Novel co-extruded electrolyte–anode hollow fibres for solid oxide fuel cells Nicolas Droushiotis, Mohd Hafiz Dzarfan Othman, Uttam Doraswami, Zhentao Wu, Geoff Kelsall, Kang Li * Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK article info Article history: Received 17 June 2009 Received in revised form 15 July 2009 Accepted 15 July 2009 Available online 18 July 2009 Keywords: Micro-tubular SOFC CGO Ni LSCF Co-extrusion Hollow fibres abstract Novel CGO/NiO–CGO dual-layer hollow fibres (HFs) have been fabricated in a single-step co-extrusion and co-sintering process. LSCF–CGO cathodes layers were then deposited onto the dual-layer HFs to con- struct micro-tubular SOFCs. The NiO in the micro-tubular HF–SOFCs was reduced at 550 °C using hydro- gen gas to form Ni anodes. Scanning electron microscope images showed that the dual-layer HFs have porous anodes and dense electrolyte layers. Preliminary measurements with a HF–SOFC fed with H 2 and atmospheric oxygen, produced maximum power densities of 420 W m 2 and 800 W m 2 at 450 °C and 550 °C, respectively. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Tubular SOFC designs have advantages over planar SOFCs be- cause of their more facile sealing and scale up [1], their ability to expand and contract with low constraints, and endurance to re- peated thermal cycling and rapid changes in electrical load [2]. However, due to economic and technological issues, e.g. high pro- duction costs and adhesion problems between electrolyte and elec- trodes, such fuel cells have yet to be mass produced. A potential improvement to the tubular SOFC technology is to co-extrude tubular electrolyte and electrode simultaneously with smaller diameters, enabling better adhesion properties of electrolyte/elec- trode layers. In addition, a smaller diameter tubular design achieves greater volumetric power densities when compared to e.g. 22 mm diameter tubular SOFCs developed by Siemens-Wes- tinghouse [3]. The use of electrolyte materials such as cerium–gad- olinium oxide (CGO) significantly decreases cell operating temperatures compared with yttria-stabilized zirconia [4] used by Siemens-Westinghouse. Additional advantages of the micro- tubular designs include improved mechanical properties and rapid start up time, desirable properties for vehicular applications. This communication reports the successful fabrication of elec- trolyte/anode dual-layer hollow fibres (HFs) using a co-extrusion/ phase inversion process, followed by co-sintering. The co-extrusion of the dual-layer HFs was accomplished in a single-step process using a triple orifice spinneret. The use of co-extrusion has many advantages over single layer extrusion methods, including minimizing fabrication steps and time, hence dramatically decreasing production costs, while ensur- ing extrusion of gas-tight electrolyte layers with controllable thick- ness and good adhesion to the electrode. Studies on dual-layer polymeric HFs began in the late 1970s for haemodialysis [5]. In 1987 and 1988, Yanagimoto invented dual-layer asymmetric flat sheet and HF membranes to improve the antifouling properties of polymeric membranes for ultrafiltration in water purification applications [6,7]. Patent disclosures about the procedures for the fabricating dual-layer polymeric HFs for gas separation were made by Du Pont [8]. Of the extensive reports, very few involved fabrica- tion of dual-layer HFs using ceramic materials [9–11], none of which were for fuel cell applications. Single layer electrolyte-sup- ported [12] and anode-supported [13,14] HF-SOFCs with yttria- stabilized zirconia (YSZ) have been reported previously, with an- ode-supported HF–SOFCs producing good performance. 2. Experimental Two ceramic suspensions, one for the anode inner layer and the other for the electrolyte outer layer, were prepared by gradually adding the dry oxide powders to dimethylsulfoxide (DMSO), in which polyethyleneglycol 30-dipolyhydroxystearate dispersant had been dissolved previously. The suspension for the anode layer incorporated a mixture of nickel oxide (NiO, 60 wt.%) and cerium– gadolinium oxide (CGO, 40 wt.%), while that for the electrolyte layer was pure CGO powder. Following the preparation of the cera- mic suspensions, the required amount of polyethersulfone (PES) 1388-2481/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2009.07.022 * Corresponding author. Tel.: +44 (0) 207 5945676; fax: +44 (0) 207 5945629. E-mail address: kang.li@imperial.ac.uk (K. Li). Electrochemistry Communications 11 (2009) 1799–1802 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom