Microwave-assisted Pechini Synthesis of Pd-Ni Nanocatalyst for Ethanol Electro-oxidation in Alkaline Medium

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1 Microwave-assisted Pechini Synthesis of Pd-Ni Nanocatalyst for Ethanol Electro-oxidation in Alkaline Medium Mark Rohwer, Kenneth Ozoemena and Mmalewane Modibedi

2 ethanol electro-oxidation in alkaline medium What is a fuel cell? A device that can convert chemical energy of a fuel directly to electricity Potentially very efficient and clean at source Challenges: Requirement for expensive PGM catalysts, usually dispersed on high-surface-area support, e.g. carbon black Efficiency, durability Why alkaline, why ethanol? Improved O 2 reduction kinetics Non-PGM catalysts can be used (cost reduction) Ethanol is renewable and easily handled Why Pd compounds? Effective catalyst for ethanol electro-oxidation CSIR 2011 Slide 2

3 P.M. Pechini, U.S. Patent (1967). Metal precursor e.g. PdCl 2 Chelate (sol) Chelate (gel) Citric acid / ethylene glycol Warm (approx. 90 C) Metal particles dispersed in polymer matrix Metal particles Heat (approx. 120 C) Supported catalyst Pyrolise (up to 400 C) in air or inert gas Microwave, support on carbon black CSIR 2011 Slide 3

4 Metal loading: mg/cm² Current density (ma/cm²) Cyclic Voltammograms for EASA (1M KOH / N2) Potential (V) Electrochemically active surface area (m²/g) Pd 35.7 Pd microwaved 66.5 Pd-Ni / C Pd-Ni / C microwaved Pd / C Pd / C microwaved Pd-Ni 35.0 Pd-Ni microwaved 28.6 CSIR 2011 Slide 4

5 Metal loading: mg/cm² Current density (ma/cm²) Cyclic Voltammograms (1M EtOH / 1M KOH) Potential (V) Pd-Ni / C Pd-Ni / C microwaved Pd / C Pd / C microwaved CSIR 2011 Slide 5

6 Metal loading: mg/cm² Current density (ma/cm²) Onset potential (mv) Linear Sweep Voltammograms Potential (V) Peak current density (ma/cm²) Pd-Ni / C Pd-Ni / C microwaved Pd / C Pd / C microwaved Pd (baseline) Pd MW (+64%) Pd-Ni (+36%) Pd-Ni MW (+226%) CSIR 2011 Slide 6

7 High resolution TEM, Pd / C: Particles vary from ca. 8 to ca. 15 nm and are often agglomerated CSIR 2011 Slide 7

8 High resolution TEM, Pd / C, microwaved: Particles vary from ca. 8 to ca. 15 nm; somewhat more agglomeration observed than before microwaving CSIR 2011 Slide 8

9 High resolution TEM, Pd-Ni / C: Particles vary from ca. 8 to ca. 15 nm and are often agglomerated CSIR 2011 Slide 9

10 High resolution TEM, Pd-Ni / C, microwaved: Particles vary from ca. 8 to ca. 15 nm; somewhat more agglomeration observed than before microwaving CSIR 2011 Slide 10

11 X-ray diffraction spectroscopy: Intensity (a.u.) Pd (111) Pd / C before and after MW Pd (200) PdO (112) PdO (211) Pd (220) Pd (311) PdO (114) Pd / C MW Pd / C Position [ 2Theta] (Cobalt(Co)) Lattice parameter: 3.90Å in both cases CSIR 2011 Slide 11

12 X-ray diffraction spectroscopy: Intensity (a.u.) Pd-Ni / C vs. Pd / C, before MW NiO (200) Pd (111) Pd (200) PdO (112) PdO (211) Pd (220) Pd (311) PdO (114) Pd-Ni / C Pd / C Position [ 2Theta] (Cobalt(Co)) Pd-Ni vs. Pd Pd (111) Pd (200) Pd (220) Pd (311) CSIR 2011 Slide 12

13 X-ray diffraction spectroscopy: Intensity (a.u.) NiO (200) Pd (111) Pd-Ni / C before and after MW Pd (200) PdO (112) PdO (211) Pd (220) PdO (114) Pd (311) After MW Before MW Position [ 2Theta] (Cobalt(Co)) CSIR 2011 Slide 13

14 No previous records found of using Pechini method in conjunction with microwave treatment on Pd-Ni catalysts. Addition of Ni to Pd enhanced current density (36%) Microwaving enhanced certain aspects of catalytic activity Current density increased (Pd: 64%, Pd-Ni: 140%) Onset potentials were not influenced significantly EASA was only enhanced for Pd, not for Pd-Ni Structural analysis showed no apparent differences after microwave treatment HR-TEM XRD Hypothesis: possible surface modification, e.g. oxidation? Investigation is ongoing. CSIR 2011 Slide 14

15 Thank you! Acknowledgements: Dr Kenneth Ozoemena and Dr Mmalewane Modibedi (co-authors) Mr Charl Jafta and Ms Haitao Zheng