Study of the water gas shift reaction on Fe in a high temperature proton conducting cell Christos Kokkofitis, George Karagiannakis, Michael Stoukides * Chemical Engineering Department, Aristotle University & Chem. Proc. Engineering Research Institute, U. Box 1517, University Campus, Thessaloniki 54124, Greece Available online 19 June 2007 Abstract The water gas shift (WGS) reaction was studied in a double-chamber high temperature proton conducting cell (HTPC). The proton conductor was a strontia–ceria–ytterbia (SCY) disk of the form: SrCe 0.95 Yb 0.05 O 3a and the working electrode was a polycrystalline Fe film. The reaction temperature and the inlet partial pressure of CO varied between 823 and 973 K, and between 1.0 and 10.6 kPa, respectively. The inlet partial pressure of steam (P H 2 O ) was kept constant at 2.3 kPa. An increase in the production of H 2 was observed upon ‘‘pumping’’ protons away from the catalyst surface. The Faradaic efficiency (L) was lower than unity, indicating a sub-Faradaic effect. The highest value of rate enhancement ratio (r) was approximately 3.2, at T = 823 K. The proton transport number (PTN) varied between 0.45 and 1.0. An up to 99% of the produced H 2 was electrochemically separated from the reaction mixture. # 2007 Elsevier B.V. All rights reserved. Keywords: High temperature proton conductor; Water gas shift reaction; H 2 production; Electrocatalytic separation of H 2 ; Fe catalyst 1. Introduction With hydrogen appearing as the energy ‘‘currency’’ of the future, there is an ongoing interest in technologies associated with hydrogen production and purification. The water gas shift (WGS) reaction is a well-established process that mostly applies to large scale steady-state operations, such as hydrogen or ammonia plants [1–3]. It is an exothermic reaction and therefore thermodynamically favored at low temperatures: CO þ H 2 O ! CO 2 þ H 2 DH  ¼41:1 kJ=mol ðat 298 KÞ: (1) Recently, the need for the development of efficient fuel processors in fuel cell applications has strongly renewed the interest for the above reaction. To this end, a large number of investigators have studied the WGS reaction over a variety of metal or metal oxide catalysts; either supported on oxide supports [1–9] or unsupported [10–15]. Although current research efforts mostly focus on noble metal-based catalysts [1–8], the interest for Fe-based catalysts is still active [14–17]. Additionally, in an effort to achieve higher H 2 yields, several research groups have studied the WGS reaction in membrane reactors [18–20]. These reactors utilized primarily Pd or Pd–Ag membranes and their operation was based on the chemical potential difference of hydrogen between the two sides of the membrane. Another alternative is a proton conducting cell- reactor. The discovery of solid state materials that exhibit protonic (H + ) conductivity at elevated temperatures made it possible to use them in catalytic hydro- and dehydrogenations of industrial interest [21,22]. The prominent advantage of such an electrochemical reactor is that it offers simultaneous production and separation of hydrogen; the catalytic reaction takes place at the anode, while high purity H 2 is recovered at the cathode. Proton conducting cell-reactors can be also used to electrochemically promote catalytic reaction rates. If the catalyst to be promoted is one of the electrodes of the cell, protons can be electrochemically ‘‘pumped’’ to or away from the catalyst during reaction. This can cause a considerable change in catalytic activity and the rate enhancement can be orders of magnitude higher than the rate of proton transport through the electrolyte [23,24]. www.elsevier.com/locate/cattod Catalysis Today 127 (2007) 330–336 * Corresponding author. Tel.: +30 2310 996165; fax: +30 2310 996145. E-mail address: stoukidi@cperi.certh.gr (M. Stoukides). 0920-5861/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2007.05.007