Charge-regulated covalent triazine frameworks for ion-selective transpiration-driven electrokinetic power generation

초록

Transpiration-driven electrokinetic power generators (TEPGs) offer a promising route for harvesting electricity from spontaneous water evaporation under ambient conditions. However, their practical performance is limited by insufficient ion selectivity and inefficient ion transport within active layers. Herein, we report chargeregulated covalent triazine frameworks (CTFs) as ion-selective active-layer additives for high-performance TEPGs. Three CTFs bearing neutral alkyl, anionic sulfonate, and cationic ammonium pendant groups were synthesized to systematically elucidate the effect of fixed framework charge on ion transport and electrokinetic power generation. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed the successful formation of triazine frameworks and the incorporation of designed pendant groups. Electrochemical impedance spectroscopy revealed charge-dependent ion selectivity governed by Donnan-type interactions: CTFN+ exhibited 271-fold higher OH- conductivity than H+ conductivity, whereas CTF-S- showed 213-fold higher H+ conductivity than OH- conductivity. Zeta potential measurements further verified the positive, neutral, and negative surface charge characteristics of CTF-N+, CTF-C3, and CTF-S-, respectively. In addition, nitrogen sorption and grazing-incidence wide-angle X-ray scattering analyses demonstrated that the CTFs possess mesopore-sized voids, while the charged CTFs form relatively ordered face-on microstructures that can support ion-accessible pathways. When incorporated into TEPGs operated with aqueous NaTFSI, CTF-N+ generated the highest positive electrokinetic output, whereas CTF-S- reversed the voltage polarity through cation-selective transport. This work establishes charge-regulated porous CTFs as a rational platform for controlling ion selectivity, voltage polarity, and electrokinetic energy conversion in evaporation-driven power generators.

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