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Energy & Environmental Science c0ee00420k
COMMUNICATION
temperature solid oxide fuel cells for marketing glycerol at 580�C.
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Direct biofuel low-temperature solid oxide fuel cells
Haiying Qin, Zhigang Zhu, Qinghua Liu, Yifu Jing,Rizwan Raza, Syedkhalid Imran, Manish Singh,Ghazanfar Abbas and Bin Zhu*
A maximum power density of 215 mW cm�2 is achieved by low-
COM � C0EE0042
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1 xide fuel cells†
g,a Rizwan Raza,ad Syedkhalid Imran,a Manish Singh,ce
4
reforming at the anode; the other is direct biofuel cell which directly
uses glycerol or ethanol at the anode.5–11 Although the steam 5
reforming of glycerol or ethanol exhibited high hydrogen production,
and power outputs. In case of internal reforming at the LTSOFCs
anode, the H2 yield can sufficiently support high fuel cell perfor-
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Dynamic Article LinksC<Energy &
COMMUNICATION
Direct biofuel low-temperature solid o
Haiying Qin,ab Zhigang Zhu,ac Qinghua Liu,a Yifu JinGhazanfar Abbascd and Bin Zhu*a
Received 8th September 2010, Accepted 24th January 2011
DOI: 10.1039/c0ee00420k
A low-temperature solid oxide fuel cell system was developed to use
bioethanol and glycerol as fuels directly. This system achieved
a maximum power density of 215 mW cm�2 by using glycerol at 580�C and produced a great impact on sustainable energy and the
environment.
High energy prices, increasing energy importation and greater
recognition of the environmental consequencees of fossil fuels have
driven interest in finding ecologically friendly fuels.1 Biofuels and
biodiesel have been increasingly heralded as possible saviours since
they can provide a net energy gain and have environmental benefits.2–
4 Glycerol and ethanol have attracted much interest as potential
biofuels for fuel cells because theoretically they are capable of
producing large amounts of hydrogen (8.7 wt% and 13.0 wt%) and
energy density (6.260 kWh L�1 and 5.442 kWh L�1).5–7 Two types of
fuel cell systems have been reported that use glycerol and ethanol as
fuel: one is the hydrogen/air proton exchange membrane fuel cell
which uses onsite H2 generated via glycerol or ethanol steam
aDepartment of Energy Technology, Royal Institute of Technology, KTH,10044 Stockholm, Sweden. E-mail: [email protected]; Tel: + 46 8 790 7403bDepartment of Chemical and Biological, Zhejiang University, 310027Hangzhou, ChinacGETT Fuel Cell AB, Stora Nygatan 33, S-10314 Stockholm, SwedendDepartment of Physics, COMSATS University, Lahore, 54000, Pakistane
Environmental Science
Cite this: DOI: 10.1039/c0ee00420k
www.rsc.org/ees
Department of ceramic engineering, Institute of Technology-BanarasHindu University, 221005 Varanasi, India
† Electronic supplementary information (ESI) available. See DOI:10.1039/c0ee00420k
Broader context
Negative environmental consequences of fossil fuels have encourag
been considered as attractive alternative energy sources since they c
Solid oxide fuel cells (SOFCs) running directly on hydrocarbon
conventional high-temperature, above 800 �C, SOFC technology is
a low-temperature (below 600 �C) SOFC system was designed and
fuels directly. This system achieved a maximum power density of 21
temperature of 580 �C is much lower than the normal operating tem
81% of the power density achieved by SOFCs operated at 800 �C (2
byproduct of biodiesel production, as fuel to generate electricity w
system. This work has a great impact on the development of commer
COM � C0EE
This journal is ª The Royal Society of Chemistry 2011
the fuel cell systems suffered from the need to remove byproducts
such as CO2 and the deactivation due to severe coke deposition.9 On
the other hand, the direct biofuel cell exhibited low power density due
to the minimal degree of oxidation.5–7,11 Arechederra et al.5 reported
that a glycroly/O2 biofuel cell employing bioanodes could yield power
density up to 1.21 mW cm�2. A direct ethanol fuel cell using
Pt75Ru15Ni10/C as anode catalyst also just achieved a maximum
power density of 4 mW cm�2 at 80 �C.6 The cost of fuel cell is high
due to the use of noble metal-based catalyst.7 These drawbacks
prevent the two fuel cell systems from being used in practical appli-
cations. Establishing an efficient and cheap biofuel cell system is
significant for the development of fuel cell technologies to meet
commercial requirements.
