Status of Regenerative Fuel Cell Membrane Electrode Assembly Development for Space-Based Energy Storage
Authors: Valdez Thomas I , Billings Keith J. 
Published: February 2020

Introduction

The National Aeronautics and Space
Administration (NASA) has led a thrust for the
development of advanced regenerative fuel cell systems
(RFCs) to be used as energy storage for space-based
robotics, mobility systems, and human habitats. The goal
of the program has been to develop an RFC system
capable of a round trip efficiency of 64%. The focus at
the Jet Propulsion Laboratory (JPL) in RFC research has
been in developing proton exchange membrane electrode
assemblies (MEAs) for both the fuel cell and the
electrolyzer subsystems [1-3].
In a RFC system, energy storage is achieved via
the electrolysis of water to hydrogen and oxygen gases
during the charge phase. Consumption of the hydrogen
and oxygen gases then occurs during the discharge phase,
with the subsequent generation of water. For space
applications, the energy for the electrolysis of water will
be supplied via solar or nuclear power. The power
delivered during the discharge of the RFC system can be
used by robots, mobility systems, and human habitats
operating on the moon, near-Earth asteroids or Mars.
Such a system could also be used for load balancing in
both space and terrestrial applications.
This paper will discuss fuel cell MEAs that have
been developed for a future NASA regenerative fuel cell
system. RFC system trades and NASA mission concepts
that will feature RFC-based energy storage systems will
also be discussed.

Results and Discussion

The current-voltage polarization of two MEAs
are shown in Figure 1. To achieve high voltage
efficiencies, the MEAs will be expected to operate at
current densities in the range of 200 to 600 mA/cm2. The
MEA will operate with reactants at a balance pressure of
30 PSIG at 70 oC. The NASA-JPL developed MEA is
designed to operate in a non-flow-through stack. The
MEA current-voltage polarization reported are for MEAs
that operate with a reactant feed rate of approximately 3x
stoic.
As shown in Figure 1, the polarization for the
NASA-JPL MEA is reported to be 0.92, 0.86 and 0.81
Volts at an applied current density of 200, 600 and 1000
mA/cm2, respectively. The polarization of the NASAJPL
MEA is approximately 80 mV greater than the
commercially available MEA at a current density of 200
mA/cm2. The voltage efficiency for the JPL-NASA MEA
at 200 and 600 mA/cm2 is approximately 75 and 70%,
respectively. To achieve the desired RFC system
efficiency, the fuel cell MEA will need to operate at
approximately 73% voltage efficiency. It is envisioned
that MEA operation at current densities above 1 A/cm2

would be for short periods (< 1 hour) for NASA
applications.
The short-term durability studies for the NASAJPL
MEA is shown as Figure 2. The MEA operated at an
applied current density of 200 mA/cm2, 70 oC, and 30
PSIG balanced reactants during the durability studies.
The initial voltage for the MEA is reported to be greater
than 0.92 Volts, the voltage drops to 0.91 Volts after 13
hours of operation. The initial voltage is recoverable after
current cycling as shown at 243 hours of operation. The
cell degradation is reported to be approximately 7 μVolts
after more than 1000 hours of operation. The degradation
is, in part, attributed to test hardware. The minimum
MEA voltage efficiency is approximately 73% for the
duration of the test. Future work will investigate the
integration of the NASA-JPL MEA in NASA RFC
hardware.

Acknowledgements

The work presented here was carried out at the Jet
Propulsion Laboratory, California Institute of Technology
for the National Aeronautics and Space Administration.

References

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Figure 1