A novel solid oxide redox flow battery for grid energy storage

Abstract

In this work we report proof-of-concept of a novel redox flow battery consisting of a solid oxide electrochemical cell (SOEC) integrated with a redox-cycle unit. The charge/discharge characteristics were explicitly observed by operating between fuel cell and electrolysis modes of the SOEC along with ''in-battery'' generation and storage of H 2 realized by an in situ closed-loop reversible steam-metal reaction in the redox-cycle unit. With Fe/FeO as the redox materials, the new storage battery can produce an energy capacity of 348 Wh/kg-Fe and round-trip efficiency of 91.5% over twenty stable charge/discharge cycles. This excellent performance combined with robustness, environmental friendliness and sustainability promise the new battery to be a transformational energy storage device for grid application.Electrical energy storage plays a critical role in grid optimization of bulk power production, system balancing of variable or diurnal renewable resources, and auxiliary power services. It is the key enabler for future smart grid. Without, or with little, energy storage capability, the power grid system must rely upon redundant generation and transmission assets to meet the reliability requirements, causing significant underuse of available grid infrastructures and therefore poor system efficiency; 1-3 an unpredictable, intermittent renewable energy input from sources such as solar and wind can easily destabilize an electricity grid with varying demand, particularly with the much more dynamic utility demand of the future. [4][5][6][7][8] Electrical energy storage is, in principle, a reversible energy conversion process that transforms electricity into other forms of energy (e.g., kinetic, potential and chemical). Its ability to store electricity for later use makes it an ideal buffer for balancing demand and supply of electrical energy. The principal requirements for a gridscale energy storage system include fast response time, high rate capacity, high round-trip efficiency, long cycle life, low life-cycle cost, and scalability. Of all the types of energy storage devices, redox flow battery (RFB) and Na-S/ZEBRA battery (NSB) technologies stand out with a potential to meet all of these requirements. [9][10][11] The more commonly known rechargeable batteries such as Li-ion are yet considered suitable for large-scale energy storage, primarily due to the concerns of safety and low rate-capacity. 12 The advantage of RFB to be flexible in system design for either power (e.g., short-term frequency regulation) or energy application (e.g., long-term load shifting) is a valuable asset for renewable integration. The high energy/power densities and capability to perform fast and deep charge/discharge cycles has positioned the NSB as a front runner in the commercial development of large-scale energy storage devices.

Energy Storage in Electrochemical Cells with Molten Sb Electrodes

“…In another variation, H 2 produced in the electrolyzer is used to reduce FeO to Fe. 13 By passing steam over the Fe, H 2 can be generated again for use in the fuel cell.…”

“…Several variations on the idea of reversible fuels cells have been proposed to reduce this storage problem. Because H 2 O and CO 2 can be electrolyzed with equal efficiency in solid oxide fuel cells (SOFC), [8][9][10][11][12][13][14] Zhan, et al 14 has suggested electrolyzing mixtures of H 2 O and CO 2 to produce syngas, which could in turn be converted to methane, greatly reducing the volume of gas that needs to be stored. In another variation, H 2 produced in the electrolyzer is used to reduce FeO to Fe.…”

A high energy density all solid-state tungsten–air battery

“…7,[9][10][11] Recently, we demonstrated a novel concept of the ''all solid-state metal-air battery'' that innovatively combines a regenerative solid oxide fuel cell (or RSOFC) and a chemical-looping redox cycle unit (RCU). 12,13 The air-electrode reactions in this battery involve only reduction and evolution of gaseous O 2 , making clogging of the airpathway no longer an issue. In addition, solid oxide-ion electrolytes are known to be stable in a broad range of gas mixtures and in contact with a variety of oxides.…”

“…The distinct advantages of this innovative battery design over conventional metal-air batteries include double electron-transfer (O 2À ), state-of-charge independent EMF (electromotive force), high specific energy and energy density, and independent design of power and energy. 12,13 More appealingly, the new battery stores chemical energy in redox couples that are physically separated from electrodes of RSOFC as illustrated in Fig. 1, avoiding the shape change problem of conventional chemical batteries.…”

Potential of Reversible Solid Oxide Cells as Electricity Storage System

“…Another important challenge to face is the cell performance degradation. In fact, the cell has to work in both oxidizing and reducing environments, and it is important to develop electrode materials, which are stable in both those operating conditions [37][38][39].…”