Use of fossil fuels produces the greenhouse gas carbon dioxide, which is the predominate reason for global warming. Developing a renewable green energy cycle is urgently needed to minimize the impact of anthropogenic climate change. The hydrogen cycle is one option for sustainable energy and can reduce global reliance on hydrocarbon fuels. Construction of stable hydrogen evolution reaction (HER) catalysts is a vital step towards the development of a renewable hydrogen infrastructure. Recently, numerous studies have developed inexpensive H2-evolving molecular catalysts based on earth abundant transition metals. Cobalt diglyoxime and cobalt diimine-dioxime complexes were classified as a first and second generation, respectively, of such HER catalysts. However, these catalysts exhibit low stability and reactivity towards HER, which inspired efforts to design effective catalytic platforms featuring high stability and reactivity. Introduction of redox-active ligands bearing extensively conjugated backbones offers a promising system to enhance catalytic activity. In this project, cobalt diimine-dioxime acenaphthene (DDAN) complexes are designed as a new class of HER catalysts. This system provides access to rich electrochemistry and may stabilize the metal center’s low oxidation states which are highly active intermediates in the catalysis. In addition to optimizing the cobalt complex’s catalytic performance, we will expand the family of complexes by varying ligand frameworks, axial ligands, and metal ions in the primary and secondary coordination spheres.

Optimizing H2 evolution by earth abundant metals with macrocyclic diimine dioxime ligands

ACS Fall 2021

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