Breakthrough oxygen electrode reaction kinetics using BaCe0.7Zr0.1Y0.1Yb0.1O3−δ based composite air electrodes for reversible solid oxide cells

For nearly half a century, composite air electrode architectures based on an oxygen-ion conducting Gd _0.1 Ce _0.9 O _2–δ (GDC) electrolyte phase and a catalytically-active, electronically conductive second phase have dominated solid-oxide electrochemical cell (SOC) design. This strategy maximizes three-phase boundary density and reduces electrode/electrolyte interfacial resistance, leading to exceptionally durable, high-performance devices. While this approach has been highly effective, performance improvements have recently plateaued. Here, we demonstrate a new strategy for SOC air electrode design by deploying mixed proton, oxygen ion, and hole-conducting BaCe _{1- x} Zr _x O ₃ (BCZ)-based materials ( e.g. , BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3−δ , BCZYYb7111 ) in place of GDC in composite electrode architectures. This approach revolutionizes SOC design by optimally balancing the electronic and ionic conductivity of the air electrode, altering the reaction pathway—leading to a lower-barrier rate-determining-step, and expanding the electrochemically active region from isolated three-phase boundary zones to the entire electrode surface area catalyst. In an optimal configuration, where the highly-active misfit-layered Gd _0.3 Ca _2.7 Co _3.82 Cu _0.18 O _9-δ (GCCCO) bifunctional oxygen catalyst is composited with BCZYYb7111, we attain fuel cell mode performance of 7.08 W‧cm ⁻² and electrolysis mode performance of –7.88 A‧cm ⁻² at 1.3 V in an otherwise conventional yttria-stabilized zirconia (YSZ)-based reversible SOC at 800℃. Even at a reduced temperature of 650℃, performance reaches 2.65 W‧cm ⁻² in fuel cell mode and –1.86 A‧cm ⁻² at 1.3 V in electrolysis mode. These remarkable results are attributed to significantly enhanced electrochemical charge transfer, highly efficient oxygen surface exchange, modified reaction pathways, and enhanced separation of oxygen ions and holes via a large built-in diffusive electric double layer at the interface of GCCCO-BCZYYb7111 composite electrode. We use the same oxygen catalyst+BCZYYb711 composting strategy to significantly enhance the performance of other popular oxygen electrocatalysts by 38-129%, including La _0.6 Sr _0.4 CoO _3-δ (LSC), La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3-δ (LSCF), PrBa _0.5 Sr _0.5 Co _1.5 Fe _0.5 O _5+δ (PBSCF), and La _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-δ (BSCF), thereby establishing this approach as a widely-applicable new air-electrode design paradigm for RSOCs.