High performance of ethanol co-laminar flow fuel cells based on acrylic, paper and Pd-NiO as anodic catalyst

Article abstract of DOI:10.1016/j.electacta.2016.05.002

Ethanol co-laminar flow fuel cells operating at room temperature have rarely been reported, primarily due to problems associated with the kinetics of ethanol oxidation. In this work, we present a study of the effect of ethanol concentration, pH of anodic and cathodic streams, and nature of the oxidant on the performances of an acrylic cell and a paper-based, membraneless co-laminar flow fuel cell (LFFC), with total cell volumes of 14.29 cm³ and 0.62 cm³_, respectively. Additionally, this work reports the synthesis of a Pd-NiO anodic nanocatalyst by a simple, fast, and environmentally friendly method in order to match the clean, easy-to-use, and simple fabrication methods of these ethanol co-laminar flow fuel cells. The synthesized Pd-NiO exhibited a crystallite size of 8.1 nm and an average particle size of 8.7 nm for Pd-NiO/C. The highest performances were obtained by combining an alkaline anodic stream with an acidic cathodic stream, increasing the cell voltage, and decreasing cathodic limitations caused by the simultaneous occurrence of oxygen reduction as well as hydrogen reduction reactions. With these improvements, power densities of 108 and 85.5 mW cm^-2 were obtained for the acrylic and the paper-based co-laminar flow fuel cell, respectively, which are the highest values reported to date for ethanol LFFCs at room temperature.

Full text of DOI:10.1016/j.electacta.2016.05.002

Electrochimica Acta 207 (2016) 164–176
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
High performance of ethanol co-laminar flow fuel cells based on
acrylic, paper and Pd-NiO as anodic catalyst
C.A. López-Ricoa,e, J. Galindo-de-la-Rosab, E. Ortiz-Ortegab, L. Álvarez-Contrerasc,
d
J. Ledesma-Garcíab, M. Guerra-Balcázarb, , L.G. Arriaga , N. Arjona
*
a,**
a
Centro de Investigación y Desarrollo Tecnológico en Electroquímica S. C., Unidad Tijuana, Tijuana, B.C., C.P. 22444, Mexico
Facultad de Ingeniería, División de Investigación y Posgrado, Universidad Autónoma de Querétaro, Querétaro, C.P. 76010, Mexico
Centro de Investigación en Materiales Avanzados S. C., Complejo Industrial Chihuahua, Chihuahua, C. P. 31109, Mexico
Centro de Investigación y Desarrollo Tecnológico en Electroquímica S. C., Querétaro, C. P. 76703, Mexico
b
c
d
e
Tecnológico Nacional de México, Instituto Tecnológico de Tijuana, Apdo. Postal 1166 Tijuana, 22444, Baja California, Mexico
A R T I C L E I N F O
A B S T R A C T
Article history:
Ethanol co-laminar flow fuel cells operating at room temperature have rarely been reported, primarily
due to problems associated with the kinetics of ethanol oxidation. In this work, we present a study of the
effect of ethanol concentration, pH of anodic and cathodic streams, and nature of the oxidant on the
performances of an acrylic cell and a paper-based, membraneless co-laminar flow fuel cell (LFFC), with
total cell volumes of 14.29 cm3 and 0.62 cm3, respectively. Additionally, this work reports the synthesis of
a Pd-NiO anodic nanocatalyst by a simple, fast, and environmentally friendly method in order to match
the clean, easy-to-use, and simple fabrication methods of these ethanol co-laminar flow fuel cells. The
synthesized Pd-NiO exhibited a crystallite size of 8.1 nm and an average particle size of 8.7 nm for Pd-NiO/
C. The highest performances were obtained by combining an alkaline anodic stream with an acidic
cathodic stream, increasing the cell voltage, and decreasing cathodic limitations caused by the
simultaneous occurrence of oxygen reduction as well as hydrogen reduction reactions. With these
improvements, power densities of 108 and 85.5 mW cmꢀ2 were obtained for the acrylic and the paper-
based co-laminar flow fuel cell, respectively, which are the highest values reported to date for ethanol
LFFCs at room temperature.
Received 13 February 2016
Received in revised form 30 April 2016
Accepted 1 May 2016
Available online 3 May 2016
Keywords:
Ionic liquids
ethanol oxidation
co-laminar flow
electrocatalysis
fuel cells
ã 2016 Elsevier Ltd. All rights reserved.
1. INTRODUCTION
others metal oxides, such as CeO2, Co3O4 and Mn3O4 [5].
Additionally, Pd-NiO mixtures have been obtained through several
Short-chain alcohols are used as liquid fuels in energy
conversion due to their high theoretical energy densities (ethanol:
sophisticated (sometimes expensive) techniques, such as inter-
mittent microwave heating [3], reactive evaporation [6], rf
sputtering, [7] and reaction under autogenic pressure at elevated
temperatures [8].
8010, glycerol: 5000, and ethylene glycol: 5300 Wh
kgꢀ1), low
ꢁ
toxicity, and ease of storage and handling [1]. The electro-oxidation
of these alcohols and therefore, the release of electrons to produce
electrical energy is usually favorable when Pd-based nano-
materials are used as electrocatalysts [2]. Metal-metal and/or
metal-metal oxide combinations could result in enhancement of
the electronic structure of materials, thereby improving their
activity and stability, as has been reported for Pd-NiO/C synthe-
sized by an intermittent microwave heating method [3]; Pt-NiO/C
synthesized by a chemical reduction method [4]; and certain
New methods are needed to address challenges related to
production costs for industrial scaling (i.e., synthesis at room
temperature and ambient pressure and reduction of the number of
involved reagents) and because of the environmental impact of
reaction by-products. In this sense, ionic liquids (ILs) are a good
alternative. ILs are considered neoteric solvents that melt at
temperatures below 100 ꢂC (this property differentiates them from
molten salts) and are sometimes called “room temperature ionic
liquids” (RTILs) when they are liquids at ambient conditions [9]. ILs
exhibit several extraordinary properties, including low vapor
pressure, low relative viscosity, high ionic conductivity, high
reactivity, and high stability to water and air [10]. According to
their nature and procedure of synthesis, ILs can be classified as: I)
* Corresponding author: Tel.: +52 442 19200 ext. 65421;
** Corresponding author: Tel: +52 664 660 20 54 ext. 4410.
E-mail addresses: minbalca@yahoo.com.mx (M. Guerra-Balcázar),
noe.arjona@yahoo.com.mx, wvelazquez@cideteq.mx (N. Arjona).
http://dx.doi.org/10.1016/j.electacta.2016.05.002
0013-4686/ã 2016 Elsevier Ltd. All rights reserved.

