Visible-Light-Active Triazine-Thiadiazole-Based p-Type Copolymer with Stable Photoelectrochemical Behavior in Acidic Electrolytes

Design and development of visible-light-active electrode materials with efficient charge separation and enhanced stability are the main criteria for solar energy conversion in photoelectrochemical devices. Herein, we report a new metal-free photoactive polymer containing thiadiazole and triazine units with a stable photo-electroactivity in strong acidic electrolytes. The reactivity of chloro groups in cyanuric chloride and the nucleophilic substitution with 2,5-dimercapto-1,3,5-thiadiazole favors the facile (electro)copolymerization at lower oxidative potentials. Spectral investigations reveal the systematic bathochromic shift toward the visible region with extensive polymerization. X-ray photoelectron spectroscopy, NMR, Raman, IR, and UV-vis spectral studies evidence the substitution of chloro units with dimercapto units. This N- and S-rich poly(2,5-dimercaptothiadiazole-triazine) exhibits p-type photoactivity with the optical band gaps in the range of 2.4-2.6 eV. On the contrary, poly-2,5-dimercaptothiadiazole displays poor n-type photoactivity. The photoelectrode shows stable, repeatable photovoltage (15-20 mV) and photocurrent (3-4 μA cm^-2) responses in acidic electrolytes, and the incremental photocurrent responses at higher cathodic potentials for longer duration are attributed to the excellent protonation capability of polymeric units. Furthermore, they exhibit good oxygen reduction reaction electrocatalysis.