Methods and apparatus for improving the cold starting capability of a fuel cell

Abstract

Apparatus and methods of ceasing operation of an electric power generating system improve the cold starting capability of the system. The system comprises a fuel cell stack connectable to an external circuit for supplying power to the external circuit. The stack comprises at least one solid polymer fuel cell, and the system further comprises a fuel passage for directing a fuel stream through the stack and an oxidant passage for directing an oxidant stream through the stack, a sensor assembly connected to the stack for monitoring a parameter indicative of stack performance, a controller for controlling at least one stack operating parameter, and a control system communicative with the sensor assembly and stack operating parameter controller. The method comprises adjusting at least one stack operating parameter to cause the stack to operate under a drying condition that causes a net outflux of water from the stack, operating the stack under the drying condition until the water content in the stack has been reduced, and interrupting supply of power from the stack to the external circuit.

1 - 34 . (canceled)  
     
     
         35 . An electric power generation system comprising: 
 (a) a fuel cell stack connectable to an external circuit for supplying electric power to the external circuit, the stack comprising at least one solid polymer fuel cell and fluid flow passages through the stack;    (b) a sensor assembly connected to the stack for monitoring at least one parameter indicative of stack performance;    (c) a controller for controlling at least one stack operating parameter; and    (d) a control system communicative with the sensor assembly and the stack operating parameter controller, such that upon receipt of a shut down instruction from the control system, the stack operating parameter controller is operable to adjust at least one stack operating parameter such that the stack operates in a drying condition that causes a net outflux of water from the stack, until the water content in the stack has been reduced.    
     
     
         36 . The electric power generation system of  claim 35  wherein the sensor assembly comprises a sensor for monitoring a parameter indicative of stack performance selected from the group consisting of: 
 the resistance of at least one fuel cell in the stack,    the impedance of at least one fuel cell in the stack, and    the voltage of at least one fuel cell in the stack.    
     
     
         37 . The electric power generation system of  claim 35  wherein the sensor assembly comprises at least one sensor for monitoring the at least one stack operating parameter.  
     
     
         38 . The electric power generation system of  claim 37  wherein the sensor assembly comprises a sensor for monitoring a stack operating parameter selected from the group consisting of: 
 the relative humidity of at least one of the oxidant and fuel streams;    the stoichiometry of at least one of the oxidant and fuel streams;    the flow rate of at least one of the oxidant and fuel streams;    the pressure of at least one of the oxidant and fuel streams; and    the stack temperature.    
     
     
         39 . The electric power generation system of  claim 35  wherein the controller comprises apparatus to control at least one stack operating parameter selected from the group consisting of: 
 the relative humidity of at least one of the oxidant and fuel streams;    the stoichiometry of at least one of the oxidant and fuel streams;    the flow rate of at least one of the oxidant and fuel streams;    the pressure of at least one of the oxidant and fuel streams; and    the stack temperature.    
     
     
         40 . The electric power generation system of  claim 35  wherein the control system comprises a microcontroller.  
     
     
         41 . The electric power generation system of  claim 39  further comprising a humidifier for humidifying at least one of a fuel or oxidant stream supplied to the stack during normal operation, and wherein the relative humidity control apparatus comprises a humidifier bypass system having at least one bypass conduit for directing at least some of at least one of fuel or oxidant to the stack in fluid isolation from the humidifier.  
     
     
         42 . The electric power generation system of  claim 41  wherein upon receipt of a shut down instruction from the control system, the humidifier bypass system directs at least some of the oxidant or fuel streams through the associated bypass conduit.  
     
     
         43 . The electric power generation system of  claim 42  wherein the bypass conduit comprises an inlet end connected to one of the reactant stream passages at a location upstream of the humidifier, and an outlet end connected to the same reactant stream passage at a location downstream of the humidifier.  
     
     
         44 . The electric power generation system of  claim 42  wherein the bypass conduit comprises an inlet end connectable to a reactant supply, and an outlet end connected to one of the reactant stream inlet passages at a location downstream of the humidifier.  
     
     
         45 . The electric power generation system of  claim 42  wherein the humidifier bypass system comprises a bypass inlet valve connected to one of the reactant passages at a location upstream of the humidifier, and a bypass outlet valve connected to the same reactant passage at a location downstream of the humidifier, and wherein the bypass conduit is connected to the bypass inlet and outlet valves.  
     
     
         46 . The electric power generation system of  claim 39  wherein the oxidant stoichiometry control apparatus comprises a compressor connected to the oxidant inlet passage.  
     
     
         47 . The electric power generation system of  claim 39  wherein the pressure control apparatus comprises a pressure regulator on at least one of an oxidant and fuel passage.  
     
     
         48 . The electric power generation system of  claim 39  wherein the stack temperature control apparatus comprises a coolant system having a coolant passage through the stack and a coolant pump communicative with the control system.  
     
     
         49 . The electric power generation system of  claim 35  wherein the control system is operable such that the drying operation is discontinued after the parameter indicative of stack performance measured by the sensor assembly reaches a threshold value.