Moderate Current Densities Research Articles

Rutile Ti0.9Ir0.1O2‐Supported Low Pt Loading: An Efficient Electrocatalyst for Ethanol Electrochemical Oxidation in Acidic Media

Developing a cost‐effective electrocatalyst toward ethanol electrochemical oxidation plays a vital role in large‐scale applications of direct ethanol fuel cells (DEFCs). Herein, a rutile Ti0.9Ir0.1O2‐supported low Pt‐loading catalyst is fabricated using a surfactant‐free one‐pot chemical reduction route at room temperature that not only reduces the amount of the Pt loading but also significantly enhances the CO antipoisoning and electrochemical stability toward ethanol electrochemical oxidation compared with the conventional carbon‐supported Pt electrocatalyst. The rutile Ti0.9Ir0.1O2 nanosupport with rod‐like morphology is first prepared via a one‐pot hydrothermal route, and then 15.5 wt% Pt nanoparticles with small size (≈3 nm) are anchored on it by the surfactant‐free chemical reduction process. For ethanol electrochemical oxidation, the rutile Ti0.9Ir0.1O2‐supported Pt catalyst shows a moderate current density (≈13.74 mA cm−2), which is comparable with the 20 wt% Pt/C electrocatalyst, despite its low loading (15.5 wt%). In addition, the rutile Ti0.9Ir0.1O2‐supported low Pt‐loading electrocatalyst demonstrates low onset potential (0.45 V vs normal hydrogen electrode [NHE]), superior CO‐tolerance, and impressive electrochemical stability compared with the carbon‐supported Pt catalyst. These enhancements are ascribable to the inherent durability of the rutile TiO2 nanostructure and the synergistic effect between Pt and Ti0.9Ir0.1O2 nanosupport.

Fate of Diclofenac and Its Transformation and Inorganic By-Products in Different Water Matrices during Electrochemical Advanced Oxidation Process Using a Boron-Doped Diamond Electrode

The focus of this study was to investigate the efficacy of applying boron-doped diamond (BDD) electrodes in an electrochemical advanced oxidation process, for the removal of the target compound diclofenac (DCF) in different water matrices. The reduction of DCF, and at the same time the formation of transformation products (TPs) and inorganic by-products, was investigated as a function of electrode settings and the duration of treatment. Kinetic assessments of DCF and possible TPs derived from data from the literature were performed, based on a serial chromatographic separation with reversed-phase liquid chromatographyfollowed by hydophilic interaction liquid chromatography (RPLC-HILIC system) coupled to ESI-TOF mass spectrometry. The application of the BDD electrode resulted in the complete removal of DCF in deionized water, drinking water and wastewater effluents spiked with DCF. As a function of the applied current density, a variety of TPs appeared, including early stage products, structures after ring opening and highly oxidized small molecules. Both the complexity of the water matrix and the electrode settings had a noticeable influence on the treatment process’s efficacy. In order to achieve effective removal of the target compound under economic conditions, and at the same time minimize by-product formation, it is recommended to operate the electrode at a moderate current density and reduce the extent of the treatment.

Interactive effects of specimen size and current density on tribological behavior of electrically-assisted micro-forming in TC4 titanium alloy

In this paper, electrically-assisted (EA) micro-ring compression tests were carried out to investigate the tribological behavior. It was found that the lubricity of conductive greases was outstanding in the moderate current density range, in which the ablation and oxidation induced by current were almost suppressed. Moreover, the presence of current would reduce the frictional size effects, and this trend increased with the increase of current density. It was attributed to the affects of the joule heating effect induced by current. Finally, a new friction model was put forward to quantify the influence of specimen scale and current by introducing the scale factor and current density, which could effectively predict the friction coefficient and explain the mechanism of friction size effects.

