Abstract: A method and an apparatus to adapt the performance of a cathode humidification unit as a membrane in a fuel cell stack degrades over time. An algorithm compares a sensed humidity profile of the fuel cell stack and model humidity profile of a cathode humidification unit model to calculate a new degradation factor. The cathode humidification unit model uses the degradation factor in the performance of the cathode humidification unit.

Abstract: A system and method for limiting voltage cycling of a fuel cell stack during a stand-by mode by providing power from a battery to the stack while the stack is turned off. The method includes monitoring the voltage of each of the fuel cells in the fuel cell stack and determining an average cell voltage of the fuel cells in the fuel cell stack. The method also determines whether the average cell voltage of the fuel cells in the fuel cell stack has fallen below a predetermined voltage value and, if so, applies a voltage potential to the fuel cell stack to increase the average cell voltage above the predetermined voltage value.

Abstract: A method for reconditioning a fuel cell stack. The method includes periodically increasing the relative humidity level of the cathode input airflow to the stack to saturate the cell membrane electrode assemblies to be greater than the relative humidity levels during normal stack operating conditions. The method also includes providing hydrogen to the anode side of the fuel cell stack at system shut down while the membrane electrode assemblies are saturated without stack loads being applied so that the hydrogen crosses the cell membranes to the cathode side and reacts with oxygen to reduce stack contaminants.

Abstract: A system and method for reconditioning a fuel cell stack to recover stack voltage loss. The method includes first operating the fuel cell stack in a wet condition where the humidity level in the stack is above 100% to provide liquid water at the cell electrodes. The method then applies a low voltage potential to the stack that causes contaminants to be released from the catalyst surface of the cell electrodes. This step can include starving the cathode side of oxygen for a limited period of time. The method then causes water to flow through the stack so that the contaminants are flushed out of the stack. The process can be performed during vehicle operation where small amounts of voltage would be recovered or during vehicle service where a relatively large amount of voltage could be recovered.

Abstract: The present disclosure relates to systems and methods that may be used to predict a performance metric of a fuel cell. A system consistent with the present disclosure may include sensors in communication with the fuel cell stack, a performance metric prediction system, and a control system. The performance metric prediction system may determine a current density based on inputs provided by the sensors at a plurality of time periods, calculate a first parameter while the current density is below a lower threshold, and calculate a second parameter while the current density is above an upper threshold. The first parameter and the second parameter may be used to selectively adjust a fuel cell polarization curve over time. Based upon the polarization curve, a performance metric of the fuel cell stack may be predicted. The control system may implement a control action based upon the performance metric.

Abstract: The present disclosure relates to systems and methods that may be used to predict a performance metric of a fuel cell. A system consistent with the present disclosure may include sensors in communication with the fuel cell stack, a performance metric prediction system, and a control system. The performance metric prediction system may determine a current density based on inputs provided by the sensors at a plurality of time periods, calculate a first parameter while the current density is below a lower threshold, and calculate a second parameter while the current density is above an upper threshold. The first parameter and the second parameter may be used to selectively adjust a fuel cell polarization curve over time. Based upon the polarization curve, a performance metric of the fuel cell stack may be predicted. The control system may implement a control action based upon the performance metric.

Abstract: A method and an apparatus to adapt the performance of a cathode humidification unit as a membrane in a fuel cell stack degrades over time. An algorithm compares a sensed humidity profile of the fuel cell stack and model humidity profile of a cathode humidification unit model to calculate a new degradation factor. The cathode humidification unit model uses the degradation factor in the performance of the cathode humidification unit.

Abstract: A system and method for recovering fuel cell stack voltage loss through humidification control. The method includes determining a rate of contamination addition to a surface of a fuel cell electrode in the fuel cell stack and determining a rate of contamination removal from the surface of the fuel cell electrode. The method compares the rate of contamination addition to the rate of the contamination removal to determine whether contaminant surface coverage of the electrode is increasing or decreasing and, if increasing, determines whether the amount of contamination of the electrode is above a predetermined value, where, if so, stack reconditioning through wet stack operation may be performed.

Abstract: A system and method for reconditioning a fuel cell stack to recover stack voltage loss. The method includes first operating the fuel cell stack in a wet condition where the humidity level in the stack is above 100% to provide liquid water at the cell electrodes. The method then applies a low voltage potential to the stack that causes contaminants to be released from the catalyst surface of the cell electrodes. This step can include starving the cathode side of oxygen for a limited period of time. The method then causes water to flow through the stack so that the contaminants are flushed out of the stack. The process can be performed during vehicle operation where small amounts of voltage would be recovered or during vehicle service where a relatively large amount of voltage could be recovered.

Abstract: A system and method for limiting voltage cycling of a fuel cell stack during a stand-by mode by providing power from a battery to the stack while the stack is turned off. The method includes monitoring the voltage of each of the fuel cells in the fuel cell stack and determining an average cell voltage of the fuel cells in the fuel cell stack. The method also determines whether the average cell voltage of the fuel cells in the fuel cell stack has fallen below a predetermined voltage value and, if so, applies a voltage potential to the fuel cell stack to increase the average cell voltage above the predetermined voltage value.

Abstract: A method for reducing the probability of an air/hydrogen front in a fuel cell stack is disclosed that includes closing anode valves for an anode side of the fuel cell stack to permit a desired quantity of hydrogen to be left in the anode side upon shutdown and determining a schedule to inject hydrogen during the time the fuel cell stack is shutdown. The pressure on an anode input line is determined and a discrete amount of hydrogen is injected into the anode side of the stack according to the determined schedule by opening anode input line valves based on the determined pressure along the anode input line so as to inject the hydrogen into the anode side of the stack.

Abstract: A method for reducing the probability of an air/hydrogen front in a fuel cell stack is disclosed that includes closing anode valves for an anode side of the fuel cell stack to permit a desired quantity of hydrogen to be left in the anode side upon shutdown and determining a schedule to inject hydrogen during the time the fuel cell stack is shutdown. The pressure on an anode input line is determined and a discrete amount of hydrogen is injected into the anode side of the stack according to the determined schedule by opening anode input line valves based on the determined pressure along the anode input line so as to inject the hydrogen into the anode side of the stack.

Abstract: A method for reconditioning a fuel cell stack. The method includes periodically increasing the relative humidity level of the cathode input airflow to the stack to saturate the cell membrane electrode assemblies to be greater than the relative humidity levels during normal stack operating conditions. The method also includes providing hydrogen to the anode side of the fuel cell stack at system shut down while the membrane electrode assemblies are saturated without stack loads being applied so that the hydrogen crosses the cell membranes to the cathode side and reacts with oxygen to reduce stack contaminants.

Abstract: A method for reconditioning a fuel cell stack. The method includes determining whether fuel cell stack reconditioning is desired based on predetermined reconditioning triggers, determining if predetermined system constraints are met that will allow reconditioning of the fuel cell stack to occur, and determining whether previous reconditioning processes have been attempted, and if so, whether predetermine reconditioning limits have been exceeded during those attempts. The reconditioning process is initiated if one or more of the reconditioning triggers has occurred, the predetermined system constraints are met and the predetermined reconditioning limits have not been exceeded. The reconditioning process increases the humidification level of a cathode side of the fuel cell stack over the humidity level of the cathode side during normal operating conditions and waiting for cell membranes in the fuel cell stack to saturate after the humidification level of the cathode has increased.