Platinum nanoparticles-cobalt oxide nanostructures as efficient binary catalyst for ethylene glycol electro-oxidation Ghada H. El-Nowihy Chemical Engineering Department, Faculty of Engineering, The British University in Egypt Supervisors Prof. Mohamed S. El-Deab Chemistry Department, Faculty of Science, Cairo University Prof. Ahmad M. Mohammad Prof. Mostafa M. H. Khalil Chemistry Department, Faculty of Science, Ain Shams University Prof. Mohamed A. El-Shahir

Outline Fuel Cells: Essence and Motivation Direct Ethylene Glycol Fuel Cells (DEGFCs) Limitations and Means of Overcoming Experimental Results & Discussion Conclusions

Energy Crisis & Alternative Energy Sources Solar energy Wind energy Hydroelectric energy Geothermal energy Bioenergy Fuel cells energy

Fuel cells: What and Why? Chemoelectric engine that convert chemical energy of the fuel direct to electricity. Clean energy: Hydrogen + Oxygen  H2O + Heat + electricity “Fuel cell vehicle” Gasoline + Oxygen  CO2 + H2O + Heat + electricity “Gasoline vehicle” “air pollutant”

Fuel cells: What and Why? High energy density (kWh/kg) : Energy produced per unit weight of the fuel High efficiency: No moving parts Combined heat and power (CHP) generation Unlimited runtime: In fuel cell, no charging time like batteries

How Fuel Cell Works

Direct Ethylene Glycol Fuel Cell (DEGFC): Advantages Ethylene glycol is liquid fuel much safer and easier to transport and handle than pressurized H2 cylinders Large Energy Density & less expensive hydrogen source HCOOH → CO2 + 2H+ + 2e- “DFAFC provide 1.4 kW.h/kg” FA CH3OH + H2O → CO2 + 6H+ + 6e- “DMFC provide 4.2 kW.h/kg” MeOH CH2OH-CH2OH + 2H2O → 2CO2 + 10H+ + 10e− “DEGFC provide 5.3 kW.h/kg” EG

Limitation: Poisoning of Pt catalyst CO poison formation: Pt-COads main catalyst poison CO2 evolution: Ptfree Surface Modifier “MOx NPs” CH2OH-CH2OH + 2H2O 2CO2 + 10H+ + 10e− EG Fig. (A) Fig. (B)

How Nanoparticles solve the problem of catalyst poisoning (1) Bifunctinal effect: Provide Oxygen containing species to adsorbed CO generating CO2   (2) Third body effect “ensemble effect”: Change the geometry required for the adsorption of CO poison on the Pt substrate “i.e.; prevent Pt atoms contiguity”. (3) Electronic effect: Change electronic structure of Pt to weaken the binding energy between Pt &CO.

Experimental A. Electrodes and pretreatments B. Electrode modification Chemicals & solutions Electrochemical measurements Potentiostat Electrochemical cell Electrodes Working electrode: GC Reference electrode: Ag/AgCl/KCl(sat.) Counter electrode: spiral Pt wire B. Electrode modification nano-Pt & nano-MOx C. Materials Characterization Electrode morphology & surface composition FE-SEM & EDS

Characterization of electrodes: Morphological FE-SEM Pt/GC electrode. FE-SEM of NiOx/Pt/GC electrode. FE-SEM of MnOx/Pt/GC electrode. FE-SEM of CoOx/Pt/GC electrode.

Characterization of electrodes: Compositional EDS of Pt/GC electrode. EDS of NiOx/Pt/GC electrode. EDS of MnOx/Pt/GC electrode. EDS of CoOx/Pt/GC electrode.

Characterization of electrodes: Electrochemical CV of Pt/GC electrode. CV of NiOx/Pt/GC electrode. Ni(OH)2 ↔ NiOOH + H+ + e-

CoOx/Pt electrode: Characterization CV of MnOx/Pt/GC electrode. CV of CoOx/Pt/GC electrode. 2 MnOOH + 2 OH− ↔ 2 MnO2 + 2 H2O + 2 e− 3 Co (OH)2 + 2 OH- → Co3O4+ 4 H2O+ 2 e− Co(II) Co(II)&Co(IV) Co3O4 + 2 OH- + H2O → 3 CoOOH + e− Co(II)&Co(IV) Co(III) CoOOH + OH- → CoO2 + H2O + e− Co(III) Co(IV)

Ip is 2 times of that obtained at Pt/GC Electrocatalytic activity of ethylene glycol (EG) oxidation at various electrodes CoOx/Pt/GC MnOx/Pt/GC Highest enhancement at CoOx/Pt/GC Ip is 2 times of that obtained at Pt/GC NiOx/Pt/GC Pt/GC LSVs for EGO at a) Pt/GC, b) NiOx/Pt/GC, c) MnOx/Pt/GC and d) CoOx/Pt/GC electrodes in 0.5 M NaOH solutions containing 0.5 M EG. Potential scan rate is 50 mV s−1.

Stability of CoOx/Pt/GC electrode NiOx/Pt CoOx/Pt/GC Pt Pt/GC I-t curve for 3 h of continuous electrolysis.  Highest activity  Highest stability

Origin of catalysis NiOx MnOx CoOx 2 pathways Ni(OH)2 ↔ NiOOH + H+ + e- Ni(II) Ni(III) MnOx 2 MnOOH + 2 OH− ↔ 2 MnO2 + 2 H2O + 2 e− Mn(III) Mn(IV) CoOx 2 pathways Co(OH)2 + OH- ↔ CoOOH + H2O + e- CoOOH + OH- ↔ CoO2 + H2O + e- Co(II) Co(III) Co(III) Co(IV) CoOOH + EG → intermediates + Co(OH)2 CoO2 + EG → intermediates + CoOOH CoOOH + intermediates → products + Co(OH)2 CoO2 + intermediates → products + CoOOH

Conclusions 1) nano-NiOx, nano-MnOx and nano-CoOx act as catalytic mediators facilitate charge transfer of the EGO. better konetis for EGO. higher energy obtained from the DEGFC. 2) CoOx/Pt/GC electrode highest catalytic activity towards EGO when compared to Pt/GC, NiOx/Pt/GC and MnOx/Pt/GC electrodes. 3) CoOx/Pt/GC electrode high stability; stable oxidation current over prolonged time of oxidation. Role of “nano-CoOx”

Origin of catalysis 2 MnOOH + 2 OH− ↔ 2 MnO2 + 2 H2O + 2 e− Mn(III) Mn(IV) 2 MnO2 + Pt−COads + H2O → 2 MnOOH + Ptfree + CO2 Mn(IV) (main poison) Mn(III) Pt−COads + 2 OH − → Ptfree + CO2 + H2O + 2 e−

Origin of catalysis Ni(OH)2 ↔ NiOOH + H+ + e- Ni(II) Ni(III) Ni(III) + EG → intermediates + Ni(II) Ni(III) + intermediates → products + Ni(II) Co(OH)2 + OH- ↔ CoOOH + H2O + e- Co(II) Co(III) CoOOH + EG → intermediates + Co(OH)2 CoOOH + intermediates → products + Co(OH)2 CoOOH + OH- ↔ CoO2 + H2O + e- Co(III) Co(IV) CoO2 + EG → intermediates + CoOOH CoO2 + intermediates → products + CoOOH