Preparation of Pt/C electrode with double catalyst layers by electrophoresis deposition method for PEMFC

https://doi.org/10.1016/j.ijhydene.2013.11.044Get rights and content

Highlights

  • Pt/C DCL electrodes are prepared by PED from Pt colloid as a plating bath.

  • Pt loading on the electrodes is controlled by varying deposition time.

  • Pt/C DCL electrode has enhanced catalytic activity than SCL electrode.

Abstract

Pt/C double catalyst layer (DCL) electrodes are prepared by pulsed electrophoresis deposition (PED) method from a Pt colloidal solution as a plating bath. The PED is optimized by varying the deposition time in a galvanostatic mode. The catalyst layers of the electrodes prepared by this method are structurally characterized by EDX and SEM studies. The catalytic activities of Pt/C DCL electrodes are evaluated by cyclic voltammetry technique. The loading amount of the Pt catalyst is controlled by varying the deposition time. With the same Pt catalyst loading, the DCL electrode has enhanced catalytic activity than single catalyst layer (SCL) electrode.

Introduction

The high cost of platinum (Pt) and Pt-group metals (PGMs), along with low Pt utilization in the catalyst layer, is a major barrier to the commercialization of fuel cell technology. The strategies and methodologies to increase catalyst layer Pt utilization and reduce Pt loading constitute a major effort in fuel cell research and development [1], [2], [3].

Thin-film catalyst layers (CLs) are widely used in current fuel cell technology. In thin-film CL fabrication, the most common method is to prepare catalyst ink by mixing the Pt/C agglomerates with a polymer electrolyte such as Nafion ionomer and then to apply this ink on a porous gas diffusion media or an electrolyte membrane. Based on the nature of catalyst ink and its application method, several thin-film CL fabrication techniques have been developed, including decal transfer [4], [5], brush painting [6], [7], spray coating [8], [9], [10], doctor blade coating [11], screen printing [12], [13], [14], inkjet printing [15], [16], and rolling [17]. Currently, screen printing and spray coating have become standard methods for conventional CL fabrication. Inkjet printing is also showing promise for fabricating low Pt loading CLs. In these catalyst ink-based methods, the CL always contain some inactive catalyst sites not available for fuel cell reactions because the electrochemical reaction is located only at the interface between the polymer electrolyte and the Pt catalyst where there is reactant access [3], [18], [19], [20], [21].

Recently, we have developed a pulsed electrophoresis deposition (PED) method to avoid above mentioned disadvantage [22], [23]. It was shown that Pt nanoparticles in a colloidal solution could be deposited onto carbon black substrate at low pH without any change in size, and the prepared electrode had an ultra-thin Pt CL with a thickness of 2–2.5 μm [22]. This method has the dual advantage of easy preparation and good control over Pt loading. However, previous studies were focused on a preparation of the single catalyst layer (SCL) electrode. Also, the mass-specific activity of the SCL electrode was considerably decreased with increasing deposition amount of Pt catalyst due to coagulation of Pt nanoparticles [22].

In this study, we develop a novel Pt/C electrode with double catalyst layers (DCL) by PED method. It is aimed for improving catalyst utilization and reducing Pt loading. The DCL electrode (schematically shown in Fig. 1) consists of two CLs, named outer CL and inner CL. The catalytic activity of the Pt/C DCL electrode was compared with that of SCL electrode.

Section snippets

Experimental

All the chemical reagents used were analytically pure. All solutions were prepared with ultrapure water obtained from a water purification system (Millipore, 18.2 MΩ cm). Toray carbon paper (TGP-H-090, 40 wt%, wet-proofed) was used as an electrode backing layer for Pt/C electrodes. Synthesis of colloidal Pt solution and chemical treatment of carbon black reported in the literature [23].

Results and discussion

TEM image of the synthesized Pt colloids is shown in Fig. 2. It is found that the Pt nanoparticles mainly consist of particles with a diameter of 2–4 nm. As explained in the experimental section, these Pt colloidal nanoparticles were electrophoretically deposited onto carbon black electrode. The carbon black electrode contains the Nafion ionomer and the electron conductive carbon particles (Fig. 3a). Apparently, the carbon black electrode has a porous coral-like microstructure. Fig. 3(b) and

Conclusions

The carbon black electrode can be coated with a dual thin platinum CL using the PED method, which is advantageous for electronic and ionic conductivity. The loading amount of Pt catalyst on the carbon black electrode was controlled by the deposition time. The electrochemical catalytic activity was increased by only changing the structure of Pt CL from single layer to double layer without changing the Pt loading amount on the electrode. Compared with the Pt/C SCL electrode, the catalytic

Acknowledgments

This study was supported by the grant of Post-doctoral Research Program in Chonbuk National University, by the National Research Foundation of Korea grant funded by the Korea Government (MEST) (NRF 2012M1A2A2671697), by the BK21 Plus program in Ministry of Education and Human-Resource Development, and by the Program of Regional Innovation Center (Woosuk Univ.) which was conducted by the Ministry of Knowledge Economy of Korea government.

References (25)

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