The energy- and waste-intensive anthraquinone oxidation (AO) process is used to manufacture hydrogen peroxide (H2O2), which is one of the world’s 100 most important chemicals.
The use of inexpensive and effective catalysts is required to replace the AO approach with a more ecologically friendly electrochemical two-electron oxygen reduction reaction (2e- ORR).
However, as a prospective contender, a metal-free, carbon-based catalyst only performs well in neutral or alkaline conditions, where H2O2 is unstable for collection or undesirable for linking applications, such as the e-Fenton reaction. Furthermore, identifying the genuine active catalytic sites and the underlying 2e- ORR mechanism remains difficult.
A research group led by Prof. Lunhui Guan from the Chinese Academy of Sciences’ Fujian Institute of Research on the Structure of Matter developed a metal-free, highly efficient acidic 2e- ORR catalyst with a record hydrogen peroxide production rate based on pyrimidine-assisted active site modulation and S, N-codoped few-layered graphene for valence electronic optimization in a study published in Chem Catalysis.
In acid, the catalyst showed excellent activity and selectivity for 2e- ORR. Over a potential range of 0.20~0.55 V, the H2O2 selectivity approaches 90%~100%, and the maximal H2O2 production rate (4.8 mol·g-1·h-1) outperforms all documented H2O2 production performance for carbon material-based catalysts.
Experiments and density-functional-theory simulations revealed that the combined oxidized sulfur and pyridinic-N functional motif can lower the Fermi level of valence electronic states of active edge carbon sites, resulting in a suitable binding strength of *OOH intermediate for high selectivity and performance 2e- ORR for H2O2 formation.
With S integration, the researchers saw a clear peak shift to the high energy of C 1s excitation in the near edge X-Ray absorption fine structure, providing good evidence for valence electronic optimization of the carbon catalyst surface.
It can also degrade a model organic pollutant (methylene blue [MB], 50 ppm) to colorless in just 15 minutes when combined with the Fenton reaction for an electron-Fenton procedure.
This research not only develops an effective carbon-based catalyst for H2O2 generation in acid but also gives a valuable electronic property optimization approach for future carbon-based catalyst tuning.
Journal Reference:
Xu, J, et al. (2022) Pyrimidine-assisted synthesis of S, N-codoped few-layered graphene for highly efficient hydrogen peroxide production in acid. Chem Catalysis doi/10.1016/j.checat.2022.04.011
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