Understanding 'electro-chemo-mechanics' in oxygen ion conducting membranes represents a foundational step towards new energy devices such as micro fuel cells and oxygen or fuel separation membranes. For ionic transport in macro crystalline electrolytes, doping is conventionally used to affect oxygen ionic association/migration energies. Recently, tuning ionic transport in films through lattice strain conveyed by substrates or heterostructures has generated much interest. However, reliable manipulation of strain states to twist the ionic conduction in real micro energy devices remains intractable. Here, we demonstrate that the oxygen ionic conductivity clearly correlates with the compressive strain energy acting on the near order of the electrolyte lattices by comparing thin-film ceria-based membrane devices against substrate-supported flat structures. It is possible to capitalize on this phenomenon with a smart choice of strain patterns achieved through microelectrode design. We highlight the importance of electro-chemo-mechanics in the electrolyte material for the next generation of solid-state energy conversion microdevices.

Samaria-doped ceria (SDC) thin films are particularly important for energy and electronic applications such as microsolid oxide fuel cells, electrolyzers, sensors, and memristors. In this paper, we report a comparative study investigating ionic conductivity and surface reactions for well-grown epitaxial SDC films varying the samaria doping concentration. With increasing doping above 20 mol % of samaria, an enhancement in the defect association is observed by Raman spectroscopy. The role of such associated defects on the films̀ oxygen ion transport and exchange is investigated by electrochemical impedance spectroscopy and electrochemical strain microscopy (ESM). The measurements reveal that the ionic transport has a sharp maximum in ionic conductivity and drops in its activation energy down to 0.6 eV for 20 mol % doping. Increasing the doping concentration further up to 40 mol %, it raises the activation energy substantially by a factor of 2. We ascribe the sluggish transport kinetics to the "bulk" ionic-near ordering in case of the heavily doped epitaxial films. Analysis of the ESM first-order reversal curve measurements indicates that these associated defects may have a beneficial role by lowering the activation of the oxygen exchange "surface" reaction for heavily doped 40 mol % of samaria. In a model experiment, through a solid solution series of samaria doped ceria epitaxial films, we reveal that the occurrence of associated defects in the bulk affects the surface charging state of the SDC films to increase the exchange rates. The implication of these findings is the design of coatings with tuned oxygen surface exchange by controlling the bulk associated clusters for future electrocatalytic applications.

Multiferroic composite materials combining ferroelectric and ferromagnetic order at room temperature have great potential for emerging applications such as four-state memories, magnetoelectric sensors, and microwave devices. In this paper, we report an effective and facile liquid phase deposition route to create multiferroic composite thin films involving the spin-coating of nanoparticle dispersions of BaTiO, a well-known ferroelectric, and CoFeO, a highly magnetostrictive material. This approach offers great flexibility in terms of accessible film configurations (co-dispersed as well as layered films), thicknesses (from 100 nm to several μm) and composition (5-50 wt % CoFeO with respect to BaTiO) to address various potential applications. A detailed structural characterization proves that BaTiO and CoFeO remain phase-separated with clear interfaces on the nanoscale after heat treatment, while electrical and magnetic studies indicate the simultaneous presence of both ferroelectric and ferromagnetic order. Furthermore, coupling between these orders within the films is demonstrated with voltage control of the magnetism at ambient temperatures.

Electronic conductivity and oxygen reduction activity are investigated in high quality La 1−x Sr x CoO 3-δ (from x = 0 to x = 0.8) thin films with regard to their use as cathodes for intermediatetemperature solid oxide fuel cells. In our study, external interference from microstructure and crystallographic orientation is avoided and therefore we decouple the complex interaction among chemical composition, bulk electronic conductivity, and ORR activity. We observe that the electronic conductivity and the polarization resistance change together, both having the best values at x = 0.4 Sr doping concentration. The Co 3+ /Co 4+ valence state and the higher overlap of the O 2p−Co 3d bands explain the electronic conductivity and the oxygen reduction activity improving with the Sr doping concentration from x = 0 up to x < 0.4. With further increasing the Sr doping content over 0.4, the shift of the O 2p band toward the Fermi level favors the oxygen vacancy formation process, demonstrated by the formation of Co 2+ to balance the charge of the system. Therefore, the Co 3+ /Co 4+ is no longer optimal for the surface oxygen reduction. The increased oxygen vacancy concentration provides more oxygen ion exchange sites for surface oxygen reduction reaction process. However, it also worsens the electronic conductivity and, thus, worsens the electronic charge transfer for the oxygen reduction process. Despite the enhanced formation of oxygen vacancies, the nonoptimal Co 3+ /Co 4+ valence state and the poorer electronic conductivity cooperatively induce a decrease of the oxygen reduction activity in the case of heavily doped LSCO thin films. We show that the electronic conductivity and the oxygen reduction activity are in an intriguing correlation with the cobalt valence state and the electronic band structure.

Exploring high-performance and low-cost bifunctional electrocatalysts is crucial for developing highly efficient overall water splitting cells. In this work, a facile and cheap co-precipitation method, which is compatible with large-scale...

In the epitaxial barium zirconate (BaZrO3) thin films deposited on NdGaO3 substrates through pulsed laser deposition, the large lattice mismatch between film and substrate can be accommodated by generating a large amount of misfit dislocations at the interface. With careful structural and chemical analyses, an enhancement in barium vacancy concentration together with charge compensating oxygen vacancies is believed to be formed near the dislocation defects, which should be mainly responsible for the great improvement of the proton conductivity. However, the crystallinity deteriorates with increasing film thickness due to the dislocations propagation. Such behavior could lead to a detrimental impact on the proton transport properties. These results could be useful for rational design of coating electrolytes with high proton conductivity by strain engineering for in-plane solid oxide fuel cell applications.

Films of controlled thicknesses and with ferroelectric properties were fabricated from BaTiO3 nanoparticle dispersions by liquid-phase deposition.

Electro-chemo-mechanics interactions in oxygen ion conductors are probed for variations of strain and extrinsic doping concentrations in free-standing micro-energy conversion membranes based on ceria solid solutions.