Electrocatalytic applications have gained significant attention due to the growing demand for sustainable energy conversion technologies. Among various materials explored, graphitic carbon nitride (g-C3N4) has emerged as a promising candidate for electrocatalytic reactions such as oxygen reduction (ORR) and hydrogen evolution (HER). Its unique nitrogen-rich structure, tunable electronic properties, and chemical stability make it suitable for these applications. However, challenges such as limited electrical conductivity and insufficient active sites must be addressed to optimize performance.

The electrocatalytic performance of g-C3N4 in ORR is influenced by its ability to facilitate the four-electron transfer pathway, which is more efficient than the two-electron pathway. The presence of pyridinic and graphitic nitrogen in the carbon nitride framework plays a crucial role in adsorbing oxygen molecules and promoting electron transfer. Studies have demonstrated that g-C3N4-based electrocatalysts can achieve onset potentials close to 0.85 V vs. RHE in alkaline media, with a dominant four-electron pathway. The incorporation of transition metals, such as iron or cobalt, further enhances ORR activity by forming metal-nitrogen coordination sites that improve oxygen adsorption and reduction kinetics.

For HER, g-C3N4 exhibits moderate activity due to its semiconductor-like properties and weak hydrogen adsorption. The nitrogen functionalities in g-C3N4 can act as proton adsorption sites, but the overall performance is limited by poor charge transport. To improve HER activity, strategies such as heteroatom doping and hybridization with conductive materials have been explored. For instance, phosphorus-doped g-C3N4 has shown a reduced overpotential of approximately 300 mV at 10 mA cm−2 in acidic conditions, attributed to the optimized electronic structure and increased active site density.

Active site engineering is a critical approach to enhance the electrocatalytic performance of g-C3N4. The intrinsic activity of g-C3N4 can be modified by introducing defects, doping with heteroatoms, or creating porous structures. Nitrogen vacancies, for example, can serve as additional active sites by exposing under-coordinated carbon atoms that facilitate reactant adsorption. Similarly, sulfur or boron doping can alter the charge distribution within the g-C3N4 framework, improving the binding energy of intermediates in ORR and HER. Metal coordination is another effective strategy, where single-atom catalysts embedded in g-C3N4 significantly boost activity. Iron single atoms coordinated with nitrogen in g-C3N4 have demonstrated superior ORR performance, with half-wave potentials comparable to commercial Pt/C catalysts.

Conductivity enhancement is equally important to overcome the inherent limitations of g-C3N4. The bulk material suffers from low electrical conductivity due to its polymeric nature and weak interlayer interactions. Several methods have been employed to improve charge transport, including carbon hybridization, exfoliation into thin layers, and integration with conductive supports. Combining g-C3N4 with graphene or carbon nanotubes forms a conductive network that facilitates electron transfer during electrocatalysis. Exfoliation of g-C3N4 into few-layer nanosheets reduces charge carrier recombination and exposes more active sites. Additionally, thermal treatment under controlled conditions can increase the degree of condensation in the g-C3N4 structure, leading to improved conductivity without compromising stability.

The structural design of g-C3N4 also impacts its electrocatalytic efficiency. Three-dimensional porous architectures provide a high surface area and improved mass transport, which are beneficial for both ORR and HER. Template-assisted synthesis can produce hierarchically porous g-C3N4 with well-defined pore structures, enhancing reactant accessibility to active sites. Another approach involves creating ultrathin nanosheets with abundant edge sites, which often exhibit higher activity than bulk counterparts due to increased exposure of catalytic centers.

Long-term stability is a key consideration for practical applications. g-C3N4-based electrocatalysts generally exhibit good durability in both ORR and HER due to their robust chemical and thermal stability. However, under harsh electrochemical conditions, degradation mechanisms such as active site poisoning or structural collapse may occur. Strategies to mitigate these issues include protective coatings, optimization of electrolyte conditions, and the use of corrosion-resistant supports. For instance, encapsulating g-C3N4 in carbon shells can prevent agglomeration and dissolution of active species during prolonged operation.

In summary, the electrocatalytic performance of g-C3N4 in ORR and HER can be significantly enhanced through active site engineering and conductivity improvement. The material’s nitrogen-rich framework provides a versatile platform for modifications that optimize reaction pathways and intermediate binding. While challenges remain in achieving performance comparable to noble metal catalysts, ongoing research into structural and electronic modifications continues to advance the potential of g-C3N4 in electrocatalysis. Future developments may focus on precise control of atomic-scale active sites and scalable synthesis methods to enable large-scale applications.