Electrochemistry Communications 11 (2009) 1530–1534

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Electrochemistry Communications

journal homepage: www.elsevier .com/locate /e lecom

A novel single electrode supported direct methanol fuel cell

Alfred Lam, David P. Wilkinson *,1, Jiujun Zhang 1

Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, BC, Canada V6T 1Z3Institute for Fuel Cell Innovation, National Research Council, 4250 Wesbrook Mall, Vancouver, BC, Canada V6T 1W5

a r t i c l e i n f o

Article history:Received 29 April 2009Received in revised form 20 May 2009Accepted 21 May 2009Available online 29 May 2009

Keywords:Single electrode supportedMembraneless fuel cellDirect methanol fuel cell (DMFC)Air breathing fuel cellPassive fuel cellMembrane electrode assembly

1388-2481/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.elecom.2009.05.049

* Corresponding author. Tel.: +1 604 822 4888; faxE-mail address: dwilkinson@chml.ubc.ca (D.P. Wil

1 ISE Member.

a b s t r a c t

In this paper a single electrode supported direct methanol fuel cell (DMFC) is fabricated and tested. Thenovel architecture combines the elimination of the polymer electrolyte membrane (PEM) and the integra-tion of the anode and cathode into one component. The thin film fabrication involves a sequential depo-sition of an anode catalyst layer, a cellulose acetate electronic insulating layer and a cathode catalystlayer onto a single carbon fibre paper substrate. The single electrode supported DMFC has a total thick-ness of 3.88 � 10�2 cm and showed a 104% improvement in volumetric specific power density over a twoelectrode DMFC configuration under passive conditions at ambient temperature and pressure (1 atm,25 �C).

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

Direct liquid fuel cells such as the direct methanol fuel cell(DMFC) offer the advantage of extended and continuous operationthrough the replacement of a fuel cartridge. Additionally, liquidfuels such as methanol have a high energy density (4820 Wh L�1

[1]) and can be easily handled, stored and transported with exist-ing infrastructure. Given the size constraints for many portableapplications, the volume of a fuel cell is an important consider-ation. A conventional DMFC membrane electrode assembly(MEA) architecture consists of a polymer electrolyte membrane(PEM) compressed between an anode and cathode electrode. Tosimplify this design, the removal, replacement or integration ofthe electrode assembly components has been studied by variousresearch groups. Previous work by the authors and others hasshown that membraneless designs are possible [2–8]. In mixedreactant strip cells [9–13] and monolithic fuel cells [14–16] the an-ode and cathode have been integrated together onto the same pla-nar side of a substrate in a side by side arrangement.

In this preliminary study a single electrode supported DMFC isfabricated by a combination of PEM removal (membraneless) andelectrode integration. This design is related to our previous study[2] where two electrodes are separated by a spacer in a membrane-less configuration. In this configuration a gap must be maintainedbetween the electrodes to prevent an electrical short circuit. An

ll rights reserved.

: +1 604 822 6003.kinson).

alternative method to prevent short circuiting is to coat one ofthe electrode surfaces with a thin electrically non-conductingmaterial so that the two separate electrodes are in physical butnot electrical contact with each other (Fig. 1a). This configurationis an example of a two electrode system. In a single electrode sup-ported architecture, as shown in Fig. 1b, an anode catalyst layer, anelectrically insulating film (entire area) and a cathode catalystlayer are sequentially deposited onto a single carbon fibre sub-strate. In the research here, a cellulose acetate (CA) polymer wasused as the electrically insulating film for the configurations shownin Fig. 1a and b. CA by itself does not conduct protons, however itshydrophilic properties allow for a liquid electrolyte (0.5 M H2SO4)to be soaked into its structure. This provides the ionic connectionbetween the anode and cathode. In the operation of the fuel cell,a fuel electrolyte (5 M CH3OH and 0.5 M H2SO4) is supplied tothe anode, and the cathode is open to the air.

In the novel architecture, the thin film deposition allows for thefabrication of an electrode assembly that is a fraction of the thick-ness for a conventional two electrode architecture. Sequential cera-mic deposition on a metal supported substrate has beeninvestigated for high temperature (>400 �C) solid oxide fuel cells[17,18] but this approach has not been done for low temperatureliquid fuel cells. Mixed reactant strip cells and monolithic fuel cellsare other examples of PEM based single substrate fuel cells. In astrip cell, described by Barton et al [9], anode and cathode catalystare deposited on the same planar side of Nafion �117 in a side byside arrangement and a mixed reactant stream is fed over the sur-face. A monolithic fuel cell described by Meyers et al. [14] has asimilar arrangement but the fuel and oxidant are fed with separate

Fig. 1b. Schematic of a single electrode supported DMFC.

Fig. 1a. Schematic of a two electrode DMFC with a cellulose acetate (CA) film overthe entire surface.

