Direct Methanol Fuel Cell Study on anode and cathode catalysts 曹殿学
Introduction • Direct methanol fuel cells • Major problems facing DMFCs Study on the anode electrocatalyst(Pt-Ruad) Study on the cathode electrocatalyst(Ru/Se) Acknowledgements
Direct Methanol Fuel Cell e- Load + - O2 (air) e- CH3OH + H2O H+ e- O2 CO2 H2O H2O +CH3OH PEM Cathode Anode Membrane Electrode Assembly (MEA) E= -0.02V E= 1.23V E= 1.21V
Power vehicles • More efficient than ICE • (97% vs. 40%). • Lower emission(no NOx). • Quite. • Power portable • electronic devices • Last longer than batteries. • Easy to refill.
Sluggish anode kinetics a • Methanol crossoverc Key Issues Hindering the Development of Practical DMFCs: Ecel l= Ecell- ( a + c ) Ecell / Ecell<< 100% --过电势 • Develop active methanol electrooxidation catalysts. • Overcome methanol crossover issue.
What I have done on the study of anode (University of Alberta, Canada)
Pt Ru Best catalyst for CH3OH electrooxidation: PtRu nanoparticles • What is the optimum surface composition? • Best Pt:Ru ratio? • Hard to measure surf. comp. • of nanoparticle PtRu. • 10~50% Ru was reported.
Ru3+ H H H Pt Pt Pt # of Ru atom Pt/Ru comp.= # of surf. Pt atom H+ K2S2O8 in 4.0 M KOH # of surf. Pt atom was measured by cyclic voltammetry(CV) Inductively Coupled Plasma- Atomic Emission Spectrometry (ICP-AES) # of Ru atom
1) Ruad form a submonolayer on the substrate at each deposition. 2) Ruad were deposited onto Ptsurf and Ruad at similar probabilities. Cao, D. X.; Bergens, S. H. Electrochimica Acta, 2003, 48, 4021-4031.
RE WE CE Ar in Ar out Ru 0.33 0.45 0.18 0.63 0.75 Pt 1 M CH3OH 1 M H2SO4 Ru 0.33 0.45 0.63 0.75 0.18 Pt Pt:Ru ~ 67:33
Membrane Electrode Assembly (MEA) Anode: Pt-Ruad Cathode: Pt black Nanoparticle catalysts Nafionionomer Nafion-117
Nafion-117 Membrane [CF2]2 [CF2]2 [CF2]2 [CF2]2 SO3- SO3- SO3- H2O SO3- H+ H+ H2O CH3OH H+ H2O H+ CH3OH H2O H2O H2O H2O H+ H2O CH3OH H+
Ink Preparation (sonication) Hot-Pressing (125oC, 1500psig) Painting Steel plate Catalyst layer Paint brush Nafion-117 membrane Teflon tape Teflon decal Catalyst / Water / Nafion Fuel Cell Hardware Membrane Electrode Assembly
T = 60oC, Pt:Ru ~ 65:35 T = 90oC, Pt:Ru ~ 50:50
RE WE CE Ar in Ar out CVs for fresh Pt-Ruad
CE RE WE H2 (H2O) Anode Pt-Ruad Cathode Pt CVs measured in fuel cells H2O (Ar)
Is Pt-Ruad stable? (Ruad might come off) Fuel Cell Stability Test
What I have done on the study of cathode (University of Illinois, USA)
Anode Cathode CH3OH O2 + e- H2O CH3OH Nafion membrane CO2 + e- Problems: Methanol crossover causes a mixed potential at cathode, increases the cathode overpotential, decreases fuel cell voltage, thereby efficiency. Solutions: • Methanol impermeable • membrane. • Methanol tolerant ORR • electrocatalysts.
Oxygen Reduction Reaction Activity Comparison Ru/Se 旋转电极 Methanol Tolerance
Acknowledgements • People: Dr. Steve Bergens Dr. Andrzej Wieckowski • Funding: Natural Sciences and Engineering Research Council of Canada. US Army Research Office (MURI grant DAAD19-03-1-0169) .