C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
165
ionic liquids and II) protic ionic liquids (PILs). ILs are frequently
composed of inorganic anions and inorganic cations. Proton
transfer is a characteristic of PIL syntheses because of the addition
of Brønsted acids to Brønsted bases [11]. The “green aspect” of
new-generation ionic liquids in chemical syntheses is related to i)
their low vapor pressure, ii) water/air stability, iii) hydrophobicity/
hydrophilicity, iv) low flammability, v) low toxicity, and vi)
biodegradability. These characteristics could allow the separation
of products and by-products, thereby enabling recycling and reuse
of ionic liquids [12–14]. Furthermore, most of the principles of
green chemistry can be satisfied using ionic liquids as greener
substitutes to common organic solvents which are volatile and
hazardous.
formic acid and ethanolamine. The resulting nanomaterials were
physicochemical and electrochemically characterized and used as
electrocatalysts toward the ethanol electro-oxidation reaction. An
acrylic and a paper LFFC were constructed to evaluate perform-
ances of Pd/C and Pd-NiO/C using ethanol as fuel varying
operational conditions, such as pH of streams, and nature of the
oxidant.
2. EXPERIMENTAL SECTION
2.1. Synthesis of protic ionic liquid
2-hydroxy ethylammonium formate protic ionic liquid was
synthesized by a simple acid-base Brønsted reaction involving
formic acid (Sigma-Aldrich, ꢃ98%) as the organic anionic source
and ethanolamine (Sigma-Aldrich, ꢃ99%) as the organic cationic
source. All reagents reported in this study were used as received
without further purification. Ethanolamine (0.5 mole fraction) was
placed in a jacked glass cell, to which formic acid (0.5 mole
fraction) was added at a flow rate of 12 mL/h using a syringe pump
(Harvard Apparatus, PHD Ultra Syringe Pump Infuse/Withdraw).
The cell was magnetically stirred conserving an inert atmosphere
using gaseous nitrogen (Infra, 99.999%), and 4 ꢂC as the working
It is desired that ionic liquids act as ideal solvents for
applications in catalysis and electrocatalysis. In order to be useful
for catalysis, ionic liquids must be able to dissolve large quantities
of starting materials, products, catalysts, and/or co-solvents.
Additionally, ILs should show specific interactions with their
surroundings, enhancing or reducing the reactivity of solute
species as required [15]. In electrocatalysis, ILs should be able to act
not only as solvents for electrosynthesis of electrocatalysts
(because of their typically large electrochemical window) but
also as “all-in-one” media for the green synthesis of electro-
catalysts. In other words, to be considered an ideal medium, ILs
should simultaneously play the role of reaction medium, molecular
precursor, and capping and reducing agent [10]. To date, RTILs have
been used only as solvents [8,16,17] or as composite constituents
[18]. Furthermore, few studies have reported the successful use of
ionic liquids as “all-in-one” solvents. Such studies are mainly
related to the synthesis of CuCl [19], Au, [20] and ZnO [21]
nanostructures, and report the synthesis of particles with sizes
from few tens of nanometers to up of hundreds of nanometers.
The use of ionic liquids in green synthesis of metal nano-
particles suggests that they could be similarly used to develop
environmentally friendly methods in order to be coupled to fuel
cell technology. The latter are considered as one of the cleanest
methods to obtain electricity [22]. Membraneless co-laminar flow
fuel cells (LFFCs) as well as fuel cells are defined as electrochemical
devices for converting chemical energy to electrical energy. In
LFFCs, the fuel and oxidant, both flow in a co-laminar manner,
forming a natural interface due to diffusional transport between
them [23]. Such cells present the advantage of ease of using liquid
fuels, liquid oxidants, and their mixtures. Almost all reports of
these fuel cells are focused on the use of methanol or formic acid as
fuels because both of these are small molecules that can be easily
broken to form CO2 [24]. Ethanol and other larger-chain molecules
such as glycerol and ethylene glycol have been rarely reported in
this class of devices. One of the most important strategies to
increase their cell performance is related with the usage of streams
with mixed-pH, combining an alkaline anodic stream with an
acidic cathodic stream. This strategy has been implemented in
proton-exchange membrane fuel cells (PEM-FCs) [25]. Recently Lu
et al., have demonstrated its usage in switchable pH unitized
regenerative fuel cells (URFC), where the URFC with mixed-pH
showed an improvement in the cell performance [26]. Moreover,
this strategy has also employed in aluminum-air cells, Chen et al.,
have recently presented a membraneless aluminum-air cell which
follows the flow-over concept in a “Y”-like cell architecture, finding
a superior performance [27]. To date, the use of mixed-pH streams
has not been tested in co-laminar flow fuel cells which operate
with a complex flow-through concept in which fuel and oxidant
react before encountering at the natural interface.
temperature.
A colorless, viscous liquid was obtained, the
existence of the PIL was corroborated by 1H nuclear magnetic
resonance (Bruker, NMR 400 MHz) finding the following signals
(Scheme 1):
d
: 8.522 ppm (s, 1H, H-COOꢀ); 7.944 ppm (s, 4H,
ꢀNH3+OH); 3.769 ppm (t, 2H, ꢀCH2N); 3.085 (t, 2H, ꢀO-CH2).
2.2. Synthesis of electrocatalysts
The synthesis of Pd, NiO, and Pd-NiO was carried out at room
temperature using Na2PdCl4 (Sigma-Aldrich, 99.8%) and NiSO4 (J. T.
Baker, 99.99%) as precursors. In a typical synthesis, 50 mg of
Na2PdCl4 or 150 mg of NiSO4 were placed in a vial containing 10 mL
of PIL and dispersed by sonication. The Palladium precursor
acquired a black coloration after 3 minutes of sonication, indicating
the formation of Pd nanoparticles. The Nickel precursor also
showed changes in coloration after 30 minutes of being in contact
with the PIL; however, it was left for 2 hours to ensure a better
reaction. The formation of bubbles was observed in all syntheses,
suggesting that the metallic reduction of precursors involves the
decomposition of the PIL when it acts as reducing agent. Further
analysis of the gaseous species is required to clarify the mechanism
of nanoparticle formation. On the other hand, 70 mg (for Pd
nanoparticles) and 150 mg (for NiO and for Pd-NiO) of Vulcan
carbon (Cabot1 XC-72) were added after the reaction times and
maintained in sonication for other 30 minutes. After this, the vials
were kept under refrigeration (–18 ꢂC) for 24 h to ensure complete
reduction of metallic precursors. These materials were centrifuged
at 4000 rpm and washed several times with deionized water.
Finally, the resulting powders were dried overnight at 80 ꢂC.
2.3. Physicochemical characterization
Pd/C, NiO/C, and Pd-NiO/C powders where characterized by
means of X-ray diffraction using a Bruker D8 Advance apparatus
operated at 30 kV and 30 mA. The X-ray fluorescence analyses were
performed using a Bruker S2 PICOFOX spectrometer. Thermogra-
vimetric analyses (TGA) were performed using a TA instrument
apparatus with a temperature ramp of 10 ꢂC minꢀ1 in air. Micro-
graphs and energy dispersive X-ray spectroscopy analyses were
obtained using a field-emission high resolution transmission
electron microscope (HR-TEM) JEOL-JEM2200 Fs + Cs with spheri-
cal aberration control for condensed lens. Ionic conductivity of
electrolytes was measured using a HACH multimeter HQ40d.
In this work, we succeeded in obtaining Pd/C, NiO/C, and Pd-
NiO/C materials with small particle sizes using 2-hydroxy ethyl-
ammonium formate protic ionic liquid as all-in-one solvent. This
protic ionic liquid was synthesized by a Brønsted reaction between

