PdeAg hydrogen diffusion cathode for alkaline water electrolysers A. Pozio a, *, M. De Francesco a , Z. Jovanovic a,1 , S. Tosti b a ENEA, C.R. Casaccia, Via Anguillarese 301, 00123 S. Maria di Galeria, Rome, Italy b ENEA, Unita ` Tecnica Fusione, C.R. Frascati, Via E. Fermi 45, 00044 Frascati, Rome, Italy article info Article history: Received 3 November 2010 Received in revised form 24 January 2011 Accepted 30 January 2011 Available online 4 March 2011 Keywords: PdeAg permeator Hydrogen permeation Alkaline electrolysers abstract This paper describes experimental work involving the direct-current electrolysis of potassium hydroxide solutions at medium temperatures (up to 80  C) and atmospheric pressure. An electrolytic cell with a palladiumesilver alloy cathode as a source of ultrapure hydrogen was designed and tested. This cathode consists of a dense PdeAg tube capable to selectively separate hydrogen from other gases. Thin wall thickness (50 mm) of the per- meator tube permitted to attain high hydrogen permeation fluxes and high hydrogen yields. Starting from results, a prototype electrolyzer is designed. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Hydrogen is widely considered as the best candidate fuel on which to base a future renewable energy economy; largely due to its applicability in highly efficient fuel cell systems, as well as its high specific energy density by mass [1,2]. Additionally, hydrogen used as either an electrochemical or combustion fuel produces water as the only by-product, without the local generation of pollutants or greenhouse gases such as CO 2 . Unfortunately, the problems related to the production of hydrogen continue to delay the realization of the hydrogen economy [3,4]. The vast majority of hydrogen used today is produced by the steam reforming of methane gas [5e7], a carbon dioxide-producing process that unfortunately is not carbon-free. Clean hydrogen can be produced via water elec- trolysis in which electrical energy is obtained from renewable energy sources [8e10]. The hydrogen produced in this way is usually of very high purity. Unfortunately, the economic penalties associated with both the costly generation of electrical power for driving the electrolysis process and the relatively expensive and complicated construction of elec- trolysis cells [11,12] have limited the interest in deploying large electrolysis units for on-site hydrogen generation in the power and chemical industries. The electrolysis of aqueous alkaline hydroxide solutions has historically been one of the most popular routes for the production of hydrogen and oxygen from water. Notable recent studies concerned with the improvement of alkaline electrolysis processes have focused on the use of advanced anode materials in electrolyzers to reduce electrode polari- zation and thereby to improve the overall electrical efficiency [13e15]. It has been appreciated for many years that electro- lytic hydrogen will diffuse through the walls of the tubular palladium cathode against which it is generated. This hitherto neglected possibility of simultaneous generation and purifi- cation were utilized in the design of some compact electrolytic cells which can yield pure hydrogen for laboratory or other small scale work. The first preliminary experiments on the * Corresponding author. Fax: þ39 06 30486357. E-mail address: alfonso.pozio@casaccia.enea.it (A. Pozio). 1 Permanent address: Vin ca Institute of Nuclear Sciences (010), University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia. Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 36 (2011) 5211 e5217 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.01.168