Effect of Single Atom Nickel on Graphite Carbon Nitride for Visible Light Photocatalytic Overall Water Splitting: X‑ray Spectroscopic and Microscopic Investigation

Yu-Cheng Huang^1*, Yanrui Li², Takuji Ohigashi³, Ying-Rui Lu⁴, Chi-Liang Chen⁴, Jeng-Lung Chen⁴, Shaohua Shen², Way-Faung Pong⁵, Wu-Ching Chou¹, Chung-Li Dong⁵

¹Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
²International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, China
³Institute for Molecular Science, Okazaki, Japan
⁴National Synchrotron Radiation Research Center, Hsinchu, Taiwan
⁵Department of Physics, Tamkang University, New Taipei City, Taiwan

* Presenter:Yu-Cheng Huang, email:ychuang0129.04g@g2.nctu.edu.tw

The application of graphitic carbon nitride (g-C₃N₄) in the photocatalytic solar hydrogen production by water splitting has attracted considerable attention owing to its environmental friendliness, earth abundance, suitable bandgapand, etc. However, rapid charge carrier recombination and sluggish water catalysis kinetics have greatly limited its photocatalytic performance for overall water splitting. In this study, the single-atom Ni terminating agent was introduced to coordinate with the heptazine unit of g-C₃N₄ to generate a new hybrid orbital. The high-efficiency phtocatalytic overall water decomposition into H₂ and H₂O₂ under visible light irradiation can be achived by the single atom Ni terminated g-C₃N₄ without loading any cocatalyst. Synchrotron-based X-ray spectroscopy and microscopy techniques were utilized to determine the origin of the improved performance of single-atom nickel doped g-C₃N₄ for photocatalytic hydrogen evolution reaction. The new hybrid orbital modulates the atomic/electronic structure and band gap of g-C₃N₄, and synergistically increase visible light absorption of solar light, accelerating the separation and transfer of photoexcited electrons and holes. This study provides evidence that single-atom Ni and the neighboring C atom served as water oxidation and reduction active sites, respectively, for efficient photocatalytic water splitting via a two-electron transfer pathway. The material design strategy and the photocatalytic mechanism thereof may be beneficial for various applications for solar energy conversion.

Keywords: X-ray absorption spectroscopy, Photocatalytic H₂ and H₂O₂ production, Graphite carbon nitride, Single-atom nickel, Scanning transmission X-ray microscopy