Water localization and dynamics in proton exchange membranes for photoelectrochemical cells

With average global temperatures rising, increasingly harsh weather conditions, and more frequent occurrences of severe storms, it is apparent that climate change due to global warming remains a main concern across the world. Carbon dioxide (CO2) is one of the most important greenhouse gases contributing to global warming, and current atmospheric CO2 concentrations keep increasing due to the growing energy demand and the continuous burning of fossil fuels. Moving towards a CO2-neutral energy economy is a huge but immensely rewarding challenge. Scientists are therefore searching for ingenious new ways to exploit renewable energy sources. Photoelectrochemical cells (PEC) are designed to store solar energy in sustainably produced hydrogen gas by means of water splitting reactions. The hydrogen gas has no carbon footprint and can be used to create a wide variety of hydrocarbon fuels and useful chemicals through industrial-scale reactions with CO2 or carbon monoxide (CO). In our lab, PECs are being developed that incorporate multiple highly advanced materials such as proton conductive polymers, photosensitive porous electrodes and various combinations catalysts and co-catalysts to drive reactions forward. Additionally, the exciting prospect of operating such a PEC in ambient air holds many advantages compared to using a liquid water feedstock. There is no bubble formation, there is a reduced possibility of corrosion or poisoning, and there is no need for a liquid pumping system. However, the proton exchange membrane (PEM) used in such a cell must be kept hydrated in order to maintain a high level of proton conduction and thus maintain a high product formation efficiency. Self-humidification can be achieved by incorporating inorganic nanoparticles into the membrane, but this does not always lead to an improved proton conductivity. A solid understanding of how such materials work and interconnect is therefore fundamental to optimizing the overall device for use in ambient air. In this respect, a technique called 'nuclear magnetic resonance (NMR) spectroscopy' is perfectly suited to study the hydration and proton conduction processes within such materials at the molecular level. The primary aim of this work is to exploit the extensive toolbox of NMR spectroscopy to study water localization and dynamics in pristine and nanocomposite Nafion membranes with respect to their use as proton conducting solid electrolytes in air-based PECs for water splitting.