Advanced electrical energy storage technology is a game changer for a clean, sustainable, and secure energy future because efficient utilization of newable energy hinges on cost-effect and efficient ...energy storage. Further, the viability of many emerging technologies depends on breakthroughs in energy storage technologies, including electric vehicles (EVs) or hybrid electric vehicles (HEVs) and smart grids. Lithium-ion batteries (LIBs), a great success in the portable electronics sector, are believed also the most promising power sources for emerging technologies such as EVs and smart grids. To date, however, the existing LIBs (with LiCoOx cathode and graphite anode) are still unable to meet the strict requirements for safety, cycling stability, and rate capability. The development of advanced anode materials, which can overcome the shortcomings of graphite anode (such as formation of dendritic lithium during charge and undesirable solid electrolyte interface), is of critical importance to enhancing the cycling stability and operational safety of LIBs. Lithium titanate (Li4Ti5O12) has recently attracted considerable attentions as a potential anode material of LIBs for high power applications due to several outstanding features, including a flat charge/discharge plateaus (around 1.55V vs. Li/Li+) because of the two-phase lithium insertion/extraction mechanism and minimum chance for the formation of SEI and dendritic lithium, dramatically enhance the potential for high rate capability and safety. In addition, there is almost no volume change during the lithium insertion and extraction processes, ensuring a high cycling stability and long operational life. However, the electronic conductivity of Li4Ti5O12 is relatively low, resulting in large polarization lose, more so at higher cycling rates, and poor rate performance. Currently, considerable research efforts have been devoted to improving the performance of Li4Ti5O12 at fast charge/discharge rates, and some important progresses have been made. In this review, we first present a general overview of the structural features, thermodynamic properties, transport properties, and the electrochemical behavior of Li4Ti5O12 under typical battery operating conditions. We then provide a comprehensive review of the recent advancements made in characterization, modification, and applications of Li4Ti5O12 electrodes to LIBs, including nanostructuring, surface coating, morphological optimization, doping, and rational design of composite electrodes. Finally, we highlight the critical challenges facing us today and future perspectives for further development of Li4Ti5O12-based electrodes. It is hoped that this review may provide some useful guidelines for rational design of better electrodes for advanced LIBs.
This review encompasses the fundamental aspects of electrophoretic deposition technique, factors influencing the deposition process, kinetic aspects, types of EPD, the driving forces, preparation of ...electrophoretic suspension, stability and control of suspension, mechanisms involved in EPD, multicomponent/composite deposition, drying of deposits obtained by EPD. Numerous applications including coatings, nanoscale assembly, micropatterned thin films, near shape ceramics and glasses, solid oxide fuel cells, laminated or graded materials, hybrid materials, infiltration in porous and woven fibre preforms for preparation of fibre reinforced ceramic matrix composites, etc. have been described. The use of mathematical modeling including kinetic equations for deposit formation and volumetric particle concentration in the suspension, together with brief description of discrete element modeling of EPD process is presented.
Development of cost-effective and efficient electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of prime importance to emerging renewable energy technologies. ...Here, we report a simple and effective strategy for enhancing ORR and OER electrocatalytic activity in alkaline solution by introducing A-site cation deficiency in LaFeO3 perovskite; the enhancement effect is more pronounced for the OER than the ORR. Among the A-site cation deficient perovskites studied, La0.95FeO3‑δ (L0.95F) demonstrates the highest ORR and OER activity and, hence, the best bifunctionality. The dramatic enhancement is attributed to the creation of surface oxygen vacancies and a small amount of Fe4+ species. This work highlights the importance of tuning cation deficiency in perovskites as an effective strategy for enhancing ORR and OER activity for applications in various oxygen-based energy storage and conversion processes.
The development of cost-effective catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for enhancing the energy efficiency of many electrochemical energy ...conversion and storage devices. Owing to their low cost and high activity, transition metal oxides have attracted much attention as alternative electrocatalysts to replace the currently used noble metal-based catalysts. Anion defects (
e.g.
