Structural evolution during calcination and sintering of a (La0.6Sr0.4)0.99CoO3-δ nanofiber prepared by electrospinning

Experimental Requirements for High-Temperature Solid-State Electrochemical TEM Experiments

The ability to perform both electrochemical and structural/elemental characterization in the same experiment and at the nanoscale allows to directly link electrochemical performance to the material properties and their evolution over time and operating conditions. Such experiments can be important for the further development of solid oxide cells, solid-state batteries, thermal electrical devices, and other solid-state electrochemical devices. The experimental requirements for conducting solid-state electrochemical TEM experiments in general, including sample preparation, electrochemical measurements, failure factors, and possibilities for optimization, are presented and discussed. Particularly, the methodology of performing reliable electrochemical impedance spectroscopy measurements in reactive gases and at elevated temperatures for both single materials and solid oxide cells is described. The presented results include impedance measurements of electronic conductors, an ionic conductor, and a mixed ionic and electronic conductor, all materials typically applied in solid oxide fuel and electrolysis cells. It is shown that how TEM and impedance spectroscopy can be synergically integrated to measure the transport and surface exchange properties of materials with nanoscale dimensions and to visualize their structural and elemental evolution via TEM/STEM imaging and spectroscopy.

Nanofiber Composites as Highly Active and Robust Anodes for Direct-Hydrocarbon Solid Oxide Fuel Cells

Direct utilization of methane fuels in solid oxide fuel cells (SOFCs) is a key technology to realize the immediate inclusion of such high-efficiency fuel cells into the current electricity generation infrastructure. However, the broad commercialization of direct-methane fueled SOFCs is critically hindered by the inadequate electrode activity and their poor longevity, which primarily stems from the carbon build-up issues. To make the technology more competitive, a novel electrode structure that can dramatically improve the tolerance against coking is essential. Herein, we present highly active and robust core-shell nanofiber anodes, La_0.75Sr_0.25Cr_0.5Mn_0.5O₃@Sm_0.2Ce_0.8O_1.9 (LSCM@SDC), directly obtained with a single-nozzle electrospinning process through the use of two immiscible polymers. The intimate coverage of SDC on LSCM not only increases the active reaction sites but also promotes resistance toward carbon deposition and thermal aggregation. As such, the electrode polarization resistance obtained with LSCM@SDC NFs is among the lowest value ever reported with LSCM derivatives (∼0.11 Ω cm² in wet H₂ at 800 °C). The facile fabrication process of such complex heterostructures developed in this work is attractive for the design of not only SOFC electrodes but also other solid-state devices such as electrolysis cells, membrane reformers, and protonic cells.

Location-specific fabrication of suspended nanowires using electrospun fibers on designed microstructure

While there have been remarkable improvements in the fabrication of suspended nanowires, placing a single nanowire at the desired location remains to be a challenging task. In this study, a simple method is proposed to fabricate suspended nanowires at desired locations using an electrospinning process and a designed microstructure. Using electrospun polymer fibers on the designed microstructure as a sacrificial template, various materials are deposited on it, and the electrospun fibers are selectively removed, leaving only nanowires of the deposited material. After the polymer fibers are removed, the remaining metal fibers agglomerate into a single nanowire. Throughout this process, including the removal of the polymer fibers, the samples are not exposed to high temperatures or chemicals, thereby allowing the formation of nanowires without oxidation or contamination. The diameter of the nanowire can be controlled in the electrospinning process, and a suspended Pd nanowire with a minimum diameter of 100 nm is fabricated. Additionally, a suspended single Pd nanowire-based H₂gas sensor fabricated using the proposed process exhibits a highly sensitive response to H₂gas.

Progress in the use of electrospun nanofiber electrodes for solid oxide fuel cells: a review

The application of one-dimensional nanofibers in the fabrication of an electrode greatly improves the performance of solid oxide fuel cells (SOFCs) due to its advantages on electron transfer and mass transport. Various mixed ionic-electronic conducting materials with perovskites and Ruddlesden-Popper-type metal oxide structures are successfully electrospun into nanofibers in recent years mostly in solvent solution and some in melt forms, which are used as anode and cathode electrodes for SOFCs. This paper presents a comprehensive review of the structure, electrochemical performance, and development of anode and cathode nanofiber electrodes including processing, structure, and property characterization. The focuses are first on the precursor, applied voltage, and polymer in the material electrospinning process, the performance of the fiber, potential limitation and drawbacks, and factors affecting fiber morphology, and sintering temperature for impurity-free fibers. Information on relevant methodologies for cell fabrication and stability issues, polarization resistances, area specific resistance, conductivity, and power densities are summarized in the paper, and technology limitations, research challenges, and future trends are also discussed. The concluded information benefits improvement of the material properties and optimization of microstructure of the electrodes for SOFCs.

Methods for Calibration of Specimen Temperature During In Situ Transmission Electron Microscopy Experiments

One of the biggest challenges for in situ heating transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) is the ability to measure the local temperature of the specimen accurately. Despite technological improvements in the construction of TEM/STEM heating holders, the problem of being able to measure the real sample temperature is still the subject of considerable discussion. In this study, we review the present literature on methodologies for temperature calibration. We analyze calibration methods that require the use of a thermometric material in addition to the specimen under study, as well as methods that can be performed directly on the specimen of interest without the need for a previous calibration. Finally, an overview of the most important characteristics of all the treated techniques, including temperature ranges and uncertainties, is provided in order to provide an accessory database to consult before an in situ TEM/STEM temperature calibration experiment.

Preparation of super-hydrophilic polyphenylsulfone nanofiber membranes for water treatment

Electrospun nanofiber membrane-supported thin film composite (TFC) membranes exhibit great potential in water purification. In this work, electrospun polyphenylsulfone (PPSU) nanofiber membranes were prepared and modified by heat and plasma treatments. The resulting membranes were used as support layers for biomimetic TFC-based forward osmosis membranes. Thermal treatment transformed a loose non-woven nanofiber structure into a robust interconnected 3-dimensional PPSU network displaying a 930% increase in elastic modulus, 853% increase in maximum stress, and two-fold increase in breaking strain. Superior hydrophilicity of PPSU nanofiber membranes was achieved by low-pressure plasma treatment, changing the contact angle from 137° to 0°. The fabricated exemplary TFC-based forward osmosis membrane showed an osmotic water flux J_w > 14 L m⁻² h⁻¹ with a very low reserve salt flux J_s (J_s/J_w = 0.08 g L⁻¹) demonstrating the potential for making high quality membranes for water treatment using PPSU-based support layers for TFC membranes.

A 3-dimensional nanofiber membrane with superior hydrophilicity and mechanical properties significantly improves flux and salt rejection in thin film forward osmosis.