Ceramic based functional electrode materials for application in solid oxide cell-based electrochemical devices

In the context of the hydrogen conversion and generation, solid oxide cell (SOC)-based technology is quite promising which can function in the reversible way, viz. solid oxide fuel cell (SOFC) to produce power by oxidation of fuel (hydrogen/NG/STP biogas, etc.) and solid oxide electrolyzer cell (SOEC) to generate hydrogen by splitting of water at high temperature. Nanocrystalline La/Ba_1−xSr_xCo_yFe_1−yO₃(LSCF or BSCF)-based air electrode materials for SOC have been synthesized by solution combustion method. Such air electrodes having extended triple-phase boundary facilitate the bulk oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) for application in SOFC and SOEC, respectively. The functionality of the air electrode is further reported in the context of the morphologically engineered conventional air electrode. As a characteristic SOFC performance, 1.2 A cm−2 current density @ 700°C at 0.5 V potential for a cell configuration of Ni-YSZ/YSZ/CGO/CGO-LSCF/LSCF is reported where no secondary insulating phases are obtained at the interfaces where H₂ is used as the fuel and O₂ as the oxidant. For such MIEC air electrode systems, current densities of 0.71 and 1.4 A cm⁻² are observed at @ 800°C and 1.3 V in SOEC mode with 0.58 NL cm⁻² h⁻¹ and 0.30 NL cm⁻² h⁻¹ rate of hydrogen generation, respectively. A maximum of 0.57 NL cm⁻² h⁻¹ hydrogen flux is obtained at an operating temperature of 800°C which is equivalent to ∼1 N m³ h⁻¹ kW⁻¹ stack with footprint area of 80 cm². Irrespective of operating temperature, BSCF exhibits higher hydrogen flux and may be correlated to the intrinsically higher charge transfer reaction for OER. The authors also intend to fabricate SOC with functional Ni/Cu@YSZ anode with unique core-shell structure. Efficacy of such anode is studied toward the oxidation of fuels with a current density @2.5 and @1.13 A cm⁻² (with hydrogen and methane), respectively. Finally, for optimizing the air electrode formulation, the authors used “ab initio” first principle to determine the density of states and are analyzed in terms of linear combination of atomic orbital (LACO) theory. Detailed discussion of material aspect of electrodes for SOC, synthesis, functionalization, and application is also discussed in detail along with the breaches which can be undertaken for future research in this arena.