CHEMICAL ENGINEERING TRANSACTIONS VOL. 41, 2014 A publication of The Italian Association of Chemical Engineering www.aidic.it/cet Guest Editors: Simonetta Palmas, Michele Mascia, Annalisa Vacca Copyright © 2014, AIDIC Servizi S.r.l., I SBN 978-88-95608-32-7; I SSN 2283-9216 Photo-Electrochemical Production of H 2 Using Solar Energy Anna Hankin a , Geoff H. Kelsall* a , Chin Kin Ong b , Fabien Petter a a Department of Chemical Engineering, Imperial College London, London, SW7 2AZ, UK b PIPDEV Ltd., PO Box 36522, London, W4 2XF, UK g.kelsall@imperial.ac.uk Ti | Sn IV -Fe 2 O 3 photo-anodes are implemented in a photo-electrochemical reactor for photo-assisted splitting of water into hydrogen and oxygen. Attention is focused on the issues concerning electrode scale- up with the aim of addressing the present need for the design, optimisation and demonstration of the commercial feasibility of photo-electrochemical reactors. 1. Introduction Synthetic hematite has attracted considerable attention as a photo-anode in photo-electrochemical reactors for solar water splitting. Theoretically, its band gap of 1.9 - 2.2 eV (Akl, 2004), enables it to absorb up to ca. 37 - 30 % of solar photons, as determined by integrating the AM 1.5 solar irradiance spectrum (ASTM G173-03 Reference Spectra (NREL)) with respect to wavelength, λ, for λ ≤ λ band gap . However, the low conductivity of hematite, even when doped, requires a conductive substrate to serve as a current feeder plate. Typically, for use in small scale reactors, hematite films are deposited onto glass substrates coated with a thin layer of conductive fluorine-doped tin oxide (FTO). However, the sheet resistivity of ca. 0.2-1.5 Ω cm 2 renders this substrate unsuitable for scale-up. Hence the development of Ti | Fe 2 O 3 photo-anodes (Ong et al., 2014) for implementation in alkaline aqueous electrolytes was motivated by the high conductivity of titanium as well as its chemical stability in such media. The possible formation of a TiO 2 layer between Ti and Fe 2 O 3 during the fabrication process is not considered disadvantageous, provided the thickness of this layer does not exceed several nanometres. The principal disadvantage of a metallic substrate in comparison to a glass substrate is that it is not transparent and hence the electrode configuration geometries are more limited. Here, we explore the performance of 0.1×0.1 m 2 Ti | Sn IV -Fe 2 O 3 photo-anodes in two configurations. 2. Experimental All electrochemical measurements were performed in 1 M NaOH solution (pH ca. 13.7, T ca. 298 K) at Ti | Sn IV -Fe 2 O 3 working electrodes, with a Ti | Pt mesh (ca. 50 % open area, The Expanded Metal Company) counter electrode and an HgO | Hg reference electrode measuring at 0.12 V against the standard hydrogen electrode (SHE). 2.1 Photo-anode preparation Tin doped iron oxide films were deposited by spray pyrolysis (Ong et al., 2014) on 0.1 × 0.1 m 2 titanium foil substrates (Alfa Aesar), previously polished using alumina powder on an automated polishing machine (Buehler), degreased with acetone, ultrasonicated and washed in de-ionised water. Titanium rods (Alfa Aesar) were pre-welded to the edges of the samples as electrical contacts. Each clean substrate was placed onto a hotplate and heated to 480 °C. The precursor solution for spray pyrolysis comprised 0.1 M FeCl 3 (Sigma Aldrich, UK) and 6×10 -4 M SnCl 2 (Sigma Aldrich, UK) dissolved in ethanol absolute (AnalaRNormapur, VWR BDH Prolabo). A quartz nebuliser (Meinhard, US) which acted as the spray nozzle was attached onto a CNC machine (Heiz T-720, Germany) and was maintained at a height of ca. 150 mm above the surface of the substrate. The DOI: 10.3303/CET1441034 Please cite this article as: Hankin A., Kelsall G., Ong C.K., Petter F., 2014, Photo-electrochemical production of hydrogen using solar energy, Chemical Engineering Transactions, 41, 199-204 DOI: 10.3303/CET1441034 199