OXIDATION OF METHANOL IN ALKALINE The features of methanol oxidation in mixed alkaline SOLUTIONS solutions were also studied using the cyclic voltammograms for 6 M Methanol in the mixed solution 1 1 2 Keith Scott , E H Yu and R W Reeves of NaOH and Na2CO3 and NaOH and NaHCO3, 1. Department of Chemical and Process Engineering respectively. There is no significant difference observed University of Newcastle upon Tyne,NE1 7R, UK from the CVs for methanol oxidation in NaOH and the 2.QinetiQ, HaslarRd. Gosport, PO122AG, UK mixture of NaOH and Na2CO3. However, the reaction current for methanol oxidation decreased severely in the Abstract mixture of NaOH and NaHCO3 compared to that in Methanol oxidation in various alkaline solutions: NaOH. This suggests that the poisoning effect of CO hydroxide, carbonate and bicarbonate has been species in alkaline solution is less significant and the investigated. Cyclic voltammograms of methanol HCO species could be the main poisoning species in oxidation on platinised electrodes were carried out with methanol oxidation in alkaline solution. various methanol concentrations, from 0.1 M up to 12 3500 M, in various alkaline media: NaOH, Na2CO3 and 2.0M NaOH

NaHCO3 with different concentrations, 0.1 M to 4 M. 3000 4.0M NaOH

2500 Introduction. 1.0M NaOH I 2000 Fuel cells have the potential to exceed the performance m of batteries by a factor of at least ten for a wide range of A 1500 military and civil applications. Proton-exchange 1000 0.5M NaOH membrane fuel cells (PEMFCs) offer the highest power 500 0.1M NaOH densities and operate at modest temperatures. However, 0 such membranes are not ideal due to their high cost, low -800 -600 -400 -200 0 200 400 600 800 fuel cell potential generated by the proton conduction E mv vs SCE reaction, the need for platinum catalysts, the sensitivity 2 to fuel impurities, and the need for specialist high-cost materials as current collectors. The development of fuel cell stacks is now well Fig. 1 Oxidation of 2.0 M methanol solution in various advanced for all applications. However, the significant concentrations of sodium hydroxide. performance advantage that the PEMFC has over the battery (rechargeable or non-rechargeable) will only be realised when a credible fuel source has been developed. The greatest performance advantages accrue 2250 2000 when the cell uses hydrogen fuel. However, to store or 1M NaOH generate hydrogen places a significant cost penalty on 1750 1500 the system such that the whole life cost will be greater I 1250 m than for the rechargeable battery. The use of a liquid A 1000

750 1M Na CO fuel such as methanol, which is directly oxidised at the 2 3 fuel cell anode, offers a simpler logistics chain and a 500 1M NaHCO whole life cost which is competitive with the 250 3 rechargeable battery, but at ten times the performance 0 -800 -600 -400 -200 0 200 400 600 800 1000 1200 1400 of an advanced battery. E mv vs SCE

2 Experimental Results and discussion. Fig. 2 Oxidation of 2.0 M methanol in sodium Methanol oxidation in various alkaline solutions: hydroxide, sodium carbonate and sodium bicarbonate. hydroxide, carbonate and bicarbonate has been investigated. Cyclic voltammograms of methanol 2500 oxidation on platinised electrodes were carried out with various methanol concentrations, from 0.1M up to 12 2000 0.8M NaOH+0.2M Na 2CO 3 M, in various alkaline media: NaOH, Na2CO3 and I 1500 1M NaOH NaHCO3 with different concentrations, 0.1 M to . The mA activity of methanol oxidation reaction for a certain concentration of methanol solution in alkaline solutions 1000 is directly related to the OH- concentration and OH on ads 0.8M NaOH+0.2M NaHCO 3 the electrode surface. A more active methanol oxidation 500 reaction and higher reaction current can be achieved by increasing the concentration of alkaline solution. On the 0 -800 -600 -400 -200 0 200 400 600 800 1000 other hand, for certain concentration of methanol and E mv vs SCE alkaline solution, the highest activity of the methanol oxidation was obtained in NaOH solution and the 2 lowest was in NaHCO3 solution, i.e. the activity decreases in the order of: NaOH > Na2CO3 > NaHCO3. Fig. 3. Oxidation of 6.0 M methanol solution in mixed The oxidation current in NaHCO3 solution was only alkaline solutions. around 10% of that in NaOH solution.