Porous gas diffusion electrodes (GDEs) were prepared using; (i) solubilised polymer binders and Au coated porous polymer substrates (ii) sintered PTFE or PVDF binders and porous carbon substrates. Type (i) GDEs were capable of catalysing H<SUB>2</SUB> oxidation at significant rates but rates of CH<SUB>3</SUB>OH oxidation were <I>ca</I>. 100 times lower. They also suffered from ohmic limitations, poor long term stability and poor reproductibility between similar electrodes. Type (ii) GDEs showed much improved rates of CH<SUB>3</SUB>OH oxidation compared with Type (i) but were highly dependant on PTFE concentration and only marginally affected by the catalyst loading. The rate of H<SUB>2</SUB> and CH<SUB>3</SUB>OH oxidation on Type (i) GDEs appeared independent of the catalyst used (Pd or Pt/Ru) while CH<SUB>3</SUB>OH oxidation on Type (ii) GDEs altered according to the Pt/Ru ratio. Various base materials ((Ni/C), Ni<SUB>3</SUB>C, (W, Fe<SUB>6</SUB>W<SUB>6</SUB>C), (W, Co<SUB>6</SUB>W<SUB>6</SUB>C)) were prepared as Type (ii) electrodes but were found to corrode rapidly in H<SUB>2</SUB>SO<SUB>4</SUB> making them unsuitable as electrocatalysts. Newly synthesised materials, (Ni/W/C), (Ni/Mo/C) and (Ni/W/Mo/C) were also prepared as Type (ii) GDEs. (Ni/Mo/C) and (Ni/W/Mo/C) were passive in hot H<SUB>2</SUB>SO<SUB>4</SUB> at <0.25V<SUB>(SCE)</SUB> respectively; beyond this they corroded transpassively which was attributed to the poor corrosion resistance of Mo<SUB>2</SUB>C under acidic conditions. Both materials showed some activity for H<SUB>2</SUB> oxidation but (Ni/Mo/C) showed no activity for CH<SUB>3</SUB>OH oxidation while (Ni/W/Mo/C) showed a low rate of oxidation in the passive region. (Ni/W/C) was passive throughout the potential range examined and showed electrocatalytic activity for H<SUB>2</SUB> and CH<SUB>3</SUB>OH oxidation; CH<SUB>3</SUB>OH oxidation occurred at over potentials significantly lower than observed on noble metal catalysed electrodes. The WC component of (Ni/W/C) was thought to passivate the Ni component rendering it catalytically active. Electrodes prepared using Pt/WC and Pt/Ru/WC showed inferior electrocatalytic activity for the oxidation of CH<SUB>3</SUB>OH than Pt/Ru of a comparable loading. In addition higher rates of corrosion were observed compared with plain WC.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:596396 |
| Date | January 1997 |
| Creators | Barnett, C. J. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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