Method of monitoring CO concentrations in hydrogen feed to a PEM fuel cell

In a method of operating a H.sub.2 --O.sub.2 fuel cell system comprising the principal steps of (1) providing a hydrogen-rich fuel gas having a first CO content sufficient to poison the fuel cell's anode, and (2) injecting controlled amounts of oxygen into said fuel gas upstream of said fuel cell to selectively oxidize said CO with O.sub.2 in the presence of said hydrogen to produce a fuel stream for said fuel cell which has a second CO content less than said first content that will not poison said fuel cell, the improvement comprising controlling the rate of injection of said oxygen into said fuel gas so as to optimize the consumption of said CO from said fuel gas while minimizing the consumption of H.sub.2 therefrom by:

• a. providing a CO-sensor including a monitoring PEM-probe comprising a proton exchange membrane having an anode and a cathode affixed to opposing first and second surfaces of said membrane, said anode confronting an anode chamber in communication with said fuel gas and comprising a catalyst susceptible to poisoning by said CO over time incident to the adsorption of CO by said catalyst and consequent progressive degradation of said catalyst as CO is adsorbed by said catalyst and said catalyst changes from a substantially CO-free condition to a CO-contaminated condition;
• b. contacting said anode with a portion of said fuel gas over a plurality of predetermined time intervals;
• c. contacting the cathode with oxygen;
• d. discharging said PEM-probe during each of said intervals;
• e. monitoring the electrical output from said PEM-probe during said discharging to generate an output signal having a behavioral pattern indicative of variations in the CO content of said stream;
• f. from a reference PEM-probe similar to said monitoring PEM-probe, determining a plurality of electrical outputs which are correlated to known CO concentrations in said stream;
• g. storing said electrical outputs from said reference PEM-probe in a readable memory;
• h. comparing said output signal from said monitoring PEM-probe to said electrical outputs from said reference PEM-probe to identify an electrical output that is substantially similar to said behavioral pattern to determine the CO concentration in said stream, and to initiate such adjustment to said rate as might be warranted to optimize said CO consumption while minimizing said H.sub.2 consumption;
• and
• i. intermittently, purging said catalyst of said CO between said intervals to maintain said catalyst at substantially said CO-free condition to provide an accurate determination of the CO concentration in said stream.

A method of controlling the operation of a H.sub.2 --O.sub.2 PEM fuel cell system by monitoring the CO concentration in a reformate feed stream thereto comprising the steps of:

• a. providing a CO-sensor including a monitoring PEM-probe comprising a proton exchange membrane having an anode and a cathode affixed to opposing first and second surfaces of said membrane, said anode confronting an anode chamber in communication with said feed stream and comprising a catalyst susceptible to poisoning by said CO over time incident to the adsorption of CO by said catalyst and consequent progressive degradation of said catalyst as CO is adsorbed by said catalyst and said catalyst changes from substantially a CO-free condition to a CO-contaminated condition;
• b. contacting said anode with a portion of said feed stream over a plurality of predetermined time intervals;
• c. contacting the cathode with oxygen;
• d. discharging said PEM-probe during said intervals;
• e. monitoring the electrical output from said PEM-probe during said discharging to generate an output signal having a behavioral pattern indicative of variations in the CO content of said stream;
• f. from a reference PEM-probe similar to said monitoring PEM-probe, determining a plurality of electrical outputs which are correlated to known CO concentrations in said feed stream;
• g. storing said electrical outputs from said reference PEM-probe in a readable memory;
• h. comparing said output signal from said monitoring PEM-probe to said electrical outputs from said reference PEM-probe to identify an electrical output from said reference PEM-probe that is substantially similar to said behavioral pattern to determine the CO concentration in said stream, and to initiate whatever corrective action to the operation of the fuel cell that might be warranted by such concentration;
• and
• i. intermittently, purging said catalyst of said CO between said time intervals to maintain said catalyst at substantially said CO-free condition to provide an accurate determination of the CO concentration in said stream.