Current state-of-the-art fuel cells depend on relatively high quantities of platinum metal to function. For fuel cells to become economically feasible as a replacement for the internal combustion engine there needs to be a drastic reduction in the quantity of platinum used within them. ACAL Energy has developed a fuel cell that allows for an 80 % reduction in the quantity of platinum required. This is achieved by replacing the solid supported cathode with an aqueous catholyte solution that contains within it a non-precious metal catalyst. The work contained in this thesis explores a library of non-heme metal complexes as potential candidates for use as catalysts for the 4 electron oxygen reduction reaction at the cathode of the FlowCath® fuel cell. The catalysts chosen, Fe(II) TPEN, Fe(II) TRILEN and Fe(II) TPTCN, are super oxidise dismutase mimics and are known to effectively reduce oxygen in a homogeneous solution. These catalysts were studied in fuel cell-like conditions to gain an understanding of their effectiveness in reducing oxygen. Attempts to decorate the complexes with sulfonate groups led to the evolution of the isoquinoline-based complexes. The change from pyridine-based complexes to isoquinoline-based complexes led to the formation of six alternative complexes, Fe(II) 1-miq TQEN, Fe(II) 3-miq TQEN, Fe(II) 1-miq TRILEN, Fe(II) 3-miq TRILEN, Fe(II) 1-miq TQTCN and Fe(II) 3-miq TQTCN, four of which (1-/3-miq TRILEN and 1-/3-TQTCN) are new to the academic literature. These complexes were analysed for their use as catalysts in the oxygen reduction reaction. In addition to the synthetic and analytical work carried out, computational models of the complexes were created. This theoretical data gave a deeper insight into the molecular structure of the complexes studied and the spin states of the Fe(II) and Fe(III) species.