Recent Advances in Electrode Design for an All-Iron Redox Flow Battery

The energy production market must increase and decrease its output to match real time demand. This makes the process very inefficient and restricts the grid’s ability to rely upon intermittent renewable sources. Grid scale energy storage, such as a Redox Flow Battery (RFB) can alleviate these issues by storing energy when it is available and distributing energy as needed. One promising RFB chemistry is the all-Iron flow battery. Iron is low cost, domestically available, and the electrolytes can be used at mildly acidic pHs. The all-iron flow battery involves the iron (II/III) redox couple on the positive electrode and iron plating/stripping on the negative electrode. In conventional stationary electrodes (i.e. felts) the iron plates inside the active cell, meaning storage capacity is dictated by the plating density. Negative electrode design is therefore important for maximizing energy storage. Two approaches are investigated in maximizing plating density. The first approach utilizes the traditional hybrid flow battery configuration and focuses on manipulating the current distribution within the porous electrode to effectively utilize the active area. An optimal electrode design will provide a balance between minimizing polarization losses and maximizing the storage capacity. The second approach involves a nontraditional electrode design for the negative electrode: using a slurry electrode in order to decouple the power and energy capabilities of the all-iron battery. Slurry electrodes are made by mixing electrically conductive particles (on which the iron can plate) in the electrolyte containing the dissolved iron species. The slurry electrode is then pumped through the electrochemical cell. The design of this type of electrode requires fundamental information on the slurry’s electrical, electrochemical, and rheological properties, along with effective pumping and flow distribution strategies.