Designing hydrogen-bonds in covalent organic frameworks: Accelerating proton-coupled electron transfer for enhanced photocatalytic H2O2 synthesis

The photocatalytic efficiency of covalent organic frameworks (COFs) toward sustainable H 2 O 2 synthesis via oxygen reduction reaction (ORR) is intrinsically constrained by compromised proton-coupled electron transfer (PCET) dynamics, where retarded water oxidation reaction kinetics and exogenous proton donor dependence create a dual kinetic-thermodynamic constraint. This work presents a precision hydrogen–bond engineering strategy through the radio-frequency plasma modification of COF linkages, establishing a hydrogen–bond strength gradient (OH···N vs. SH···N) to probe the structure-function interplay that modulates PCET pathways. Systematic investigations reveal that hydrogen–bond strengthening at imine linkages enables dual functionality: creating both dynamic proton reservoirs and more accessible proton conduction pathways. This synergistic regulation reduces the energy barrier for direct 2e − ORR by 19.6% while suppressing high-energy intermediates in stepwise pathways, as confirmed by experiments and density functional theory calculations. The optimized SH-COF with appropriately stronger hydrogen bonds achieves exceptional photocatalytic H 2 O 2 production: 2.97 and 4.70 times that of corresponding OH-COF and pristine COF, respectively. Integrated crystal orbital Hamilton population analysis quantitatively correlates hydrogen–bond strength with charge transfer efficiency, establishing a relationship between hydrogen–bond energy and PCET kinetics. Our findings not only demonstrate plasma modification as an effective strategy for post-synthetic hydrogen–bond tuning but fundamentally advance the understanding of how hydrogen-bond thermodynamics govern PCET mechanisms.