# US 7,608,352 B2 · Method for shutting down a fuel cell system using an air purge > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,608,352 B2 - Document ID: US7608352B2 - Status: Granted - Kind: B2 - Application number: 11/836,557 - Filed: 2007-08-09 - Published: 2008-01-03 - Granted: 2009-10-27 - Earliest claimed: 2004-08-18 - Assignees: GM Global Technology Operations LLC - Inventors: Paul T. Yu; Frederick T. Wagner - Web page: https://patentgrep.com/patent/US7608352B2 ## CPC - H01M 8/04231: {Purging of the reactants} - Y02E 60/50: Fuel cells - H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract A method for delaying an air purge of a fuel cell stack at system shut-down until the temperature of the stack is reduced below a predetermined temperature. The fuel cell stack includes an anode side, a cathode side, an anode input, a cathode input and an anode exhaust. A temperature sensor monitors the temperature of a cooling fluid flowing through the stack. The anode side of the fuel cell stack is purged at the stack shut-down by directing air from the cathode input line to the anode input line after the temperature of the cooling fluid is reduced to the predetermined temperature. ## Claims ### Claim 1 A method for purging a fuel cell stack at stack shut-down, said fuel cell stack including an anode side, a cathode side, an anode input line, a cathode input line and an anode exhaust line, said method comprising: monitoring the temperature of a cooling fluid flowing through the fuel call stack; maintaining the temperature of the cooling fluid at an operating temperature during operation of the fuel cell stack; and purging the anode side of the fuel cell stack at the stack shut-down after the temperature of the cooling fluid is reduced to a predetermined temperature that is cooler than the operating temperature, wherein purging the anode side includes directing air from the cathode input line to the anode input line. ### Claim 2 (depends on 1) The method according to claim 1 wherein purging the anode side includes directing anode exhaust on the anode exhaust line to the environment. ### Claim 3 (depends on 1) The method according to claim 1 further comprising switching an output of the fuel cell stack from a primary load to an auxiliary load at the stack shut-down to eliminate remaining hydrogen in the fuel cell stack. ### Claim 4 (depends on 3) The method according to claim 3 further comprising operating a pump to pump the cooling fluid through the fuel cell stack with power from the auxiliary load at the stack shut-down. ### Claim 5 (depends on 3) The method according to claim 3 wherein the time it takes the auxiliary load to consume the remaining hydrogen is about the same as the time it takes the temperature of the cooling fluid to be reduced from the operating temperature to the predetermined temperature. ### Claim 6 (depends on 1) The method according to claim 1 further comprising disconnecting the fuel cell stack from an auxiliary load when the anode purge begins. ### Claim 7 (depends on 1) The method according to claim 1 wherein the predetermined temperature is about 50° C. or less. ### Claim 8 A method for purging a fuel cell stack at stack shut-down, said method comprising: monitoring the temperature of a cooling fluid flowing through the fuel cell stack; maintaining the temperature of the cooling fluid at an operating temperature during operation of the fuel cell stack; purging an anode side of the fuel cell stack at the stack shut-down using cathode input air after the temperature of the cooling fluid has dropped to a predetermined temperature that is less than the operating temperature; and opening an anode exhaust valve at the stack shut-down to vent the purge air from the anode side of the stack. ### Claim 9 (depends on 8) The method according to claim 8 further comprising switching an output of the fuel cell stack from a primary load to an auxiliary load at the stack shut-down to eliminate remaining hydrogen in the fuel cell stack. ### Claim 10 (depends on 9) The method according to claim 9 further comprising operating a pump to pump the cooling fluid through the fuel cell stack with power from the auxiliary load at the stack shut-down. ### Claim 11 (depends on 9) The method according to claim 9 wherein the time it takes the auxiliary load to consume the remaining hydrogen is about the same as the time it takes the temperature of the cooling fluid to drop from the operating temperature to the predetermined temperature. ### Claim 12 (depends on 8) The method according to claim 8 further comprising disconnecting the fuel cell stack from an auxiliary load when the anode purge begins. ### Claim 13 (depends on 8) The method according to claim 8 wherein the predetermined temperature is about 50° C. or less. ### Claim 14 A method for purging a fuel cell stack at stack shut-down, said method comprising: monitoring the temperature of a cooling fluid flowing through the fuel cell stack; maintaining the temperature of the cooling fluid at an operating temperature during operation of the fuel cell stack; purging an anode side of the fuel cell stack at the stack shut-down using cathode input air after the temperature of the cooling fluid has dropped to a predetermined temperature that is less than the operating temperature; and disconnecting the fuel cell stack from an auxiliary load when the anode side purge begins. ### Claim 15 (depends on 14) The method according to claim 14 further comprising switching an output of the fuel cell stack from a primary load to the auxiliary load at the stack shut-down to eliminate remaining hydrogen in the fuel cell stack. ### Claim 16 (depends on 15) The method according to claim 15 wherein the time it takes the auxiliary load to consume the remaining hydrogen is about the same as the time it takes the temperature of the cooling fluid to drop from the operating temperature to the predetermined temperature. ### Claim 17 (depends on 14) The method according to claim 14 further comprising operating a pump to pump the cooling fluid through the fuel cell stack with power from the auxiliary load at the stack shut-down. ### Claim 18 (depends on 14) The method according to claim 14 wherein the predetermined temperature is about 50° C. or less. ### Claim 19 A method for purging a fuel cell stack at stack shut-down, said fuel cell stack including an anode side, a cathode side, an anode input line, a cathode input line and an anode exhaust line, said method comprising: monitoring the temperature of a cooling fluid flowing through the fuel cell stack; maintaining the temperature of the cooling fluid at an operating temperature during operation of the fuel cell stack; purging the anode side of the fuel cell stack at the stack shut-down after the temperature of the cooling fluid is reduced to a predetermined temperature that is cooler than the operating temperature; switching an output of the fuel cell stack from a primary load to an auxiliary load at the stack shut-down to eliminate remaining hydrogen in the fuel cell stack; and operating a pump to pump the cooling fluid through the fuel cell stack with power from the auxiliary load at the stack shut-down. ### Claim 20 A method for purging a fuel cell stack at stack shut-down, said fuel cell stack including an anode side, a cathode side, an anode input line, a cathode input line and an anode exhaust line, said method comprising: monitoring the temperature of a cooling fluid flowing through the fuel cell stack; maintaining the temperature of the cooling fluid at an operating temperature during operation of the fuel cell stack; purging the anode side of the fuel cell stack at the stack shut-down after the temperature of the cooling fluid is reduced to a predetermined temperature that is cooler than the operating temperature; and switching an output of the fuel cell stack from a primary load to an auxiliary load at the stack shut-down to eliminate remaining hydrogen in the fuel cell stack, wherein the time it takes the auxiliary load to consume the remaining hydrogen is about the same as the time it takes the temperature of the cooling fluid to be reduced from the operating temperature to the predetermined temperature.