Micro-tubular solid oxide fuel cells fabricated from hollow fibres

Abstract

Recent literature is reviewed on a phase inversion process followed by sintering, used to fabricate ceramic hollow fibres (HFs) as precursors to micro-tubular solid oxide fuel cells (MT-SOFCs) with sub-millimetre inner diameters. These aimed to address the outstanding technological and economic issues that have delayed mass production of SOFCs, by increasing electrode surface areas per unit volume relative to planar structures, increasing power outputs per unit volume/mass, facilitating sealing at high temperatures, and decreasing fabrication costs per kW. Some recent experimental results are presented of the effects of temperature, hydrogen flow rate, thermal cycling and time of NiO reduction with H₂ on the subsequent performance of 25 mm long H₂|Ni–CGO|CGO|LSCF|air MT-SOFCs, incorporating cerium–gadolinium oxide (CGO) electrolyte, nickel anodes and lanthanum strontium cobalt ferrite–CGO (LSCF–CGO) cermet cathodes, designed to operate at 500–600 °C. Maximum power densities of 3–5.5 kW m⁻² were achieved as the temperature was increased from 550–600 °C. The co-extruded MT-SOFCs were resilient to three thermal cycles when heated to operating temperature in ca. 5 min. Their performance was intimately related to the reduction time, suggesting slow conversion of the NiO to Ni within the fabricated anodes. At constant cell voltage, mass transport limited current densities increased from ca. 11 to ca. 13.5 kA m⁻² as hydrogen flow rates were increased from 15 to 60 cm³ min⁻¹, though had residual NiO in the anode been fully reduced, current densities would have been significantly greater.