166
C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
Scheme 1. 1H NMR of the 2-hydroxy ethylammonium formate ionic liquid.
2.4. Electrochemical characterization
PMMA LFFC, corresponded to a LFFC constructed using hard plates
of poly-(methyl methacrylate) PMMA. The second LFFC was a
miniaturization of the first design but using adhesive paper as the
top and bottom plates. The PMMA LFFC has been reported
previously and details of its construction can be found elsewhere
[28]. Briefly, the PMMA plates were patterned using a CNC
machine. Six holes for the screws were patterned in both plates in
order to close the cell. In the top plate, two holes were made and
used as inlets for fuel and oxidant solutions. Additionally, a small
vent was constructed in the top plate, to be used as an oxygen
source from air. A single outlet was patterned in the bottom plate. A
Electrochemical characterization was accomplished by obtain-
ing electrochemical profiles of materials through cyclic voltam-
metry using a three-electrode electrochemical cell and a BioLogic
VSP Potentiostat/Galvanostat. Glassy carbon plates (SPI1, geomet-
rical area: 1.2 cm2) were used as working electrodes. A saturated
calomel electrode (0.241 V vs. NHE, BASi1) and a graphite rod were
used as the reference and the counter electrode, respectively. 0.3 M
KOH (J. T. Baker, 87%) solution was used as electrolyte and N2 (Infra,
99.999%) as inert atmosphere. Cyclic voltammograms were
recorded at 50 mV sꢀ1 and the 10th cycle was presented. The same
electrochemical configuration was used for electrocatalytic evalu-
ation of the ethanol electro-oxidation reaction (J. T. Baker, 99.99%).
The scan rate for these experiments was 20 mV sꢀ1. The electro-
catalysts were deposited onto glassy carbon electrodes by ink
deposition using isopropyl alcohol as dispersant and Nafion as
binding agent. For this purpose, 3 mg of catalysts were added to the
silicone film (Silastic1, 200
mm thickness) was prepared and used
as gasket. In the case of the adhesive paper LFFC, the cell design,
including inlets and the outlet, was patterned using a Silhouette1
plotter. In this case, the adhesive paper (Adhesives Research1
,
100 mm thickness) replaced screws and thus allowed the reduction
of LFFC dimensions. The electrodes were fabricated using a
commercial carbon nanofoam paper (Marketech International
Inc.1) and were composed of slides of 20 mm length and 1 mm
width. The final geometrical area in contact with the anodic and
cathodic streams for both cells was 0.015 cm2; which value was
used for normalization of the LFFCs.
alcohol (75
was then added to this mixture (7
stirred by sonication for another 20 minutes. Finally, 5 layers
(20 L ink per layer) of catalysts were deposited on glassy carbon
m
L per milligram) and sonicated for 20 minutes. Nafion
m
L per milligram) which was
m
electrodes.
2.6. Operation of membraneless co-laminar flow fuel cells
2.5. Construction of membraneless co-laminar flow fuel cells
Pd-NiO/C and commercial Pt/C (ETEK, 30%) were used as anodic
and cathodic catalysts, respectively. Both were prepared according
to the methodology described in the electrochemical characteri-
zation section (2.4). Additionally, both were deposited on carbon
Pd-NiO was evaluated in two membraneless co-laminar flow
fuel cells (LFFCs), mainly differentiated by the materials used as top
and bottom plates in these cells. The first design), hereafter called

