1D Co₄S₃ nanoneedle array with mesoporous carbon derived from double comb copolymer as an efficient solar conversion catalyst

This study investigates the use of a one-dimensional (1D) cobalt sulfide/mesoporous carbon heterogeneous electrocatalyst as counter electrode for high solar energy conversion efficiency in dye-sensitized solar cells (DSSCs). The 1D cobalt oxide (Co₃O₄) was in situ hydrothermally grown on the fluorine-doped tin oxide glass substrate, followed by sulfurization to form 1D cobalt sulfide (Co₄S₃) nanoneedle array. The Co₄S₃ is characterized by a high electrocatalytic activity for reducing/oxidizing the redox couple in the electrolyte. Additionally, the 1D structural feature of the Co₄S₃ allows fast electron transport through the oriented diffusion pathway. However, the Co₄S₃ still has relatively low chemical stability and poor electrical conductivity than conventional Pt catalyst. Herein, we incorporated the mesoporous carbon layer derived from the double comb copolymer, i.e., PVDC-g-POEM, which can act as a mesoporous structural template and sufficient carbon source. This strategy increased the electrocatalytic activity and chemical durability of the heterogeneous catalytic materials. The 1D Co₄S₃/mesoporous carbon heterogeneous catalyst exhibited excellent electrocatalytic activity for the reduction of triiodide, thereby outperforming the conventional Pt counter electrode. The catalytic properties were demonstrated by electrochemical analysis, i.e., cyclic voltammetry and electrochemical impedance spectroscopy. Results suggest that solid-state DSSCs (ssDSSCs) fabricated with the 1D Co₄S₃/mesoporous carbon counter electrode exhibited a higher solar energy conversion efficiency of 6.2% than the corresponding ssDSSC with conventional Pt (5.7%). The pure 1D Co₄S₃ or mesoporous carbon showed relatively lower performance than conventional Pt. Accordingly, the 1D Co₄S₃/mesoporous carbon synergetic approach represents a new strategy for enhancing the catalytic activity and chemical stability for highly efficient ssDSSCs.