Abstract: Graphitic carbon nitride (g-C3N4) emerges as a promising eco-friendly material for catalysis and sensing applications due to its unique properties. However, limitations like low specific surface area, insufficient light absorption, and poor conductivity hinder their broader usability. Elemental doping is 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 research involves the synthesis and validation of several materials and composites, employing characterization techniques to confirm the success of the synthesis methods. The selection of suitable materials for applications in humidity sensing and water splitting reaction prioritizes facile synthesis, good electrical conductivity, efficiency, water sensitivity, and chemical stability. The work reports on the fabrication of cost-effective and stable g-C3N4, cobalt-doped g-C3N4 (Co@g-C3N4), tungsten oxide embedded g- C3N4 (WO3@g-C3N4), and silver-doped WO3@g-C3N4 (Ag/WO3@g-C3N4) via two simple synthesis routes: one-step calcination process, and hydrothermal treatment. The humidity sensing performance of the four sensors (g-C3N4, Co@g-C3N4, WO3@g- C3N4, Ag/WO3@g-C3N4) is evaluated across a broad relative humidity range (7% - 94% RH) at various testing frequencies. The doped sensors demonstrate superior humidity sensing and good reversibility compared to pristine g-C3N4. The Ag/WO3@g-C3N4 outstand the other sensors in the humidity sensing performance. Furthermore, the g- C3N4 and Co@g-C3N4 are assessed for their suitability as electrochemical water splitting catalysts for hydrogen production, representing a step towards energy-efficient fuel cells. Notably, Co@g-C3N4 display enhanced performance with a lower onset potential (420 mV) and a lower Tafel slope (65.4 mV dec-1) for the hydrogen evolution reaction compared to undoped counterparts. Additionally, Co@g-C3N4 nanorods exhibit remarkable performance for the oxygen evolution reaction, 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.