Solar fuels from sustainable feedstock using Earth-abundant catalysts: Can light drive affordable electrocatalysts for fuel production?

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The proposed research targets new technology to synthesise fuels from sustainable feedstocks and renewable energy. This is important work since three fifths of all global energy usage is in the form of fuel burning for transportation and heating. While renewable electricity generation from solar and wind amongst others is on track to reduce the carbon emissions of electricity generation, only two fifths of end use energy is in the form of electricity. It is globally critical to find sustainable and cost effective ways to decarbonise transport and heating. Synthesising fuels from CO2 feedstocks using the only infinite source of renewable energy - solar - would be an ideal solution. Yet no viable technology have been developed.Why not?Traditional catalysts for conversion of CO2 are Nobel-metal based, expensive, and not suitable for mass deployment. Rhenium, which is the basis of the most broadly used catalysts for CO2 reduction, is extremely expensive and rare. Its analog, Manganese, is 1.3 million times more abundant, constituting 0.1% of the Earth's crust. In 2011, researchers showed that Mn-complexes with diimine ligands and carbonyls could be even more active then their Re analogs in reducing CO2. These catalysts are used now used in electrochemical reduction, where the electrons flow from the "mains" to the electrode, then to the catalyst, and finally to CO2. In 2016, we developed a new class of versatile Mn-based catalysts which can be attached to surfaces.Can we use renewable energy to activate these cheap, versatile, Earth-abundant catalysts?The major obstacle so far has been that these catalysts are light-sensitive, and we can not use sunlight to activate them directly. We propose to combine the cheap catalysts (Mn-based) with available feedstock (CO2) and renewable energy (solar) in a device which uses sunlight indirectly. We will build on recent (2016) progress in light-absorbing semiconductors and investigate an integrated technology that could provide the sought after breakthrough. The overall vision is a plate based technology (much like a solar photovoltaic panel) that can be manufactured cheaply in high volumes, that absorbs sunlight and transfers the solar energy to a catalyst that is anchored on the light absorbing surface. The catalyst is fed CO2 in a water based electrolyte and the energy from the sunlight reduces the CO2 to CO, a reactive intermediate from which further, well-known, reactions can make fuels.Our plan is to use a particular light absorbing electrode (Cu2O/AlZnO protected by TiO2) that has been shown to be highly effective in combination with scarce rhenium based catalysts. We will substitute Rhenium for highly abundant Manganese catalysts and measure how effective they are. The catalyst needs to be anchored to the electrode and must not be directly exposed to sunlight. Our research will overcome these constraints using chemical modification of the catalyst to attach it to the light-absorbing semiconductor electrode, and by illuminating the absorbing electrode from the back of the structure.In addition, we will build a prototype industrial process scheme from which we will investigate the energy economic performance and carbon emissions of the proposed device. This will allow us to evaluate the likely impact of the technology in terms of mitigation of climate change, and in providing cost effective access to fuels.We have a team of researchers with expertise spanning chemistry, physics, materials and devices, and techno-economic analysis - the cross-section that is vital for such research to succeed. Overall, finding a way to solar-power these cheap, versatile catalysts, will make a huge step forward towards clean, renewable ways of producing fuels, and energy, for all. It will invigorate research in cheaper catalysts, materials and devices, improve quality of life - and help the Planet.