Carbon Fibre Paper

Cellulose Acetate

Anode Catalyst Layer

Cathode Catalyst Layer

Fig. 2. SEM of a single electrode supported DMFC at a 210x magnification.

A. Lam et al. / Electrochemistry Communications 11 (2009) 1530–1534 1531

streams in adjacent channels on the same planar side. The sequen-tial layered approach shown in this paper overcomes several disad-vantages associated with both of these configurations. For instance,limitations with the area specific power density (W cm�2) due to a50% share a single substrate surface [14] and ohmic losses resultingfrom in-plane current collection are avoided by utilizing the entiresubstrate area and through plane current collection. Mixed reac-tant strip cells also have the added disadvantage of poor mass spe-cific catalyst activity of the selective electrocatalysts used whencompared with platinum based catalysts [9].

2. Experimental

An ink spray deposition method with an AccuSpray spray gunwas used to fabricate the electrodes for a two electrode DMFC withcellulose acetate film (Fig. 1a). Etek-TGPH-060 carbon fibre paperwith 20% wet proofing was used as a base substrate for the respec-tive electrodes. The anode had a loading of 4.00 mg cm�2 carbonsupported (Vulcan XC-72) 40 wt% Pt–Ru (1:1 atomic ratio, or a/o)catalyst with a Nafion� loading of 30 wt% and the cathode had aloading of 1.34 mg cm�2 carbon supported (Vulcan XC-72) 20wt% Pt catalyst with a Nafion� loading of 30 wt% and a 1.10 mgcm�2 Cabot carbon sublayer with 20 wt% PTFE. Powdered CA

(39.8 wt% acetyl content; Mn 30,000) purchased from Sigma Al-drich was dissolved in acetone to 5 wt% and was deposited overthe entire anode surface to thickness of 2.00 � 10�3 cm.

For the single electrode supported DMFC a single Etek-TGPH-060 carbon fibre paper with 20% wet proofing was used as a basesubstrate. The first anode layer, had a loading of 4.00 mg cm�2 car-bon supported (Vulcan XC-72) 40 wt% Pt–Ru (1:1 atomic ratio, ora/o) catalyst with a Nafion� loading of 30 wt%. The electricallyinsulating CA film was loaded from a 5 wt% CA/acetone solutionto a thickness of 2.07 � 10�3 cm over the entire active area andthe final cathode layer had a loading of 1.36 mg cm�2 carbon sup-ported (Vulcan XC-72) 20 wt% Pt catalyst with a Nafion� loading of30 wt%. In the fabrication of a single electrode structure, short cir-cuiting can become an issue if the cathode catalyst ink penetratesthe insulating layer during the spray deposition process. Isopropylalcohol was used as a solvent to make the catalyst ink. CA was cho-sen because it is soluble in acetone but not in isopropyl alcoholthus it is a barrier to penetration of the catalyst ink duringfabrication.

The electrode assembly was incorporated into a holder withperforated graphitic foil and Pt current collectors. A 2.0 cm2 activearea single chamber glass cell at ambient temperature and pres-sure (25 �C, 1 atm) and an aqueous 5 M methanol/0.5 M H2SO4

anolyte was used to examine the electrode assembly performance.The polarization curves were developed with a Solartron 1420EMultistat operated in galvanostatic mode and the specific electrodepotentials were monitored with a double junction saturated calo-mel electrode (SCE) located in the anodic chamber. The fuel cellresistance as a function of the electrode assembly configurationwas recorded at an operating frequency of 1000 Hz using a Solar-tron 1260 FRA.

3. Results and discussion

The size reduction of a fuel cell into a compact design is a keyfactor for the integration into portable electronic devices and otherapplications. This can be accomplished through the elimination

1532 A. Lam et al. / Electrochemistry Communications 11 (2009) 1530–1534

and/or integration of components and a reduction of certain geo-metric parameters (i.e., thickness and area). Previously, we haveshown that it is possible to eliminate the membrane in direct liquidfuel cells by using a 3D anode structure in conjunction with a con-ductive fuel electrolyte. In a fuel cell a significant contribution tothe overall voltage losses is attributed to ohmic overpotentials.The overall ohmic loss, gohmic (V), shown in Eq. (1), is the sum ofthe resistance of each component (n) in the electrode assemblymultiplied by the current density, I (A�cm�2). Each individual resis-tance is a function of component thickness, ln (cm), resistivity, qn

(ohm�cm) and area, A (cm2).

gohmic ¼ I � Roverall ¼ IX

n

Rn ¼ IX

n

ln � qn

A

� �ð1Þ

Fig. 3b. Individual reference potential of the anode and cathode for a two electrode DMsupported DMFC.

Fig. 3a. Polarization and power density curve on an area basis for a two electrode DMsupported DMFC at ambient temperature and pressure. The anode layer has a loading ofhas a loading 1.36 mg cm�2 carbon supported (Vulcan XC-72) 20 wt% Pt catalyst.

