Abstract: A fuel cell stack system having multiple sub-stacks that are replaceable online is disclosed. In one aspect of the present disclosure, the fuel cell stack system includes multiple fuel cell sub-stacks electrically coupled to one another, the multiple fuel cell sub-stacks include multiple fuel cells electrically coupled to one another enclosed in a sub-stack vessel. Each of the multiple fuel cells can include a composite cathode element and an anode chamber coupled to the composite cathode element. In one embodiment, each of the multiple fuel cell sub-stacks is replaceable online.

Abstract: Reaction mechanisms in a fuel cell device are disclosed. In one aspect of the present disclosure, the fuel cell includes a composite cathode element that is vertically oriented. The composite cathode element further comprises a porous matrix holding electrolyte, a cathode, and/or a cathode current collector. One embodiment of the fuel cell further includes, an anode chamber coupled to the composite cathode element, the anode chamber being vertically oriented. During operation, fuel injected into the fuel cell is oxidized in the anode chamber by oxidizer ions are generated from oxidizer gas. The oxidizer gas can include a mixture of oxygen and carbon dioxide or just oxygen.

Abstract: A fuel cell stack system having multiple sub-stacks that are replaceable online is disclosed. In one aspect of the present disclosure, the fuel cell stack system includes multiple fuel cell sub-stacks electrically coupled to one another, the multiple fuel cell sub-stacks include multiple fuel cells electrically coupled to one another enclosed in a sub-stack vessel. Each of the multiple fuel cells can include a composite cathode element and an anode chamber coupled to the composite cathode element. In one embodiment, each of the multiple fuel cell sub-stacks is replaceable online.

Abstract: Fuel cells having cathode elements that are oriented such that dispersion of injected fuel through the fuel cell is caused at least in part by buoyancy force are disclosed. In one aspect of the present disclosure, the fuel cell includes a composite cathode element that is oriented such that dispersion of injected fuel through the fuel cell is caused at least in part by buoyancy force. For example, the composite cathode element and may be vertically oriented such that it is substantially parallel to the line of buoyancy. The composite cathode element further comprises, a porous matrix holding electrolyte, a cathode, and/or a cathode current collector. One embodiment of the fuel cell further includes, an anode chamber coupled to the composite cathode element. During operation, fuel injected into the fuel cell is oxidized in the anode chamber by oxidizer ions generated at the composite cathode element and transported to the anode chamber via the electrolyte in the porous matrix.