Facile Proton Relay in the Triazole Framework to Promote the Electrocatalytic Hydrogen Evolution Reaction

Because of the high proton conductivity and thermal stability, Nafion is a reliable material for proton-exchange membranes (PEMs) and is inevitably used in fuel-cell studies. As an alternative to Nafion, covalent-organic frameworks containing sulfonate or phosphate terminals can be used. However, to achieve considerable proton conductivity, high temperature (ca. 120 °C) is often required. Herein, a microporous triazole-functionalized organic polymer (TPOP) is prepared via the condensation of 3,5-diaminotriazole and formaldehyde. The repeating unit of TPOP was identified by ¹³C cross-polarization magic angle spinning (CPMAS) and core-level C 1s and N 1s X-ray photoelectron spectroscopy (XPS) studies. TPOP possesses a specific surface area (SA_BET) of 380 m² g^-1 with a pore volume of 1.02 cm³ g^-1, while multimodal pore distribution (0.4, 0.9, and 2.2 nm) implicates its microporous nature. The presence of triazole units in the pores of TPOP results in facile proton conduction with a solution-state conductivity of 0.025 S cm^-1. An experimentally determined activation energy of 0.285 eV highlights the fact that proton shuttling follows the Grotthuss pathway. The crucial role of the triazole unit in proton conduction is established by considering a reference polymer made of 1,3-diaminobenzene and formaldehyde (MPOP), which contains a phenyl ring in the repeating unit instead of a triazole ring. MPOP shows poor conduction and requires a high activation barrier. This emphasizes the role of triazole nitrogen as a strong Lewis base center to facilitate the proton relay. The facile proton conduction of TPOP provides further scope to study the electrocatalytic hydrogen evolution reaction (HER) using TPOP as a metal-free cathode material. The HER activity of TPOP is not only better than MPOP but also fair compared to some reported porous organic polymers. Considering the demand for low-cost materials for PEM and suitable replacement of noble metals for HER, this triazole-based polymer, TPOP, can serve as a bifunctional metal-free energy material.