, oxygen vacancies, interstitials, and anion dopants) can significantly change the electronic structure of oxides or the stability of adsorbed intermediates, thus greatly enhancing the electrocatalytic activities of the oxide surface. Anionic defect engineering represents a potential new direction for rational design of high-performance electrocatalysts. In this review, recent progress in manipulating the anion defects in transition metal oxides for enhancing their activity and stability is summarized and the proposed mechanisms for enhanced performance are discussed in detail. Challenges and prospects are also discussed in the development of a new generation of highly efficient ORR and OER electrocatalysts.
Techniques for anionic defect engineering in transition metal oxides and mechanisms of how anion defects affect their oxygen reaction activities.
Perovskite oxides are demonstrated for the first time as efficient electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solutions. A‐site praseodymium‐doped ...Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3–δ (Pr0.5BSCF) exhibits dramatically enhanced HER activity and stability compared to Ba0.5Sr0.5Co0.8Fe0.2O3–δ (BSCF), superior to many well‐developed bulk/nanosized nonprecious electrocatalysts. The improved HER performance originates from the modified surface electronic structures and properties of Pr0.5BSCF induced by the Pr‐doping.
Developing low‐cost, high‐performance electro‐catalysts is essential for large‐scale application of electrochemical energy devices. In this article, reported are the findings in understanding and ...controlling oxygen defects in PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) for significantly enhancing the rate of oxygen evolution reaction (OER) are reported. Utilizing surface‐sensitive characterization techniques and first‐principle calculations, it is found that excessive oxygen vacancies promote OH− affiliation and lower the theoretical energy for the formation of O* on the surface, thus greatly facilitating the OER kinetics. On the other hand, however, oxygen vacancies also increase the energy band gap and lower the O 2p band center of PBSCF, which may hinder OER kinetics. Still, careful tuning of these competing effects has resulted in enhanced OER activity for PBSCF with oxygen defects. This work also demonstrates that oxygen defects generated by different techniques have very different characteristics, resulting in different impacts on the activity of electrodes. In particular, PBSCF nanotubes after electrochemical reduction exhibit outstanding OER activity compared with the recently reported perovskite‐based catalysts.
Oxygen vacancies in PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) are found to promote OH‐ affiliation and lower the theoretical energy for the formation of O* on the surface. However, oxygen vacancies also increase the energy band gap and lower the O 2p band center of PBSCF. Careful tuning of these competing effects has resulted in enhanced oxygen evolution reaction activity for PBSCF with oxygen defects.
Solid oxide cell (SOC) based energy conversion systems have the potential to become the cleanest and most efficient systems for reversible conversion between electricity and chemical fuels due to ...their high efficiency, low emission, and excellent fuel flexibility. Broad implementation of this technology is however hindered by the lack of high-performance electrode materials. While many perovskite-based materials have shown remarkable promise as electrodes for SOCs, cation enrichment or segregation near the surface or interfaces is often observed, which greatly impacts not only electrode kinetics but also their durability and operational lifespan. Since the chemical and structural variations associated with surface enrichment or segregation are typically confined to the nanoscale, advanced experimental and computational tools are required to probe the detailed composition, structure, and nanostructure of these near-surface regions in real time with high spatial and temporal resolutions. In this review article, an overview of the recent progress made in this area is presented, highlighting the thermodynamic driving forces, kinetics, and various configurations of surface enrichment and segregation in several widely studied perovskite-based material systems. A profound understanding of the correlation between the surface nanostructure and the electro-catalytic activity and stability of the electrodes is then emphasized, which is vital to achieving the rational design of more efficient SOC electrode materials with excellent durability. Furthermore, the methodology and mechanistic understanding of the surface processes are applicable to other materials systems in a wide range of applications, including thermo-chemical photo-assisted splitting of H
O/CO
and metal-air batteries.
