Cobalt Complexes with Bis-Imidazole and Bis-Benzazole Ligands as Catalysts for the Hydrogen Evolution Reaction

99% of our energy originates from the sun. For millions of years, plants have captured and stored this energy in chemical bonds, converting CO2 into sugar, that later resulted in fossil fuels. Today, we use these fossil fuels much more rapidly than they were produced causing abrupt changes in our climate that lead to severe weather events and the loss of ecosystems and biodiversity. To reduce climate change (a little bit late!), we aim to replace fossil fuels with sustainable energy carriers that are produced with renewable energy. A promising energy carrier is hydrogen gas, a clean burning fuel that produces water and no greenhouse gas upon combustion. Hydrogen gas can be produced from water with renewable energy, but the chemical bonds in water molecules are extremely strong and the breaking of these bonds causes the loss of an enormous amount of energy (to heat) making it a very inefficient use of our (renewable) energy. Not surprisingly, nature has found a way to bypass the loss of energy by using very complex molecular structures (enzymes) that are efficient in hydrogen production by pushing and pulling on molecules in the right position and with the right amount of power. Most inspiring is that these enzymes are built from earth-abundant elements only. As scientists, we are of course thrilled by this achievement and wish to reproduce the efficiency in the laboratory. In this thesis, we built molecular complexes, “artificial enzymes”, based on abundant elements, with which we aimed to facilitate the production of hydrogen gas. We were able to produce hydrogen gas with a cobalt-based molecular complex in which we incorporated a molecular functionality, a proton (substrate) relay, that facilitates the hydrogen gas-making process. With this achievement, we are a small step closer to understanding the fascinating processes in nature and a small step closer to (but still far from) energy-efficient hydrogen production using earth-abundant elements.