C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
167
nanofoam slides using the spray ink method. The final catalyst load
was 1 mg per electrode (including weight of Vulcan carbon as
support). The anodic stream was prepared using 1.5 M ethanol as
fuel and 0.3 M KOH as electrolyte. The cathodic stream consisted of
an oxygen-saturated (Praxair, 4.3 U.A.P.) solution of 0.3 M KOH as
alkaline electrolyte or 0.5 M H2SO4 as acidic electrolyte. Addition-
ally, 0.2 M hydrogen peroxide (J. T. Baker, 30%) was used as oxidant
in an alkaline electrolyte. These cells are characterized by the
combined use of oxygen from air as well as that from a saturated
solution in order to enhance the oxidant concentration. On the
other hand, both streams were pressure-driven using two Cole-
Parmer syringe pumps (single-syringe infusion pump, 115 VAC).
The flow rate was investigated through cell performance measure-
ments, and a rate of 9 mL hꢀ1 was determined to be optimal for
both streams. Data were collected through
Potentiostat/Galvanostat, and the scan rate of all experiments
was 10 mV sꢀ1
The experiments were performed at room
a Biologic VSP
.
temperature, which was fixed at 25 ꢂC. Polarization and power
density curves were performed by triplicated, reporting only the
average values. The standard deviation for both, polarization and
power density experiments was <3% for the acrylic-based co-
laminar flow fuel cell, and lower than 7% for the paper-based NFC.
Control experiments without metallic catalysts, without fuel, and
using NiO as anodic catalyst are presented in the supplementary
information.
3. RESULTS AND DISCUSSION
3.1. Physicochemical characterization
The X-ray diffraction patterns for Pd/C, NiO/C and Pd-NiO/C are
shown in Fig. 1A. For Pd electrocatalyst, the (111), (200), (220),
(311), and (222) crystallographic planes were observed at 40.0,
46.59, 68.02, 81.95, and 86.49ꢂ 2
u, respectively, revealing a typical
face-centered cubic structure. For NiO, the (111), (200), and (220)
peaks corresponding to a face-centered cubic structure were
located at 36.85, 43.01 and 62.39ꢂ. In the case of Pd-NiO, the Pd
(111), (200), (220), (311), (222), and the NiO (200) peaks were
observed at 39.76, 46.3, 67.86, 81.88, 86.49, and 42.91ꢂ, respec-
tively. The (111), (200), and (220) planes related to Pd were slightly
shifted due to the presence of NiO in its structure. Crystallite sizes
were calculated using the Scherrer equation. For Pd/C, an average
size of 8.8 nm was determined through analysis of the (111), (200),
(220), and (311) planes. In the case of Pd-NiO/C, an average size of
8.1 nm was calculated from the (111) and (220) planes. For NiO/C, a
crystallite size of 2.45 nm from the (200) plane. The lattice
parameters were calculated by the application of Bragg’s Law to the
(220) plane, resulting in values of 3.9065 Å and 3.9077 Å for Pd/C
and Pd-NiO/C, respectively (Pd = 3.8898 Å, JCPDS card # 5-681). The
metallic compositions were determined by X-ray fluorescence and
electron dispersive X-ray spectroscopy analyses and are shown in
Table 1. Peaks related to Pd and Ni materials were observed
through XRF, while no traces of their precursors (i.e., Na, S, or Cl)
were observed. This finding can be related to the use of 2-hydroxy
ethylammonium PIL as an all-in-one solvent which, when
combined with water as washed solvent, may well separate
Fig. 1. A) X-ray diffraction pattern for NiO/C, Pd/C and Pd-NiO/C electrocatalysts.
Crystalline planes of Pd and NiO were labelled in grey and black, respectively. B)
Thermogravimetric analysis for Pd/C (black line) and Pd-NiO/C (grey line).
products, by-products, and remnants of precursors from the
resulting powders.
The EDX analyses on single particles (Table 1) were in
concordance with the XRF results, corroborating the presence of
palladium, carbon, nickel, and oxygen in the NiO electrocatalyst.
TGA curves are shown in Fig. 1B. The first loss of weight, observed
at approximately 100 ꢂC, was related to the residual water used to
wash the catalysts. A second drop was observed at approximately
150 ꢂC and this was attributed to the decomposition of ionic liquid
remnants [29]. A third drop was observed starting from 250 ꢂC
(Fig. 1B, grey line) and was attributed to the decomposition of Ni
species [30]. The drop at 500 ꢂC was attributed to rapid oxidation of
Table 1
XRF and EDX analyses for Pd/C, NiO/C and Pd-NiO/C.
Electrocatalyst
XRF
EDX
Pd mass %
Ni mass %
Pd atomic%
Ni atomic%
C atomic%
O atomic%
Pd/C
NiO/C
Pd-NiO/C
100
–
–
21.41
–
–
78.59
31.43
97.71
–
100
11
26.44
0.25
42.13
2.05
89
1.61

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C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
Vulcan carbon. The residual metal content was calculated through
these TGA curves and used to normalize the electrocatalytic
activity, which was found to be 26% for the Pd/C catalyst and 6.2%
for the Pd-NiO/C catalyst.
Morphology of materials is shown in Fig. 2; while particle size
distribution calculated from TEM micrographs is shown in Fig. 3. In
general, particles with undefined semispherical shape were
observed. This behavior may be related to the complex ionic
network which was affecting the electrostatic stabilization during
nanoparticle formation. Duant et al., [31] have mentioned that
cations can serve as ionic stabilizers (or anions, depending on
precursor salt charge) but their counter-ion will also adsorb on the
resulting particle surface due to the effect of electrostatic
attractions. The above discussion and the nanoparticle shape
(Fig. 2 Pd-I and 2 Pd-II) suggest that charges of complex ion lattices
present in the surrounding environment of seed crystals, have high
influence on the electrostatic interactions of ions (attraction/
repulsion) which act as stabilizers. It is also most likely that
Fig. 2. TEM micrographs at different magnifications for NiO/C, Pd/C and Pd-NiO/C electrocatalysts.