A series of flexible nanocomposite electrodes were fabricated by facile electro-deposition of cobalt and nickel double hydroxide (DH) nanosheets on porous NiCo2O4 nanowires grown radially on carbon ...fiber paper (CFP) for high capacity, high energy, and power density supercapacitors. Among different stoichiometries of Co x Ni1–x DH nanosheets studied, Co0.67Ni0.33 DHs/NiCo2O4/CFP hybrid nanoarchitecture showed the best cycling stability while maintaining high capacitance of ∼1.64 F/cm2 at 2 mA/cm2. This hybrid composite electrode also exhibited excellent rate capability; the areal capacitance decreased less than 33% as the current density was increased from 2 to 90 mA/cm2, offering excellent specific energy density (∼33 Wh/kg) and power density (∼41.25 kW/kg) at high cycling rates (up to150 mA/cm2).
Solid oxide fuel cells (SOFCs) have the potential to be one of the cleanest and most efficient energy technologies for direct conversion of chemical fuels to electricity. Economically competitive ...SOFC systems appear poised for commercialization, but widespread market penetration will require continuous innovation of materials and fabrication processes to enhance system lifetime and reduce cost. One early technical opportunity is minimization of resistance to the oxygen reduction reaction (ORR) at the cathode, which contributes the most to performance degradation and efficiency loss in the existing SOFCs, especially at temperatures <700 °C. Detailed study over the past 15 years has revealed the positive impact of catalyst infiltration on SOFC cathode performance, both in power density and durability metrics. However, realizable performance improvements rely upon strongly-coupled relationships in materials and morphology between the infiltrate and the backbone, and therefore efficacious systems cannot be simply generated with a set of simple heuristics. This article reviews recent progress in enhancing SOFC cathode performance by surface modification through a solution-based infiltration process, focusing on two backbone architectures - inherently functional and skeletal - infiltrated using wet-chemistry processes. An efficient cathode consists of a porous mixed-conducting backbone and an active coating catalyst; the porous backbone provides excellent ionic and electronic conductivity, while the infiltrated surface coating possesses high catalytic activity and stability. As available, performance comparisons are emphasized and reaction schematics for specific infiltrate/backbone systems are summarized. While significant progress has been achieved in enhancing surface catalytic activity and durability, the detailed mechanisms of performance enhancement are insufficiently understood to obtain critical insights and a scientific basis for rational design of more efficient catalysts and novel electrode architectures. Recent progress in characterization of surfaces and interfaces is briefly discussed with challenges and perspectives in surface modification of SOFC electrodes. Surface modification through infiltration is expected to play an increasingly important role in current and next-generation commercial SOFC development, and this review illustrates the sophisticated technical considerations required to inform judicious selection of an infiltrate for a given SOFC system.
Wet chemical infiltration processes have been demonstrated to be effective to enhance electrocatalytic activity and stability in SOFC cathodes.
In this paper, we present a four-layer tunable wideband electromagnetic shield based on cold plasma. It consists of two dielectric matched layers, one backside housing dielectric layer and one vacuum ...chamber in between where cold plasma can be produced through a glow discharge. No plasma is produced within the vacuum chamber when low-power communication signal impinges on the shield and it can easily propagate through with very low return and absorption loss. When a high-power microwave pulse impinges on the shield, cold plasma can be timely produced within the chamber to reflect and absorb the high-intensity microwave energy. Input impedance, standing wave ratio, transmission and reflection coefficients and shielding effectiveness for proposed four-layer structure electromagnetic shield are deduced and formulated. Transparent mode of the electromagnetic shield for communication frequency at 3.5GHz is developed based on transmission line and plane wave theory. Simulation results show that the transmission coefficient is close to unity, and the reflection coefficient is near to zero. The half-power transmission bandwidth is 16% for proposed structure with central communication frequency of 3.5GHz. The impact of plasma frequency and plasma collision frequency on the absorption, reflection, shielding effectiveness for interference frequency between 0-6GHz are investigated. Simulation results show that higher the plasma frequency, better the shielding effectiveness is in the investigated frequency band when plasma collision frequency is fixed. It was also demonstrated that the shielding effectiveness of proposed structure can be tuned by changing plasma collision frequency.