3D Boron doped Carbon Nanorods/Carbon-Microfiber Hybrid Composites: Synthesis and Applications as Highly Stable Proton Exchange Membrane Fuel Cell

Transcription

1 Electronic Supplementary Information for Journal of Materials Chemistry 3D Boron doped Carbon Nanorods/Carbon-Microfiber Hybrid Composites: Synthesis and Applications as Highly Stable Proton Exchange Membrane Fuel Cell Jiajun Wang, Yougui Chen, Yong Zhang, Mihnea Ioan Ionescu, Ruying Li, Xueliang Sun *, Siyu Ye, and Shanna Knights Department of Mechanical and Materials Engineering, University of Western Ontario, London, Ontario, Canada N6A 5B9, Ballard Power Systems Inc., 9000 Glenlyon Parkway, Burnaby, BC, Canada V5J 5J8A *Address correspondence to 1

2 Experimental Synthesis of BCNRs. The growth of BCNRs was carried out on carbon papers by spray pyrolysis method. 75 mg ferrocene and 75 mg boron oxide were dissolved in 10 ml alcohol. Prior to the growth of carbon nanomaterials, argon was introduced into the quartz tube to eliminate the air. The synthesis process was carried out at 800 o C and the solution was introduced into the furnace by a spray pump at a flow rate of 200 sccm. For comparison, CNTs were also grown on carbon paper using the same method without B source and other parameters were kept the same as that of BCNRs. Deposition of Pt nanoparticles. The supports were purified by mild acidic treatment prior to the Pt deposition. For the deposition of Pt, 0.15 ml of an aqueous of 200 mm H 2 PtCl 6 was mixed with 20 ml H 2 O in a beaker, and the CNTs or BCNRs electrode were suspended in the Pt precursor solution, followed by the addition of 6 mg trisodium citrate. After several minutes, a mixture of trisodium citrate and KBH4 was injected into the beaker with a low speed and the reaction lasted for 1 h. The resulting electrode was washed with distilled water and dried in vacuum at 60 o C overnight. Electrochemical characterization. Electrochemical measurements were performed with CHI 600 C electrochemical working station. A conventional three-electrode cell was used, including a Ag/AgCl (saturated KCl) electrode as reference electrode, a platinum wire as counter electrode, and the above carbon nanotubes electrodes as working electrodes. For convenience, all potentials are referred to standard hydrogen electrode (SHE) hereinafter. The ECSA of the electrode was determined by CV which was conducted from 0.05 to 1.2 V in N 2 purged 0.5 mol L -1 H 2 SO 4 solutions at 25 o C. Current-potential relation for ORR is measured from 0.2 V to 1.0 V (scan rate 5 mv s -1 ) to obtain current-potential current in oxygen-saturated 0.5 mol L -1 H 2 SO 4 solution. Durability investigation of the electrode was carried out by ADT method, which was conducted by potential cycling between 0.60 and 1.20 V in oxygen-saturated 0.5 mol L -1 H 2 SO 4 solutions. Physical characterization. The similar Pt loading in the electrodes was determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES). The morphologies of BCNRs and CNTs 2

3 were characterized with a field emission scanning electron microscope (SEM, Hitachi S-4800) operated at 5.0 kv. The morphologies of Pt nanoparticles dispersed on the surface of BCNRs and CNTs were characterized by transmission electron microscopy (TEM) (Philips CM 10) and high-resolution transmission electron microscopy (HRTEM) (JEOL 2010 FEG). X-ray photoelectron spectroscopy (XPS) analysis was performed using Kratos AXIS Nova spectrometer operated at 14 kv. Electron energy loss spectroscopy (EELS) measurements were carried out using a JEOL 2010F TEM at 70 kv with an imaging filter (Gatan Tridiem model). 3

4 Figure S1. Schematic representation of the spray/cvd apparatus to prepare CNT and BCNR. 4

5 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry Figure S2. Digital pictures of carbon paper (left), BCNR/carbon paper (middle), carbon nanotube/carbon paper (right). 5

6 x Name Fe 2p3/2 O 1s C 1s B 1s Pos FWHM Area At% C 1s 8 CPS 6 Fe LMM c Fe 2s Fe LMM b B 1s Fe LMM a Fe 3s Fe 2p Fe 3p O 1 s 4 O K LL Binding Energy (ev) Surface Science Western Figure S3. Survey XPS spectra of BCNRs 6

7 (a) (b) STEM B mapping C mapping Figure S4. (a) HAADF image of BCNRs bundles supported on carbon grids. (b) STEM-HAADF image taken from the dashed square region and the responding EELS elemental mapping of B and C. 7

8 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry (a) (c) (b) (d) Figure S5. TEM images of original Pt/BCNRs (a), post-adt Pt/BCNRs (b), original Pt/CNTs (c), and post-adt Pt/CNTs (d). 8