Designing Nanoplatelet Alloy/Nafion Catalytic Interface for optimization of PEMFCs:

Transcription

1 Supporting Information Designing Nanoplatelet Alloy/Nafion Catalytic Interface for optimization of PEMFCs: Performance, Durability, and CO Resistance Likun Wang a, Yuchen Zhou a, Janis Timoshenko a, Shizhong Liu a, Qiao Qiao b, Kim Kisslinger c, Michael Cuiffo a, Ya-Chen Chuang a, Xianghao Zuo a, Yuan Xue a, Yichen Guo a, Cheng Pan a, Hongfei Li a, *, Chang-Yong Nam c, Stoyan Bliznakov a, Ping Liu d, Anatoly I. Frenkel a,d, Yimei Zhu b, Miriam H. Rafailovich a, * a Department of Materials Science and Chemical Engineering, State University of New York at Stony Brook, NY 11794, USA b Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY 11973, USA c Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA d Department of Chemistry, Brookhaven National Laboratory, Upton, NY 11973, USA *Correspondence to: Prof. M. H. Rafailovich ( miriam.rafailovich@stonybrook.edu), Tel: (516) Dr. H. Li ( hongfei.li@stonybrook.edu), Tel: (631)

2 Optimization of nanoparticle composition: The two-phase synthesis method relies on the competition between thiol stabilization and ion agglomeration. Hence the process depends on multiple, but little-known parameters, such as the solubility of the salts, the chemical potentials of the different ions, and the thiol/metal reaction kinetics. 1 Here we experimented with three different ratios of the salts and measured the resulting ratios in the particles using TEM- EDS, as listed in Table S1. The maximum power enhancement was then measured as described in the manuscript, using the PEMFC test station, and plotted in Figure S1 for the three compositions. Table S1. Au and Pd salts ratio in the synthesis and the resulting elemental ratio in the particles Au:Pd molar ratio Salts 2:1 1:1 1:2 Particles 3:1 2:1 1:1 Figure S1. Comparison of PEMFCs maximum power enhancement percentage using AuPd NPs, with different Au to Pd ratio (3:1, 2:1 and 1:1 resulting from 2:1, 1:1 and 1:2 ratio form synthesis, respectively), coated Nafion.

3 Particle characterization (a) (b) Figure S2. (a) TEM image and (b) Size distribution histogram of AuPd NPs drop casted onto the TEM grid.

4 Intesity (counts) Au (111) Pd (111) theta (degree) Au NPs AuPd NPs Table S2. Lattice constant and crystallite size determined from the XRD spectra Lattice Constant a [Å] D(cryst.size) [ Å ] Au NPs AuPd NPs Au-PDF# Pd-PDF# Figure S3. XRD spectra of powder samples of as synthesized Au and AuPd NPs.

5 Table S3. Au to Pd elemental ratio from the XRF spectra Element At. % Error Pd ± 0.27 Au ± 0.31 Figure S4. XRF spectra of AuPd NPs powder sample.

6 (a) (b) (c) 2mN/m 5mN/m 10mN/m Figure S5. TEM characterization of LB films lifted at the surface pressure of (a) 2 mn/m, (b) 5 mn/m, and (c) 10 mn/m. Schemes of particle assembles at corresponding surface pressures are also presented, respectively.

7 Figure S6. EDS elements analysis result of as-synthesized AuPd NPs.

8 Details of EXAFS data fitting Conventional least-square fitting to theoretical standards, as implemented in FEFFIT code, 2 was applied. Theoretical phases and amplitudes were obtained in self-consistent ab-initio calculations with FEFF8.5 3 code for bulk material. The complex exchange-correlation Hedin- Lundqvist potential and default values of muffin-tin radii as provided within the FEFF8.5 code were employed. Single shell fitting of Pd and Au foil data was used to obtain the values of amplitude reduction factors S Obtained S 0 values for Au and Pd foils are 0.95±0.02 and 0.82±0.02, respectively. In addition, we also performed fitting of PdS EXAFS data from Ref. 4 For metallic NPs, fitting of EXAFS spectra χ(k)k 2 was carried out in R-space in the range from Rmin = 1.2 Å up to Rmax = 3.0 Å (for Pd K-edge data) and Rmax = 3.5 Å (for Au L3-edge data). Fourier transform was carried out in the k range from 2.4 Å -1 up to 11.0 Å -1 for Pd K-edge and in the k range from 3.0 Å -1 up to 10.0 Å -1 for Au L3 edge (up to 8.0 Å -1 for Au L3 edge in AuPd NPs). Fitting parameters were coordination numbers N, interatomic distances R and disorder factors σ 2 for Pd S, Au S, Pd Pd, Pd Au, Au Au and Au--Pd pairs, and corrections to photoelectron reference energies ΔE0. For AuPd NPs, Pd K-edge and Au L3-edge were fitted simultaneously, to obtain a single structure model, consistent with all experimental information. In these fits we constrain Pd Au and Au Pd distances and σ 2 factors to be the same. Preliminary fitting results showed that there are no significant differences in the corresponding σ 2 factors for monometallic and bimetallic NPs samples. Similarly, no significant differences in ΔE0 between different NPs samples were detected. Therefore, to reduce the uncertainties of the analysis, in our final fitting model we fitted all EXAFS spectra for mono- and bimetallic NPs simultaneously, where we constrained ΔE0 for Pd K-edge, ΔE0 for Au L3-edge, σ 2 for Pd--S bond, σ 2 for Pd--Pd bond, σ 2 for Pd--Au bond, σ 2 for Au--S bond and σ 2 for Au--Au bond to be the same for all samples. Such fitting model allowed us to find structure models in a good agreement with all experimental data (see Figure 5 in the main text and Figure S7). Fitting results for monometallic and bimetallic NPs and reference materials are summarized in Table S4.

