Sulfated zirconium oxide as electrode and electrolyte additive for direct methanol fuel cell applications
Introduction
Direct Methanol Fuel Cells (DMFCs) are attractive portable power generation devices due to high energy density, low operating temperature, and to the ease of handling, storing and transporting methanol, as compared to hydrogen [1], [2]. However, DMFC market diffusion is still limited by high costs and performance still far from target mainly because of materials constraints [3], [4], [5], [6], [7]. Over the last decades, extensive research efforts have been carried out to replace Nafion and Platinum, which are still the state of the art materials as electrolyte and catalyst, respectively. Despite its high chemical stability, Nafion performance is impaired by methanol crossover and proton conductivity limitations. In fact, at temperatures higher than 90 °C, Nafion undergoes an irreversible swelling process that damages the membrane dimensional stability [8] and introduces interfacial complications when the electrolyte is assembled with electrodes, including high resistance and poor adhesion between membrane and electrodes [9], [10]. To overcome this drawbacks, the fabrication of composite polymer electrolyte membranes has been explored and the use of inorganic fillers as Nafion additives has been found to have a beneficial effect on the water retention properties of the resulting composite membranes [11], [12], [13], [14], [15]. However, the role of polymer/filler interaction on methanol and proton transport through the membrane is far to be completely understood and its consequence on the final DMFC performance is anything but obvious, so that the optimal electrolyte material has yet to emerge.
The use of platinum as both anode and cathode catalyst not only raises the costs of DMFC devices but also limits their performance. On one hand, the self-poison of reaction intermediates on the Pt catalyst results in poor kinetics at the anode. Moreover, the parasitic methanol oxidation at the cathode, which arises as a consequence of methanol crossover through the membrane, brings out a significant cathode depolarization because of the occurrence of a mixed potential and poisoning of Pt active sites [16], [17]. This leads to the need of exploring of new catalyst materials, including noble and non-noble metals [18]. Up to now, numerous Pt-based alloys including Pt–Cr, Pt–Fe, Pt–Co, Pt–Ni and Pt–Au have been investigated as methanol-tolerant cathode catalysts [19], [20], [21], [22], [23] and they have been found to be effective in reducing the active sites for methanol adsorption. Non-noble catalysts such as pyrolyzed transition metal nitrogen-containing complexes [24] transition metal chalcogenides [25], metal oxides/carbides/nitrides/oxynitrides/carbonitrides [26], and organometallic complexes [27], [28] have also been investigated [29] but, although great progress has been achieved, there are still some challenges in the oxygen reduction reaction (ORR) activity and stability. Hence, current hurdles persist and progress is still needed to achieve further materials (both electrolyte and catalyst) improvements and alignment with current targets. In this work, we developed composite Nafion-based electrolyte membranes and composite Pt-based electrocatalysts both containing sulfated zirconium oxide (S-ZrO2) as both electrolyte and catalyst additive.
The use of zirconium oxides as catalysts for ORR reaction has been reported [30] and good methanol tolerance, electrochemical stability in acidic environment, and to some extent also ORR activity, even if still much lower than platinum, have been demonstrated. The use of zirconium oxide and its sulfated form (S-ZrO2) as electrolyte additive has also been explored to prepare composite polymer membranes based on Nafion. Sulfated oxide led to the improvement of Nafion water retention, dimensional stability and proton conductivity, allowing at the same time decreasing of methanol crossover through the membrane [7], [12], [13]. These features motivated us to use S-ZrO2 as additive of both electrolyte (Nafion) and catalyst (carbon-supported platinum) with the aim to i) fabricate a polymer electrolyte with improved proton conductivity with respect to Nafion at the optimal operative conditions of DMFC (T > 90 °C); ii) fabricate a methanol-tolerant cathodic catalyst with high ORR activity; iii) guarantee chemical continuity at electrode/electrolyte interface through the use of the same additive to catalyst and electrolyte. ORR activity and tolerance towards methanol of composite Pt/S-ZrO2 catalysts were assessed by cyclic and linear sweep voltammetry. The final DMFC performance of these materials was also tested and compared with that of reference unfilled Platinum.
