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Significance Statement
Hydrogen is considered to be an ideal energy carrier to reduce the greenhouse gas emission for solving the global environmental and energy issues. However, the price for electrochemical/photochemical hydrogen production is still much higher than expected due to the relatively low efficiency and the use of noble metal (platinum) containing materials. Graphitic carbon nitride (g-C3N4) has been proposed to be a promising metal free catalyst for hydrogen production, but currently suffers from low hydrogen evolution reaction (HER) activity. Using density functional theory calculations, the work [published in J. Catalysis, 332 (2015) 149] by Aijun Du from Queensland University of Technology in Australia for the first time reported that the hydrogen binding free energy on the g-C3N4 
, a dominant descriptor for measuring hydrogen evolution reaction activity, is very sensitive to the mechanical strain. The strained g-C3N4 will lead to the substantial tuning of the hydrogen evolution reaction performance in the g-C3N4 at different coverages of hydrogen atoms, suggesting g-C3N4 to be an efficient mechanocatalyst toward the hydrogen evolution reaction. Additionally, the experimentally-observed high hydrogen evolution reaction activity in nitrogen doped graphene supported g-C3N4 [Nature Communications, 5 (2014) 3783] can be attributed to the induced strain arising from the charge transfer at the hetero-interface between g-C3N4 and doped graphene. An alternative strategy to introduce the mechanical strain in g-C3N4 is proposed by doping a bridge carbon atom in g-C3N4 with an isoelectronic silicon atom with a larger ionic radius. This theoretical finding reported here is consistent with most recent experimental measurements [Nature Materials 15 (2016) 48-53] where the mechanical strain also plays an important role in tuning electrochemical reaction activity.
Journal Reference
Guoping Gao1,Yan Jiao2,Fengxian Ma1,Yalong Jiao1,Eric Waclawik1,Aijun Du1
[expand title=”Show Affiliations”]- School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Garden Point Campus, Brisbane, QLD 4001, Australia
- School of Chemical Engineering, University of Adelaide, Adelaide, SA 5005, Australia
Abstract
Graphitic carbon nitride (g-C3N4), as a promising metal-free catalyst for photo-catalytic and electrochemical water splitting, has recently attracted tremendous research interest. However, the underlying catalytic mechanism for the hydrogen evolution reaction (HER) is not fully understood. By using density functional theory calculations, here we have established that the binding free energy of hydrogen atom () on g-C3N4 is very sensitive to mechanical strain, leading to substantial tuning of the HER performance of g-C3N4 at different coverages. The experimentally-observed high hydrogen evolution reaction activity in N-doped graphene supported g-C3N4 (Zheng et al., 2014) is actually attributed to electron-transfer induced strain. A more practical strategy to induce mechanical strain in g-C3N4 is also proposed by doping a bridge carbon atom in g-C3N4 with an isoelectronic silicon atom. The calculated on the Si-doped g-C3N4 is ideal for hydrogen evolution reaction. Our results indicate that g-C3N4 would be an excellent metal-free mechano-catalyst for hydrogen evolution reaction and this finding is expected to guide future experiments to efficiently split water into hydrogen based on the g-C3N4 materials.
