Preparation and thermal treatment influence on Pt-decorated electrospun carbon nanofiber electrocatalysts

Abstract

Crystalline platinum nanoparticles supported on carbon nanofibers were synthesized for use as an electrocatalyst for polymer electrolyte membrane fuel cells. The nanofibers were prepared by a method of electrospinning from polymer solution with subsequent pyrolysis. Pt nanoneedles supported on polyacrylonitrile pyrolyzed electrospun nanofibers were synthesized by chemical reduction of H 2 [PtCl 6 ] in aqueous solution. The synthesized electrocatalysts were investigated using scanning, high resolution transmission and scanning transmission electron microscopies, EDX analysis and electron diffraction. The shape and the size of the electrocatalyst crystal Pt nanoparticles were controled and found to depend on the method of H 2 [PtCl 6 ] reduction type and on conditions of subsequent thermal treatment. Soft Pt reduction by formic acid followed by 100 C thermal treatment produced needle-shape Pt nanoparticles with a needle length up to 25 nm and diameter up to 5 nm. Thermal treatment of these nanoparticles at 500 C resulted in partial sintering of the Pt needles. When formic acid was added after 24 h from the beginning of platinization, Pt reduction resulted in small-size spherical Pt nanoparticle of less than 10 nm in diameter. Reduction of H 2 [PtCl 6 ], preadsorbed on electrospun nanofibers in formic acid with further treatment in H 2 flow at 500 C, resulted in intensive sintering of platinum particles, with formation of conglomerates of 50 nm in size, however, individual particles still retain a size of less than 10 nm.Electrochemically active surface area (ECSA) of Pt/C catalyst was measured by electrochemical hydrogen adsorption/desorption measurements in 0.5 M H 2 SO 4 . ECSA of needle-shape Pt nanoparticles was 25 m 2 g À1 . It increased up to 31 m 2 g À1 after thermal treatment at 500 C, likely, due to amorphous structures removal from carbon nanofibers and retaining of Pt nanoneedle morphology. ECSA of small-size spherical Pt nanoparticles was 26 m 2 g À1 . Further thermal treatment at 500 C in vacuum decreased ECSA down to 20 m 2 g À1 due to Pt sintering and Pt active sites deactivation. The thermal treatment of small-size spherical Pt nanoparticles in H 2 flow at 500 C produced agglomerates of Pt nanoparticles with ECSA of 14 m 2 g À1 .

New Carbon Nanofiber Composite Materials Containing Lanthanides and Transition Metals Based on Electrospun Polyacrylonitrile for High Temperature Polymer Electrolyte Membrane Fuel Cell Cathodes

“…The material contains 5.1% Ni, 0.92% Zr, and 0.85% Ce according to elemental analysis. The electrical conductivity of this material reached 12.3 S cm −1 which makes it sufficient for use in fuel cell electrodes as it was confirmed by our previous studies [ 31 , 32 , 33 ].…”

“…Earlier we have shown [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ], that platinized highly macroporous CNF self-supporting mats, which were obtained by the method of electrospinning (ES) from polyacrylonitrile (PAN) polymer solution [ 38 , 39 ] with further stabilization in air, pyrolysis under vacuum [ 40 ], and platination in hexachloroplatinic acid solution, can be successfully used in HT-PEMFC as gas diffusion electrodes (GDEs), both on cathode and anode sides. Thus, polybenzimidazole membrane PBI-OPht was developed in our group for this purpose [ 41 , 42 ].…”

Cardo Polybenzimidazole (PBI-O-PhT) Based Membrane Reinforced with m-polybenzimidazole Electrospun Nanofiber Mat for HT-PEM Fuel Cell Applications

“…To obtain the CNF electrode, a procedure similar to those that have already been described in our previous studies was employed [ 14 , 15 , 16 , 17 , 18 , 19 ]. Zirconium (IV) chloride, nickel (II) acetate, polyacrylonitrile (PAN), H 2 [PtCl 6 ]·6H 2 O, and DMF (Merck KGaA, Darmstadt, Germany) were used as received.…”

“…Despite the advantages listed above, the PBI-O-PhT membrane requires further improvement. This becomes even more important when using the latest electrospun carbon-nanofiber (CNF)-based gas-diffusion electrodes (GDEs) Pt/CNF with a higher stability [ 15 , 16 , 17 , 18 , 19 ] compared with the commercial Celtec ® P1000 (BASF, Ludwigshafen am Rhein, Germany). The necessity to replace carbon-black-based electrodes for HT-PEM fuel cells with more stable ones, for example, based on carbon nanostructured materials, such as CNF, has been extensively discussed in the literature [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ].…”

Plasma-Devised Pt/C Model Electrodes for Understanding the Doubly Beneficial Roles of a Nanoneedle-Carbon Morphology and Strong Pt-Carbon Interface in the Oxygen Reduction Reaction

“…Under these conditions, the fine understanding of the doubly beneficial effects of support nanoscale morphology and a strong metal-support interface based on controlled surface fabrication and high-energy metal deposition is essentially challenging due to their multiple interrelated structural factors. Due to the instability of carbon black in fuel cell operations, alternative carbon supports for ORR have been developed, e.g., electrospun carbon nanofiber, 14 multiwalled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), and a nanocomposite of indium tin oxide with rGO, 15 where MWCNTs showed the smallest degradation.…”