C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
169
NiO/C), subnanometric particles were observed together with
particles of few nanometers in size (Fig. 2-NiO I and II). For the Pd-
NiO electrocatalysts (Fig. 2, Pd-NiO I and II), the EDS analysis shows
that subnanometric particles are single NiO particles and the
bigger particles are Pd-NiO nanoparticles. The subnanometric size
of NiO particles was not unexpected. These are frequently obtained
in typical aqueous chemical reductions where it has been observed
that NiO promotes the decrease of particle size of Pd and Pt based-
materials; [33,34] This phenomenon could explain the decrease of
size from 33.3 nm for monometallic Pd nanoparticles to 8.7 nm for
Pd-NiO. Considerable work remains to be performed for detailing
the mechanism of nanoparticle formation in the ionic liquid
method. Nuclear magnetic resonance (NMR) experiments have
been planned in order to identify the role of each component of the
ionic liquid in the nanoparticle formation mechanism. The
summary of XRD, TEM, and TGA data are presented in Table 2.
A poor particle size distribution was observed (Fig. 3), which
can be related to several factors, such as i) the relatively high
viscosity of the ionic liquid (223 cP) which limited mass transport;
ii) ineffective sonication leading to poor dispersal of metallic
precursors over the entire solution, due to their confinement to
vials; and iii) the effect of the surrounding ions (i.e., electrostatic
and steric interactions) was not sufficient to control the particle
growth resulting in nanoparticles with multiple sizes. Alternative
methodologies are now being explored to improve this aspect,
such as the use of an ultrasonic probe and the use of small amount
of water to reduce the viscosity of the 2-hydroxy ethylammonium
formate ionic liquid.
a)
40
30
20
10
0
2
3
4
5
6
7
8
9
10
Particle size / nm
40
35
30
25
20
15
10
5
b)
0
16
20
24
28
32
36
40
3.2. Electrochemical characterization
Particle size / nm
The electrochemical profiles of NiO/C, Pd/C, and Pd-NiO/C are
shown in Fig. 4. NiO/C showed the characteristic peaks related to
the Ni2+/Ni3+ redox couple observed at 0.67 V vs. NHE in the
forward scan and at 0.43 V vs. NHE in the backward scan. [35] For
Pd/C, the formation of Pd oxides was observed in the region from
ꢀ0.2 to 0.3 V vs. NHE, while, their reduction was observed at ꢀ0.2 V
vs. NHE. In the case of Pd-NiO/C the redox couple of Ni species was
slightly shifted as was the peak related to the reduction of Pd
oxides (found at ꢀ0.22 V vs. NHE). In addition, the reduction peak
of NiO was located at ꢀ0.16 V vs. NHE. Electrochemical characteri-
zation in alkaline medium (Fig. 4) was performed, not only to
corroborate the electrochemical presence of metals but also to
calculate the electrochemically active surface area (Eq. ((1)).
50
40
30
20
10
0
c)
QE
5
6
7
8
9
10 11 12 13 14
ECSA ¼
ð1Þ
QT
Particle size / nm
Where QE is the experimental charge determined by integrating
the reduction peak of palladium oxides. QT is the theoretical charge
needed to reduce a full monolayer of Pd or Ni oxides; in alkaline
Fig. 3. Particle distribution histograms for a) NiO/C, b) Pd/C and c) Pd-NiO/C.
medium, these values correspond to 405 and 430 m ,
C cmꢀ2
electrostatic interactions with ions acting as reducing agents
result in disordered crystal growth and non-homogeneous
particle sizes [31,32]. Electrocatalysts showed average particle
sizes of 5.3, 33.3, and 8.7 nanometers for NiO, Pd, and Pd-NiO,
respectively. In the case of nickel-based materials (NiO/C and Pd-
respectively [36,37]. Pd/C, NiO/C and Pd-NiO/C (Fig. 4) exhibited
electrochemical areas of 46.0988, 18.1582, and 18.60 cm2, respec-
tively. These ECSA values together with the Pd mass obtained from
TGA curves (0.38 mg for Pd/C and 0.08 mg for Pd-NiO/C), were used
Table 2
Summary of crystal and nanoparticle sizes, lattice parameters and metallic loadings of Pd, NiO and Pd-NiO electrocatalysts.
Material
XRD
TEM
TGA
Crystal size/nm
Lattice parameter/Å
Particle size/nm
Metal content/%
Pd
Pd-NiO
NiO
8.8
8.1
2.5
3.9065
3.9077
–
33.3
8.7
5.3
26
6.2
–

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C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
6
3
0
0.8
0.5 M
NiO/C
A
1 M
2 M
3 M
0.6
-3
0.4
0.2
0.0
10
Pd-NiO/C
Pd/C
5
0
-5
3
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0
Potential / V vs. NHE
-3
-6
0.5 M
1 M
B
20
-0.6
-0.3
0.0
0.3
0.6
0.9
2 M
3 M
Potential / V vs. NHE
15
10
5
Fig. 4. Cyclic voltammograms of Pd/C, NiO/C and Pd-NiO/C obtained using 0.3 M
KOH as electrolyte. Scan rate: 50 mV sꢀ1
.
to normalize voltammograms for the evaluation of electrocatalytic
activity. NiO is known to exhibit antiferromagnetic behavior, [38]
which, in this case, impeded data acquisition by TGA. Therefore,
NiO was arbitrarily normalized, using the mass content of Pd-NiO.
Furthermore, NiO is only presented in Fig. 5C for its demonstrated
lack of activity toward the electro-oxidation reactions.
0
In the ethanol electro-oxidation reaction (Fig. 5), Pd/C as well as
Pd-NiO/C showed an increase of current density as a function of
ethanol concentration (Fig. 5A and 5B, respectively). Both
materials showed the maximum current density at the highest
ethanol concentration evaluated herein (3 M). Comparing both
materials, Pd-NiO/C exhibited an almost 24-fold higher current
density than Pd/C. This could be due to the effect of incorporation
of Ni into the Pd structure, which, i) decreased the particle size of
Pd-NiO/C, ii) adsorbed additional hydroxyl species renewing the Pd
surface [3], and iii) promoted oxidation of CO by Ni, enhancing the
tolerance to poisoning of Pd-NiO [40]. In terms of reaction
potential, Pd/C showed a value close to ꢀ0.4 V and Pd-NiO/C was
approximately at ꢀ0.37 V vs. NHE. Both materials showed similar
oxidation potentials compared to Pd nanocubes enclosed in the
(100) plane [43], which was previously reported by our group (the
electrocatalytic activity for this reaction follows the order:
100 > 110 > 111) [44]. A further comparison with other Pd and Pt-
based Ni materials is presented in Table 3. As observed, the Pd-NiO/
C catalyst has been previously reported by different authors.
However, this is the first time in which the successful use of an
ionic liquid for the green synthesis of Pd-NiO/C is reported.
Moreover, the Pd-NiO/C nanoparticles presented herein showed
higher current densities and similar onset potentials, compared to
those found in literature (Table 3, considering values normalized
by geometrical area).
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
Potential / V vs. NHE
Pd
C
20
15
10
5
NiO
PdNiO
0
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
Potential / V vs. NHE
Fig. 5. Cyclic voltammograms of the electrocatalytic evaluation of a) Pd/C and b)
Pd-NiO/C for the ethanol electro-oxidation reaction at function of concentration
and c) comparison of activity at 3 M ethanol for Pd/C, NiO/C and Pd-NiO/C. Scan rate:
3.3. Evaluation of acrylic-based membraneless co-laminar flow fuel
cell
20 mV sꢀ1
.
Components of the fabricated alkaline ethanol membraneless
co-laminar flow fuel cell with PMMA plates are shown in Fig. 6A.

