Bis(formazanate) Iron(II) Complexes as Cathode Material for One-Compartment H2O2 Fuel Cell

In this paper, we describe the synthesis of two six-coordinate, pseudo(octahedral) bis(formazanate) Fe(II) complexes based on new redox-active benzothiazole substituted formazanate ligands. Complexes [Fe^II(L1)₂], 1 and [Fe^II(L2)₂], 2 were synthesized by reacting 1-(benzothiazol-2-yl)-5-phenyl-3-(pyren-1-yl)formazan (L1H) and 1-(benzothiazol-2-yl)-5-(2-benzoyl-4-chlorophenyl)-3-phenylformazan (L2H) respectively with the appropriate Fe(II) precursors at room temperature. The molecular structure of both the bis(formazanate) iron complexes has been established using Single-Crystal XRD, and other characterization methods were utilized to characterize these complexes further, as well as the newly synthesized ligands. Furthermore, the cyclic voltammetry of these compounds is documented, revealing that both complexes may undergo electrochemical reductions to create anionic and dianionic species. These complexes were further employed as the cathode of one-compartment membrane-less H₂O₂ fuel cells, operating in 0.5 M H₂O₂ with nickel foam serving as the anode. The maximum power densities achieved by the designed H₂O₂ fuel cell for complexes 1 and 2 were 1.88 mW cm^-2 and 3.08 mW cm^-2, respectively. This study demonstrates the significant potential for investigating formazanate-based compounds in the development of cathode materials for H₂O₂ fuel cells.