High-performance Polymer Electrolyte Research Articles

Proton conduction in Nafion composite membranes filled with mesoporous silica

Studies of proton-conductive polymer membranes are vital for the future development of high-performance polymer electrolyte membrane fuel cells (PEM-FC). In particular, a method for inhibiting the volatility of water in the polymer matrix at high temperatures is a crucial issue, directly related to the operation of PEM-FC system. In this study, we focus on polymer composite membranes, which consist of commercial Nafion and mesoporous silica (MPSi) as novel inorganic additives, and investigate an improvement in the total proton conductivities and the good electrochemical stability at high temperatures. MPSi, which can be synthesized with pore sizes from 1 to 10 nm, has a wide range of potential applications because of its extraordinary properties, such as extremely large surface area, flawless surface condition and well-regulated porous structure. We found that the Nafion composites filled with MPSi have approximately 1.5 times higher proton conductivities (more than 0.1 S cm −1 at 80 °C and 95%RH) than pure Nafion and can display good temperature performance relative to pure Nafion and the particle SiO 2 composite. Moreover, the conductivity of Nafion/sulfonated MPSi was the highest (0.094 S cm −1) at 40 °C and 95%RH. These are probably due to the large surface area of MPSi, which can increase the water adsorption in Nafion matrix.

Advanced, lithium batteries based on high-performance composite polymer electrolytes

Progress in lithium battery technology may be achieved by passing from a conventional liquid electrolyte structure to a solid-state, polymer configuration. In this prospect, great R&D effort has been devoted to the development of suitable lithium conducting polymer electrolytes. In previous papers [F. Croce, L. Settimi, B. Scrosati, Electrochem. Commun. 8 (2006) 364 [1]; F. Croce, S. Sacchetti, B. Scrosati, J. Power Sources, in press [2]], we have shown that composite membranes based on blends between poly(ethylene oxide) and lithium salts with the dispersion of functionalized ZrO 2 ceramic filler, have unique transport and interfacial properties. In this paper, we complete the study of these advanced polymer electrolytes by evaluating their use in rechargeable lithium batteries. The results confirm the practical interest of these electrolytes which appear to be suitable for the fabrication of batteries directed to application in emerging technologies, such as those associated to hybrid and electric vehicles.

Advanced, high-performance composite polymer electrolytes for lithium batteries

Progress in lithium battery technology may be achieved by passing from a conventional liquid electrolyte structure to a solid-state, polymer configuration. In this prospect, great R&D effort has been devoted to the development of suitable lithium conducting polymer electrolytes. The most promising results have been obtained with systems based on blends between poly(ethylene oxide) and lithium salts. In this work we show that the transport and interfacial properties of these electrolytes may be greatly enhanced by the dispersion of a ceramic filler having an unique surface state condition. The results, in addition to their practical reflection in the lithium polymer electrolyte battery technology, also provide a valid support to the model which ascribes the enhancement of the transport properties of ceramic-added composites to the specific Lewis acid–base interactions between the ceramic surface states and both the lithium salt anion and the PEO-chains .

High performance polymer electrolyte fuel cells with ultra-low Pt loading electrodes prepared by dual ion-beam assisted deposition

Ultra-low pure Pt-based electrodes (0.04–0.12 mg Pt/cm 2) were prepared by dual ion-beam assisted deposition (dual IBAD) method on the surface of a non-catalyzed gas diffusion layer (GDL) substrate. Film thicknesses ranged between 250 and 750 Å, these are compared with a control, a conventional Pt/C (1.0 mg Pt(MEA)/cm 2, E-TEK). The IBAD electrode constituted a significantly different morphology, where low density Pt deposits (largely amorphous) were formed with varying depths of penetration into the gas diffusion layer, exhibiting a gradual change towards increasing crystalline character (from 250 to 750 Å). Mass specific power density of 0.297 g Pt/kW is reported with 250 Å IBAD deposit (0.04 mg Pt/cm 2 for a total MEA loading of 0.08 mg Pt/cm 2) at 0.65 V. This is contrasted with the commercial MEA with a loading of 1 mg Pt(MEA)/cm 2 where mass specific power density obtained was 1.18 g Pt/kW (at 0.65 V), a value typical of current state of the art commercial electrodes containing Pt/C. The principal shortcoming in this effort is the area specific power density which was in the range of 0.27–0.43 W/cm 2 (for 250–750 Å IBAD) at 0.65 V, hence much below the automotive target value of 0.8–0.9 W/cm 2 (at 0.65 V). An attempt to mitigate these losses is reported with the use of patterning. In this context a series of patterns ranging from 45 to 80% Pt coverage were used in conjunction with a hexagonal hole geometry. Up to 30% lowering of mass transport losses were realized.

