**Seong Jun Mun and Soo-Jin Park \***

Department of Chemistry, Inha University, 100 Inharo, Incheon 22212, Korea; dajoasj@gmail.com **\*** Correspondence: sjpark@inha.ac.kr; Tel.: +82-32-876-7234

Received: 19 August 2019; Accepted: 23 September 2019; Published: 25 September 2019

**Abstract:** The generation of photocatalytic hydrogen via water splitting under light irradiation is attracting much attention as an alternative to solve such problems as global warming and to increase interest in clean energy. However, due to the low efficiency and selectivity of photocatalytic hydrogen production under solar energy, a major challenge persists to improve the performance of photocatalytic hydrogen production through water splitting. In recent years, graphitic carbon nitride (g-C3N4), a non-metal photocatalyst, has emerged as an attractive material for photocatalytic hydrogen production. However, the fast recombination of photoexcited electron–hole pairs limits the rate of hydrogen evolution and various methods such as modification, heterojunctions with semiconductors, and metal and non-metal doping have been applied to solve this problem. In this review, we cover the rational design of g-C3N4-based photocatalysts achieved using methods such as modification, metal and non-metal doping, and heterojunctions, and we summarize recent achievements in their application as hydrogen production photocatalysts. In addition, future research and prospects of hydrogen-producing photocatalysts are also reviewed.

**Keywords:** graphitic carbon nitride; photocatalysis; H2 generation; water splitting
