Monodisperse MnS Nanocrystals Anchored on Reduced Graphene Oxide as Catalysts for Triiodide Reduction

Transition metal sulfides are widely used in energy conversion technologies due to their abundance, low cost, excellent functional properties, and catalytic activity. However, their challenging synthesis and moderate conductivity limit their practical applications. In this study, we employed a colloidal synthesis method using manganese oleate as a precursor to successfully grow monodisperse, small-sized, uniformly distributed, and highly crystalline MnS nanocrystals (NCs) in situ on the surface of reduced graphene oxide (rGO). The use of manganese oleate significantly enhanced the reactivity of the metal source, promoting a high dispersion and uniform distribution of MnS NCs on the rGO surface. This unique precursor strategy greatly optimized the reaction kinetics, ensuring the monodispersity of MnS NCs and effectively preventing nanocrystal aggregation, resulting in a highly monodisperse nanostructure. The resulting MnS/rGO composite material efficiently combines the high-density catalytically active sites of MnS with the excellent conductivity of rGO, thereby exhibiting outstanding electrocatalytic activity. When tested as a counter electrode (CE) in dye-sensitized solar cells (DSSCs), the MnS/rGO composite significantly outperformed conventional Pt-based counter electrodes. The power conversion efficiency of the MnS/rGO-based CE reached 8.32%, surpassing the 7.87% achieved by the Pt-based CE in DSSCs. Density functional theory (DFT) calculations indicated that the superior electrocatalytic performance of the MnS/rGO composite is attributed to its excellent I 3 – adsorption capacity and strong interfacial charge transfer capability. These results demonstrate that the MnS/rGO composite is a promising candidate to replace Pt as the CE in DSSCs.