Composition-Dependent Electrocatalytic Activity of Cobalt Sulfides for Triiodide Reduction in Dye-Sensitized Solar Cells

A new nanoarchitecture of cobalt sulfide (CoS_x) is designed by exploiting a Prussian blue analogue. Depending on the sulfidation temperatures, CoS_x materials with different compositions and morphologies are obtained. This investigation of the composition-dependent electrocatalytic activity of CoS_x for triiodide reduction reaction (IRR) reveals that sulfur-deficient CoS_x is more active than sulfur-rich CoS_x. When utilized in dye-sensitized solar cells (DSSCs), sulfur-deficient CoS_x with a hollow nanocube morphology outperforms platinum (Pt), showing great promise as a Pt alternative. This composition dependency on IRR is attributed to different surface characteristics and electrical properties that vary with CoS_x composition. This work highlights the importance of understanding the surface properties of sulfide-based electrocatalysts that are intimately dictated by their compositions as part of a new design principle for a highly active electrocatalyst.