Low-temperature solid oxide fuel cells (LTSOFCs) developed by
Zhu et al. have recently become one of the hottest research fields
related to solid oxide fuel cells (SOFCs). LTSOFCs exhibit excellent
performance at much lower temperatures of 300–600 �C compared to
SOFCs operating at 800–1000 �C.12,13 LTSOFCs are very suitable for
direct operation of biofuel since most biofuels can thermally crack
into H2 and CO in this operating temperature range. Thus biofuel can
directly supplied to LTSOFCs for syngas operations at high efficiency
mance. Therefore, the LTSOFCs could demonstrate promising high
performances for biofuels rather than hydrogen when a non-noble
catalyst is used. For example, a maximum power density of 250 mW
ed the search for renewable fuels. Biofuels and biodiesel have
an provide a net energy gain and have environmental benefits.
fuels have attracted much attention recently. However, the
expensive which prevents its commercialization. In this study,
developed for commonly marketing bioethanol and glycerol as
5 mW cm�2 at 580 �C when using glycerol as fuel. The operating
perature of SOFCs, but its maximum power density is close to
65 mW cm�2). It is a great opportunity to use glycerol, an excess
ith high energy efficiency through the low-temperature SOFC
cial SOFC technology, sustainable energy and the environment.
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A maximum power density of 215 mW cm�2 is achieved in the cell
Fig. 2 XRD patterns of the as-prepared Li0.2Ni0.7Cu0.1O catalyst with
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cm�2 was achieved for directly operating with methanol at 560 �C
when C-MO-SDC (C¼ activated carbon/carbon black, M¼ Cu, Ni,
Co, SDC ¼ Ce0.9Sm0.1O1.95) was used as anode catalyst.14 The
performance was improved when tri-metal oxide (CuNiOx–ZnO) was
used as cathode catalyst. A maximum power density of 500 mW cm�2
was obtained at 580 �C for direct methanol operation.15 However,
methanol is toxic and has a low theoretical energy density compared
with glycerol and ethanol. Many studies have been carried out and
demonstrated that glycerol and ethanol can be steam reformed
during 400–600 �C.8,16 Therefore, it is our intention to demonstrate
that the LTSOFCs can be designed at more commercially practical
way and developed for the use of commercially available bioethanol
and glycerol as fuels directly.
This work describes the first attempt to use glycerol and
commercially available bioethanol as the fuel in LTSOFCs. The
scheme of the reactor and fuel cell test system is shown in Fig. 1. The
biofuels are decomposed and steam reformed firstly in a stainless steel
tube without reforming catalyst, and then the product is imported
into the test fuel cell directly for testing. A low cost metal oxide,
Li0.2Ni0.7Cu0.1O composite with samarium doped ceria-sodium
carbonate composite (NSDC) was prepared and used as anode and
cathode materials at the same time. The anode composite material
can achieve internal reforming and catalytic oxidation of fuel
simultaneouly (see ESI† for details).
The X-ray diffraction (XRD) pattern of the Li0.2Ni0.7Cu0.1O
catalyst is shown in Fig. 2. The peaks at 37.4�, 43.4�, 63.1� and 75.6�
correspond to the (111), (200), (220) and (311) crystalline planes of
NiO, respectively. The peaks at 35.6�, 38.8�, 48.8� and 61.6� corre-
spond to the (�111), (111), (�202)and (�113)crystalline planes of CuO,
respectively. The peaks at 30.6� and 31.8� correspond to the (�202)and
(002) crystalline planes of Li2CO3, which indicates that a trace of
Li2CO3 still exists after sintering at 800 �C. The XRD result suggests
the co-existence of NiO, CuO and Li2CO3 in the catalyst. The average
crystallite sizes of NiO, CuO and Li2CO3 estimated by Scherrer’s
equation are about 29, 28 and 44 nm deduced from the half width of
the diffraction peaks, respectively.
The current–voltage characteristics and corresponding power
densities of the single cell using glycerol or bioethanol as the fuel are
illustrated in Fig. 3. The steady open-circuit voltage (OCV) values are
measured to be 0.91 V and 0.81 V for glycerol and bioethanol,
respectively. The polarizations of the cells are almost linear due to
Fig. 1 The scheme diagram of the reactor and fuel cell system.
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2 | Energy Environ. Sci., 2011, xx, 1–5
ohmic polarization, which indicates that the anode catalyst exhibits
good electrocatalytic activity for the reactive gas. Compared to bio-
ethanol, the cell using glycerol demonstrates even better performance.
standard XRD cards of NiO, CuO and Li2CO3.
using glycerol, which is 45% higher than that in the case of using
bioethanol (148 mW cm�2).
Many studies showed that ethanol and glycerol could be thermally
decomposed and steam reformed in 400–600 �C and the resulting fuel
compositions were mainly H2 and CO as in the following reaction.17–19
C2H6O + H2O / 2CO + 4H2 (1)
C3H8O3 / 3CO + 4H2 (2)
Then the LTSOFCs can directly convert the chemical energy of
both H2 and CO into electricity as described in the following fuel cell
processes:
H2 + CO + O2 / H2O + CO2 (3)
while in the ethanol case,
Fig. 3 Cell performance of the LTSOFCs using Li0.2Ni0.7Cu0.1O-NSDC as
the anode and cathode materials. Conditions: electrolyte, NSDC; oxidant,
dry air at a flow rate of 100 mL min�1 (1 atm); fuel, aqueous solution of
bioethanol (50 wt%), or glycerol (50 wt%) at a fuel flow rate of 1.0 mL min�1,
a reforming gas flow rate of 100 mL min�1; cell temperature, 580 �C.