Looking Deep inside the Cathode of Li-O2 Batteries: Unraveling the Local Distribution of Li2O2 with a Combined Experimental and Model-Based Approach

Carbon-based, high surface area gas diffusion electrodes (GDEs) are commonly used as cathodes in Li-O2 batteries. These GDEs provide an sufficient amount of active sites to deposit the main discharge product, Li2O2. Despite the fast electron transfer at the electrode surface to form Li2O2, experimental results show that the very high theoretical energy densities of Li-O2 batteries cannot be achieved at the moment. Instead of the desired formation of high amounts of soluble LiO2, predominantly insoluble Li2O2 precipitates at the active sites of the cathode during discharge. Unfortunately Li2O2 is poorly conductive for electrons, which leads to a low amount of deposited Li2O2 per active site and a fast passivation of the cathode. Thus, only the cathode surface area and not the pore volume is utilized by Li2O2, which explains the discrepancy between theory and experiments. Furthermore, the precipitation leads to continuous changes in porosity, available active surface area and predominant reaction pathway. For this reason a detailed analysis of the distribution of Li2O2 at all points in the GDE and of the factors that influence the Li2O2 morphology is needed to overcome performance limitations. [1]In this work, we elucidate how the local distribution of Li2O2 inside the GDE and its particle size evolve as a function of discharge current density. We apply a powerful combination of experimental and model-based analysis. To the best of our knowledge, this is the first study on the cathode surface utilization by Li2O2 and its particle sizes performed for different locations and states of discharge (SOD). The impact of the distribution and the resulting changes in transport resistance and active surface area on the battery performance are derived thereof.In the experimental part, decreasing capacities and Li2O2 particle sizes are observed for increasing discharge current densities (see SEM analysis of discharged battery cathodes in fig. 1 a)). Furthermore, the experimental results show that particle precipitation starts mainly at the side of the cathode that faces the oxygen reservoir of the battery (see fig. 1 b)). Discharging a battery at low current densities leads to a uniform cathode surface coverage by Li2O2 even at low SOD whereas discharging at high current densities yields a gradient of blocked active sites through the cathode.Simulations based on a physical GDE model show that a two-step reaction mechanism with the soluble species LiO2 as reaction intermediate can quantitatively explain the experimental findings. Depending on the current density, either a chemical or an electrochemical particle growth process predominates, which leads to the distinct different particle size distributions (see fig. 1 c) and d)). The strong dependence of capacity on the current density is related to different capacities per carbon cathode surface area at the end of discharge. At high discharge rates and thereby lowered potential more nucleation takes place. As a result, the particle number is higher and the average size smaller. Due to the surface volume ratio, smaller particles entail lower capacities per cathode surface area. The results point out that even at moderate current densities the battery capacity is limited by the surface area of the GDE and not by the concentration of dissolved O2 in the liquid electrolyte. Therefore, the solubility and reaction kinetics of the reaction intermediate LiO2 play a crucial role to enhance Li2O2 particle size and with it the obtainable discharge capacity.The presented results provide detailed insight into the cathode surface utilization and the underlying processes that limit the performance of GDEs in Li-O2 batteries. In the end, the study will help to achieve higher discharge capacities for this type of battery and thus will propel the ongoing research and the efforts in commercialization of metal-oxygen batteries.Acknowledgement:The authors are thankful for financial support by the BMBF (Federal Ministry of Education and Research) within the project “MeLuBatt” (03XP0110A).

Temperature Impact on the Internal Resistance of a Polymer Electrolyte Fuel Cell Considering the Electrochemical Impedance Spectroscopy Diagnosis

A polymer electrolyte fuel cell (PEFC) is an electrochemical device that converts the chemical energy presents in the hydrogen into electricity and heat having as by product only water. The energy conversion process is carried out in a clean and noiseless manner. Depending on the applications, a PEFC works at different operating temperature. In this study, the internal resistance of a PEFC is evaluated by using Electrochemical Impedance Spectroscopy (EIS) at moderate low current density, i.e., 0.5 A/cm2, in the temperature range of 40 – 80°C. The evaluation is carried out considering frequencies between 3.1kHz and 1Hz. An equivalent Randle circuit is considered as adjusted model and the Nyquist and Bode diagram were obtained to analyze the internal resistance. Results show that the ohmic resistance and charge transport increase when the operating temperature is low, decreasing the cell performance. A voltage drop of 42 mV was obtained for the evaluated temperature sweep. At the same time, it was demonstrated that the double layer capacitance increases at high temperatures, increasing its operating performance.