C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
171
Table 3
Comparison of current densities and onset potentials of different Pd and Pt Ni-based materials toward the ethanol electro-oxidation reaction.
Material
Electrolyte
Fuel
Current density/mA cmꢀ2
Potential/V vs. NHE
Reference
Pd-NiO/C
Pt-NiO/C
PdNi/MWCNT
NiPd/Ti
PdNi/C
Pd-NiO/C
Pd-NiO/C
1 M KOH
1 M KOH
1 M KOH
1 M KOH
0.5 M NaOH
1 M KOH
0.3 M KOH
1 M Et.
1 M Et.
1 M Et.
1 M Et.
1 M Et.
1 M Et.
3 M Et.
14.76
11.5
ꢀ0.30*
ꢀ0.35*
ꢀ0.36
ꢀ0.41*
ꢀ0.46*
ꢀ0.46
ꢀ0.37
[3]
[3]
[39]
[40]
[41]
[42]
This work
ꢄ25
ꢄ2.35
100NS
94NS
24.98
Fig. 6. A) Scheme of the acrylic membraneless co-laminar flow fuel cell and performances B) using Pd-NiO/C (circles) and Pd/C (squares) as anode catalysts using alkaline
streams and the combined source of oxygen as oxidant, C) anodic alkaline stream and acidic cathodic stream with the two sources of oxygen, and D) alkaline streams but using
0.2 M H2O2 in 0.3 M KOH as oxidant.
Polarization and power density curves are illustrated in Fig. 6B for
Pd-NiO/C and Pd/C. The latest data were used for comparison
3O2 þ 6H2O þ 12eꢀ ! 12OHꢀ
E0 = 0.40 V
ð3Þ
ð4Þ
purposes because Pd/C has shown superior performance than
commercial Pd/C (ETEK), as previously reported [45].
The ethanol electro-oxidation by a direct pathway in alkaline
medium is illustrated in Eq. (2). Additionally, the oxygen reduction
reaction (ORR) using an alkaline electrolyte is shown in Equation 3.
The overall cell reaction for an alkaline ethanol fuel cell is
illustrated in Eq. (4).
CH3CH2OH þ 3O2 ! 2CO2 þ 3H2O
Ecell = 1.14 V
CH3CH2OH þ 12OHꢀ ! 2CO2 þ 9H2O þ 12eꢀ
ð2Þ
From Fig. 6B, cell voltages of 0.55 V and 0.6 V for Pd-NiO/C and
Pd/C were observed in the polarization region. Both values were
E0 = ꢀ0.74 V

172
C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
lower than the theoretical cell voltage using oxygen as oxidant
(Equation 4), exhibiting voltage efficiencies of 48 and 53%,
respectively. Nonetheless, these voltages were consistent with
typical values for direct ethanol proton exchange membrane fuel
cells (PEMFCs), which operate at higher temperatures (60–100 ꢂC)
than membraneless co-laminar flow fuel cells (ꢄ25 ꢂC). For
example, PEMFCs containing Pd-based anodes have shown typical
values from 0.63 to 0.78 V for Pd/MWCNT and PdSn/MWCNT at
60 ꢂC, [46] and 0.7 and 0.88 V for Pd/C and PdNi/C, respectively, at
80 ꢂC. [47] Pt-Ru supported in Vulcan and Pt-Ru/MWCNTs showed
cell voltages of 0.6 V and 0.81 V, respectively, when both were
operated at 100 ꢂC [48]. On the other hand, in the ohmic region,
voltages at maximum power density were 0.29 and 0.30 V for Pd/C
and Pd-NiO/C, respectively. At these voltages, the current densities
of both materials were 52.6 and 43.9 mA cmꢀ2, respectively. In
general, these low voltages at maximum current density can be
associated to ohmic losses and mass transport limitations, due to
the fast drop in current density observed in the polarization curves
presented in Fig. 6B. In the mass transport region, it was observed
The employment of mixed streams not only resulted in an
increase of cell voltage but also in a decrease of ohmic losses,
probably because of the rise in ionic conductivity by using 0.5 M
H2SO4 (220 mS cmꢀ1) as electrolyte instead of 0.3 M KOH (71.7 mS
cmꢀ1). The decrease of ohmic losses also resulted in a voltage at
maximum power density of 0.72 V. Meanwhile, the resulting
maximum power density was 108 mW cmꢀ2 (Fig. 6C). In the region
of mass transfer, this LFFC showed a steady state from 0.4 V, with
an enhancement of current density from 105 mA cmꢀ2 in an all-
alkaline LFFC to 242 mA cmꢀ2 for the mixed-stream LFFC. The
performances in alkaline and the mixed-stream LFFCs can be
globally related to the high surface area of three dimensional
electrodes, highly active anodes, and the combined used of two
sources of oxygen (from air and from an aqueous solution). This
last point is important because aqueously dissolved oxygen has
shown limitations as an oxidant, due to its low solubility,
diffusivity, and concentration (4 mM in solution) [49]. Further-
more, the use of air as a source of oxygen has been highly explored
in membraneless micro and nanofluidic fuel cells because of the
higher diffusivity of oxygen in air (10,000-fold higher) and slightly
higher concentration (10 mM) than in aqueous solution [50–53].
However, even though both the alkaline and the mixed-stream
LFFC had the same source of oxygen (Fig. 6B and 6C), the latter
showed a current density twice higher than that of the former. The
change of pH should not has an important effect in current density
than it has in cell voltage. The only possible explanation is related
to secondary reactions that could occur at both electrodes. E. R.
Choban et al. observed the evolution of hydrogen (Eq. 7) in a Pt-
based cathode working with an alkaline/acidic mixed stream in a
methanol membraneless microfluidic fuel cell [54].
that Pd/C showed a maximum current density of 125 mA cmꢀ2
.
Meanwhile, Pd-NiO/C showed a maximum current density of
105 mA cmꢀ2. The resulting maximum power densities were 15.3
and 13.8 mW cmꢀ2 for Pd/C and Pd-NiO/C LFFCs, respectively. The
fuel utilization at the condition of maximum current density using
1.5 M ethanol and at a flow rate of 150 m
L minꢀ1, was 0.26% for Pd/C
and 0.217% for Pd-NiO/C. Additionally, the oxidant utilization for
10 mM oxygen was 19.34 and 16.28% for Pd and Pd-NiO,
respectively. The net cell efficiency was calculated by multiplying
the voltage efficiency and the fuel utilization, resulting in cell
efficiencies of 13.78% for Pd/C and 10.416% for Pd-NiO/C. It is
important to remark that the Pd/C-based LFFC had an almost 6-fold
higher amount of Pd that the Pd-NiO/C based LFFC. For equivalent
amounts of Pd, the membraneless co-laminar flow fuel cell which
employed Pd-NiO/C as anode catalyst showed a current density of
1750 mA mgꢀ1 cmꢀ2, while the LFFC with Pd/C as anode catalyst
12Hþ þ 12eꢀ ! 6H2
ð7Þ
7 E0 = 0 V
showed a current density of 416.17 mA mgꢀ1 cmꢀ2
.
In these terms, and from the results of cell voltage and current
density (Fig. 6C), it can be inferred that hydrogen reduction could
occur simultaneously with oxygen reduction in the cathode,
increasing the current density (up to 2-fold) but decreasing cell
voltage from 1.97 V to 1.11 V. The use of mixed-pH streams resulted
in a voltage efficiency of 56.34% which was slightly higher than of
all-alkaline acrylic LFFC (48%). Values of 0.499% and 37.48%,
respectively, were obtained for fuel and oxidant utilization
percentages. Additionally, the net cell efficiency for this configu-
ration was 28.11%.
The second strategy to enhance cell performance was related to
the use of hydrogen peroxide as alternative oxidant to oxygen
(Fig. 6D). Hydrogen peroxide shows advantages such as higher
solubility, can be used at higher concentrations in aqueous
solution, and shows a more positive reduction potential than
oxygen (0.48 V). In alkaline medium, hydrogen peroxide is reduced
at 0.88 V (Eq. (8)) and, combined with an alkaline anodic stream,
gives a cell voltage of 1.62 V (Eq. (9)).
Two strategies were followed to increase the cell performance
of the acrylic-based membraneless co-laminar flow fuel cell
operating with Pd-NiO/C as anode catalyst. The first strategy was to
employ streams with different pH because, following the Nernst
equation, pH has a considerable effect on thermodynamic potential
of both reactions, and hence on cell voltage, as demonstrated in
Fig. 6C. The combination of an alkaline anodic stream and an acidic
cathodic stream resulted in a cell voltage of 1.11 V, which was twice
that for a completely alkaline LFFC (Fig. 6B, circles). The increase in
cell voltage was expected because the ethanol electro-oxidation
has a potential of ꢀ0.77 V in alkaline medium (Eq. (2)), and the
oxygen reduction reaction rises from 0.4 V in alkaline medium
(Eq. (3)) to 1.23 V in acidic medium (Eq. (5)), thus improving the
theoretical cell voltage from 1.14 up to 1.97 V in mixed streams
(Eq. (6)). The use of an acidic anodic stream/acidic cathodic stream
was neglected because of the lower cell voltage than the alkaline/
acidic mixed streams and due to the lack of activity of Pd-NiO/C
toward ethanol oxidation in acidic medium.
6H2O2 þ 12eꢀ ! 12OHꢀ
ð8Þ
3O2 þ 12Hþ þ 12eꢀ ! 6H2O
ð5Þ
E0 = 0.88 V
E0 = 1.23 V
CH3CH2OH þ 6H2O2 ! 2CO2 þ 9H2O
Ecell = 1.62 V
ð9Þ
CH3CH2OH þ 12OHꢀ þ 12Hþ þ 3O2 ! 2CO2 þ 15H2O
ð6Þ
Ecell = 1.97 V

