Investigation of Ion and Electron Conduction in the Mixed Ionic-Electronic Conductor- La-Sr-Co-Fe-Oxide (LSCF) Using Alternating Current (AC) and Direct Current (DC) Techniques

Among many mixed ionic electronic conductors (MIECs), lanthanum strontium cobalt iron oxide (LSCF) has been proven as a promising material for use as cathode in SOFCs. The ion and electron conduction in LSCF need to be studied separately. To measure the ionic conductivity of LSCF, YSZ disks were applied to block the electronic current, and multilayered samples were made with YSZ disks in series with an LSCF disk. Both AC and DC techniques were used for the measurements. An LSCF(porous)/LSCF(dense)/LSCF(porous) bar-shaped sample was made to measure the electronic conductivity of LSCF. DC technique was utilized for the measurement. Results show that the ionic conductivity of LSCF is much lower than its electronic conductivity. The ionic conductivity of LSCF increases with increasing temperature (600-900°C), and the electronic conductivity decreases with increasing temperature (600-900°C). Measurements were also made on a foil of silver to investigate oxygen transport through it. From this, oxygen ion conductivity through silver was estimated.

Faradaic efficiency in protonic-ceramic electrolysis cells

Proton-conducting ceramics (e.g., doped barium zirconates or cerates) are typically mixed ionic-electronic conductors (MIEC). The electronic conduction, typically in the form of positively charged small polarons or electron holes, leads to “electronic leakage.” In an ideal steam-electrolysis cell, one gas-phase H2 molecule is produced from every two electrons delivered from an external power source. In other words, such ideal behavior achieves 100% faradaic efficiency. However, the electronic flux associated with MIEC membranes contributes to reduced faradaic efficiency. The present paper develops a model that predicts the behavior of faradaic efficiency as a function of electrolysiscell operating conditions. Although the model framework is more general, the paper focuses on the behavior of a cell based upon a BaCe0.7Zr0.1Y0.1Yb0.1O3−δ (BCZYYb) membrane. The study predicts the effects of operating conditions, including temperature, pressure, and gas compositions.

High performance ambipolar organic mixed ionic-electronic conductor for adaptive logic circuits and neuromorphic electronics

Organic mixed ionic-electronic conductors (OMIECs) are central to bioelectronic applications such as biosensors, health monitoring devices and neural interfaces, and have facilitated efficient next-generation brain-inspired computing and biohybrid systems. Most OMIECs are hole-conducting (p-type) materials, while complimentary logic circuits and various biosensors require electron-conducting (n-type) materials too. Here we show an ambipolar mixed ionic-electronic polymer that achieves high on/off ratios with high ambient p- and n- type stability. We highlight the versatility of the material by demonstrating its use as a neuromorphic memory element, an adaptable ambipolar complementary logic inverter, and a neurotransmitter sensor. The ambipolar operation of this material allows for straightforward monolithic fabrication and integration, and opens a route towards more sophisticated complex logic and adaptive circuits.

Characterization of Vegard strain related to exceptionally fast Cu-chemical diffusion in Cu$$_2$$Mo$$_6$$S$$_8$$ by an advanced electrochemical strain microscopy method

Electrochemical strain microscopy (ESM) has been developed with the aim of measuring Vegard strains in mixed ionic-electronic conductors (MIECs), such as electrode materials for Li-ion batteries, caused by local changes in the chemical composition. In this technique, a voltage-biased AFM tip is used in contact resonance mode. However, extracting quantitative strain information from ESM experiments is highly challenging due to the complexity of the signal generation process. In particular, electrostatic interactions between tip and sample contribute significantly to the measured ESM signals, and the separation of Vegard strain-induced signal contributions from electrostatically induced signal contributions is by no means a trivial task. Recently, we have published a compensation method for eliminating frequency-independent electrostatic contributions in ESM measurements. Here, we demonstrate the potential of this method for detecting Vegard strain in MIECs by choosing Cu$$_2$$ 2 Mo$$_6$$ 6 S$$_8$$ 8 as a model-type MIEC with an exceptionally high Cu chemical diffusion coefficient. Even for this material, Vegard strains are only measurable around and above room-temperature and with proper elimination of electrostatics. The analyis of the measured Vegards strains gives strong indication that due to a high charge transfer resistance at the tip/interface, the local Cu concentration variations are much smaller than predicted by the local Nernst equation. This suggests that charge transfer resistances have to be analyzed in more detail in future ESM studies.