MS-2-P-2219 Surface formation of electrospun carbon nanofiber mats controlled by HRSEM

Hydrogen fuel cells will play the leading role among alternative energy sources in the XXI century. Electrocatalytic and gas diffusion layers of a fuel cell consist of electroconductive materials and metal layers, which are the most critical components. Carbon nanofiber nonwoven materials are the most promising materials owing to their thermal and chemical resistance, higher sorption capacity, electrical conductivity and mechanical properties. Their properties determine the most important fields of their application: for purifying various liquid and gaseous media, as a reinforcing filler in composites for accumulating gaseous or condensed substances and also for creating catalysts with higher activity, selectivity and stability. Polyacrylonitrile is the most promising and the most used polymer for producing carbon nanofiber nonwoven materials. Recently electrospinning has been used to create new materials for various alternative power supplies [1]. By this method highly porous fiber mats can be molded from solutions of polymers. Due to various additives the properties and characteristics of the produced materials can differ widely.
The main problems are to improve the porosity of the carbon nanofiber mats, to reduce their electroresistivity and to decrease the precious catalytic metal concentration. The aim of the present work is to investigate the influence of different treatments on the morphology, metal particle distribution and surface structure of electrospun polyacrylonitrile mats.
The surface investigation of obtained mats was performed by a high resolution scanning electron microscopy (HRSEM) in a FEI Quanta 250 FEG and a FEI Helios 600 DualBeam^TM with EDX analysis.
The obtained electrospun polyacrylonitrile fiber mats were 10-100 μm thick, which depends on the molding conditions and treatment temperature with the fiber diameters in the range of 50-400 nm. Most of the fibers had a characteristic diameter of 100-150 nm and a length of several tens of microns [2]. These mats with a smooth surface are shown in Fig. 1. High temperature annealing (at 1200 and additional 2800 ^oC) and chemical treatment (by polyvinylpyrrolidone and polyimide) led to significant changes in the morphology, length and surface condition (Fig. 2). The chemical treatment was performed for a better deposition of Pt particles because of the formation of cavities on the fibers’ surface [3]. As a result, a thick Pt nanoparticles coating was formed on their surface (Fig. 3).

1. Dong Z, Kennedy SJ, Wu Y Journal of Power Sources 2011 196 4886
2. Ponomarev II et al. Doklady Physical Chemistry 2013 448(6) 670
3. Zhigalina VG et al. Nanomaterials and Nanostructures - XXI Century 2012 4 36