Long duration energy storage (LDES) is an economically attractive approach to accelerating clean renewable energy deployment. The newly emerged solid oxide iron-air battery (SOIAB) is intrinsically suited for LDES applications due to its excellent low-rate performance (high-capacity with high efficiency) and use of low-cost and sustainable materials. However, rechargeability and durability of SOIAB are critically limited by the slow kinetics in iron/iron-oxide redox couples. Here the use of combined proton-conducting BaZr 0.4 Ce 0.4 Y 0.1 Yb 0.1 O 3 (BZC4YYb) and reduction-promoting catalyst Ir to address the kinetic issues, is reported. It is shown that, benefiting from the facilitated H + diffusion and boosted FeO x -reduction kinetics, the battery operated under 550 °C, 50% Fe-utilization and 0.2 C, exhibits a discharge specific energy density of 601.9 Wh kg -1 -Fe with a round-trip efficiency (RTE) of 82.9% for 250 h of a cycle duration of 2.5 h. Under 500 °C, 50% Fe-utilization and 0.2 C, the same battery exhibits 520 Wh kg -1 -Fe discharge energy density with an RTE of 61.8% for 500 h. This level of energy storage performance promises that SOIAB is a strong candidate for LDES applications.

Long duration electricity storage (LDES) with 10+ hour cycle duration is an economically competitive option to accelerate the penetration of renewable energy into the utility market. Unfortunately, none of the available energy storage technologies can meet the LDES’ requirements for duration and cost. We here report a focused kinetic study on Fe-oxide reduction process, which is a key step for solid oxide iron-air battery; the latter has been recently demonstrated as a LDES compatible battery. The study clearly shows that Ir is an excellent catalyst to boost the sluggish Fe-oxide reduction kinetics.

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