Section snippets
Materials
Nafion (5% wt.% in low aliphatic alcohol), N,N-dimetilacetammide (DMA), zirconium (IV) propoxide (Zr(n-PrO)4), solution at 70 wt. % in 1-propanol), Polytetrafluorethylene (PTFE) 60 wt.% dispersion in water, and 1-propanol (99% Aldrich) were purchased from Sigma–Aldrich; isopropanol, ethanol and sulfuric acid 95% were purchased from Carlo Erba. Vulcan XC72R was purchased by Cabot Corporation (MA, USA), Platinum 10% on Vulcan (C-10-Pt, labeled as Pt/C) and plain carbon cloth CC-G-5N with PTFE
Results and discussion
S-ZrO2 was characterized as previously reported [12] and further analyzed via FTIR (Fig. 1). The main peak in the FTIR spectrum of S-ZrO2 centered at 1140 cm–1 can be ascribed to the symmetric stretching of SO vibrations and points at the formation of bidentate sulphate groups coordinated to zirconium particles [7].
Composite membranes based on Nafion with an optimized load of 5 wt. % S-ZrO2 (N/S-ZrO2) were prepared as previously reported [12]. The thickness of membranes ranged between 90 and
Conclusions
The use of Sulfated zirconium oxide (S-ZrO2) as electrode and electrolyte additive for direct methanol fuel cells (DMFCs) was studied.
To obtain methanol-tolerant cathodic catalysts with high ORR activity, composite electrocatalysts based on carbon-supported platinum and S-ZrO2 at different additive loading were prepared. Morphology and catalytic activity were investigated by SEM-EDX and cyclic voltammetry. The presence of S-ZrO2 in the catalytic Pt/C ink increased the electrochemical active
Acknowledgments
This work was realized with the financial support of the Italian Ministry of Education, Universities and Research (Project: PRIN 2011, NAMED-PEM) the Italian Ministry for Foreign Affairs.
References (46)
- et al.
Performance evaluation of direct methanol fuel cells for portable applications
J Power Sources
(2009) - et al.
Review and advances of direct methanol fuel cells (DMFCs). Part I: design, fabrication, and testing with high concentration methanol solutions
J Power Sources
(2013) - et al.
Alkaline direct alcohol fuel cells
J Power Sources
(2010) - et al.
Small direct methanol fuel cells with passive supply of reactants
J Power Sources
(2009) - et al.
Influence of the acid–base characteristics of inorganic fillers on the high temperature performance of composite membranes in direct methanol fuel cells
Solid State Ionics
(2003) - et al.
A review of polymer electrolyte membrane fuel cells: technology, applications, and needs on fundamental research
Appl Energ
(2011) - et al.
Organically functionalized titanium oxide/nafion composite proton exchange membranes for fuel cells applications
J Power Sources
(2014) - et al.
The stability of Pt–M (M = first row transition metal) alloy catalysts and its effect on the activity in low temperature fuel cells: a literature review and tests on a Pt–Co catalyst
J Power Sources
(2006) - et al.
Effect of surface composition of Pt–Au alloy cathode catalyst on the performance of direct methanol fuel cells
Int J Hydrogen Energy
(2010) - et al.
Carbon-supported Pt–Fe alloy as a methanol-resistant oxygen-reduction catalyst for direct methanol fuel cells
J Electroanal Chem
(2004)
investigation of bimetallic Pt–M/C as dmfc cathode catalysts
Electrochim Acta
Progress in non-precious metal oxide-based cathode for polymer electrolyte fuel cells
Electrochim Acta
Recent development of non-platinum catalysts for oxygen reduction reaction
J Power Sources
Influence of sputtering power on oxygen reduction reaction activity of zirconium oxides prepared by radio frequency reactive sputtering
Electrochim Acta
Preparation of superacids by metal oxides for reactions of butanes and pentanes
Appl Catal A Gen
Influence of nafion loading in the catalyst layer of gas-diffusion electrodes for PEFC
J Power Sources
Increased performance of single-chamber microbial fuel cells using an improved cathode structure
Electrochem Commun
surface-oxide growth at platinum electrodes in aqueous H2SO4: reexamination of its mechanism through combined cyclic-voltammetry, electrochemical quartz-crystal nanobalance, and Auger electron spectroscopy measurements
Electrochim Acta
Stability of platinum based alloy cathode catalysts in PEM fuel cells
J Power Sources
The methanol oxidation reaction on platinum alloys with the first row transition metals: the case of Pt–Co and –Ni alloy electrocatalysts for DMFCs: a short review
Appl Catal B Environ
Catalytic activity of titanium oxide for oxygen reduction reaction as a non-platinum catalyst for PEFC
Electrochim Acta
On the decay of nafion proton conductivity at high temperature and relative humidity
J Power Sources
A review on methanol crossover in direct methanol fuel cells: challenges and achievements
Int J Energ Res
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