Due to the intermittent nature of renewable energy sources like wind and solar, efficient energy storage and distribution is essential when these sources are dormant. Among potential candidates for chemical energy storage, ammonia is gaining more attention, owing to its zero-carbon footprint, relatively efficient synthesis on a global scale, and well-established transportation infrastructure. If ammonia is synthesized via renewable energy sources, the efficient conversion of NH3 to N2 and H2 would complete an energy cycle where H2 stored as NH3 can fuel hydrogen/hybrid vehicles that are being commercialized. The efficiency of ammonia electrolysis to N2 and H2 can be improved by catalysts designed to lower the high overpotentials for oxidation and reduction at conventional electrodes. This work first describes the synthesis of tris and mono(ammine) iron complexes with tridentate phosphine ligands and their role in increasing current densities for NH3 oxidation relative to current densities generated using standard anodes. Electrocatalytic ammonia oxidation by a mononuclear ruthenium ammine complex supported by an isoindole-based tridentate ligand has been investigated next and its oxidation potential has been compared to previously reported mononuclear ruthenium ammine catalysts. At the end, a dinuclear polypyridine ruthenium bis(ammine) complex was reported in which ruthenium centers are held in close proximity by a bridging ligand in a way two NH3 ligands have a syn relationship, allowing the possibility of intramolecular oxidative N-N coupling.
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