9 Figure S7. Fits of experimental EXAFS spectra for monometallic Au and Pd NPs (shifted vertically for clarity). Partial contributions of Pd S and Au S are shown separately. Table S4. Structure parameters (coordination numbers N, interatomic distances R and disorder factors σ2), obtained in fitting of experimental EXAFS data. Number in parenthesis show the uncertainty in the last digit. Sample N Au S R Au S 2 σ Au S N Au Au R Au Au 2 σ Au Au N Au Pd R 2 Au Pd σ Au Pd ΔE 0 (Au) R (Å) (Å 2 ) (Å) (Å 2 ) (Å) (Å 2 ) (ev) factor Au foil (2) (2) (2) 0.7% Au NPs, LB 0.4(3) 2.28(5) 0.001(2) 9(3) 2.81(3) 0.013(1) (7) 0.6% PdAu, LB 1.0(6) 2.26(5) 0.001(2) 5(6) 3.0(1) 0.013(1) 2(2) 2.74(6) 0.005(4) 6.2(7) 6.4% Sample N Pd S R Pd S 2 σ Pd S N Pd Pd R Pd Pd 2 σ Pd Pd N Pd Au R 2 Pd Au σ Pd Au ΔE 0 (Pd) R (Å) (Å 2 ) (Å) (Å 2 ) (Å) (Å 2 ) (ev) factor Pd foil (1) (2) (2) 0.6% PdS (1) 0.003(1) (2) 4.0% Pd NPs, LB 2.0(7) 2.31(3) 0.004(1) 1(1) 2.77(5) 0.006(4) (1) 6.6% PdAu, LB 2.4(8) 2.32(2) 0.002(1) (2) 2.74(6) 0.005(4) -5(1) 4.4%

10 (a) (b) (c) (d) (e) Figure S8. (a) Cross-sectional TEM, (b) STEM image and (c-e) Silicon, gold and palladium elemental mapping of AuPd NPs lifted on a silicon wafer at surface pressure of 5 mn/m.

11 (a) (b) (c) Figure S9. Polarization and power curves of PEMFC with AuPd NPs, Au NPs and control under H2 and 0.1% CO in H2. (b) Polarization and (b) power curves of PEMFC with AuPd NPs under different surface pressure and control under H2 and 0.1% CO in H2.

12 (a) (b) Figure S10. Polarization curve and power output of PEMFC (a) without and (b) with AuPd NPs. Initially, after 5k, 10k and 15k CV cycles.

13 Mass activity assessment The estimated mass activity from the ir-corrected curves at 0.9 V is 0.14 A/mgPt and 0.16 A/mgPt, for the control and modified MEAs, respectively. It is seen that the mass activity of the modified MEA is enhanced slightly due to the presents of AuPd NPs. The estimated mass activity from the ir- corrected curves at 0.9 V is 0.06 A/mgPt and 0.10 A/mgPt, for the control and modified MEAs, respectively. It is seen that the mass activity of both MEAS decreases after the AST cycling, but the decrease in the control MEA is more pronounces in comparison to the modified MEA (a) (b) Cell Voltage, V Polarization curves, H 2 /O 2, 80 o C,150 kpa abs Contcrol ir drop corrected Cell Voltage, V Polarization curves, H 2 /O 2, 80 o C,150 kpa abs PdAu modified ir drop corrected Current Density, A/cm 2 Current Density, A/cm (c) (d) Cell Voltage, V Polarization curves after 30 K AST cycles, H 2 /O 2, 80 o C,150 kpa abs Contcrol ir drop corrected Cell Voltage, V Polarization curves after 30K AST cycles, H 2 /O 2, 80 o C,150 kpa abs PdAu modified ir drop corrected Current Density, A/cm 2 Current Density, A/cm 2 Figure S11. The initial polarization curves measured at 80 C, in H2/O2 atmosphere with the (a) control and (b) AuPd modified MEAs. The polarization curves measured after 30k AST cycles measured at 80 C, in H2/O2 atmosphere with the (c) control and (d) AuPd modified MEAs.

14 Figure S12. Actual maximum output power under different surface pressures during the LB process.

15 (a) (b) (c) Figure S13. Polarization and power curves of PEMFC with/without AuPd NPs under different gas atmosphere: (a) O2 vs air, (b) 0.1% CO in H2 vs H2 and (c) 0.1% CO in O2 vs O2.

16 Figure S14. Comparison of decrease percentage with/without AuPd NPs coating on Nafion under mixture feed gases of 0.1% CO in oxygen.

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