Spinels with the formula of AB2O4 (where A and B are metal ions) and the properties of magnetism, optics, electricity, and catalysis have taken significant roles in applications of data storage, biotechnology, electronics, laser, sensor, conversion reaction, and energy storage/conversion, which largely depend on their precise structures and compositions. In this review, various spinels with controlled preparations and their applications in oxygen reduction/evolution reaction (ORR/OER) and beyond are summarized. First, the composition and structure of spinels are introduced. Then, recent advances in the preparation of spinels with solid-, solution-, and vapor-phase methods are summarized, and new methods are particularly highlighted. The physicochemical characteristics of spinels such as their compositions, structures, morphologies, defects, and substrates have been rationally regulated through various approaches. This regulation can yield spinels with improved ORR/OER catalytic activities, which can furth...

Spinels: Controlled Preparation, Oxygen Reduction/Evolution Reaction Application, and Beyond

Over the past decade, electrochemical energy storage (EES) devices have greatly improved, as a wide variety of advanced electrode active materials and new device architectures have been developed. These new materials and devices should be evaluated against clear and rigorous metrics, primarily based on the evidence of real performances. A series of criteria are commonly used to characterize and report performance of EES systems in the literature. However, as advanced EES systems are becoming more and more sophisticated, the methodologies to reliably evaluate the performance of the electrode active materials and EES devices need to be refined to realize the true promise as well as the limitations of these fast-moving technologies, and target areas for further development. In the absence of a commonly accepted core group of metrics, inconsistencies may arise between the values attributed to the materials or devices and their real performances. Herein, we provide an overview of the energy storage devices from conventional capacitors to supercapacitors to hybrid systems and ultimately to batteries. The metrics for evaluation of energy storage systems are described, although the focus is kept on capacitive and hybrid energy storage systems. In addition, we discuss the challenges that still need to be addressed for establishing more sophisticated criteria for evaluating EES systems. We hope this effort will foster ongoing dialog and promote greater understanding of these metrics to develop an international protocol for accurate assessment of EES systems.

Towards establishing standard performance metrics for batteries, supercapacitors and beyond.

As a new class of crystalline porous materials, metal-organic frameworks (MOFs) have received great attention owing to their unique advantages of ultrahigh surface area, large pore volume and versatile applications. Developing different strategies to control the morphology and size of MOFs is very important for their practical applications. Recently, micro/nanosized MOFs have been regarded as promising candidates for electrode materials with excellent performances, which not only bridge the gap between fundamental MOF science and forward-looking applications, but also provide an opportunity to make clear the relationship between morphologies and properties. This review focuses on the design and fabrication of one-, two- and three-dimensional MOFs at micro/nanoscale, and their direct applications in batteries, supercapacitors and electrocatalysis. A discussion on challenges and future prospects of the synthesis and electrochemical applications of micro/nanoscaled MOF materials is presented.

Synthesis of micro/nanoscaled metal-organic frameworks and their direct electrochemical applications.

Electrochemical energy storage technology is of critical importance for portable electronics, transportation and large-scale energy storage systems. There is a growing demand for energy storage devices with high energy and high power densities, long-term stability, safety and low cost. To achieve these requirements, novel design structures and high performance electrode materials are needed. Porous 1D nanomaterials which combine the advantages of 1D nanoarchitectures and porous structures have had a significant impact in the field of electrochemical energy storage. This review presents an overview of porous 1D nanostructure research, from the synthesis by bottom-up and top-down approaches with rational and controllable structures, to several important electrochemical energy storage applications including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-oxygen batteries and supercapacitors. Highlights of porous 1D nanostructures are described throughout the review and directions for future research in the field are discussed at the end.

Porous One-Dimensional Nanomaterials: Design, Fabrication and Applications in Electrochemical Energy Storage.

Metal-organic frameworks (MOFs) are a class of porous materials with unprecedented chemical and structural tunability. Their synthetic versatility, long-range order, and rich host–guest chemistry make MOFs ideal platforms for identifying design features for advanced functional materials. This review addresses synthetic approaches to control MOF attributes for realizing material properties such as charge conductivity, stability, surface area, and flexibility. Along with an updated account on MOFs employed in batteries and supercapacitors, new directions are outlined for advancing MOF research in emergent technologies such as solid-state electrolytes and battery operation in extreme environments. Synthetic tenability of metal organic frameworks renders them versatile platform for next-generation energy storage technologies. Here the authors provide an overview of selected MOF attributes for applications in solid-state electrolytes and battery operation in extreme environments.

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Metal-organic framework functionalization and design strategies for advanced electrochemical energy storage devices

Exploring metal organic frameworks for energy storage in batteries and supercapacitors

Porous NiCo2O4 nanotubes have been successfully synthesized using a facile and cost-effective electrospinning method and used as a noble-metal-free catalyst for rechargeable Li–O2 batteries. The as-synthesized NiCo2O4 nanotubes possess hollow cavities and porous walls, and were found to significantly improve the electrochemical performance of Li–O2 batteries, by endowing them with a high initial discharge capacity, reduced overpotential as well as good rate capability. Excellent cycling stability over 110 cycles with a highly discharged voltage platform of 2.4 V at 200 mA gc−1 was achieved. By means of FESEM, XRD, Raman spectroscopy and GITT analysis, toroidal-shaped Li2O2 particles were identified as the dominant discharge product and it was revealed that the Li2O2 can be completely decomposed during the charging process, indicating its superior reversibility as an effective bifunctional catalyst for Li–O2 batteries. All the results indicated that the porous NiCo2O4 nanotubes expressed intriguing properties and great potential applications as a noble-metal-free effective bifunctional catalyst for rechargeable Li–O2 batteries.

Porous NiCo2O4 nanotubes as a noble-metal-free effective bifunctional catalyst for rechargeable Li–O2 batteries

CO poisoning of Pt-group metal catalysts is a long-standing problem, particularly for hydrogen oxidation reaction in proton exchange membrane fuel cells. Here, we report a catalyst of Ru oxide-coated Ru supported on TiO2 (Ru@RuO2/TiO2), which can tolerate 1-3% CO, enhanced by about 2 orders of magnitude over the classic PtRu/C catalyst, for hydrogen electrooxidation in a rotating disk electrode test. This catalyst can work stably in 1% CO/H2 for 50 h. About 20% of active sites can survive even in a pure CO environment. The high CO tolerance is not via a traditional bifunctional mechanism, i.e., oxide promoting CO oxidation, but rather via hydrous metal oxide shell blocking CO adsorption. An ab initio molecular dynamics (AIMD) simulation indicates that water confined in grain boundaries of the Ru oxide layer and Ru surface can suppress the diffusion and adsorption of CO. This oxide blocking layer approach opens a promising avenue for the design of high CO-tolerant electrocatalysts for fuel cells.

Laiyang Li

Papers

Exploring metal organic frameworks for energy storage in batteries and supercapacitors

Porous NiCo2O4 nanotubes as a noble-metal-free effective bifunctional catalyst for rechargeable Li–O2 batteries

High CO-Tolerant Ru-Based Catalysts by Constructing an Oxide Blocking Layer.

Low-cost polymer acceptors with noncovalently fused-ring backbones for efficient all-polymer solar cells

Non-contact biomimetic mechanism for selective hydrogenation of nitroaromatics on heterogeneous metal nanocatalysts