Thermal Noise-Boosting Effects in Hot-Wire-Based Micro Sensors

This article proposes an original approach aimed at modelling the noise density in sensors based on a single hot wire or pairs of thermally coupled wires. The model consists in an original combination of a previous electrothermal model of the wire with well-established assumptions on the thermal noise in conductors that carry moderate current densities. A simple method for estimating the model parameters with simple impedance spectroscopy is suggested. The predicted power spectral densities of the wire thermal noise differ from the result of previously presented analytical models, stimulating further experimental studies. The effects of the electrothermal feedback of both hot wires and hot-wire pairs on flicker noise is also intrinsically covered by the proposed approach.

Recombination rates in green-yellow InGaN-based multiple quantum wells with AlGaN interlayers

The recombination rates in InGaN/AlGaN/GaN multiple quantum wells (MQWs) emitting in the green-yellow and grown with different Al compositions in the AlGaN interlayer (IL) are shown. By transforming measurements on radiative efficiency, absorption, and differential carrier lifetime, the radiative and nonradiative rates are determined. The IL Al composition controls lattice relaxation of the MQWs, as determined by X-ray reciprocal space mapping, and, therefore, defect formation. For the most pseudomorphic MQWs, the Shockley-Read-Hall (SRH) A coefficient is minimized and is similar to reports at shorter (blue and green) wavelengths. It is an order of magnitude smaller than a conventional InGaN/GaN MQW and is the most significant factor behind the improvement in radiative efficiency using the IL. The radiative B coefficient is also reduced and a minimum for the most pseudomorphic MQWs due to a reduction in the electron-hole wavefunction overlap. However, the decrease in A is more significant and leads to an overall improvement in the radiative efficiency. These recombination rate measurements confirm that if the SRH recombination is controlled, then the severe reduction of radiative recombination with an increased emitting wavelength is one of the main challenges in realizing high efficiency, long-wavelength InGaN-based MQW emitters operating at low to moderate current densities.

How Metallic Protection Layers Extend the Lifetime of NASICON-Based Solid-State Lithium Batteries

The use of solid-state electrolytes (SSEs) within batteries is a promising strategy to safely access the high capacity of lithium metal anodes. However, most SSEs with practical ionic conductivity are chemically unstable in contact with lithium metal, which is detrimental to battery performance. Lithium aluminum germanium phosphate (LAGP) is an SSE with high ionic conductivity (10−4-10−3 S cm−1) and good environmental stability, but it forms an amorphous interphase region that continuously grows in contact with Li, leading to chemo-mechanical failure within solid-state batteries. Here, we find that thin (∼30 nm) chromium interlayers deposited between the lithium electrode and LAGP extend cycle life to over 1000 h at moderate current densities (0.1–0.2 mA cm−2), compared to ∼30 h without protection. This significantly improved stability occurs because the metallic interlayer alters the trajectory of interphase formation and the nature of the electrochemical reaction at the interface. This work shows the promise of interface engineering for a variety of SSE materials within solid-state batteries, while emphasizing the necessity of understanding how protection layers affect dynamic evolution of interfaces.

The Role of Metallic Protection Layers in Extending the Stability of Nasicon Electrolytes for Solid-State Batteries

Solid-state batteries with lithium metal anodes are promising candidates for next-generation energy storage devices with improved safety and higher energy density. However, most solid electrolytes with practical ionic conductivities are thermodynamically unstable against lithium metal. Upon interfacial contact with lithium metal, unstable solid electrolytes undergo phase transformations that can be detrimental to battery performance. Lithium aluminum germanium phosphate (LAGP) is a NASICON-type solid electrolyte with relatively high ionic conductivity (10-4 - 10-3 S/cm) and chemical resistance to air and moisture. However, LAGP reacts with lithium to form an electrically-conducting interphase. This interphase continues to propagate from the interface towards the bulk of the solid electrolyte, ultimately leading to failure by causing the solid electrolyte to fracture [1]. In this work, we find that a thin layer of a metal that does not alloy with Li can extend the cycle life of LAGP in symmetric lithium cells from 30 h to more than 800 h at moderate current densities. Interestingly, this significantly improved electrochemical stability is not due to the prevention of interphase formation. Instead, the metal layer alters the morphology evolution of the interphase, creating a uniform and compact interphase. In addition, we find that the inclusion of an electrically insulating thin film, such as Al2O3, between the metal protection layer and the solid electrolyte favors lithium plating and prevents interphase formation over short periods of time. This dual layer approach also extends the electrochemical stability to more than 1000 h during cycling. However, using only the insulator without a metal is not beneficial for electrochemical stability. These results suggest that metallic protection layers may be necessary for attaining stable cycling even if suitable electrically insulating protection layers are developed to completely prevent interphase formation. Our findings are important for enabling the use of a wider range of solid electrolyte materials in solid-state batteries. [1] J.A. Lewis, et at. Interphase Morphology between a Solid-State Electrolyte and Lithium Controls Cell Failure. ACS Energy Lett. 2019, 4, 2, 591-599

