1. ___
* Editors and peer reviewers.
Improvements to well-developed fuel cell systems for use in
micro-CHP systems: a review
A. Baugher, P. Brussarski*, K. Fownes*, G. Zaylor*
Advanced Writing, College of Engineering
Northeastern University, Boston MA
A R T I C L E I N F O A B S T R A C T
Article history: Energy independence, from foregin fossil fuels as well as thelocal
Received 20 November 2014 grid, is a burgeoining area of study. As such, various methods of
Reviewed 24 November 2014 energy (electricity and heating) production are being researched for
Accepted 5 December 2014 small-scale grids and even single homes/dwellings. This paper
reviews the utilization of fuel cell systems, specifically polymer-
Keywords: electrolyte membrane (PEMFC), solid oxide (SOFC), and molten
Fuel cell system carbonate fuel cells (MCFC), for combined heat and power (CHP)
Micro-CHP applications in residences and commercial buildings. It aims to
Steam reformation emphasize components and characteristics of each that would
Bipolar plates maximize performance and overall system efficiency, specifically
Catalyst poisoning with consideration to operation temperatures.
1. Introduction
As concerns regarding energy independence, climate
change, and ecological impact rise, a need for distributed
energy generation to match increasing energy demand with
relative grid independence has also grown.1
Distributed
microgeneration, on-site electrical generation for
commercial building and residential use, has shown limited
yet promising success in tackling these issues, especially
when coupled with renewable generation sources such as
wind, photovoltaics, and most effectively, fuel cells. So far,
PEMFCs, SOFCs, and MCFCs show the most promise
because of their relatively high efficiencies and low to zero
emissions of pollutants.1,2
Another exciting advance in
distributed and efficient energy generation is the
development of combined heat and power (CHP) systems.
These systems utilize “waste heat” from
the heating of fuel, and through a series of heat exchangers
heats potablewater and other HVAC systems, increasing the
overall energy efficiency (electricity and heating) of
conventional fuel cell systems to upwards of 80% from its
lone electrical efficiency of 40%.3,4
As a budding field, fuel cell technology has shown
widespread development over the past years, particularly
with membranes, catalysts and other sub-system level
components. While a large part of the debate revolves
around the operating temperature conditions, some of the
emphasis is on novel membrane make-ups or alternative fuel
sources, seeing as steam reformation of hydrogen is a viable
yet costly method for supplyingproper fuel, and the natural
gas typically fed to steam reformers is itself not a renewable
source.5
This paper aims to emphasize the role of these
different components and the advantages/disadvantages

2. 2
Figure 1: Diagram of typical PEMFC configuration6
inherent in their use, hopefully demonstrating how to
maximize efficiencies and create a vastly improved system
for electrical and heat generation located on-site.
2. System structure
Fuel cell systems areall similar in therespect that they utilize
fuels to generate electricity through reduction-oxidation
reactions at anodes and cathodes via oxygen or another
oxidizing reagent, as is evident in Figure 1. The large
difference usually arises in thespecifichalf reactions that are
taking place and thus the composition of the membrane that
will act as the catalyst to the reaction. This in turn largely
affects theoperating temperatureand other chemical kinetics
factors that may improve or hinder the overall electrical
potential of the system. Because of their commercial
availability and overall preparedness for implementation,
PEMFCs, SOFCs, and MCFCs are further reviewed.
2.1. PEMFCs
Polymer electrolytemembrane fuel cells are by far the most
researched and hence developed fuel cell systems on the
market today, mostly because of their quick start-up and
rapid responseto load changes for more robust applications.7
As is evident in Table1, PEMFCs arefed with hydrogen fuel
and air to create the two
half reactions seen at cathode/anode. They are typically
operated at lower temperatures (60-140°C), but this again is
a specific consideration in the case of CHP systems.
2.2. SOFCs
Solid oxide fuel cells, while completing the same overall
reaction, utilize their zirconia-based oxide ions as the main
electron carrier, migrating across the electrolyte material to
react with hydrogen gas or even carbon monoxide to produce
thecorresponding chemical byproducts, despitethepresence
of pure hydrogen fuel as a competent electron exchanger.8
SOFCs, much like PEMFCs, can be run at different
categories of operating temperatures: intermediate (IT) and
high temperature (HT). It should also be noted that these
terms are relative; the range for IT-SOFC operation is 550-
800°C compared to the HT-PEMFC range from 100-200°C.
