Co9S8-Ni3S2@WS2 hierarchical yolk-shelled nanospheres as superior Pt-free catalytic materials for highly efficient dye-sensitized solar cells

The hierarchical polymetallic sulfide electrocatalysts are endowed with high expectations in various energy conversion/storage fields. Herein, a facile two-step solvothermal method was employed to synthesize a series of hierarchical transition metal sulfide nanospheres with defined-well yolk-shelled structures (Co9S8-Ni3S2@WS2, Co9S8@WS2 and Ni3S2@WS2). Noteworthily, the resultant samples as the bifunctional electrocatalysts for the dye-sensitized solar cells possessed prominent electrocatalytic performances. Benefiting from the higher specific surface area, unique morphology, the synergistic effect of multi-elements and more favorable chemical compositions, the quaternary Co9S8-Ni3S2@WS2 nanospheres showed great advantaged features at promoting the reduction of triiodides in comparison with ternary Co9S8@WS2 and Ni3S2@WS2 nanospheres. Among these samples, the counter electrode with Co9S8-Ni3S2@WS2 catalysts exhibited a noteworthy power conversion efficiency of 9.67% for solar cell, which was much superior to that of Pt (8.16%).