Electrochimica Acta 97 (2013) 320–325 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al h om epa ge: www.elsevier.com/locate/electacta Solid-state photoelectrochemical H 2 generation with gaseous reactants Kingsley O. Iwu a , Augustinas Galeckas b , Andrej Yu. Kuznetsov b , Truls Norby a,∗ a Department of Chemistry, University of Oslo, Centre for Materials Science and Nanotechnology, FERMiO, Gaustadalleen 21, NO-0349 Oslo, Norway b Department of Physics, University of Oslo, Centre for Materials Science and Nanotechnology, P.O. Box 1048 Blindern, NO-0316 Oslo, Norway a r t i c l e i n f o Article history: Received 25 January 2013 Received in revised form 3 March 2013 Accepted 4 March 2013 Available online 13 March 2013 Keywords: Photoelectrochemical Hydrogen TiO2 Solid-state Nafion ® a b s t r a c t Photocurrent and H 2 production were demonstrated in an all solid-state photoelectrochemical cell employing gaseous methanol and water vapour at the photoanode. Open circuit photovoltage of around -0.4 V and short circuit photocurrent of up to 250 A/cm 2 were obtained. At positive bias, photocurrent generation was limited by the irradiance, i.e., the amount of photogenerated charge carriers at the anode. Time constants and impedance spectra showed an electrochemical capacitance of the cell of about 15 F/cm 2 in the dark, which increased with increasing irradiance. With only water vapour at the anode, the short circuit photocurrent was about 6% of the value with gaseous methanol and water vapour. The photoanode and electrocatalyst on carbon paper support were affixed to the proton conducting mem- brane using Nafion ® as adhesive, an approach that yielded photocurrents up to 15 times better than that of a cell assembled by hot-pressing, in spite of the overall cell resistance of the latter being up to five times less than that of the former. This is attributed, at least partially, to reactants being more readily available at the photoanode of the better performing cell. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Solid-state electrolytes have potential advantages over liquid ones for use in conventional electrolysis of water or steam as well as in photoelectrochemical (PEC) cells. The ion conducting membrane in this case acts as a support to both the cathode and anode, with the possibility of a compact and robust construction, besides the separation of the products at the electrode compartments. Polymer electrolyte membrane (PEM) electrolysers are typical examples of such a design. PEC water splitting cells with PEM electrolyser-like designs have been demonstrated with acidic solution [1,2], alkaline solution [3], and pure water [4,5] as anode reactants, but little work has been done with gaseous feedstock for the anode. Meanwhile, the use of gaseous water has been shown to be more efficient than liquid water in a PEM electrolyser operating in the current density range that future commercial PEC water splitting cells are expected to operate [6], while the feasibility of PEC purification of air (decom- position of organics) has been demonstrated with all solid-state, PEM-electrolyser type PEC devices [7–10]. A report on the use of a mixture of gaseous ethanol and water vapour as anode reactants for solid-state PEC hydrogen generation only indicated that the use ∗ Corresponding author. Tel.: +47 22840654; fax: +47 22840651. E-mail addresses: k.o.iwu@smn.uio.no (K.O. Iwu), augustinas.galeckas@fys.uio.no (A. Galeckas), andrej.kuznetsov@fys.uio.no (A.Yu. Kuznetsov), truls.norby@kjemi.uio.no (T. Norby). of the gaseous reactants gave a superior PEC performance in com- parison to their liquid counterparts but did not provide information on the PEC and material limitations of such a system [11]. In this work, an all solid-state PEC H 2 generating cell based on a composite proton conducting Nafion ® + Mo 0.5 W 0.5 O 3 ·1/3H 2 O membrane (NA-Mo 0.5 W 0.5 O 3 ·1/3H 2 O), P25 TiO 2 photocatalyst anode, and Vulcan Pt-C (10 wt% Pt) cathode is presented. Voltam- metry and impedance spectroscopy studies have been used to characterise the cell in order to identify the limitations to enhancing the efficiency of a PEM electrolyser-type PEC hydrogen generating cell. 2. Experimental Nafion ® perfluorinated resin solution (20 wt%) was obtained from Sigma–Aldrich. Carbon paper (190 m thick), Nafion ® perflu- orinated membrane (127 m thick) and platinum coated carbon, Pt-C (Pt/Vulcan XC-72R, 10 wt% Pt) were obtained from Quintech, Germany. All dilutions and suspensions were made using iso- propanol as solvent. Mo 0.5 W 0.5 O 3 ·1/3H 2 O was prepared according to the procedure reported elsewhere [12]. Its composite membrane with Nafion ® , NA-Mo 0.5 W 0.5 O 3 ·1/3H 2 O (1:4 weight ratio) was made by drying a 33 mg/ml suspension of the mixture in a 20 cm diameter Teflon cylinder at 50 ◦ C for 30 h. Dark blue membranes about 420 m thick were obtained. It was necessary to use such a high solid loading of 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.03.013