Solar Hydrogen Generation Using Homogeneous, Heterogeneous and Biphasic Catalytic Systems

Husain N. Kagalwala
2019
Using sunlight to generate hydrogen from water has captivated the attention of researchers as it would prove to be a completely renewable method of fuel production. For several decades, scientists have been trying to achieve 'totalwater splitting', which is a highly complex and energetically demanding process. To overcome this barrier, the process is treated separately as two half reactions, namely water oxidation and reduction, with the majority of the research directed at the reduction side
more » ... he reduction side which pertains to H2 evolution. Of late, research is also being conducted on using other H2 sources like acids and alcohols which arethermodynamically easier to dehydrogenate. The usual components for photocatalytic hydrogen evolution include a light-absorbing chromophore/photosensitizer, a proton reducing catalyst and a sacrificial donor/ redox mediator which mimics the oxidative half of water photolysis.These reactions have been carried out using both molecular and heterogeneous systems, mainly employing noble metal-based photoharvesters and catalysts, due to their inherent low overpotentials, high activity and stability. To ensurecommercial viability of the hydrogen generation process, recent focus has been on utilizing earth-abundant materials. With this background in mind, this dissertation aims to explore different routes to photocatalytic hydrogengeneration. Both molecular and heterogeneous methods of water reduction were probed, using an earth-abundant Ni-based hexameric cluster and a metal-free nanocarbon, respectively as proton reducing catalysts. Both systems were photodriven using state-of-the-art iridium-based photosensitizers, which are robust and well-known to probe the capability of new catalysts. While the Nibased molecular system achieved up to 30,000 catalyst turnovers, the metal-free nanocarbon was able to outperform platinum catalysts in terms of total hydrogen generation. As an example of replacing synthetic sacrificial agents with naturallyoccurring compoun [...]
doi:10.1184/r1/10069787.v1 fatcat:5cqn4v44sbfaxidpmprjqjgsuq