AB-stacked bilayer graphene zigzag nanoribbons: sensors for interlayer single molecule detection

A device is proposed consisting of a bilayer zigzag graphene nanoribbon (ZGNR) in AB stacking and β edge alignment to detect the presence of simple molecules in its interlayer space. Interlayer molecule detection is accomplished through analysis of the I-V characteristics of the device. Ab initio simulation is performed by applying spin-unpolarized density functional theory (DFT) and non-equilibrium Green’s function methods (NEGF) to the proposed model system. For interlayer molecule detection with improved sensitivity, we propose as model system a couple of AB-stacked ZGNR nanoribbons which are known to present edge states and edge magnetism at zero bias. For interlayer single molecules, we try CO, CO2, and H2O. Interlayer molecules induce local deformations into the ZGNR structure specific to each species and get efficiently trapped in the interlayer space experiencing subtle structural distortions under applied bias. I-V characteristics are fingerprints of molecules in the interlayer space displayed through negative differential resistance (NDR) phenomena and asymmetric behavior with respect to the sign of applied bias. The appearance of NDR can be understood in terms of the Landauer-Buttiker formalism. NDR in our device may be characterized as a rather weak and sharp one with a moderate peak current density.

A Computational Analysis on the Operational Behaviour of Open-Cathode Polymer Electrolyte Fuel Cells

Polymer electrolyte membrane fuel cell (PEMFC) is a promising sustainable energy conversion technology to replace conventional fossil fuel based applications. The products of the fuel cell operation are electricity, water, and heat. A common strategy to achieve high power density is to operate at high current densities. However, the rate of heat generation is approximately proportional to the current density and waste heat removal is therefore a challenge for high power density systems. Overheating can cause drying of the conductive polymeric membrane inside the cell causing significant ohmic loss. It can also create local hot spots in the membrane electrode assembly (MEA) that are susceptible to degradation [1]. Hence, liquid coolant such as water or other thermal fluids is used in conventional PEMFCs by embedding separate cooling channels in the flow field plates. However, this type of cooling adds extra balance-of-plant (BOP) components into the system. This can be eliminated by using air as both oxidant and coolant, which is denoted as ‘open-cathode’ design. Even though open-cathode systems considerably reduce BOP cost [2], the open-cathode cell performance is limited by ambient air quality and temperature. The objective of the present work is to simulate the operational behaviour of open-cathode PEMFCs in order to better understand their performance limitations compared to conventional, liquid cooled cells. A comprehensive, 3D computational fuel cell model was developed for this purpose and utilized to study the operational and hygrothermal behaviour of an open-cathode PEMFC at various ambient conditions. Furthermore, the distribution of different cell parameters was analysed across the cell and a relationship was established that the temperature gradient across the cell guides the humidity distribution and hence the overall water management in the cell. These parameters contribute to the net membrane conductivity of the cell which dictates the actual cell performance. Overheating in such kind of a system was found to be key factor limiting the net cell performance while in operation at moderate and higher current densities. The results obtained were also compared with an equivalent liquid cooled cell and a cell operating in hypothetical isothermal condition at similar operating conditions as described in Figure 1. These three sets of modelling results clearly distinguish the operational behaviour of an open-cathode cell against that of a liquid cooled cell and also draws conclusion on factors affecting the low cell performance for an open-cathode system. The results from the study also suggests the inlet air flow rate to be crucial in terms of heat extraction. The net cell performance shifts upwards cushioning the gap between an open-cathode system and a liquid cooled system operating at similar conditions when the inlet air flow rate is increased optimally. AcknowledgementsThis work is supported by the funding provided by Indian Oil R&D and Simon Fraser University under the SFU-IOCL joint PhD program in clean energy. Funding from Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation and British Columbia Knowledge Development Fund is appreciated. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program.