C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
173
The cell voltage for the alkaline LFFC with H2O2 as oxidant and
Pd-NiO/C as anode catalyst was 0.69 V (Fig. 6D). This value was
nearly half the theoretical cell voltage, showing a voltage efficiency
of 42.59%. This fall in potential could be related to the formation of
O2 (Eq. (3)) as an undesired by-product of H2O2 in the cathodic
reaction. This behavior occurs at Pt surfaces, such as the
commercial Pt/C (ETEK) used in this work. [55] Further work in
modification of Pt-based cathodes for membraneless co-laminar
flow fuel cells is ongoing. In the region of ohmic losses, a lower
resistance was observed using H2O2 instead of O2 (Fig. 6B), for the
same cell configuration. This was complemented by better mass
transport of reactants because of a higher availability of both fuel
(1.5 M) and oxidant (0.2 M). For this reason, the current density
increased to 150 mA cmꢀ2 and the power density to 33.6 mW cmꢀ2
,
2.5-fold higher than those using the combined source of oxygen. In
summary, cell voltage, current density and hence, power density of
the LFFC which use hydrogen peroxide as oxidant showed higher
values than the LFFC operated with the combined source of oxygen.
This improvement in performance can be related to the lower
activation barrier and hence, faster kinetics of oxidation using
H2O2 compared with O2; because the reaction of H2O2 involves
breakage of single dioxygen bonds rather than breakage of double
dioxygen bonds which is required for O2. [56,57] The analysis of
fuel and oxidant utilization for this alkaline LFFC operating with
0.2 M hydrogen peroxide as oxidant resulted in percentages of
0.3125 and 2.344, respectively. The net cell efficiency was also
calculated for this cell configuration resulting in an efficiency of
13.31%.
8.1. Evaluation of the paper-based membraneless co-laminar flow fuel
cell
Finally, the components of an adhesive paper-based co-laminar
flow fuel cell are illustrated in Fig. 7A. This cell design has been
recently reported by our group [58]. It was observed that the usage
of paper decreased the number of components to only the gasket,
paper slides, and electrodes. The gasket design used in the acrylic
LFFC did not work in the paper LFFC, generating fuel/oxidant
leakage. For this reason, a hexagon-like design was employed.
Results for an alkaline anode/cathode LFFC with Pd-NiO/C as
anode catalyst are shown in Fig. 7B. The cell voltage was 0.6 V with
a maximum current density of almost 130 mA cmꢀ2, with a
resulting power density of 22.5 mW cmꢀ2. Contributions from
polarization and ohmic losses decrease the voltage of maximum
power density to 0.33 V. A voltage efficiency of 52.63% was
obtained which was similar to that obtained in the acrylic LFFC.
Additionally, the fuel utilization was slightly enhanced to a value of
0.2667%. The net cell efficiency was calculated with these values of
voltage efficiency and fuel utilization, resulting in an efficiency of
14.03%, almost 3% higher than that of the acrylic LFFC. This increase
in efficiency is related to the decrease of ohmic resistances because
of the closer positioning of electrodes which results in a smaller
volume for the paper LFFC (23-fold lower). A mix of streams
involving an alkaline anodic stream and an acidic cathodic stream
was made for the paper-based LFFC, as performed for the acrylic
LFFC. The results for this mixture are presented in Fig. 7C. In this
figure, it is observed that the use of an acidic electrolyte in the
cathode increased the cell voltage to 1.05 V, resulting in a voltage
efficiency of 53.30%. Compared with the all-alkaline paper-based
LFFC (Fig. 7B), the cell voltage was improved to 0.45 V. Bigger
ohmic losses are presented in the mixed-stream LFFC compared
with the all-alkaline LFFC and are related to deformation of the
natural interface and leakage of flows because of loss of
adhesiveness in the paper-based LFFC. This loss only occurred
when an alkaline and an acidic electrolyte were combined in the
co-laminar flow fuel cell, regardless of its compartment structure
Fig. 7. A) Design of a membraneless co-laminar flow fuel cell constructed using
adhesive paper, B) Cell performance using an ethanol LFFC with alkaline electrolytes
and C) cell performance employing an alkaline anodic electrolyte and an acidic
cathodic electrolyte. Ethanol concentration: 1.5 M. Scan rate: 10 mV sꢀ1
.
(alkaline-anode & acidic-cathode or acidic-anode & alkaline-
cathode). Despite these limitations, a current density of 365 mA
cmꢀ2 was obtained, being the highest value obtained in this work
and others (Table 4). The combination of streams (Fig. 7C)
increased the power density by a factor of 3.8, when compared
with the all-alkaline LFFC (Fig. 7B). Further, the combined used of
streams with different pH and decrease of the cell volume resulted
in
a fuel and oxidant utilization of 0.757% and 113.559%,
respectively. In the case of oxidant utilization, it is clearly observed
the contribution of hydrogen reduction as secondary reaction,
increased the efficiency to values upward of 100%. The resulting net
cell efficiency was 40.348%, the highest found among all the cell
configurations herein presented.
A
comparison between the acrylic and the paper-based
membraneless co-laminar flow fuel cells was made, and their
results are illustrated in Fig. 8. Dimensions of the acrylic LFFC were

