Elsevier

Journal of Power Sources

Volume 195, Issue 23, 1 December 2010, Pages 7776-7780
Journal of Power Sources

Short communication
Metal oxide nanoparticles synthesized by pulsed laser ablation for proton exchange membrane fuel cells

https://doi.org/10.1016/j.jpowsour.2009.09.060Get rights and content

Abstract

We report on the development of a modified gas diffusion layer for fuel cells consisting of a simple or teflonized carbon cloth pulsed laser deposited with metal oxide nanostructures designed to operate both as co-catalyst, and oxidic support for other electrochemically active catalysts. We selected TiO2, ZnO and Al2O3 doped (2 wt.%) ZnO which were uniformly distributed over the surface of gas diffusion layers in order to improve the catalytic activity, stability and lifetime, and reduce the production costs of proton exchange membrane fuel cells. We evidenced by scanning electron microscopy and energy dispersive spectroscopy that our depositions consisted of TiO2 nanoparticles while in the case of ZnO and Al2O3 doped (2 wt.%) ZnO transparent quasi-continuous films were synthesized.

Introduction

A fuel cell is the device that directly converts the energy of a supplied gas, such as hydrogen, to electricity [1], [2]. In case of proton exchange membrane fuel cells (PEMFCs), the base unit consists of a polymer electrolyte sandwiched by a pair of electrodes supported by gas diffusion layers (GDLs) [3], [4], [5].

Despite their simplicity, many difficulties have prevented the widespread usage of fuel cells, one of them being the low activity and high content of platinum electro-catalyst used for oxygen reduction. Till now, the best oxygen catalyst was considered Pt-based, but the drive to reduce metal loadings and costs and improve their efficiency requires the development of new materials and structures.

We herewith report the synthesis and characterisation of modified GDL containing metal oxide nanostructures as a possible solution to overcome the difficulties related to electro-catalysis and stability of electrodes. This type of structure was designed to function both as co-catalyst and oxidic support for other electrochemically active catalysts made of noble (Pt, Pd, Ru, etc.) or non-noble metals [6].

The oxide modified GDLs presented in this paper were synthesized using catalytically active components such as TiO2, ZnO and Al2O3 doped (2 wt.%) ZnO uniformly distributed over the entire volume of GDL. We selected these compounds because they are expected to remain stable inside the oxidizing and acid media specific for PEM fuel cells. Moreover, the metal oxide-containing GDL structure is expected to prevent conductivity losses and allowing a good water and gases management [7], [8], [9], [10].

Many different chemical and physical methods have been applied for the production of nanoparticles [11]. Among them, pulsed laser ablation (PLA) appeared to be one of the most promising alternatives. Nevertheless, the formation of nanoparticles during the PLA process is not yet completely understood. It is therefore important to continue the studies in order to elucidate the role of the various deposition parameters: incident laser fluence, ambient gas nature and pressure, number of applied pulses.

We applied PLA of pure targets for nanoparticles transfer to simple (SCC) or teflonized (TCC) carbon-based GDL. This method ensures an optimum stoichiometric transfer and uniform dispersion of the particles over the substrate surface and very good access of the reactants to the catalytically active sites.

Section snippets

Experimental details

The deposition of the metal oxide nanoparticles was performed inside a stainless steel vacuum chamber (Fig. 1). Before each deposition, the chamber was pumped down to a residual pressure of 10−4 Pa. UV laser pulses generated by a COMPEXPro 205 KrF* excimer laser source (λ = 248 nm, τFWHM  25 ns) were applied for the ablation of the TiO2, ZnO and Al2O3 doped (2 wt.%) ZnO targets. The laser radiation was focused with an AR coated MgF2 lens on target surface in order to melt, evaporate and ionize the

TiO2 nanoparticles

The SEM micrographs recorded for the TiO2 structures deposited at two different laser fluence on teflonized carbon cloth are given in Fig. 2a and b. In the case of 5 J cm−2 laser fluence our studies confirmed the presence of TiO2 nanoparticles. The deposited particles have sizes of tens to hundreds of nanometers. We observed (Fig. 2a) a uniform spatial distribution of the nanoparticles over the substrate surface. The density of TiO2 nanoparticles was ∼5 × 10−2 μm−2. In the case of lower fluence (

Conclusions

The stoichiometric transfer of the material from TiO2, Al2O3:ZnO, and ZnO targets on simple or teflonized carbon cloth substrates was obtained by optimizing the pulsed laser ablation regime. We synthesized by PLA TiO2 nanoparticles with sizes within the range from tens to hundreds of nanometers on both TCC and SCC. We observed that the generation of well-defined nanoparticles with controlled size, shape and distribution can be tailored by the variation of the incident laser fluence. In case of

Acknowledgment

GD, DE, EA, FS, NS, CR and INM acknowledge with thanks the financial support of this work by 21-030/2007-CEREPC contract, under PNCDI II Romanian Program.

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