Main Group Element Based Catalysis for Photolytic HX-Splitting

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As global populations increase and standards of living improve, so does humanity's dependence on fossil fuel reliant processes, which is accompanied by an unwanted increase in CO2 emissions. As such, much of modern science is unified by a common goal - to reduce global CO2 emissions by finding "green" alternatives to these fossil fuel-based processes. The dominant form of energy consumption is the generation of electricity, with alternatives such as wind and solar energy considered viable routes to do so in a sustainable manner. However, these approaches have their inherent drawbacks, mainly in the form of geographical constraints and intermittency of power output. Essentially: not all areas of the globe have equal wind and sun coverage, and even in those with plenty, these natural processes do not operate reliably at all times. Therefore, methods of maximising power output and efficiently storing such power must be developed to make these green approaches reliable on a large scale. Concerning the storage of renewable energy, one particular method has caught the attention of the scientific community - energy storage in chemical bonds. The chemical bond arises when two or more atoms share electrons with one another, resulting in these electrons existing somewhere in-between the bonded atoms. The formation of this bond results in energy being stored in the resulting molecule - we call this "Chemical Energy".The question now is - what bonds do we use and how do we store the resulting molecule/fuel?The obvious starting point is to only consider fuels which do not contribute to global warming - for example by scrapping those which contain carbon and opting instead for those which release non- polluting compounds upon both formation and combustion. For this reason, the use of hydrogen, H2, as a fuel has gained significant attention. The large-scale synthesis of hydrogen is already an established and widely implemented procedure, however it currently requires the use of a chemical process known as Methane Steam Reforming. As the name suggests, this method, which is responsible for 95% of hydrogen production in the United States, requires the use of methane (CH4, a.k.a natural gas) as the main chemical precursor and results in the release of CO2. Clearly, this route towards hydrogen is not viable when aiming to achieve net-zero carbon emissions. Therefore, a new route needs to be devised.Efforts in this field have led to one particular approach emerging as most attractive - electrochemical water splitting. What this means is: splitting water (H2O) into its constituent parts - H2 and O2 - using electricity (itself sustainably generated). This process, however, suffers an intrinsic penalty as water- splitting is energetically unfavourable, requiring a large energy input to break strong O-H bonds. This issue may be simplified by using a different feedstock - the chemically more-straightforward hydrohalic acids, HX (X = F, Cl, Br, I). HX-splitting is a two-electron, two-proton reaction, thus reducing the complexities associated with the four-electron, four-proton water-splitting reaction. The focus of this project, which falls within the EPSRC Energy research theme, is to develop new phosphorous- containing compounds which enable the HX-splitting reaction to occur efficiently. Traditionally, research into this field focuses on the use of precious metals to provide a similar result, but by turning attention to the much more accessible and abundant phosphorous, this approach becomes more attractive for large scale adoption.