EFFECT OF ANODIC AND CATHODIC CURRENT DENSITIES ON THE CAVITATION DAMAGE CHARACTERISTICS OF ALUMINUM ALLOY IN SEAWATER

In this study, the influences of electrolytic gas generation on the surface of aluminum as a cushioning media against cavitation bubbles were experimentally investigated. The electrolytic gas evolution was controlled by applying electric current to the metal with different polarity and current densities. The surface of the metal specimen was either polarized anodically or cathodically while simultaneously being subject to vibratory cavitation. It was revealed that the surface damage behavior was mainly dependent on the current densities applied to the metal. It was apparent that a moderate current density range of between [Formula: see text] and [Formula: see text] A/cm2 applied cathodically can produce electrolytic gas evolution to cushion the cavitation bubbles sufficiently. However, application of a too a high current density (greater than [Formula: see text] A/cm[Formula: see text] may lead to cathodic corrosion of Al alloys.

Quality enhancement of low temperature metal organic chemical vapor deposited MoS2: an experimental and computational investigation

Electronic quality of chemical vapor deposited MoS2 is a function of crystallinity, which tends to decline with decrease in deposition temperature. Conventional thermal annealing can improve the quality but requires very high temperatures. In this study, we investigate a novel low temperature (room temperature to 400 °C) annealing process that exploits the electron wind force during passage of current. Here, moderate current density gives rise to atomic scale mechanical force whenever the electrons encounter defects in the lattice or grain boundaries (GBs). After hypothesizing that this force can significantly enhance defect mobility without any temperature field, we demonstrate the process using in situ transmission electron microscope and molecular dynamics simulation. Monolayer metal organic chemical vapor deposited MoS2 deposited at 400 °C was post processed at temperature as low as 20 °C. Experimental results show five times enhancement in electrical conductivity, which is supported by electron diffraction patterns indicating significant grain growth. Discrete spots in diffraction indicate evolution of high crystallinity even at room temperature. Our computational model shows the mechanisms behind healing lattice defects as well as reorienting the GBs. The enhancement in microstructure of the specimen is also reflected in mechanical properties simulations on pre- and post-annealed specimens.

Polyphenylamine-Based Cathode Material for Ultrafast Charging Lithium, Sodium and Potassium Batteries

