Design and testing of a 9.5 kWe proton exchange membrane fuel cellesupercapacitor passive hybrid system Billy Wu a,b, *, Michael A. Parkes b , Vladimir Yufit b , Luca De Benedetti a , Sven Veismann a , Christian Wirsching a , Felix Vesper a , Ricardo F. Martinez-Botas a , Andrew J. Marquis a , Gregory J. Offer a , Nigel P. Brandon b a Department of Mechanical Engineering, Imperial College London, SW7 2AZ, UK b Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK article info Article history: Received 4 October 2013 Received in revised form 23 February 2014 Accepted 10 March 2014 Available online 13 April 2014 Keywords: Proton exchange membrane fuel cell Supercapacitors Passive system Balance of plant Electric vehicle abstract The design and test of a 9.5 kWe proton exchange membrane fuel cell passively coupled with a 33  1500 F supercapacitor pack is presented. Experimental results showed that the system reduced dynamic loads on the fuel cell without the need for additional DC/DC converters. Fuel efficiency gains of approximately 5% were achieved by passive hybrid- isation in addition to addressing two main operational degradation mechanisms: no-load idling and rapid load cycling. Electrochemical Impedance Spectroscopy measurements indicated that the super- capacitor capacitance dropped with decreasing cell voltage and suggested that operation below 1.3 V is not recommended. Knee-frequency measurements suggested little benefit was gained in using passive systems with load cycles that have frequency components above 0.19 Hz. Analysis of system sizing suggested using the minimum number of supercapacitors to match the open circuit voltage of the fuel cell to maximise load buffering. Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Introduction Fuel Cells (FC) are electrochemical energy conversion devices that turn a chemical fuel into electrical energy at an efficiency typically higher than direct combustion. Of the different varieties of FCs, low temperature proton exchange membrane fuel cells (PEMFC) fuelled by hydrogen have received the greatest attention with respect to their automotive applica- tions as a possible replacement for the Internal Combustion Engine (ICE) [1]. Barriers to mainstream adoption of Fuel Cell Vehicles (FCV) include cost, durability and lack of hydrogen * Corresponding author. Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK. E-mail address: billy.wu06@imperial.ac.uk (B. Wu). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 39 (2014) 7885 e7896 http://dx.doi.org/10.1016/j.ijhydene.2014.03.083 0360-3199/Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.