Fuel utilisation coefficient

However, in practice it is found that not all the fuel that is fed to a fuel cell can be used, for reasons discussed later. Some fuel usually has to pass through um-eacted. A fuel utilisation coefficient can be defined as... 

The loss of methanol is often transposed into a crossover current - the current equivalent to that which would be produced by the methanol, had it reacted properly on the fuel anode. This current, ic, can be used with the useful output current i to give an important figure of merit for a DMFC, which is the fuel utilisation coefficient r)f. This gives the ratio of the fuel that is usefully and properly reacted on the anode to the total fuel supplied, the difference being accounted for by some fuel crossing-over and being lost at the cathode. 

It is important to monitor the concentration of methane using a sensor as the fuel crossover may occur. The problem of fuel crossover is severe for the PEM direct methanol fuel cell. Methanol dissolves quickly in water and reaches the cathode. The presence of platinum catalyst on the cathode will oxidise the fuel, though not as effectively as the anode catalysts. Hence, fuel wastage will occur at the cathode reducing the cell voltage. This phenomenon yields mixed potential and the fuel utilisation coefficient //f is defined as... 

Table 10,1 Contributions to ASR for a Rise-type anode-supported cell (Nl-YSZ/YSZ/tSM-YSZ) at 8S0°C tested in a plug flow-type configuration at S and 8S% fuel utilisation (FU). Rehji is calculated using a specific conductivity of YSZ of 0.045 S/cm, Sconnect is an estimation, Rp.eichem is the sum of typical anode and cathode polarisation resistances measured in separate electrode experiments, Rp.aiff is calculated using a diffusion coefficient of 10 cm /s, 30% porosity, a tortuosity factor of 3 and a thickness of 0.1cm, and fip,conver is Calculated using Eq. (10) with i = 0,5 A/cm ...

Differences in the extraction coefficients with different cations may be utilised in the separation of uranium, transition metals and rare earths. This is a well-established method for the extraction of U in the processing of nnclear fuels. Hafnium ean also be separated from zirconium by this technique, using TBP. 

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