Molten carbonate fuel cells (MCFCs) are operated to provide enhanced CO.sub.2 utilization. This can increase the effective amount of carbonate ion transport that is achieved. The enhanced CO.sub.2 utilization is enabled in part by operating an MCFC under conditions that cause transport of alternative ions across the electrolyte. The amount of alternative ion transport that occurs during enhanced CO.sub.2 utilization can be mitigated by using a more acidic electrolyte.

Systems and methods are provided for using fuel cell staging to reduce or minimize variations in current density when operating molten carbonate fuel cells with elevated CO.sub.2 utilization. The fuel cell staging can mitigate the amount of alternative ion transport that occurs when operating molten carbonate fuel cells under conditions for elevated CO.sub.2 utilization.

Fuel cell systems configured for efficient byproduct recovery and reuse are disclosed herein. In one embodiment, a fuel cell system includes a reformer configured to reform a fuel containing methane (CH.sub.4) with steam to produce a reformed fuel having methane (CH.sub.4), carbon monoxide (CO), and hydrogen (H.sub.2). The fuel cell system also includes a fuel cell configured to perform an electrochemical reaction between a first portion of the reformed fuel and oxygen (O.sub.2) to produce electricity and an exhaust having carbon dioxide (CO.sub.2), water (H.sub.2O), and a second portion of the reformed fuel. The fuel cell system further includes an oxygen enricher configured to generate an oxygen enriched gas and a combustion chamber configured to combust the second portion of the reformed fuel with the oxygen enriched gas.

A hydrogen supply control system for a fuel cell is provided. The system includes a fuel cell stack that generates electricity using supplied hydrogen and air and a recirculation line that supplies hydrogen discharged from an outlet of the fuel cell stack back to an inlet of the fuel cell stack. A purge valve is disposed at an outlet side of the fuel cell stack of the recirculation line and discharges hydrogen in the recirculation line to the outside as the outlet is opened. A recirculation determining processor determines a recirculation state of the recirculation line and a concentration estimator estimates a purge amount for each gas, which is purged by the purge valve, based on the determined recirculation state and estimates a concentration of hydrogen in the recirculation line based on the estimated purge amount for each gas.

A fuel cell system and a control method thereof are provided. In the system, an oxygen sensor is mounted on the anode inlet side and the anode outlet side of a fuel cell stack to measure an oxygen concentration. Based on the measured oxygen concentration, a control operation is performed on the fuel cell system to reduce the oxygen concentration on the anode side. Accordingly, the irreversible deterioration of the fuel cell occurring due to the reverse voltage of the cell during driving of the fuel cell vehicle and the cathode carbon corrosion occurring due to the inflow of air during parking are effectively reduced, thereby increasing the durability of the fuel cell and the fuel cell vehicle.

The present disclosure is directed to a fuel cell system for generating oxygen depleted air. The fuel cell system may include a fuel cell having an anode, a cathode, and an electrolyte positioned between the anode and the cathode. The cathode may be configured to receive an air flow and discharge an oxygen depleted air flow. The fuel cell system may further include a sensor configured to generate a first signal indicative of a presence of hydrogen in the oxygen depleted air flow and a controller in communication with the sensor and the fuel cell. The controller may be configured to detect the presence of hydrogen in the oxygen depleted air flow based on the first signal, and in response to detecting the presence of hydrogen in the oxygen depleted air flow, selectively cause a current density of the fuel cell to decrease and/or increase a flow rate of the air flow to the cathode.

Molten carbonate fuel cells (MCFCs) are operated to provide enhanced CO.sub.2 utilization. This can increase the effective amount of carbonate ion transport that is achieved. The enhanced CO.sub.2 utilization is enabled in part by operating an MCFC under conditions that cause transport of alternative ions across the electrolyte. The amount of alternative ion transport that occurs during enhanced CO.sub.2 utilization can be mitigated by using a more acidic electrolyte.

A fuel cell system includes a fuel cell stack having a plurality of fuel cells that each contain a plurality of fuel electrodes and air electrodes. The system includes a fuel receiving unit connected to the fuel cell stack, which receives a hydrocarbon fuel from a fuel supply. The system includes a fuel exhaust processing unit fluidly coupled to the fuel cell stack by a slip stream, where the fuel exhaust processing unit processes fuel exhaust from the fuel cell stack, and the slip stream is fluidly connected to an exhaust stream flowing from the fuel cell stack. The fuel processing unit removes a first portion of carbon dioxide (CO.sub.2) from fuel exhaust within the slip stream, outputs the first portion of CO.sub.2 in a first stream, and outputs a second portion of CO.sub.2 remaining from the fuel exhaust in the slip stream into a second stream, which includes hydrogen.

A fuel cell system that has a fuel cell stack is provided. The system includes an electrolyte membrane, and a cathode and an anode that are a pair of electrodes disposed on opposite sides of the electrolyte membrane. A controller applies voltages to the cathode and the anode of the fuel cell stack before hydrogen that operates the fuel cell stack is supplied to the anode. When the voltages are applied to the cathode and the anode, hydrogen that resides in the cathode flows to the anode through the electrolyte membrane to decrease the concentration of the hydrogen in the cathode. The fuel cell system reduces the concentration of hydrogen discharged to the outside of the vehicle by reducing the concentration of hydrogen in the cathode before driving of the fuel cell is initiated.

The present disclosure generally relates to monitoring and controlling emissions produced by a fuel cell or fuel cell stack in a fuel cell engine of a vehicle and/or powertrain.