Surface characterization
Journal of Power Sources
Performance of vertically oriented graphene supported
platinum-ruthenium bimetallic catalyst for methanol oxidation
Zheng Bo * , Dan Hu, Jing Kong, Jianhua Yan, Kefa Cen
*State Key Laboratory of Clean Energy Utilization, Department of Energy Engineering, Zhejiang University, Hangzhou, Zhejiang
Province 310027, China
By Barbora Pijáková
Aim of the work
● Preparation of catalyts for methanol fuel cells
● Vertically oriented graphene substrate covered by Pt-Ru nanoparticles
acting as catalyst for methanol oxidation reaction
● Comparison of electrocatalytic performance (mass loading; size of
nanoparticles; catalytic stability) of Pt-Ru/VG products with the Pt-Ru/CP
Preparation of Pt-Ru/VG catalyst
● Substrate CP
1. VG grown via PECVD
● Microwave source
● 5 min pretreatment, 350 W, 50 sccm of hydrogen
● 2 min deposition, 50 V bias, 50 sccm of hydrogen + 10 sccm of methane
2. Co-electrodeposition of Pt-Ru
● Electrolyte: H2PtCl6.6H2O (1-9 mM)+RuCl3.xH2O (9‑1 mM)+H2SO4 (0.5 M)
● Three-electrode system (Pt foil = counter electrode; saturated calomel
electrode = reference electrode; substrate = working electrode)
● Pulse potentials approach; 300 cycles; -0.40 V for 100 ms (deposition);
0.60V for 300 ms (diffusion of metal cations in electrolyte)
Characterization
1. Electrochemical measurement
● Cyclic voltammetry – catalytic activity
● Chronoamperometry – stability of catalyst
2. Material characterization
● Scanning electron microscopy – surface morphology; size and dispersion
of Pt-Ru particles
● High resolution transmission electron microscopy
● X-ray diffraction – crystalline structures of Pt, Ru
● X-ray photoelectron spectroscopy – chemical states of Pt and Ru
● Inductively coupled plasma mass spectrometry – catalyst loading mass
on substrate
Used instrumentation
● SEM: SU-70 scanning electronic microscopy (SEM, Hitachi)
● TEM: Tecnai G2 F30 STwin transmission electron microscopy (TEM,
Philips-FEI)
● XRD: XRD-6000 Diffractometer with Cu Kα source (λ = 0.15425 nm,
Shimadzu)
● XPS: VG Escalab Mark II with a monochromatic Mg Ka X-ray source
(1253.6 eV, West Sussex)
● ICP: XSENIES, Thermo Electron Corporation
Scanning electron microscopy (SEM)
High resolution transmission electron microscopy
(HRTEM)
● Interaction of electrons with surface
● Source of electrons – cathode – thermoemission, field-emission
● Focusing lens for electron beam
1. SEM
● Electron beam energy: 0.2 – 40 keV; scanning the surface
● Detection of secondary electrons + backscattered electrons
(topography); photons of characteristic x-ray (chemical composition);
light (luminiscence – special phases)
● Penetration depth vs. substrate and layer thickness
● High vacuum vs. ESEM
● Resolution ≈ tens of nm
2. TEM
● Energy of electron beam
● Detection of transmitted electrons – CCD camera/fluorescence screen;
bright field + dark field; diffraction; electron energy loss (chemical
composition); 3D imaging
● Thin specimen; high vacuum
● Resolution ≈ Å
● HRTEM: higher energy of beam; thin specimen; UHV; resolution 0.05nm
● SEM images of Pt–Ru/CP and Pt–Ru/VG
obtained from three typical electrolyte
compositions. (a) and (b) [H2PtCl6]:
[RuCl3] = 3:7, average catalyst diameter:
103.5 ± 3.1 nm and 46.3 ± 1.5 nm; (c) and
(d) [H2PtCl6]:[RuCl3] = 1:1, average catalyst
diameter: 111.1 ± 2.8 nm and 51.2 ± 1.8 nm;
(e) and (f) [H2PtCl6]:[RuCl3] = 7:3, average
catalyst diameter: 98.3 ± 1.9 nm and
45.9 ± 1.1 nm. Insets: SEM images with a
smaller magnification. (g) HRTEM image of
Pt–Ru/VG obtained from the electrolyte
composition of [H2PtCl6]:[RuCl3] = 1:1.
X-ray diffraction (XRD)
● Interaction of X-rays with the specimen
● Diffraction according to Bragg's law
● Source of X-rays – termoemission + single crystal diffraction on Cu
(CuKα source with λ = 0.15425nm)
● Detection of diffracted X-rays
● Sample rotates in a path of collimated incident X-ray beam at angle θ +
detector collects the X-rays at 2θ
● Observation of phases coexistence; crystallinity; lattice parameters
● XRD patterns of Pt–Ru/VG obtained from
different electrolyte compositions
X-ray photoelectron spectroscopy (XPS)
● Interaction of X-rays with specimen
● X-ray sources: Kα Al (monochromatic); Kα Mg (non-monochromatic)
● Detecting the ecsaped photoelectrons (amount + carrying the information
about binding energy)
● Observation of chemical composition; chemical state; surface
contamination/ surface functionalization; empirical formula; depth
analysis (if equipped with ion beam etching)
● HV/UHV required; starting at Li; surface sensitive (few nm); difficult fitting
(overlapping peaks); limited size of samples
● (c) Pt 4f XPS spectra and (d) Ru 3p XPS spectra of the catalyst Pt–Ru/VG
with a precursor of [H2PtCl6]:[RuCl3] = 1:1
Inductively coupled plasma mass spectrometry
(ICP-MS)
● Introduction of analyte to plasma (solid - laser ablation; gas – direct;
liquid – direct)
● Ionization of analyte in plasma (other methods: MALDI; electrospray;
thermospray; chemical ionization; field desorption )
● Separation of ions based on m/z (quadrupole; octapole; sector separator;
TOF; ion trap)
● Detection of ionized molecules/fragments/particles (induced charge;
produced current)
● Qualitative and quantitative (if calibrated) technique
● Pt and Ru loadings on (a) pristine CP and (b) VG-coated CP
with a varying electrolyte composition
Results
1. Introducing VG – increasing of
● Loading mass of Pt and Ru; catalytic stability; catalytic activity
2. introducing VG – decreasing of
● Size of Pt, Ru nanoparticles
3. analysis
● SEM + HRTEM – size of graphene
● XRD – Pt in fcc, however Ru absent
● XPS – oxidation number for Pt, Ru unproven (non-monochromatic source
– lower resolution)
4. what to improve
● Presentation of mass spectra
● Evidence of presence of Ru
● Hydrogen content/contamination of VG; Pt-Ru/VG
Thank you for your attention