited activity due to poor intrinsic conductivity, whereas both Cu modification strategies significantly enhanced electrocatalytic performance. Both Cu/gCN and CuO/gCN showed promising activity for overall water splitting, with CuO/gCN delivering superior results. This material achieved lower Tafel slopes of 91 mV dec⁻¹ for OER and 73 mV dec⁻¹ for HER, along with reduced activation energies of 43.29 kJ mol⁻¹ (OER) and 30.57 kJ mol⁻¹ (HER). The novelty of this work lies in the systematic comparison of two eco-friendly and scalable modification routes, revealing the distinct contributions of Cu doping and CuO incorporation to catalytic enhancement. The improved kinetics, coupled with high thermal and operational stability, highlight Cu/gCN and CuO/gCN as cost-effective and sustainable electrocatalysts for water-splitting applications.