Micro-pompon-like metal organic chalcogenides of [Fe₂(6mna)₂]_n as electrocatalyst for Cu-neocuproine mediated dye-sensitized solar cells

Metal-organic chalcogenide (MOC) of [Fe₂(6mna)₂]_n (6mna= 6-mercaptonicotinic acid) was bottom-up synthesized on a conductive carbon cloth (CC) substrate by a simple ligand-assisted method. By varying the volume ratio of toluene/dimethylformamide (Tol/DMF) during MOC coordination, the micro-ball-like, micro-pompon-like, and micro-cactus-like particles were obtained by [Fe₂(6mna)₂]_n-2/5 (Tol/DMF= 2/5), [Fe₂(6mna)₂]_n-3/4 (Tol/DMF= 3/4), and [Fe₂(6mna)₂]_n-4/3 (Tol/DMF= 4/3), respectively. Among these [Fe₂(6mna)₂]_n analogues, the CC/[Fe₂(6mna)₂]_n-3/4 electrode outperformed the others due to its numerous active sites within the nano-particle-decorated micro-pompons. Meanwhile, a hierarchical 1D-to-1D charge-transfer pathway was established by a core/shell structure of CC/[Fe₂(6mna)₂]_n-3/4; where each 1D carbon fiber in CC worked as the conductive core, and the 1D (−Fe−S−)_n helical chains in the [Fe₂(6mna)₂]_n micro-pompon functioned as electro-catalytic shell. As the electro-catalytic cathodes in dye-sensitized solar cells (DSSCs), all the CC/[Fe₂(6mna)₂]_n triggered a diffusion-controlled [Cu(dmp)₂]^2+/1+ (dmp= 2,9-dimethyl-1,10-phenanthroline; neocuproine) redox reaction; however, it performed a kinetic-controlled I⁻/I₃⁻ redox reaction. The optimal CC/[Fe₂(6mna)₂]_n-3/4 electrode reached a superior cell efficiency of 8.08% than CC/Pt in [Cu(dmp)₂]^2+/1+ (7.68%), illustrating its potential as an earth-abundant electrocatalyst.