174
C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
Table 4
Comparison of cell performances of ethanol membraneless co-laminar flow fuel cells at room temperature with air-breathing cathodes an all-alkaline streams.
Anode & cathode catalyst
Catalyst ink loading (mg)
Fuel & concentration/M
E/V
0.67
J/mA cmꢀ2
W/mW cmꢀ2
Ref.
Cu@Pd/C & Pt/C
Pt/Ru black & Pt black
PdNiO/C & Pt/C
2.2 & 2.9
10 & 2 mg cmꢀ2
1 mg
0.1 M EtOH
1 M EtOH
1.5 M EtOH
1.5 M EtOH
153.7
ꢄ90
242
25.75
12.21
108
[52]
[59]
This work
This Work
ꢄ0.7
1.11
PdNiO/C & Pt/C
1 mg
1.05
365
85.5
(Fig. 8A). Cell performance of the all-alkaline paper-based
membraneless co-laminar flow fuel cell was almost twice as high
as that of the acrylic LFFC (Fig. 8B). Enhancement in open circuit
potential was observed together with a decrease of ohmic losses,
resulting in the increment of current and power density. Both can
be related to the reduction of size, increase in the surface-to-
volume ratio, and enhancement of the reaction kinetics and mass
transport. For mixed streams (Fig. 8C), the acrylic LFFC showed
lower ohmic resistance and hence, better power density (1.23-fold
higher). However, the paper LFFC showed higher current density
(1.5-fold higher) because of the enhanced surface-to-volume ratio,
where the loss of power density was related to leakage of streams
which increased the polarization and ohmic losses (Fig. 8C).
9. CONCLUSIONS
2-hydroxy ethylammonium formate as air and water-stable
protic ionic liquid was used at room temperature in the green
synthesis of NiO, Pd, and Pd-NiO materials. Changes in Pd
coloration from orange to a darkened solution at low contact
times (less than 3 minutes) indicated the formation of Pd
nanoparticles. The X-ray diffractograms revealed that those
materials had crystallite sizes of 2.45, 8.8, and 8.1 nm for NiO,
Pd, and Pd-NiO. TEM images confirmed that nanoparticulate Ni
and Pd-based materials can be successfully obtained through the
use of this PIL. The introduction of Ni on Pd-NiO/C decreased its
particle size compared with Pd/C, resulting in an improvement of
the electrocatalytic properties for ethanol, as determined by the
three-electrode electrochemical configuration. A 24-fold higher
current density was obtained for Pd-NiO/C (6% of residual metal
content) compared with Pd/C; where Pd-NiO/C had a 4-fold lower
metal content than Pd/C. Both materials were successfully used in
a membraneless co-laminar flow fuel cell based on both acrylic
and paper as supporting plates. In the acrylic LFFC, Pd-NiO/C
showed the maximum cell performance working with an alkaline
anodic stream combined with an acidic cathodic stream, showing
values of current density, cell voltage, and a power density of
242 mA cmꢀ2, 1.11 V, and 108 mw cmꢀ2, respectively. The paper-
based LFFC as well as the acrylic LFFC showed maximum
performance with combined streams, the paper-based LFFC
showed 1.05 V in cell voltage, 365 mA cmꢀ2 in current density
and 85.5 mW cmꢀ2 in power density were obtained. In summary,
membraneless co-laminar flow fuel cells with high net cell
efficiencies (from 10% to up 40%) that employ Pd-NiO/C as anode
catalyst can be easily constructed using PMMA or paper as simple
and low-cost materials. Furthermore, this clean energy source
was combined with green methods of synthesis of nanoparticles,
such as the use of 2-hydroxy ethylammonium formate protic ionic
liquid, leading to the development of a greener technology for
energy conversion.
Fig. 8. Comparison between an acrylic and a paper-based LFFC a) in volume, B) in
performance using alkaline-alkaline streams and C) using a mixed stream alkaline-
acidic streams. Anode: Pd-NiO/C. Ethanol concentration: 1.5 M. Scan rate: 10 mV sꢀ1
.
ACKNOWLEDGEMENTS
42 mm length, 32 mm width, and 10 mm thickness with a vent of
11 ꢅ2 mm. Compared with this, dimensions of the paper LFFC were
decreased to 30 ꢅ 20 ꢅ1 millimeters with a vent of 14 ꢅ1 mm and
a total volume of 0.62 cm3, 23-times smaller than the acrylic LFFC
The authors gratefully acknowledge to the Mexican Council of
Science and Technology (CONACYT) for the support through the
project SEP-CONACYT-2012-01-17992. Dr. Raúl Ortega from

C.A. López-Rico et al. / Electrochimica Acta 207 (2016) 164–176
175
CIDETEQ for share with us his knowledge in ionic liquids. The
technical support for TEM images offered by Carlos Elías Ornelas
Gutiérrez from the nanotechnology laboratory (nanotech México)
at Centro de Investigación en Materiales Avanzados CIMAV S. C. The
authors also acknowledge to Daniel Lardizabal Gutiérrez and Paola
Hernández Salcedo (CIMAV) for TGA analyses and technical
support, and to Marie-Noëlle Ragel & Virginie Lair from ParisTech
for NMR assistance.
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