Interlaced W₁₈O₄₉ nanofibers as a superior catalyst for the counter electrode of highly efficient dye-sensitized solar cells

Sufficient contact, high catalytic activity, free electron transport and ionic diffusion are desired for liquid-solid heterogeneous electrocatalysis. However, preparing catalysts that simultaneously possess all of these four advantages has proven challenging. Nanostructures originating from anisotropic growth always exhibit specific structural advantages and unique physical, chemical or catalytic properties. Herein, via a facile and template-free solvothermal approach, we synthesized W₁₈O₄₉ nanofibers (NFs) and nanofiber bundles (NFBs), as well as hierarchical spheres (HSs). As catalyst for the counter electrode (CE) of dye-sensitized solar cells (DSCs), W₁₈O₄₉ NFs demonstrated remarkable electrocatalytic activity because: (i) abundant oxygen vacancies offered sufficient active sites for reduction of I₃^- into I^-; (ii) the one dimensional NFs were more beneficial to electron transport; (iii) the two phases, the liquid electrolyte and the solid NFs, could fully contact each other, and meanwhile ions could diffuse freely among the networks constructed by the interlaced NFs. Notably, DSCs using the NF-based semitransparent CE achieved high photoelectric conversion efficiencies (PCEs) up to 8.58%, superior to those based on NFBs or HSs, and comparable to that of 8.78% using Pt as the CE. Furthermore, it was proven that both the electrolytic activity and the PCE deteriorated drastically when the NFs were destroyed. Our work here will be of great interest for both fundamental research and practical applications of W₁₈O₄₉ nanomaterials in other fields.