High-Temperature Variant of Oxygen-Rich Covalent Triazine Frameworks as Bifunctional Electrocatalysts

Abstract

Metal-free electrocatalysis provides a sustainable alternative to platinum-based catalysts by lowering cost, resource dependence, and environmental impact while offering high stability, poison resistance, and tuneable active sites. Herein, we report two oxygen-rich covalent triazine frameworks (CTFs), ht-Oxy-CTF750 and ht-Oxy-CTF850, synthesized from 2,5-dimethoxyterephthalonitrile via ZnCl 2 -mediated nitrile trimerization under ionothermal conditions at 750 and 850 °C -temperatures well beyond those conventionally employed (≤600 °C). These conditions exploit the dynamic polymerization and simultaneous framework rearrangement intrinsic to CTF chemistry, wherein the methoxy groups function as thermally labile self-templates and oxygen dopants, ultimately leading to a pronounced enhancement in bifunctional electrocatalytic activity. Comprehensive structural and spectroscopic analysis reveals that ht-Oxy-CTF850 possesses a higher proportion of catalytically active pyridinic-N and graphitic-N species (85.8%), enriched carbonyl/methoxy functionalities, and an increased defect density (I D /I G = 1.33), which collectively modulate the framework's electronic properties, optimizing charge distribution, facilitate O 2 adsorption/activation, and enhance hydrophilicity and mass transport pathways within the framework. As a result, ht-Oxy-CTF850 delivers outstanding ORR performance with a half-wave potential of 0.88 V vs RHE and excellent HER activity with an overpotential of 81.5 mV at 10 mA cm -2 . When applied as a cathode in a zinc-air battery, ht-Oxy-CTF850 achieves a high discharge specific capacity of 792 mA h g⁻¹, superior rate capability across 5-100 mA cm -2 , and exceptional cycling stability over 205 h, rivalling commercial Pt/C. These results highlight synergistic heteroatom chemistry, defect engineering, and oxygen functionalization as an effective strategy for advanced metal-free electrocatalysts for sustainable energy storage and generation.