Organic redox-active compounds are considered as one of the most promising alternatives to conventional inorganic electrode materials. Organic cathodes, comprising of abundant elements (C, H, N, O), can be obtained from renewable resources and also have a number of other advantages. [1] In particular, batteries based on certain groups of organic materials have higher rate capabilities due to their fast oxidation-reduction kinetics and soft amorphous structure which facilitates ion diffusion. The diversity of organic molecules allows for tailoring their structure and properties to improve specific capacity, rate capability and operation stability of batteries. Inorganic intercalation-type compounds are usually constrained by their crystal lattice to a certain ion (e.g. Li+) with a specific ionic radius. On the contrary, the vast majority of known organic cathode materials are, in principle, electroactive with respect to a variety of metal ions since they are soft solids and have simple redox chemistry. Therefore, there is also a considerable potential in the development of potassium, sodium, magnesium, zinc and aluminium ion batteries if appropriate organic electrode materials and electrolytes are provided. This feature opens up wide opportunities for switching from scarce Li+ to some more abundant metal ions such as Na+ or K+. The recent flow of publications highlights four promising families of organic cathode materials represented by conjugated carbonyl compounds, free radical polymers, organosulfides, and conducting polymers. [2] The nitroxyl-based radical ion polymers and other redox-active conjugated polymers demonstrated impressive performances in terms of rate capabilities due to their high porosity, insolubility in conventional electrolytes and high operation voltages, while their capacity in batteries is typically limited by ~100 mA h g-1. Polytriphenylamine [3] and its analogues represent emerging group of redox-active polymers, which are expected to deliver superior gravimetric and volumetric capacities as well as high rate capability and good operational stability. [4] Herein, we report the synthesis and investigation of a novel redox-active poly(N,N’-diphenyl-p-phenylenediamine) (PDPPD) polymer obtained via Buchwald-Hartwig C-N cross-coupling reaction. PDPPD has a high density of redox-active amine groups enabling the theoretical specific capacity of 209 mA h g-1, which is nearly twice higher compared to all other materials of this family reported so far. The obtained polymer was evaluated as a cathode material for dual-ion batteries and demonstrated promising operation voltages of 3.5-3.7 V and decent practical gravimetric capacities of 97, 94 and 63 mA h g-1 in lithium, sodium and potassium half-cells, respectively, while being tested at the moderate current density of 1C. A specific capacity of 84 mA h g-1 was obtained for the ultrafast lithium batteries operating at 100C (full charge and discharge takes 36 seconds only), which is, to the best of our knowledge, the highest battery capacity reported so far for such high current densities. The PDPPD//Li batteries also showed promising stability reflected in 67% capacity retention after 5000 cycles. The obtained results prove that the designed PDPPD polymer indeed represents a highly promising organic cathode material for metal-ion batteries. Further rational design and exploration of this family of compounds might result in the development of a new generation of organic redox-active materials for advanced energy storage devices. In particular, the demonstrated in this work ultrafast batteries are of special interest in the view of multiple applications in the “electric push” devices emerging at the interface between the metal-ion batteries and supercapacitors.

Computational Screening for Developing Optimal Intermetallic Transition Metal Pt-Based ORR Catalysts at the Predictive Volcano Peak

Practical development of cost-effective and environmentally sustainable oxygen reduction reaction (ORR) catalysts has not yet been fully realized despite years of effort. Specifically, state-of-the-art ORR catalysts typically require high Pt-loading while still suffering significant overpotential losses and only providing moderate current density. In this work, we present results from new DFT calculations screening a wide range of Pt3(MN)1 ternary catalysts to see the range of values for oxygen adsorption energy (the known ORR volcano plot descriptor) such systems can achieve. Our results identify many promising materials based purely on performance via this descriptor; unfortunately, many of these promising candidates still require a very high loading of rare precious transition metals in the guest (MN) composition role. We have further used our results to generate a predictive fitted model for the ORR descriptor value itself based on the normalized valence and mass of a given fcc(111) Pt3(MN)1 surface c...

Rapid room-temperature synthesis of ultrasmall cubic Mg-Mn spinel cathode materials for rechargeable Mg-ion batteries.

Reducing the particle size of cathode materials is effective to improve the rate capability of Mg-ion batteries. In this study, ultrasmall cubic Mg–Mn spinel oxide nanoparticles approximately 5 nm in size were successfully synthesized via an alcohol reduction process within 30 min at room temperature. Though the particles aggregated to form large secondary particles, the aggregation could be suppressed by covering the particles with graphene. The composite exhibited a specific capacity of 230 mA h g−1, and could be cycled more than 100 times without any large capacity loss even at a moderate current density with the Mg(ClO4)2/CH3CN electrolyte.

Facile thermochemical conversion of FeOOH nanorods to ZnFe2O4 nanorods for high-rate lithium storage.

We successfully prepared ZnFe2O4 nanorods (ZFO-NRs) by a simple thermochemical reaction of FeOOH nanorods with Zn(NO3)2 to use as an anode material in lithium-ion batteries. The FeOOH nanorod shape was well maintained after conversion into ZFO-NR with the formation of porous structures. The nanorod structure and porous morphology facilitate Li+ transport, improve the reaction rates owing to the larger contact area with the electrolyte, and reduce the mechanical stress during lithiation/delithiation. The ZFO-NR electrode exhibited a reversible capacity of 725 mA h g−1 at 1 A g−1 and maintained a capacity of 668 mA h g−1 at 2 A g−1; these capacities are much higher and more stable than those of ZFO nanoparticles prepared by a hydrothermal method (ZFO-HT) (216 and 117 mA h g−1 at 1 and 2 A g−1, respectively). Although ZFO-NRs exhibited high, stable capacities at moderate current densities for charging and discharging, the capacity rapidly decreased under fast charging/discharging conditions (>4 A g−1). However, carbonized ZFO-NR (C/ZFO-NR) exhibited an improved reversible capacity and rate capability resulting from an increased conductivity compared with ZFO-NRs. The specific capacity of C/ZFO-NRs at 1 A g−1 was 765 mA h g−1; notably, a capacity of 680 mA h g−1 was maintained at 6 A g−1.