Cross-Linked Nanocomposite Polymer Electrolytes Reinforced with Cellulose Whiskers

In a previous work [Macromolecules 2004, 37,1386], a new way of processing cellulose whisker reinforced nanocomposites from an organic solvent (N,N-dimethylformamide) without a surfactant addition or a chemical surface modification was investigated. This technique is used to prepare nanocomposite polymer electrolytes based on a cross-linked polyether and lithium imide (LiTFSI) reinforced with tunicin whiskers. Both the mechanical and ionic conductive properties of the resulting electrolytes are presented. These performances are compared to those obtained for unfilled cross-linked polyether matrices exhibiting several cross-linking densities. It is observed that the ionic conduction of cellulose whisker filled electrolytes is higher than the one of highly cross-linked polyether networks. In addition, the mechanical stiffness of the former is much higher than that of the latter, allowing the processing of high-performance nanocomposite polymer electrolytes.

燃料電池用高分子膜の最前線 炭化水素系高分子電解質膜の可能性と問題点

This paper presents an overview of the possibility and problems of new proton-conducting polymer electrolyte membranes based on hydrocarbon polymers. Due to their chemical stability, high degree of proton-conductivity, and remarkable mechanical properties, perfluorinated polymer electrolytes such as Nafion®, Aciplex®, Flemion®, and Dow membranes are some of the most promising electrolyte membranes for polymer electrolyte fuel cells. A number of reviews on the synthesis, electrochemical properties, and fuel cell applications of perfluorinated polymer electrolytes have also appeared. While perfluorinated polymer electrolytes have satisfactory properties for a successful fuel cell electrolyte membrane, the major drawbacks to large-scale commercial use involve high cost and low proton-conductivities at high temperatures and low humidities. Presently, one of the most promising ways to obtain high-performance proton-conducting polymer electrolyte membranes is the use of hydrocarbon polymers for the polymer backbone. The present paper attempted to summarize the synthesis, chemical and electrochemical properties, and fuel cell application of new proton conducting polymer electrolytes based on hydrocarbon polymers that have been made during the past decade.

In situ x-ray absorption fuel cell

An in situ x-ray absorption spectroscopy cell was designed to study the structural and electronic properties of high performance polymer electrolyte fuel cell electrocatalysts. The cell was operated as a standard fuel cell and x-ray absorption data were collected simultaneously as the fuel cell operating conditions were varied. The cell was used to examine platinum–ruthenium alloy electrocatalysts incorporated in the anode of a fuel cell membrane and electrode assembly. In situ Pt LIII and Ru K edge x-ray absorption near-edge structure (XANES) data were collected at five selected current densities of the operating fuel cell. The XANES data show that under normal fuel cell operating conditions, the metallic nature of the Pt–Ru catalyst is retained. The cell design enabled an in situ fuel cell study at a synchrotron source in which no additional electrolytes were required.

The use of boroxine rings for the development of high performance polymer electrolytes

Boroxine ring containing additives, Bx( n)=B 3O 3[O(CH 2CH 2O) n CH 3] 3, were found to be compatible with a wide variety of polymer hosts. Polymer electrolytes exhibiting room temperature conductivities of up to 10 −5 S cm −1 were obtained by incorporation of Bx( n) and LiCF 3SO 3 into poly(methyl methacrylate) and propylene oxide–ethylene oxide co-polymers. Polymers composed of inter-connecting networks of boroxine rings were also investigated as suitable hosts for the boroxine additives B 3O 3[O(CH 2CH 2O) n CH 3] 3. Poly(methyl methacrylate) systems exhibited an electrochemical stability window in the region of 4.9 V, while transference number measurements indicated high Li + ion conductivity.

Lithium insertion into carbonaceous materials and transition metal oxides from high performance polymer electrolytes

The electrochemical characteristics of gel-type polymer electrolyte membranes of interest for the development of plastic lithium ion batteries are presented and discussed. Particular attention is devoted to the interfacial behavior of both negative (i.e. carbonaceous materials) and positive (i.e. lithium transition metal oxides) electrodes.