| The oxygen evolution reaction (OER) is the anodic half reaction required to convert water into storable chemical fuels and remains a key bottleneck in sustainable energy production. Numerous synthetic molecular complexes, primarily Ru polypyridyls, have been reported that perform OER catalysis. This thesis work is divided into two main areas of focus: the development of methods for attaching alkyne-modified Ru complexes to electrode surfaces via Cu-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry to generate functionalized electrodes, and the development of a new class of molecular OER catalysts based on earth abundant Co. Efforts to attach Ru complexes to electrode surfaces initially targeted an alkyne-modified derivative of a previously reported Ru polypyridyl OER catalyst. The modified complex was successfully prepared and attached to azide-functionalized graphite electrodes, though the graphite electrodes proved insufficient to withstand the strongly oxidizing conditions required for OER catalysis. Attempts to attach the catalysts to functionalized conductive diamond electrodes proved successful and redox chemistry was observable on the time scale of cyclic voltammetry, however the attachment proved unstable to electrolysis at potentials relevant to OER catalysis. In order to demonstrate the fundamental stability of the functionalized diamond electrodes separate from catalysis an alkyne-modified Ru(tpy)2 derivative was prepared and tethered to conductive diamond. This functionalized diamond electrode showed good stability in aqueous solvents and excellent stability in non-aqueous solvents for >500,000 cycles. In a separate project, structural analogies between known Ru OER catalysts and CoIII bridging-peroxo dimers inspired the evaluation of such Co complexes as OER catalyst candidates. When the known compounds studied were shown to be unstable in aqueous media, a new series of peroxo dimers supported by a bridging bispyridylpyrazolate (bpp) ligand were prepared. These complexes display excellent stability in water and aqueous electrochemistry supports their ability to serve as electrocatalysts for OER. Oxidized intermediate species have been identified and characterized suggesting an OER mechanism that resembles mechanisms proposed for CoOx heterogeneous OER catalysts. In addition to OER activity the bpp-Co peroxo complexes are shown to perform the oxygen reduction reaction, making these complexes among the few examples of molecular complexes capable of performing both catalytic processes. |
