Owing to the rising pressure on the requirement of commercializing sustainable and environmentally friendly energy technologies such as proton exchange membrane fuel cells (PEMFCs), metal-Air batteries, and water splitting electrolyzers, it is urgent to develop highly efficient electrocatalysts to replace costly platinum group metals. Graphitic carbon nitrides (g-C3N4) have attracted intensive focus due to their unique properties and impressive performance in challenging the widely accepted nitrogen-doped carbon materials in electrocatalytic fields. However, the relatively poor conductivity limits further improvement of g-C3N4-based electrocatalysts. Thus, this Review is primarily focused on recent progress in the functionalization of g-C3N4 materials for oxygen reduction and water splitting reactions. Especially, an innovative and in-depth understanding of g-C3N4 materials is presented by systematically summarizing the function of g-C3N4 materials, such as serving as active sites, coordination complexes, and supporter/protective coatings, in contributing to the catalytic performance. Finally, the main challenges and future perspectives of g-C3N4-based nanomaterials in electrocatalytic fields are also discussed. It should be noted that in the text we acknowledge that many (in fact, most) of the g-C3N4 materials have been polymeric amorphous phases within the C-N-H system. To avoid debate and confusion on the naming of previously reported graphitic carbon nitride materials in our Review, we decided to call all these of materials g-C3N4 in accordance with previous reports
