A redox flow battery with an electrochemical balancing cell having first and second chambers. The first chamber includes a catalyst coated substrate and the second chamber includes an electrode. Each receives an electrolyte from the redox flow battery. There is a single interface between the two chambers. The balancing cell reverses parasitic reactions in the first chamber that occur in the redox flow battery. The products of the reversed reactions are carried away from the electrochemical balancing cell and back to the redox flow battery in the electrolyte that carried the reactant to the first chamber. Also, processes for reversing a parasitic reaction in a redox flow battery.

Provided is a fuel cell system capable of further increasing electric power generation efficiency, compared to the current circumstances, with respect to a fuel cell SOFC that generates electric power by supplying a reformed gas obtained by steam reforming to a fuel electrode. A steam reformer that reforms a hydrocarbon fuel by a steam reforming reaction; a fuel cell that operates by introducing a reformed gas to a fuel electrode; and an anode off-gas circulation path that removes condensed water while cooling an anode off-gas, and introduces the anode off-gas to the steam reformer are provided. A condensation temperature in a condensing device is controlled by a control unit that controls a steam partial pressure of the anode off-gas circulated to the steam reformer, and S/C adjustment is adapted to high-efficiency electric power generation.

A flow battery has an electrochemical stack, a positive electrolyte, a negative electrolyte, a positive electrolyte tank, and a negative electrolyte tank. The positive electrolyte and the negative electrolyte are respectively stored in the positive and negative tanks. A positive electrolyte pump, a negative electrolyte pump, a mixing pump is embedded in the bypass pipeline or in a dedicate circuit. The positive and the negative tanks, are mutually connected by means of a connection pipe, said connection pipe is embedded just immediately above the electrolyte levels.

Devices powered by fuel cells can be operated for extended durations when the fuel cells are adapted to extract the necessary reactants for generating power from the surrounding environment and when the concentration of reactants in that environment is maintained at a sufficient level by interaction between the environment and a reactant-enriched atmosphere.

A reforming element for a molten carbonate fuel cell stack and corresponding methods are provided that can reduce or minimize temperature differences within the fuel cell stack when operating the fuel cell stack with enhanced CO.sub.2 utilization. The reforming element can include at least one surface with a reforming catalyst deposited on the surface. A difference between the minimum and maximum reforming catalyst density and/or activity on a first portion of the at least one surface can be 20% to 75%, with the highest catalyst densities and/or activities being in proximity to the side of the fuel cell stack corresponding to at least one of the anode inlet and the cathode inlet.

A fuel supply control system and method for a fuel cell are disclosed. The system includes: a fuel cell configured to receive a fuel gas and an oxidation gas and generate electric power; a recirculation line configured to circulate gas containing the fuel gas and connected to a fuel electrode of the fuel cell; a discharge valve provided in the recirculation line and configured to allow the gas to be discharged to the outside when open; a discharge amount estimator configured to estimate a discharge amount of the discharged gas based on a supply amount of the fuel gas supplied to the recirculation line, a consumption amount of the fuel gas consumed in the fuel cell, and a change in the amount of the gas in the recirculation line; an offset calculator configured to calculate the discharge amount of the gas estimated by the discharge amount estimator with the discharge valve closed, as a discharge offset; and a controller configured to control opening/closing of the discharge valve.

A system for estimating the amount of purge of a fuel cell is provided. The system includes a fuel cell that generates power by receiving hydrogen at an anode side and receives oxygen at a cathode side. A recirculation line is connected with the anode side of the fuel cell, and the gas included hydrogen therein is circulated in the recirculation line. A flow amount estimator estimates the flow amount of gas inside the recirculation line. A purge valve is positioned in the recirculation line and discharges the gas in the recirculation line to the outside when opened. A purge amount estimator estimates the amount of purge for each gas discharged through the purge valve by reflecting the flow amount of the gas estimated by the flow amount estimator.

A fuel cell system and a control method thereof reduce a hydrogen exhaust amount and perform precise control in a low output section through the control of an air recirculation line and an air recirculation valve that recirculate the air discharged from the cathode of a fuel cell stack to the cathode.

An air supply system for a fuel cell includes: a fuel cell stack in which multiple unit cells are stacked and that generates electricity through chemical reactions, an air channel to supply incoming air containing oxygen to the fuel cell stack and to transfer air discharged from the fuel cell stack to the outside of the air supply system, and a gas adsorption unit that is disposed on the air channel, positioned near an outlet of the fuel cell stack, and adsorbs oxygen contained in the air introduced into the air channel.

A fuel cell system for air vehicles, wherein the fuel cell system comprises: a fuel cell, a fuel gas system for supplying fuel gas to the fuel cell, a potential sensor, and a controller; wherein the fuel gas system comprises a fuel gas supplier; wherein the controller determines whether or not a potential of the fuel cell measured by the potential sensor, is a reversal potential; and wherein, when the controller determines that the potential of the fuel cell is a reversal potential, the controller increases a fuel gas supply from the fuel gas supplier to the fuel cell.