A method is provided for restoring an electrolyte of vanadium (V) redox flow battery (VRFB). Electrolyte data of an original system are analyzed in advance. A reusable positive electrode is further equipped with a V electrolyte. A reductant for a stack of VRFB is used in coordination as an electrolysis device. After a long-term reaction with a VRFB having a high valence (greater than 3.5), an electrolyte at the positive electrode is directed out to a negative electrode of the electrolysis device; and, then, electrolysis is processed after accurate calculation. In the end, the internal fluid balancing method of the original system is combined. Thus, a harmless and quick valence restoration is processed for the electrolyte of the original system, which is a final resort for the restoration of V electrolyte.

Methods and systems are provided for a rebalancing reactor of a flow battery system. In one example, a pH of a battery electrolyte may be maintained by the rebalancing reactor by applying a negative potential to a catalyst bed of the rebalancing reactor. A performance of the rebalancing reactor may further be maintained by treating the catalyst bed with deionized water.

A redox flow battery system includes an anolyte having chromium ions in solution; a catholyte having iron ions in solution, where a molar ratio of chromium in the anolyte to iron in the catholyte is at least 1.25; a first electrode in contact with the anolyte; a second electrode in contact with the catholyte; and a separator separating the anolyte from the catholyte.

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.

Embodiments of the invention relate to an open metal-air fuel cell system capable of uninterrupted supply power, which relates to the field of metal-air fuel cell stacks and comprises a sensing subsystem, a controller, a circulating filtration subsystem, an electrolyte solution tank and several open metal-air fuel cell units. Open metal-air fuel cell units are sequentially arranged within the electrolyte solution tank, and each open metal-air fuel cell unit is connected with each other in parallel. An air electrode of the open metal-air fuel cell unit has a tank structure, and the trough structure has a concave surface upwards. The sensing subsystem is arranged within the electrolyte tank. The electrolyte solution tank is connected with a circulating filtration subsystem. The controller is used for controlling a circulating flow of the circulating filtration subsystem depending on electrolyte solution temperature information collected by the sensing subsystem.

A redox flow battery includes a tank configured to store an electrolyte and a distribution mechanism to distribute the electrolyte to a battery cell. The tank has a partition portion partitioning a space inside the tank into a first space and a second space, the distribution mechanism has a distribution passage through which the electrolyte is distributed between the first space and the second space via the battery cell, and the partition portion is composed of a flexible material.

Methods and systems are provided for a rebalancing reactor of a flow battery system. In one example, a pH of a battery electrolyte may be maintained by the rebalancing reactor by applying a negative potential to a catalyst bed of the rebalancing reactor. A performance of the rebalancing reactor may further be maintained by treating the catalyst bed with deionized water.

Methods and systems are provided for a rebalancing reactor of a flow battery system. In one example, a pH of a battery electrolyte may be maintained by the rebalancing reactor by applying a negative potential to a catalyst bed of the rebalancing reactor. A performance of the rebalancing reactor may further be maintained by treating the catalyst bed with deionized water.

A method for determining a storage capacity or average oxidation state (AOS) of a redox flow battery system including an anolyte and a catholyte includes discharging a portion of the anolyte and catholyte of the redox flow battery system at a discharge rate that is within 10% of a preselected discharge rate; after discharging the redox flow battery system, determining an end OCV; and determining the storage capacity or AOS from the end OCV. Other methods can be used to determine the storage capacity or AOS using a measured OCV.

A redox flow battery system includes an anolyte having a first ionic species in solution; a catholyte having a second ionic species in solution, where the redox flow battery system is configured to reduce the first ionic species in the anolyte and oxidize the second ionic species in the catholyte during charging; a first electrode in contact with the anolyte, where the first electrode includes channels for collection of particles of reduced metallic impurities in the anolyte; a second electrode in contact with the catholyte; and a separator separating the anolyte from the catholyte. A method of reducing metallic impurities in an anolyte of a redox flow battery system includes reducing the metallic impurities in the anolyte; collecting particles of the reduced metallic impurities; and removing the collected particles using a cleaning solution.