With respect to the overall resistance, Roverall (Ohm), the electrolyteplays a significant role. A reduction in gap separation would reducethe overall resistance. In theory, a zero gap separation would elim-inate the electrolyte component in Eq. (1). However, in practicethere exist limitations to achieving a zero gap separation. Imperfec-tions or highly rough surfaces will result in short circuiting of cer-tain parts of the electrode when the electrodes are brought closetogether.

In order to reduce the gap separation further a thin electricallynon-conductive coating can be applied to the surface of the elec-trode. This prevents short circuiting and enables the two electrodesto be in physical but not electrical contact with each other. For thisstudy, CA was chosen as the coating material for its ease of appli-cation onto an electrode surface and its hydrophilic and electrically

FC with a cellulose acetate (CA) film over the entire surface and single electrode

FC with a cellulose acetate (CA) film over the entire surface and single electrode4.00 mg cm�2 carbon supported (Vulcan XC-72) 40 wt% Pt–Ru and the cathode layer

Fig. 4. Polarization and power density curve on a volumetric basis for a two electrode DMFC with a cellulose acetate (CA) film over the entire surface and single electrodesupported DMFC at ambient temperature and pressure. The anode layer has a loading of 4.00 mg cm�2 carbon supported (Vulcan XC-72) 40 wt% Pt–Ru and the cathode layerhas a loading 1.36 mg cm�2 carbon supported (Vulcan XC-72) Pt catalyst.

A. Lam et al. / Electrochemistry Communications 11 (2009) 1530–1534 1533

insulating properties. Although the proof of concept was carriedout with CA, the single electrode supported DMFC is not limitedby the use of this polymer. A CA layer was deposited onto the an-ode surface to a thickness of �2.00 � 10�3 cm for both the twoelectrode and single electrode supported configuration as shownin Fig. 1a and b. A distinct separation between the cathode catalystlayer and the anode catalyst layer formed by the CA layer is shownin Fig. 2 for an SEM of a single electrode supported DMFC. The CAfilm (entire area) represents only a small fraction of the electrodethickness and has provided an effective coating to prevent shortcircuiting between the anode and cathode catalyst layers. Theresistance of the electrode assembly at 1000 Hz was 0.373 Ohmand 0.537 Ohm for the two electrode DMFC with a CA film (entirearea) and single electrode supported architecture, respectively.One would expect a lower resistance for the thinner electrodeassembly, however a higher interfacial resistance resulted whenthe cathode diffusion layer was removed and the current was col-lected directly from catalyst layer. This was confirmed by testingthe resistance of the single electrode supported DMFC with an EtekTGPH-060 carbon fibre paper placed on the cathode surface. Theresistance was 0.297 Ohm in this case.

Fig. 3a shows, a comparison in performance of a two electrodeand a single electrode supported DMFC with a similar CA filmthickness of �2.00 � 10�3 cm. The power density on an area basisbetween the single and two electrode configuration is comparableat of 3.54 mW cm�2 versus 3.02 mW cm�2, respectively. To exam-ine the individual contribution of each electrode to the overall cellvoltage, a plot of the reference potentials after IR correction isshown in Fig. 3b. This plot reveals that difference in performanceis primarily associated with the anode electrode. The true benefitin the integration onto a single substrate is not fully realized untilthe performance is normalized on a volume basis. The area specificperformance in Fig. 3a for the two electrode and single electrodesupported architecture was divided by the respective electrodeassembly thickness of 6.69 � 10�2 cm and 3.88 � 10�2 cm. Fig. 4shows that the single electrode supported DMFC significantly out-performs the two electrode architecture when the volume of theelectrode assembly was considered. The maximum volumetricpower density improved from 45.2 mW cm�3 to 92.2 mW cm�3.

The move toward a structure where the PEM and cathode diffusionlayer is removed and all the layers are supported on a single sub-strate significantly reduces the electrode assembly thickness, vol-ume and weight and overall material cost.

4. Conclusions

A proof of concept single electrode supported DMFC with a totalthickness of 3.88 � 10�2 cm has been successfully demonstrated.The thin film fabrication involved a sequential deposition of an an-ode catalyst layer, a cellulose acetate (CA) electronic insulatinglayer and a cathode catalyst layer onto a single carbon fibre papersubstrate. The single electrode supported DMFC has significantlyreduced the cost (membraneless and only one diffusion support)and manufacturing. The simple fabrication and compact nature ofthis electrode architecture shows promise for implementation intoportable electronic devices and other applications where size isimportant. The maximum area specific power density was3.54 mW cm�2 and based on the electrode assembly volume, thevolume specific power density was 92.2 mW cm�3 under passiveconditions at ambient temperature and pressure (25 �C, 1 atm).This is comparable to the 2010 Department of Energy (DOE) powerdensity target of 100 mW cm�3 for consumer electronics [19]. Fur-ther performance improvements are expected especially with re-spect to the material properties (e.g., optimization of the ionicconductivity in the porous insulating film).

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