Estimating Production Rates for Hydrogen and Fluorine

As shown in Fig. 14,4 reference flows (known flow rates of nitrogen, or on occasion, helium) are introduced into the cathode and anode chambers, where they mix with the hydrogen and fluorine. 

The gas chromatograph (GC) is a Hewlett-Packard 5890 GC with a thermal conductivity detector. A 5A mole sieve column is used with argon carrier gas this gives peaks going in the same direction for both hydrogen and nitrogen. 

A side stream from the cathode product mixture is passed over a room temperature alumina bed to remove HF. The nitrogen/hydrogen ratio is estimated, and from this ratio and the known flow rate of the nitrogen reference stream, the current efficiency for hydrogen production is calculated. 

A side stream from the anode product mixture is passed over a hot (100-115°C) alumina bed where the fluorine reacts quantitatively to produce aluminum fluoride and oxygen. The nitrogen/oxygen ratio is 

Over the range of 100 to 600 mA cm 2, the current efficiency for the production of hydrogen was 100%, with a standard deviation of 2%. Over the range of 100 to 600 mA cm-2, the current efficiency for the production of fluorine was 100% with a standard deviation of 2%. Essentially the same results were obtained with helium reference flows. 

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