Methods for improving the cold starting capability of an electrochemical fuel cell

Abstract

Temperature dependent methods can be used to improve the cold start capability of fuel cell electric power generation systems. A method of ceasing operation of an electric power generation system improves the cold start capability and freeze tolerance of a fuel cell stack by reducing the amount of water remaining within the passages of the stack. The method involves purging one or more of the fuel cell stack oxidant and fuel passages at shutdown prior to allowing the fuel cell stack to drop to temperatures below the freezing point of water. Preferably purging at shutdown is conducted at a temperature below the stack operating temperature. Another method, used at start-up, involves directing a coolant fluid stream to the fuel cell stack only after a predetermined temperature above the freezing temperature of water is exceeded. Preferably, after freezing the fuel cell stack is heated to a temperature above its normal operating temperature before operation is commenced.

What is claimed is:  
     
         1 . A method of commencing operation of an electric power generation system comprising a fuel cell stack connectable to an external electrical circuit for supplying electric current to said external circuit, said stack comprising at least one fuel cell, said at least one fuel cell comprising a membrane electrode assembly comprising an anode, a cathode, and an ion exchange membrane interposed between said anode and said cathode, said system further comprising a fuel stream and an oxidant stream, each of said streams being flowable to said fuel cell stack, said method comprising: 
 supplying electric current from said fuel cell stack to said external circuit such that the temperature of said at least one fuel cell increases to a temperature above the normal operating temperature range of said stack; and    reducing the operating temperature of said stack to within said normal operating temperature range.    
     
     
         2 . The method of  claim 1  wherein said temperature above said normal operating temperature range of said stack is at least 10° C. above said normal operating temperature range.  
     
     
         3 . The method of  claim 1  wherein said temperature above said normal operating temperature range of said stack is in the range of 95° C. to 105° C.  
     
     
         4 . The method of  claim 1  wherein the temperature above said normal operating temperature range of said stack is adjusted in accordance with at least one monitored operating parameter of said system.  
     
     
         5 . The method of  claim 1  wherein said stack is operated at said temperature above said normal operating temperature range of said stack for a predetermined duration.  
     
     
         6 . The method of  claim 5  wherein said stack is operated at said temperature above said normal operating temperature range of said stack for a duration of about 1-2 minutes.  
     
     
         7 . The method of  claim 1  wherein the duration for which said stack is operated at said temperature above said normal operating temperature range of said stack is adjusted in accordance with at least one monitored operating parameter of said system.  
     
     
         8 . The method of  claim 1  wherein said system further comprises a coolant fluid stream flowable in thermal contact with said fuel cell stack, and said method comprises: 
 commencing flow of coolant fluid stream in thermal contact with said fuel cell stack only after the operating temperature of said stack exceeds said normal operating temperature range of said stack.  
 
     
     
         9 . The method of  claim 8  wherein said coolant flow is continued at least until the operating temperature of said stack is reduced to within said normal operating temperature range.  
     
     
         10 . A method of commencing operation of an electric power generation system comprising a fuel cell stack connectable to an external electrical circuit for supplying electric current to said external circuit, said stack comprising at least one fuel cell, said at least one fuel cell comprising a membrane electrode assembly comprising an anode, a cathode, and an ion exchange membrane interposed between said anode and said cathode, said system further comprising a fuel stream and an oxidant stream, each of said streams being flowable to said fuel cell stack, said method comprising: 
 increasing the temperature of said at least one fuel cell to a temperature above the normal operating temperature range of said stack prior to supplying electric current from said fuel cell stack to said external circuit.    
     
     
         11 . The method of  claim 10  further comprising reducing the operating temperature of said stack to within said normal operating temperature range.  
     
     
         12 . The method of  claim 11  wherein said operating temperature of said stack is reduced to within said normal operating temperature range prior to supplying electric current from said fuel cell stack to said external circuit.