Highly Efficient Photocatalytic H2 Evolution from Water using Visible Light and Structure-Controlled Graphitic Carbon Nitride

• Published in: Angewandte Chemie International Edition 2014-08, Vol.53 (35), p.9240-9245
• Main Authors: Martin, David James, Qiu, Kaipei, Shevlin, Stephen Andrew, Handoko, Albertus Denny, Chen, Xiaowei, Guo, Zhengxiao, Tang, Junwang
• Format: Article
• Language: English
• Subjects: Communications; graphitic carbon nitride; hydrogen production; polymerization; protonation; water splitting
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201403375

The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low‐cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g‐C3N4) from a low‐cost precursor, urea, is reported. The g‐C3N4 exhibits an extraordinary hydrogen‐evolution rate (ca. 20 000 μmol h−1 g−1 under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g‐C3N4 photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen‐evolution rate is significantly enhanced. A recipe for success: Graphitic carbon nitride exhibited an internal quantum yield of 26.5 % at 400 nm when prepared by a specific tailored recipe. The activity was shown to be inversely proportional to the protonation status at specific nitrogen sites in heptazine units (see picture; N blue, C gray, H white). Theoretical results indicated that protonation significantly influences reductive power and charge migration to active sites.