Design and Development of Photo-electrochemical Reactors for Hydrogen Production with Solar Energy

Anna Hankin^a, Geoff Kelsall^a, Franky Bedoya-Lora^a, Ned Ekins-Daukes^b, Keith Barnham^b, Jose Videira^b

^aDepartment of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London, United Kingdom

Materials for Sustainable Development Conference (MATSUS)
Proceedings of September Meeting 2016 (NFM16)

Berlin, Germany, 2016 September 5th - 13th

Organizers: Marin Alexe, Enrique Cánovas, Celso de Mello Donega, Ivan Infante, Thomas Kirchartz, Maksym Kovalenko, Federico Rosei, Lukas Schmidt-Mende, Laurens Siebbeles, Peter Strasser, Teodor K Todorov, Roel van de Krol and Ulrike Woggon

Oral, Anna Hankin, presentation 058
Publication date: 14th June 2016

Industrial deployment of photo-electrochemical systems for hydrogen production via solar-powered water splitting still necessitates considerable progress to be made in the development and operation of scalable demonstration units. Research efforts are presently largely focused on the development of photo-electrode materials that perform the combined function of light absorption, charge transport and reaction catalysis, at the same time as demonstrating adequate chemical stability and requiring low production costs. However, in addition to material development, the engineering of scalable photo-electrochemical reactors that would utilise these materials is also constrained by many requirements that must be satisfied simultaneously. The factors that govern reactor design include: (a) electrode scale-up; (b) mode of photo-electrode illumination; (c) current distribution (and associated losses); (d) the utilisation of a membrane; (e) electrolyte recirculation; (f) product harvesting; (g) heat dissipation. These and other design considerations must enable the reactor to be suitable for operation in industrial conditions.

We have developed a photo-electrochemical demonstration unit capable of splitting water into hydrogen and oxygen using only photon energies. The reactor incorporates a hematite (Ti|Sn^IV-Fe₂O₃) photo-anode, an array of triple junction solar cell photo-cathodes (Ge|GaAs|InGaP|TiO₂) and is coupled to a novel light distribution system based on waveguides [1]. The hematite photo-anode absorbs visible light photons with energies greater than its 2.2 eV band gap. Each triple junction solar cell absorbs photons with energies greater than 0.69 eV and delivers up to 2.2 V of bias and 0.18 A W^-1 of current. Two PMMA waveguides are illuminated by concentrated solar photons and re-direct these photons laterally into the reactor, thereby separately irradiating the photo-anode and photo-cathode.

I shall discuss the effects of electrode materials, geometries and relative configurations within a photo-electrochemical reactor on its design, overall performance and further scale-up, as well as the future role of photo-electrochemical systems in energy storage.

[1] J. J. H. Videira, K. W. J. Barnham, A. Hankin, J. P. Connolly, M. Leak, J. Johnson, G. H. Kelsall, K. Kennedy, J. S. Roberts, A. J. Cowan and A. J. Chatten, 2015, IEEE PVSC 42, 1.

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