Journal of Membrane Science 351 (2010) 196–204 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Single-step fabrication and characterisations of electrolyte/anode dual-layer hollow fibres for micro-tubular solid oxide fuel cells Mohd Hafiz Dzarfan Othman, Zhentao Wu, Nicolas Droushiotis, Uttam Doraswami, Geoff Kelsall, K. Li ∗ Department of Chemical Engineering and Chemical Technology, Imperial College London, London SW7 2AZ, UK article info Article history: Received 11 October 2009 Received in revised form 21 January 2010 Accepted 24 January 2010 Available online 2 February 2010 Keywords: Co-extrusion Co-sintering Dual-layer Hollow fibre Micro-tubular SOFC abstract An electrolyte/anode hollow fibre (HF) for micro-tubular solid oxide fuel cells (SOFCs), i.e. a cerium–gadolinium oxide (CGO)/Ni–CGO dual-layer HF, has been developed in this study via a novel single-step co-extrusion and co-sintering technique, and followed by a reduction process. The microstruc- ture of the developed dual-layer HFs, which are co-sintered at 1450–1550 ◦ C, can be characterised by an electrolyte outer layer of approximately 80 m supported by an anode inner layer of around 220 m. Benefiting from the advantages of this fabrication technique, great adhesion between the anode layer and the electrolyte layer can be achieved without any crack formation during the co-sintering. More- over, no elemental inter-diffusion between layers, such as Ni, was observed even at 1550 ◦ C. With the increasing co-sintering temperature, mechanical strength of the developed dual-layer HF, gas-tightness of the electrolyte layer and electrical conductivity of the anode layer are increased. However, gas per- meability through the anode layer decreases dramatically with the increasing temperature, which may greatly reduce the efficiency of the related micro-tubular SOFC. According to the investigations on the effects of co-sintering temperature on the mechanical, structural and electrical conducting properties of the dual-layer HFs, a co-sintering temperature at 1500 ◦ C is recommended for the construction of the electrolyte/anode half-cell for micro-tubular solid oxide fuel cells (SOFCs). © 2010 Elsevier B.V. All rights reserved. 1. Introduction Solid oxide fuel cells (SOFCs) have been considered as a promis- ing electricity-generation technology because of the high efficiency in converting chemical energy to electrical power [1]. To date, two types of SOFC designs, i.e. planar and tubular SOFCs, have been widely studied. Although planar SOFCs in a highly compact con- figuration show high power density, the design of this type is challenged by the high temperature sealing near the edges of the cell because only few sealants can endure thermal cycles experi- enced during the operation [2]. Another concern over this design is the low start-up times as a consequence of crack formation in the thin planar structures. In contrast, the tubular geometry is more reliable and can be operated in the absence of high tempera- ture seals, showing excellent resistance to rapid thermal cycling. However, it is difficult to achieve high power density due to a less efficient cell packing and higher cell losses associated with elongated electronic pathways. In order to improve the volumetric power density, the diameter of tubular designs needs to be reduced ∗ Corresponding author at: Department of Chemical Engineering and Chemical Technology, Imperial College London, Sough Kensington Campus, London SW7 2AZ, UK. Tel.: +44 0207 5945676; fax: +44 0207 5945629. E-mail address: kang.li@imperial.ac.uk (K. Li). from a few centimeters (SW cell) to the order of 1 mm, namely micro-tubular SOFCs as they are often referred to in the literatures. The design of this type can significantly increase the specific surface area of electrodes, improve mechanical properties and more impor- tantly, speed up the start-up and the shut-down processes. As a result of these advantages, the micro-tubular SOFCs have attracted increasing interests in recent years [3–9]. Conventionally, the supports of micro-tubular SOFCs, i.e. anode or cathode layer, are fabricated by extrusion followed by high tem- perature sintering [3–5]. Electrolyte layer is then deposited using a number of techniques such as dip coating, chemical vapour depo- sition (CVD) and spray technique, followed by another sintering process. The whole fabrication process is usually time-consuming and cost-intensive. In contrast, a combined co-extrusion and co-sintering technique shows a number of advantages for the pro- duction of electrode/electrolyte dual-layer hollow fibres in a single step [10]. The preparation process of this type was introduced for fabricating polymeric membrane about 30 years ago [11–13], and intensive investigations have been carried out in the recent 10 years [14–19]. However, very limited researchers are involved in fabricat- ing ceramic dual-layer membranes [10,20] as the result of a number of challenges in the fabrication processes. In the co-extrusion process, a dope is extruded through the outer orifice of a triple orifice spinneret, whereas another one is simultaneously extruded through the inner orifice. The internal 0376-7388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2010.01.050