Cobalt-doped graphitic carbon nitride: A multifunctional material for humidity sensing, electrochemical water splitting and environmental remediation applications

Graphitic carbon nitride (g-C₃N₄) has emerged as a promising eco-friendly material for catalysis and sensing applications due to their unique properties. However, limitations like low specific surface area, insufficient light absorption, and poor conductivity hinder their broader usability. Elemental doping has been established as an effective approach to modify the electronic structure and bandgap of g-C₃N₄ thus significantly expanding its light-responsive range for enhanced charge separation. This work reports on the fabrication of cost-effective and stable g-C₃N₄ and cobalt-doped g-C₃N₄ (Co@g-C₃N₄) via a simple one-step calcination process. The humidity sensing performance of both g-C₃N₄ and Co@g-C₃N₄ was evaluated across a broad humidity range (7 % - 94 % RH) at various testing frequencies. The results demonstrated good reversibility with Co@g-C₃N₄ exhibiting superior performance compared to pristine g-C₃N₄. Furthermore, the synthesized materials were assessed for their suitability as photoelectrochemical water splitting catalysts for hydrogen production, representing a step towards energy-efficient fuel cells. Notably, Co@g-C₃N₄ displayed enhanced performance with a lower onset potential (420 mV) and a lower Tafel slope (65.4 mV dec-1) for the hydrogen evolution reaction (HER) compared to undoped counterparts. Additionally, Co@g-C₃N₄ nanorods exhibited remarkable performance for the oxygen evolution reaction (OER), showcasing a lower onset potential (1.505 V) and a considerably low overpotential (270 mV), surpassing numerous reported electrocatalysts and even rivaling precious-metal-based ones. Finally, enhanced photocatalytic activities for organic dyes degradation were recorded for the mentioned materials. Therefore, g-C₃N₄ and related materials have great potential for their industrial electrochemcial applications.