Anode contamination hydrogen production

Ammonia in the hydrogen fuel originates from the hydrogen production process. The impact on fuel cell performance is as described for the cathode contamination, and is similar whether it is introduced in the cathode or anode. 

NH3 is another typical contaminant in PEM fuel cell anodes. Trace amounts of NH3 in a fuel cell system will cause significant fuel cell degradation [82-86]. NH3 in the fuel stream originates mainly from hydrogen production and storage, due to several causes ... 

At the fuel cell anode side, the main contaminants are CO, HjS, and NH3. These can originate from the reformate gas and hydrogen production processes. Both CO and H2S reduce fuel cell performance by strong adsorption on the Pt catalyst surface, thus poisoning the catalyst and retarding H2 oxidation. NH3 causes a decrease in membrane conductivity by forming NH and then replacing H+ in the Nafion membrane and ionomer in both anode and cathode catalyst layers. 

In the decomposer, deionized water reacts with the amalgam, which becomes the anode to a short-circuited cathode. The caustic soda produced is stored or evaporated, if higher concentration is required. The hydrogen gas is cooled by refrigeration to remove water vapor and traces of mercury. Some of these techniques are employed in different facilities to maximize the production of chlorine, minimize the consumption of NaCl, and also to prevent the buildup of impurities such as sulfate in the brine.26 The production of pure chlorine gas and pure 50% sodium hydroxide with no need for further concentration of the dilute solution is the advantage that the mercury cell possesses over other cells. However, the cell consumes more energy and requires a very pure brine solution with least metal contaminants and above all requires more concern about mercury releases into the environment.4... 

Fuel cells must carry the costs of conditioning the two reactant gases as well as their own capital charges. Hydrogen requires transport to the anode side of the fuel cells. This is usually by rotary blower, but it also should be possible to operate membrane cells at some positive pressure and then to deliver the hydrogen without mechanical aid. The temperature and water content of the hydrogen must be considered in the overall heat and mass balance. Air and oxygen are candidates for use at the cathodes. The classical balance between cost and efficiency determines the choice. Wth alkaline fuel cells, the carbon dioxide in the air is of concern. It can consume the hydroxide value and contaminate the end product. It is possible to scrub the air to remove the CO2 before... 

Recent examples of contamination of electrochemical reactors include the production of (1) adiponitrile and (2) glyoxylic acid." In (1) the source of the problem is the anode and polymer formation in (2) the anode, process hardware, and feedstock impurities contribute. Operation in both suffers from a gradual decrease in current efficiency due to increasing hydrogen evolution which accompanies the cathodic reaction. 

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