Table 1: Classification of fuel cells8
2.3. MCFCs
Similar to both PEMFCs and SOFCs, molten carbonate fuel
cells again producewater as a byproduct of feed gas and air.
However, their electrolyteis made of amembrane composed
of carbonate anions that are simultaneously broken down
and reformed, releasing electrons to pass from the anode to
the cathode through a separate load circuit and producing
electricity. As is evident in Figure 1, molten carbonate fuel
cells operatein therange of temperatures between PEMFCs
and SOFCS (around 650°C). Intriguingly enough, MCFCs
are incredibly “fuel flexible” and thus can run on a gambit

3. 3
of feed gases, such as hydrogen, carbon monoxide, natural
gas, propaneand even such components as marine diesel and
landfill gas, just to demonstrate its applicable versatility.9
3. Advantages & Limitations
To better gauge the overall impact each of these candidate
systems would make in the CHP market, it’s beneficial first
to consider each systems benefits and disadvantages. Here,
points of contention in the research of each system are
addressed.
3.1. PEMFCs: High or low temperature?
As stated previously, many of today’s PEMFCs operateat a
low temperature relative to alternative fuel cell structures8
,
the reason being that the polymer conducting membrane
supposedly reaches a maximum conductivity at the higher
end of the low temperature PEMFC (LT-PEMFC) operating
temperature spectrum.10
Unfortunately, the catalyst
implemented in LT-PEMFCs is pure hydrogen, a very
expensive and largely inaccessible fuel source.11
Also, it
requires a very complex water management system, as
evident in Figure 2.
Because of the price and overall availability of
“syngases”, high temperature PEMFCs (HT-PEMFCs) are
becoming increasingly popular; they are able to reduce the
adsorption rate of CO reformate gas onto the catalyst sites,
which would otherwise poison the catalyst and damage the
functionality of the fuel cell over time.4
However, thepower
density while working at such high temperatures is
decreased due to inefficient use of waste heat, and also
requires substantial modifications to the membrane.
Table 2: Temperature comparisons for PEMFCs
LOW TEMP.
PEMFC
HIGH TEMP.
PEMFC
OPERATING
TEMPERATURE
80-100 °C Up to 200 °C
ELECTROLYTE Water-based Mineral acid-based
PT LOADING 0.2-0.8mg/cm2
1.0-2.0 mg/cm2
CO
TOLERANCE
<50 parts per
million
1 - 5 % by Volume
OTHER
IMPURITY
TOLERANCE
Low Higher
POWER
DENSITY
Higher Lower
COLD START? Yes No
WATER
MANAGEMENT
Complex None
It also appears some research has met in the middle to
identify H2/air HT-PEMFCs as the most promising
technology, because “rates of electrochemical kinetics are
enhanced, water management and cooling is simplified,
useful waste heat can be recovered, and lower quality
reformed hydrogen may be used as the fuel.”7
3.2. Use of different PEMFC membranes
The type of membrane used in the fuel cell is perhaps
inherently thelargest area of research on PEMFCs. Modified
PFSA (perfluorosulfonic acid) membranes are common in
fuel cells that run on standard hydrogen fuel due to their
great ionic/conductive properties and their mechanical and
thermal stability under stress.12
Interestingly enough, the
conductivity of PFSA membranes such as Nafion
dramatically decreases when moving towards higher
temperatures than 100 °C. Much headway has been made to
modify these membranes and even replace them, such as the
introduction of ionic liquid-based gel-type proton
conducting membranes. Ionic liquids “possess unique
properties, such as non-volatility, non-flammability, wide
electrochemical windows, high ionic conductivity, and
excellent thermal and chemical stability,”making them very
attractive alternatives especially at high temperatures.13
On
an even more novel level, nano-composite membranes are
being applied to fuel cells operation on methanol to make up
for high permeability and low conductivity of typicalPFSA
membranes associated with higher temperatures.14
3.3. SOFC temperature considerations
Intermediate temperature operation for SOFCs is nice
because of the expanded availability of materials for use in
that range, as well as cost-effective fabrication. It is also
beneficial because of the natural reduction in direct internal
reforming (DIR) reaction rate at lower temperatures,
allowing the use of methane gas without a separate gas
reformer while avoiding dangerous temperature gradients.15
On the other hand, Hawkes also notes that SOFC
operation at intermediate temperatures experiences some
very high ohmic losses (losses in resistivity due to the
electrolyte and/or electrodes8
), and as a result must undergo
large structural changes to mitigate these losses. These
changes include increasing the size of expensive bipolar
plates (electrodes), and thus are disadvantageous. Also,
while the temperaturegradients mentioned earlier have been
reduced, they are still very much present and create a large
constraint on current density, and thus power output.15
3.4. System tradeoffs (especially MCFCs)
It is well established in the fuel cell community that the
success of novel prototype systems as they are brought to
market-level production is significantly hampered by the
cost of expensive and sometimes unique cell components;
perhaps nowhere is this more evident than with MCFCs.
