Electrifying H₂O₂ synthesis with g-C₃N₄-based single atom catalysts

Abstract

This article highlights the recent work of Zhang, Peng et al. (Nanoscale Horiz., 2023, 8, 695, https://doi.org/10.1039/D2NH00564F) on transition metal single atom embedded graphitic carbon nitride nanosheets for the neutral electrosynthesis of hydrogen peroxide.

Jungki Ryu

Jungki Ryu is a Professor at Ulsan National Institute of Science and Technology (UNIST) and member of the Nanoscale Horizons Advisory Board. Prof. Ryu's research focuses on developing innovative electrochemical and photoelectrochemical systems using nanomaterials for hydrogen production, CO2 conversion and biomass/waste utilization.

Electrifying the synthesis of commodity chemicals can play a critical role in achieving carbon neutrality, as well as addressing global energy and environmental problems. Among the diverse range of chemicals, hydrogen peroxide (H₂O₂) has emerged as a promising green oxidant and liquid hydrogen carrier.¹ However, H₂O₂ is currently produced by the anthraquinone autooxidation process under harsh conditions with huge energy consumption.² Consequently, researchers have been actively exploring alternative approaches for the synthesis of H₂O₂ using renewable resources under milder conditions.

In this regard, extensive studies have focused on the green synthesis of H₂O₂ using renewable electricity and employing either electrocatalysts³ or photocatalysts⁴ directly powered by sunlight. Most conventional studies on electrochemical H₂O₂ production have been conducted under alkaline conditions, which are known to facilitate efficient H₂O₂ production. However, it is important to note that H₂O₂ becomes unstable at high pHs.⁵ Moreover, from an environmental standpoint, there is a strong desire to develop electrocatalysts that can operate at neutral pH.

In this context, a recent paper by Yang et al. reports very interesting results (https://doi.org/10.1039/D2NH00564F). The researchers prepared graphitic carbon nitride (g-C₃N₄) nanosheets (CNNS) embedded with various transition metal single atoms (TM SAs) and discovered that TM SA-embedded CNNS show high electrocatalytic activity for H₂O₂ production at neutral pHs (Fig. 1). Among the various TM SAs tested, Ni SAs on CNNS were particularly effective and showed the highest mass-specific activity of ∼503 mmol g_cat⁻¹ h⁻¹ and H₂O₂ selectivity of ∼98%. According to their mechanistic analysis, the introduction of TM SAs promotes the formation of N–C=N sites, which are beneficial for H₂O₂ production via a two-electron oxygen reduction reaction (2e⁻ ORR), while suppressing the formation of C–C/C=C sites, which are beneficial for H₂O production via a 4e⁻ ORR. This suggests the excellent function of g-C₃N₄ as a support for TM SAs in selectively producing H₂O₂.

Fig. 1 Schematic of H₂O₂ production from H₂O and O₂ on a transition metal embedded graphitic carbon nitride sheet. Reproduced from https://doi.org/10.1039/D2NH00564F with permission from the Royal Society of Chemistry.

Notably, this paper is also intriguing from an academic perspective, as it demonstrates the efficient use of g-C₃N₄ as a support material for electrocatalysts, deviating from its traditional application as a photocatalyst in conventional studies.⁶ The findings offer new insights into the potential of g-C₃N₄ in catalytic systems and open avenues for further research in the field of sustainable chemical synthesis.

Acknowledgements

This work was also supported by the Basic Science Research Program (2021R1A2C2013684) and the Regional Leading Research Center (RLRC) (RS-2023-00217778) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT of Korea.

References

1. J. Y. Tang, T. S. Zhao, D. Solanki, X. B. Miao, W. G. Zhou and S. Hu, Joule, 2021, 5, 1432–1461.
2. J. M. Campos-Martin, G. Blanco-Brieva and J. L. G. Fierro, Angew. Chem., Int. Ed., 2006, 45, 6962–6984.
3. S. C. Perry, D. Pangotra, L. Vieira, L.-I. Csepei, V. Sieber, L. Wang, C. P. de León and F. C. Walsh, Nat. Rev. Chem., 2019, 3, 442–458.
4. H. Hou, X. Zeng and X. Zhang, Angew. Chem., Int. Ed., 2020, 59, 17356–17376.
5. H. M. Cota, T. Katan, M. Chin and F. J. Schoenweis, Nature, 1964, 203, 1281.
6. L. Xie, X. Wang, Z. Zhang, Y. Ma, T. Du, R. Wang and J. Wang, Small, 2023, 19, 2301007.

Footnote

† This content was originally published on our blogs platform at https://blogs.rsc.org/nh/2023/08/22/electrifying-h2o2-synthesis-with-g-c3n4-based-single-atom-catalysts/.

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