Triple perovskite, Nd _1.5 Ba _1.5 CoFeMnO _9−δ , enriched with oxygen defects shows high activity and durability as a bifunctional oxygen electrocatalyst.

Despite the recent substantial progress in reversible protonic ceramic cells (RPCCs) it remains essential to further develop oxygen electrode materials that show superior activity and stability for oxygen reduction and evolution reactions due to the intrinsically sluggish kinetics of oxygen electrode reactions at lower temperature (<700 °C). We report a novel misfit-layered compound Gd_0.3Ca_2.7Co_3.82Cu_0.18O_9−δ (GCCCO) as a superior and durable bifunctional oxygen electrode material for RPCCs. The maximum power densities achieved with GCCCO cells are notably high, reaching 1.16 and 2.05 W cm⁻² at 600 and 700 °C, respectively, in the fuel cell mode, surpassing previously reported results. Moreover, in the electrolysis mode, the GCCCO cells reached current densities of −1.53 and −9.35 A cm⁻² at 500 and 700 °C, respectively, at an applied voltage of 1.5 V. The superior catalytic performances of GCCCO are correlated to the oxygen defect rich structure, triple (O²⁻/H⁺/e⁻)-conducting property, needle-like grain morphology, and suitable thermal expansion coefficient.

Further development of oxygen catalysts with high electrocatalytic activity and hydration ability is crucial to improve the performance of electrochemical energy storage and conversion devices such as reversible fuel cell/electrolysis cells, because the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) kinetics often limit the performance of these cells. Particularly, significant research efforts are focused on triple conducting (H⁺/O²⁻/e⁻) oxide (TCO) catalysts, owing to their excellent performance in reversible ceramic cells. In this study, we propose a novel strategy to further enhance TCO electrocatalyst performance via exsolution. We demonstrate this approach by doping monovalent alkali metals with high basicity into BaCo_0.4Fe_0.4Zr_0.18Y_0.02O_3−δ, a well-known TCO, which enables the exsolution of barium oxides under humidified air conditions. The main objective of this strategy, which involves water-mediated exsolution coupled with doping of high basicity elements, is to facilitate high proton uptake and conduction pathways within the TCOs, boosting the ORR/OER activity. Our study confirms that BaO_x exsolved K_0.05Ba_0.95Co_0.4Fe_0.4Zr_0.18Y_0.02O_3−δ (KBCFZY) exhibits higher activity and stability for both ORR and OER compared to other perovskites, enabling reversible devices surpassing previously reported performance metrics, including >1.65 W cm⁻² peak power density in fuel cell (FC) mode and >6.5 A cm⁻² in electrolysis (EC) mode at 1.3 V at 650 °C (with >2.5 W cm⁻² and >10.5 A cm⁻² for these same FC and EC metrics at 700 °C). Density functional theory calculations suggest that the alkali-metal doping not only triggers the exsolution of catalytically active barium oxide nanoparticles, but also lowers the bulk oxygen vacancy formation energy and reduces the barrier for proton migration through the BCFZY structure, explaining the observed increases in activity and performance. These results provide new opportunities for the rational engineering of the exsolution process, facilitating the fast transfer of H⁺/O²⁻/e⁻ species for highly active TCO catalysts.

In this study, we investigated an energy harvesting effect of tensile stress using piezoelectric polymers and flexible electrodes. A chemical-vapor-deposition grown graphene film was transferred onto both sides of the PVDF and P(VDF-TrFE) films simultaneously by means of a conventional wet chemical method. Output voltage induced by sound waves was measured and analyzed when a mechanical tension was applied to the device. Another energy harvester was made with a metallic electrode, where Al and Ag were deposited by using an electron-beam evaporator. When acoustic vibrations (105 dB) were applied to the graphene/PVDF/graphene device, an induced voltage of 7.6 V_pp was measured with a tensile stress of 1.75 MPa, and this was increased up to 9.1 V_pp with a stress of 2.18 MPa for the metal/P(VDF-TrFE)/metal device. The 9 metal/PVDF/metal layers were stacked as an energy harvester, and tension was applied by using springs. Also, we fabricated a full-wave rectifying circuit to store the electrical energy in a 100 μF capacitor, and external vibration generated the electrical charges. As a result, the stored voltage at the capacitor, obtained from the harvester via a bridge diode rectifier, was saturated to ~7.04 V after 180 s charging time.