BaCe0.7Zr0.1Y0.1Yb0.1O3-d (BCZYYb) is a promising ceramic electrolyte for reversible protonic ceramic cells. It is reported that BCZYYb-based cells show excellent long-term durability, particularly in the electrolysis mode, in contrast to the cells based on the conventional electrolyte yttria-stabilized zirconia. In this study, we investigate the chemo-mechanical stability behavior (a low tendency of delamination) of the BCZYYb-based protonic ceramic cells in terms of local electronic conduction in the electrolyte. The local electronic conductivity of the BCZYYb electrolyte is determined using Pt-probe-embedded cells near each electrode interface. The BCZYYb electrolyte exhibits sufficient p-type conductivity (~10-3 S cm-1) near the oxygen electrode (corresponding p_(O_2 ): 5.27–21 x 10-2 atm) and n-type conductivity (~10-4 S cm-1) near the hydrogen electrode (corresponding p_(O_2 ): 0.99–1.30 x 10-24 atm) at 600 °C. A standard cell is prepared and tested over long-term in the fuel cell (at positive and negative voltages) and electrolysis modes. The cell exhibits stable performance without delamination or cracks in both operating modes, owing to local electronic conduction.

A simple and innovative technique was developed in this work creating a stable, fully established porous three dimensional (3D) dendritic structure, which can be adopted as electrode for redox supercapacitors and catalytic energy conversion reactions 1,2. By controlling the surfactant and etching chemistry a series of different micro-architectured morphologies was created for Cu-Ni heterostructures (Fig. 1a) during their dendritic growth at suitable electrodeposition potentials. This work examines in detail the effect of the deposition conditions on the mass and chemical composition (Fig. 1b), and morphology (Fig. 1c-d), mass and chemical composition (Fig. 1e) of the deposited Ni/Cu electrodes and the resulting 3D architectures of the dendritic growth. The porosity, architecture, geometric confinement, and the exposed crystallographic facets were found to play crucial roles in the energy storage and catalytic outcomes yielding insightful structure-activity correlations3. Cyclic Voltammetry (CV) studies reveal clear pseudocapacitive nature of the electrodes with the 10 minutes deposited Ni/Cu redox electrode exhibiting very high specific capacitance of 643 F.g−1 at 1 A.g−1 (Fig. 1e-f). The fabricated electrode delivers the capacitance retention of 84% after 5000 consecutive charge discharge cycles (Fig. 1g). These results spotlight the mechanism involved in the electrodeposition and the influence of the observed mass and deposition duration that modifies the electrode content and morphology, as well as its electrochemical activity. Furthermore, the microtraps present in the architectural matrix and the relative composition of Cu to Ni was fine tuned to efficiently direct the reaction pathway towards C2 products during CO2 electroreduction (eCO2R)4. The local confinement of the suitable intermediates and production of CO and H* in proximal sites leads to controlled product tunability towards higher carbon containing hydrogenated products with high faradaic efficiency5. The structure-activity correlations developed here through operando and postmortem analyses corroborated by computational studies, will help guide future material design strategies for enhanced energy storage and catalytic applications. Keywords: electrodeposition, CuNi structures, microtraps, pseudocapacitor, CO2 reduction Fig. 1. a) XRD pattern and b) XPS spectrum of Cu-Ni heterostructure, c) and d) SEM micrographs of the micro-architectured morphologies obtained by controlling the surfactant and etching chemistry, e) and f) CV studies of 10 min deposited Ni/Cu redox electrode, and g) Charge-discharge cycles of the fabricated electrode. References Zou, R. et al. Dendritic Heterojunction Nanowire Arrays for High-Performance Supercapacitors. Sci. Reports 2015 51 5, 1–7 (2015). Zang, D., Huang, Y., Li, Q., Tang, Y. & Wei, Y. Cu dendrites induced by the Anderson-type polyoxometalate NiMo6O24 as a promising electrocatalyst for enhanced hydrogen evolution. Appl. Catal. B Environ. 249, 163–171 (2019). Sebastiá n-Pascual, P., Jordã Pereira, I. & Escudero-Escribano, M. Tailored electrocatalysts by controlled electrochemical deposition and surface nanostructuring. Chem. Commun 56, 13261 (2020). Zhuang, T. T. et al. Copper nanocavities confine intermediates for efficient electrosynthesis of C3 alcohol fuels from carbon monoxide. Nat. Catal. 1, (2018). Sebastián‐Pascual, P., Mezzavilla, S., Stephens, I. E. L. & Escudero‐Escribano, M. Structure‐Sensitivity and Electrolyte Effects in CO 2 Electroreduction: From Model Studies to Applications. ChemCatChem 11, 3626–3645 (2019). Figure 1