Bismuth(III) Coordination Linkage with Dimercaptothiadiazole: A p-Type Metallopolymer Photocathode Stable in Protic Electrolytes

Visible light-active photoelectrode materials that can exhibit simultaneous photo- and electroactivity are essential for photoelectrosynthesis. Herein, we report a coordination metallo-organic system based on bismuth with 2,5-dimercapto-1,3,4-thiadiazole (DMcT) as a linker ligand, which displays a p-type behavior with stable photoelectroactivity in neutral and protic electrolytes. The UV-visible spectral investigation reveals the systematic bathochromic shift with a gradual increment in the concentration of the Bi³⁺ ions to DMcT and the bandgap of 1.7 eV. The XPS, Raman, and FT-IR spectral data suggest the presence of a −S-Bi-S- linkage in the c-Bi-DMcT coordination polymeric structures. A photocathode prepared by electrooxidation shows a relatively less bismuth content with a disulfide linkage and lower photoactivity compared with c-Bi-DMcT prepared by chemical synthesis. The observed photocurrent values are in the range of −25 to −30 μA cm^-2 in protic electrolytes and evidence their p-type behavior and stability. The stabilization of photogenerated electrons, their transfer toward the electrolyte interface, and protonatable units of DMcT with a tautomeric shuttle and bismuth redox activity play a crucial role in the enhancement of photoinduced multiproton-coupled electron transfer (m-PCET) reactions in the protic electrolyte. In contrast, the electrodeposited e-BiDMcT shows a relatively lower p-type photocurrent response, and metal-free poly-DMcT exhibits poor n-type photoelectrochemical responses in protic electrolytes. Furthermore, the Bi-DMcT thin film displays good photoinduced oxygen reduction activity under both neutral and protic electrolytic conditions, which is essential for photoinduced m-PCET reactions.