New Route to Zero Carbon Hydrogen

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In order to decrease the environmental impact of humanity we need to rapidly move away from the use of fossil fuels both for energy and chemical production. Hydrogen is now being pursued as an alternative energy carrier since its use yields water as a by-product (as opposed to the carbon dioxide produced when a fossil fuel is used). The challenge is therefore how we obtain molecular hydrogen (i.e., H2) in a carbon neutral manner. The conventional route for hydrogen production is known as steam reforming. This process traditionally uses a fossil fuel (i.e., natural gas) as feedstock and is an energy intensive process and so results in considerable carbon dioxide emissions. Water splitting (2H2O = 2H2 + O2) has long been viewed as an alternative option for hydrogen production but still faces some challenges, such as the process cost. It is therefore highly desirable to develop further methods for hydrogen production. In this project, we are taking inspiration from nature and considering how the use of nature's catalysts (enzymes) can assist in the production of zero-carbon hydrogen. In order to achieve this, two distinct processes must work in harmony:Step 1: Hydrogen transfer from substrate to a cofactor by enzymatic dehydrogenation.Step 2: Release of hydrogen from the cofactor so that it can be recycled back into Step 1.The 'substrate' in Step 1 is a molecule which will have two hydrogen atoms removed as a proton (H+) and a hydride (H-) by an enzyme. The hydride will then be transferred to a cofactor (known as NAD+) to yield NADH, which temporarily holds the hydride. In order for the system to be cyclic, it is therefore vital to be able to remove the hydride so that the NAD+ cofactor is regenerated and in doing so, hydrogen will be produced (via the recombination of hydride and proton). This project will therefore look to explore the use of a catalyst for this particular step. A heterogeneous catalyst (i.e., a solid catalyst) is preferred for a number of reasons. Firstly, these materials are relatively well studied and understood, easy for scaling up. Secondly, since many catalysts are based on the use of expensive metals (e.g., platinum, rhodium, gold etc) it is important to be able to separate and reuse the catalyst to decrease cost and this is far more feasible with a heterogeneous/solid catalyst.In order for the process described above to be zero-carbon it is important that the so-called substrate (which is converted into a by-product) is chosen carefully. The substrates that will be explored will be from renewable sources (i.e., naturally produced alcohols, aldehydes, acids, sugars, and polyols, etc.) and chosen such that the by-product is in its own right a value-added chemical. In other words, this project will simultaneously target the production of the key energy carrier H2 in a zero-carbon manner whilst also offering a fossil fuel free route to certain chemical compounds.