Review Article SOFC-APU systems for aircraft: A review M.D. Fernandes a , S.T. de P. Andrade b , V.N. Bistritzki a , R.M. Fonseca a , L.G. Zacarias a , H.N.C. Gonc ¸alves c , A.F. de Castro a , R.Z. Domingues a , T. Matencio a,* a Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil b Petrobras, Betim, Minas Gerais, Brazil c Federal Centre of Technology Education of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil article info Article history: Received 26 April 2018 Received in revised form 25 June 2018 Accepted 2 July 2018 Available online xxx Keywords: Auxiliary power unit Solid oxide fuel cell More electric aircraft Clean energy Less noise Hydrogen abstract This review brings together publications in the form of articles, reports, theses and patents related to the use of solid oxide fuel cells in aircraft with a focus on replacing the current auxiliary units with a hybrid system. The potential advantages and main challenges of the new technology are reported, indicating some possible trends in this technology. However, even after many studies, some initial challenges remain. For example, the hybrid system did not achieve the necessary weight-efficiency-ratio, and there seems to be no consensus on the choice of the best fuel. We conclude that the most viable short-term applications appear to be unmanned units, particularly because of security issues and low technology maturity. Smaller power applications, in which the new system is responsible for pe- ripheral services such as a power supply for air conditioning, toilets, and heating up food, are candidates to enter the market in the short or medium term. In the long term, appli- cations for fully electric aircraft and clean fuels will certainly be the focus of larger aircraft manufacturers. © 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Contents Introduction ...................................................................................................... 00 Fuel cells ......................................................................................................... 00 Aircraft auxiliary power unit ....................................................................................... 00 Motivation for the use of fuel cells in aircraft ....................................................................... 00 Conventional APU systems versus SOFC-APU systems ............................................................... 00 Minimum architecture ....................................................................................... 00 System improvements for use in APUs ......................................................................... 00 Fuel ................................................................................................... 00 Recycling .............................................................................................. 00 Water recovery ........................................................................................ 00 * Corresponding author. E-mail address: tmatencio@ufmg.br (T. Matencio). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (2018) 1 e23 https://doi.org/10.1016/j.ijhydene.2018.07.004 0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Fernandes MD, et al., SOFC-APU systems for aircraft: A review, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.07.004