Self-Transforming Configuration Based on Atmospheric-Adaptive Materials for Solid Oxide Cells

Solid oxide cells (SOC) with a symmetrical configuration have been focused due to the practical benefits of such configurations, such as minimized compatibility issues, a simple fabrication process and reduced cost compared to SOCs with the asymmetrical configuration. However, the performance of SOCs using a single type of electrode material (symmetrical configuration) is lower than the performance of those using the dissimilar electrode materials (asymmetrical configuration). Therefore, to achieve a high-performance cell, we design a ‘self-transforming cell’ with the asymmetric configuration using only materials of the single type, one based on atmospheric adaptive materials. Atmospheric-adaptive perovskite Pr0.5Ba0.5Mn0.85Co0.15O3-δ (PBMCo) was used for the so-called self-transforming cell electrodes, which changed to layered perovskite and metal in the fuel atmosphere and retained its original structure in the air atmosphere. In fuel cell mods, the self-transforming cell shows excellent electrochemical performance of 1.10 W cm−2 at 800 °C and good stability for 100 h without any catalyst. In electrolysis mode, the moderate current densities of −0.42 A cm−2 for 3 vol.% H2O and −0.62 A cm−2 for 10 vol.% H2O, respectively, were observed at a cell voltage of 1.3 V at 800 °C. In the reversible cycling test, the transforming cell maintains the constant voltages for 30 h at +/− 0.2 A cm−2 under 10 vol. % H2O.

A 3D mesoporous flowers of nickel carbonate hydroxide hydrate for high-performance electrochemical energy storage application

3D hierarchical mesoporous structure, micron-sized flowers composed of nickel carbonate hydroxide hydrate (Ni2(CO3)(OH)2·H2O) (NCH) nanopetals were successfully synthesized by single-step facile hydrothermal method. The processing parameters appears to play vital role in governing nano-petaled flowers, provides high electroactive surface area. The mesoporous structure of 3D hierarchical structure offers a specific capacity of 353 mAh/g at a scan rate of 1 mV/s and ∼245 mAh/g under the current density of 1.83 A/g, respectively. The material has outperformed during the cycling stability when tested for the moderate and highest current density of 20 A/g and 40 A/g, respectively; it retained excellent capacity retention of ∼80% and 64%, respectively. The electrochemical impedance spectroscopy analysis was employed to probe the charge-transfer kinetics and charge storage performance and found to be in correlation with other charge storage analysis. The outstanding electrochemical performance is accredited to the intrinsic nature of nanostructured NCH, forming a unique miro-3D flower-like morphology. This ingenious synthesis strategy resulted in overall excellent electrochemical properties; indicating the NCH is a potential candidate for high-performance battery-like energy storage applications.

Low temperature annealing of metals with electrical wind force effects

Conventional annealing is a slow, high temperature process that involves heating atoms uniformly, i.e., in both defective and crystalline regions. This study explores an electrical alternative for energy efficiency, where moderate current density is used to generate electron wind force that produces the same outcome as the thermal annealing process. We demonstrate this on a zirconium alloy using in-situ electron back scattered diffraction (EBSD) inside a scanning electron microscope (SEM) and juxtaposing the results with that from thermal annealing. Contrary to common belief that resistive heating is the dominant factor, we show that 5 × 104 A/cm2 current density can anneal the material in less than 15 min at only 135 °C. The resulting microstructure is essentially the same as that obtained with 600 °C processing for 360 min. We propose that unlike temperature, the electron wind force specifically targets the defective regions, which leads to unprecedented time and energy efficiency. This hypothesis was investigated with molecular dynamics simulation that implements mechanical equivalent of electron wind force to provide the atomistic insights on defect annihilation and grain growth.