State-of-the-art review of morphological advancements in graphitic carbon nitride (g-CN) for sustainable hydrogen production

Considering the technological benefits, the generation of hydrogen (H2) via solar-powered enabled water splitting is not only an ideal route to harvest and stock the sustainable sun-energy for meeting the increasing energy demands but also to mitigate the global warming by reducing carbon footprints. Ideally, the photocatalyst involved in the process of solar-to-hydrogen (STH) production should remain unaffected by the undesirable catalytic processes and charge separation and transportation taking place at its surface. In the quest of lowering down the cost of producing H2, the challenge of developing a cheaper photocatalyst material which can efficiently split water into hydrogen has become more prominent. Although, the metal-free semiconductor graphitic carbon nitride (g-CN or g-C3N4), owing to its 2D architecture and apposite band-energy gap and relatively lower production cost has shown immense potential in H2 production via water splitting, yet the concerns for its low specific surface area (SSA) and rich defect density have limited its photocatalytic performance and water-splitting efficiency. This mini review features the recent research accomplishments made in the design strategies of g-CN nanostructures based on its pore texture/surface area tailoring, dimensionality tuning, band-gap modulation, defect control, metal-doping and semiconductor heterojunction formation and the corresponding application in H2 generation. The reviewing of important state-of-the-art developments and prospect of high surface area g-C3N4 can provide new avenues in designing the g-CN with high SSA for utilization in H2 evolution, fuel cell, solar cell, supercapacitor and lithium battery.