Manfred Bischoff believes the system is limited in
commercialization not only by cost, but by the specially
made (sometimes even by hand) modules and parts
necessary to produce a well-functioning MCFC. In order to
unlock the high CHP efficiency and fuel versatility
associated with MCFCs, manufacturing for volume
production must be vastly improved.9

4. 4
4. Conclusions
To come to any formal conclusion regarding themost energy
efficient and cost-effective system and therefore the best
system, we must derive conclusions about each systemon a
case-by-case basis.
It is apparent that each option of PEMFC has its own
merits and drawbacks. However, themajor drawback to LT-
PEMFCs is the procurement of pure hydrogen gas and the
sheer lack of byproduct heat to boost overall system
efficiency. As for HT-PEMFCs, not enough research has
gone into their market implementation. While the promises
of HT-PEMFCs in regards to hydrogen usage are very
appealing, large amounts of research and general experience
has gone into utilizing LT-PEMFCs currently. So until more
research can be compiled regarding hydrogen at higher
operating temperatures, the focus should be on creating the
necessary hydrogen infrastructure and developing next-gen
membranes while still working at low temperatures. If the
hydrogen distribution systemwere to be developed rapidly,
then most of the disadvantages of LT-PEMFCs disappear
and the pure hydrogen LT-PEMFC becomes relatively
advantageous given residences are not looking towards fuel
cells for the primary source of water and building heating.
Typical variants of PFSA membranes have proven
themselves as a sturdy yet inexpensive staplein the PEMFC
production scheme. However, better alternatives have been
developed and are increasingly efficient, stable, and durable
relative to the likes of Nafion and other PFSA membranes.
While many novel ideas aim to replace thePFSA membrane
for good, theseoptions are conceptual or even micro-scale at
best, and are relatively expensive; in the meantime,
modifications to existing PFSA membranes should be
utilized for desired variations in fuel cell operating
temperature, power density, water usage, etc.
In summation, it would appear low temperature
PEMFCs using modified PFSA membranes and on-site
steam reformers or methane gas as a feed would be most
effective in residential applications. A large consideration
for homeowners and apartment leasees is theincurred capital
cost of the system, and because of the widespread use and
subsequent commercialization of the low temperature
PEMFC, it is much less costly to run this systemthan more
recently discovered and complex systems like SOFCs or
MCFCs. While the system would only be viable as a
supplement for heating because of its low thermal effluent,
the electrical efficiency and output of these PEMFCs are
perfect for residential-sized electrical loads and thus are the
best candidate for residential energy production until
advances in technology and commercialization of said
technology can improve the cost-benefit tradeoffs of HT-
PEMFCs and alternative membranes.
PEMFCs were designed with small-load, mostly
mobile applications in mind; commercial entities (like office
buildings and local power plants) require more robust
systems, such as SOFCS or MCFCs, capable of both
responding to large electrical loads and offsetting large
heating requirements, if not supplying all of it. SOFCS are
tricky because operating at high temperature (around 1000
°C) is extremely hazardous in this case and exponentially
more likely to cause fires, while operating at intermediate
temperatures causes drastic losses in power output. MCFCs,
on the other hand, are most efficient at relatively high
temperature, and some infrastructure has even been
developed to harness the heating potential of these specific
fuel cells, like the HotModule.9
For these reasons, it would
appear MCFCs operating at their regular conditions would
be most advantageous in this commercial setting; granted,
the parts are expensive and manufacturing schemes for
MCFCs is weak to date, but thelarger entities owning these
buildings and plants have the necessary resources to push
demand up for these particular fuel cells and perhaps pave
theroad to full commercialization. Thefuel cell industry has
a lot of improvement ahead of them, but directing our efforts
towards commercialization of these systems to ease energy
dependence is of paramount importance. □
__________
I would like to acknowledge my peer editors, Prof. Akbari,
and my peers (roommates) for helping shape this document
into its best form.

5. 5
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