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Overall reaction:
C2H5OH + 3O2 / 2CO2 + 3H2O (overall) (4)
and in the glycerol case,
Overall reaction:
C3H8O3 þ7
2O2/3CO2 þ 4H2O ðoverallÞ (5)
most of glycerol was transformed into H2, CO and CH4, which can
be reacted as fuel in the SOFCs. As a result, the performance of fuel
cell using glycerol as fuel is better than that of the cell using bio-
ethanol.
Massimiliano et al.24 completed some theoretical work and
reported that the SOFC using glycerol could achieve a maximum
power density of 327 mW cm�2. Won et al.22 used glycerol as fuel for
SOFCs with internal reforming and investigated the influence of
operating temperature on the cell performance. They obtained
a maximum power density of 265 mW cm�2 at 800 �C and 125 mW
cm�2 at 650 �C. On the other hand, the direct glycerol biofuel cells
operated at room temperature only exhibited a maximum power
density of 1.21 mW cm�2.5 In this work, a power density of 215 mW
cm�2 has been achieved at only 580 �C using glycerol as fuel. The
OCV (0.91 V) and maximum current density (630 mA cm�2) of the
LTSOFCs using glycerol are almost close to the thermodynamic and
analysis performed for the direct utilization of glycerol in SOFCs
(OCV is 1.029 V and the threshold current density is 564 mA
cm�2).19,25 Furthermore, the operating temperature of 580 �C is much
lower than the operating temperature of conventional SOFCs (800�C), but its maximum power density is close to 81% of the power
density achieved by SOFCs operated at 800 �C (265 mW cm�2) and
nearly two times higher than that of the SOFCs operated at 650 �C
(125 mW cm�2).22 The simplicity and high performance of the
LTSOFCs system (Fig. 1) using glycerol as fuel has succeeded with
a great potential for commercialization and impact on energy and the
environment.
Valliyappan et al.18 reported that the dehydration reaction led to
the formation of the products such as liquid (acetaldehyde, acrolein,
ethanol and water et al.), gas (H2, CO and CH4 et al.) and char when
the pyrolysis of glycerol occurred at 650 �C. Therefore, the fuel fed
into the anode of the LTSOFC in this study should be a mixture of
liquid, gas and char. How could the cell still exhibit so good
a performance with the mixed fuel? The main reason should be the
use of Li0.2Ni0.7Cu0.1O-NSDC nanocomposite as anode material.
This nanocomposite mainly contains CeO2, NiO and CuO. It has
been confirmed that CeO2 performed such functions, the promotion
of water-gas shift, steam-reforming reactions, stabilization of the
surface area of the catalyst and maintenance of the dispersion of the
catalytic metals.8,23,26 Otherwise, the transition metal oxides of CuO
and NiO have good catalytic activity for electrochemical oxidation of
liquid hydrocarbon fuels.14 Since carbon could be electrochemically
converted in the SOFCs,27 it is proposed that char could be converted
in the LTSOFCs as well. Energy-dispersive X-ray spectroscopy test of
the Li0.2Ni0.7Cu0.1O-NSDC anode shows that there is 11.78 at%
carbon at the anode surface before operating and 12.68 at% after
operating, which suggests there is little carbon deposition during
operation.
Therefore, the liquid, syngas, and char might be further used as
fuels on the Li0.2Ni0.7Cu0.1O-NSDC nanocomposite anode material.
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This journal is ª The Royal Society of Chemistry 2011
The excellent fuel cell performances achieved in this study suggest
that Li0.2Ni0.7Cu0.1O-NSDC nanocomposite electrode is appropriate
for catalyzing the syngas produced from glycerol. The combination
of several metal oxides as catalyst may be beneficial as an effective
way for catalyzing a mixture fuel in the LTSOFCs.
This work has demonstrated direct biofuel LTSOFCs using the
NSDC electrolyte and the Li0.2Ni0.7Cu0.1O-NSDC electrode. The
LTSOFC using glycerol as fuel exhibited better performance than
that using bioethanol. A maximum power density of 215 mW cm�2
was achieved when using glycerol as fuel at 580 �C. The maximum
power density of 215 mW cm�2 is the 177 time higher than that
obtained by proton exchange membrane fuel cell at room tempera-
ture and is close to 81% of the power densityachieved by SOFCs
operated at 800 �C. The successful biofuel LTSOFC has a great
potential for commercialization and impact on energy and the envi-
ronment.
Acknowledgements
Funding from VINNOVA (Swedish Agency for Innovation Systems)
is highly acknowledged.
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Authors Queries
Journal: EE
Paper: c0ee00420k
Title: Direct biofuel low-temperature solid oxide fuel cells
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