Electron-proton duet in covalent organic frameworks for efficient direct oxygen reduction to hydrogen peroxide

doi:10.1016/S1872-2067(26)64990-X

Abstract

Abstract:

The proton adsorption capacity, equally critical as photogenerated electron accumulation at active sites, jointly governs efficient hydrogen peroxide (H₂O₂) production through the one-step 2e^- direct oxygen reduction reaction (ORR) in covalent organic frameworks (COFs). Herein, TPNN-COF incorporates precisely tailored triazine and pyridine nitrogen centers, establishing an optimal proton harvesting interface that enables direct proton capture from aqueous phase to catalytic ORR sites. Concurrently, the complementary electronic effects of triazine and pyridine nitrogen moieties collectively optimize the donor-acceptor (D-A) architecture in TPNN-COF, thereby significantly improving photogenerated charge separation. This dual optimization of proton and electron dynamics creates a harmonious interplay that fundamentally restructures the reaction pathway from conventional two-step 1e^- indirect mechanisms to efficient one-step 2e^- direct ORR processes. The resulting photocatalytic system achieves an exceptional hydrogen peroxide production of 3584.9 μmol g^-1 h^-1 under visible light irradiation in sacrificial-agent-free pure aqueous media under air, representing 4.1-fold and 3.4-fold improvements over pyridine-deficient TPNB-COF and triazine-deficient TPBN-COF respectively, while demonstrating an impressive 4.1% apparent quantum yield at 420 nm. These insights provide a novel strategy for constructing efficient direct ORR reaction sites while advancing the mechanistic understanding of ORR processes in advanced photocatalytic systems for sustainable chemical synthesis.

Key words: Photocatalysis, Hydrogen peroxide preparation, Covalent organic frameworks, Proton adsorption, Reaction mechanism

Jingyao Wu, Yujing Lv, Qiang Zhao, Shuo Wang, Ying Wang, Na Wen, Zhengxin Ding, Zizhong Zhang, Jinlin Long. Electron-proton duet in covalent organic frameworks for efficient direct oxygen reduction to hydrogen peroxide[J]. Chinese Journal of Catalysis, 2026, 84: 288-300.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(26)64990-X

https://www.cjcatal.com/EN/Y2026/V84/I5/288

Figures/Tables 6

Scheme 1. Synthesis procedure of TPNN-COF, TPNB-COF and TPBN-COF.

Fig. 1. PXRD maps of TPNN-COF (a), TPNB-COF (b) and TPBN-COF (c). (d) FT-IR spectra of TPNN-COF, TPNB-COF and TPBN-COF and the related monomers. (e) 13C NMR spectra of TPNN-COF, TPNB-COF and TPBN-COF. (f) XPS patterns of TPNN-COF, TPNB-COF and TPBN-COF. N2 adsorption-desorption isotherms of TPNN-COF (g), TPNB-COF (h) and TPBN-COF (i). (Inset in (g-i) are the pore size distribution).

Fig. 2. (a) Solid state UV-vis DRS spectra of three COFs. (b) Optical band gaps calculated in Tauc plot. (c) Mott-Schottky plots for TPNN-COF. (d) Energy band structures of TPNN-COF, TPNB-COF, and TPBN-COF. (The formula for calculating the valence band position is EVB = ECB + Eg) (f) Photocatalytic H2O2 production activities of TPNN-COF, TPNB-COF and TPBN-COF. (g) Photocatalytic H2O2 production yields of other COF materials under identical experimental conditions. (h) AQY of TPNN-COF at different wavelengths. (i) Cycling tests of TPNN-COF.

Fig. 3. Electrochemical impedance spectra of TPNN-COF (a), TPNB-COF (b) and TPBN-COF (c) at the same humidity, different temperatures. (d) Proton conductivity of TPNN-COF, TPNB-COF and TPBN-COF in aqueous solution at 293.15 to 333.15 K. (e) Proton transfer activation energies of TPNN-COF, TPNB-COF and TPBN-COF. (f) Proton binding energy maps of TPNN-COF at carbonyl oxygen, pyridine nitrogen, and triazinyl nitrogen. Hydrophilicity test of TPNN-COF (g), TPNB-COF (h), TPBN-COF (i).

Fig. 4. KPFM images of TPNN-COF (a), TPNB-COF (b) and TPBN-COF (c) in the dark and under 420 nm visible light irradiation and the corresponding surface potential distributions. two-dimensional fs-TAS spectra of TPNN-COF (d), TPNB-COF (e), and TPBN-COF (f). two-dimensional fs-TAS spectra of TPNN-COF (g), TPNB-COF (h), and TPBN-COF (i) fs-TAS kinetic curves at the indicated wavelengths.

Fig. 5. (a) Photocatalytic H2O2 activity of TPNN-COF, TPNB-COF and TPBN-COF under different atmospheres and sacrificers. (b) EPR profiles of the three COFs in the dark and in the light. (c) Koutecky-Levich plots of three COFs in PBS (pH = 7) solution. In situ DRIFTS spectra of TPNN-COF (d), TPNB-COF (e), and TPBN-COF (f) versus illumination time. (g) Gibbs free energy diagram of three COFs with direct O2 adsorption. (h) Gibbs free energy plot of three COFs with protons adsorbed first. (“*” represents COF adsorption sites. The illustration shows the optimal intermediate product of TPNN-COF.)

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