Advanced Energy Materials
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Formation of Yolk‐Shelled Ni–Co Mixed Oxide Nanoprisms with Enhanced Electrochemical Performance for Hybrid Supercapacitors and Lithium Ion Batteries Yolk‐shelled particles with tailored physical and chemical properties are attractive for electrochemical energy storage. Starting with metal acetate hydroxide with tetragonal prism‐like shapes, yolk‐shelled Ni–Co mixed oxide nanoprisms with tunable composition have been prepared by simple thermal annealing in air. It is found that the yolk‐shelled structure is formed due to the fast thermally driven contraction process. With the favorable porous structure and composition, these yolk‐shelled Ni–Co oxide particles manifest greatly enhanced electrochemical properties when evaluated as electrodes for both hybrid supercapacitors and lithium ion batteries. In particular, the resultant Ni0.37 Co oxide sample delivers very high specific capacitance of over 1000 F g−1 at a current density of 10 A g−1 with remarkably high capacitance retention of 98% after 15 000 cycles.
Advanced Energy Materials - Tập 5 Số 21 - 2015
The Application of Metal Sulfides in Sodium Ion Batteries The high demand for clean and renewable energy has fueled the exploration of advanced energy storage systems. As a potential alternative device for lithium ion batteries, sodium ion batteries (NIBs) have attracted extraordinary attention and are becoming a promising candidate for energy storage due to their low cost and high efficiency. Recent progress has demonstrated that metal sulfides (MSs) are very promising electrode candidates for efficient Na‐storage devices, because of their excellent redox reversibility and relatively high capacity. In this review, recent developments of MSs as anode materials for NIBs are presented. The corresponding electrochemical mechanisms are briefly discussed. We also present critical issues, challenges, and perspectives with the hope of providing a fuller understanding of the associated electrochemical processes. Such an understanding is critical for tailoring and designing metal sulfides with the desired activity and stability.
Advanced Energy Materials - Tập 7 Số 3 - 2017
One‐to‐One Comparison of Graphite‐Blended Negative Electrodes Using Silicon Nanolayer‐Embedded Graphite versus Commercial Benchmarking Materials for High‐Energy Lithium‐Ion Batteries While existing carbonaceous anodes for lithium–ion batteries (LIBs) are approaching a practical capacitive limit, Si has been extensively examined as a potential alternative because it shows exceptional gravimetric capacity (3579 mA h g−1 ) and abundance. However, the actual implementation of Si anodes is impeded by difficulties in electrode calendering processes and requirements for excessive binding and conductive agents, arising from the brittleness, large volume expansion (>300%), and low electrical conductivity (1.56 × 10−3 S m−1 ) of Si. In one rational approach to using Si in high‐energy LIBs, mixing Si‐based materials with graphite has attracted attention as a feasible alternative for next‐generation anodes. In this study, graphite‐blended electrodes with Si nanolayer‐embedded graphite/carbon (G/SGC) are demonstrated and detailed one‐to‐one comparisons of these electrodes with industrially developed benchmarking samples are performed under the industrial electrode density (>1.6 g cc−1 ), areal capacity (>3 mA h cm−2 ), and a small amount of binder (3 wt%) in a slurry. Because of the favorable compatibility between SGC and conventional graphite, and the well‐established structural features of SGC, great potential is envisioned. Since this feasible study utilizes realistic test methods and criteria, the rigorous benchmarking comparison presents a comprehensive understanding for developing and characterizing Si‐based anodes for practicable high‐energy LIBs.
Advanced Energy Materials - Tập 7 Số 15 - 2017
Hybrid Graphene Ribbon/Carbon Electrodes for High‐Performance Energy Storage Abstract The utility of supercapacitors for both fixed and portable energy storage would be greatly enhanced if their energy density could be increased while maintaining their high power density, fast charging time, and low cost. This study describes a simple, solution‐phase, scalable modification of carbon materials by a covalently bonded “brush” of hydrogen‐terminated graphene ribbons (GRs) with layer thicknesses of 2–20 nm, resulting in a 20–100 times increase in the areal capacitance of the unmodified electrode surface. On a flat sp2 carbon surface modified by GRs, the capacitance exceeds 1200 µF cm−2 in 0.1 m H2 SO4 due to a distinct type of pseudocapacitance during constant current charge/discharge cycling. Modification of high surface area carbon black electrodes with GRs yields capacitances of 950–1890 F g−1 , power densities >40 W g−1 , and minimal change in capacitance during 1500 charge/discharge cycles at 20 A g−1 . A capacitance of 1890 F g−1 affords an energy density of 318 Wh kg−1 operating at 1.1 V and 590 Wh kg−1 at 1.5 V. The projected energy density of a hybrid GR/carbon supercapacitor greatly exceeds the current 10 Wh kg−1 for commercial supercapacitors and approaches that of lithium ion batteries.
Advanced Energy Materials - Tập 8 Số 35 - 2018
Nature of FeSe<sub>2</sub>/N‐C Anode for High Performance Potassium Ion Hybrid Capacitor Abstract Potassium ion hybrid capacitors have great potential for large‐scale energy devices, because of the high power density and low cost. However, their practical applications are hindered by their low energy density, as well as electrolyte decomposition and collector corrosion at high potential in potassium bis(fluoro‐sulfonyl)imide‐based electrolyte. Therefore, anode materials with high capacity, a suitable voltage platform, and stability become a key factor. Here, N‐doping carbon‐coated FeSe2 clusters are demonstrated as the anode material for a hybrid capacitor, delivering a reversible capacity of 295 mAh g−1 at 100 mA g−1 over 100 cycles and a high rate capability of 158 mAh g−1 at 2000 mA g−1 over 2000 cycles. Meanwhile, through density functional theory calculations, in situ X‐ray diffraction, and ex situ transmission electron microscopy, the evolution of FeSe2 to Fe3 Se4 for the electrochemical reaction mechanism is successfully revealed. The battery‐supercapacitor hybrid using commercial activated carbon as the cathode and FeSe2 /N‐C as the anode is obtained. It delivers a high energy density of 230 Wh kg−1 and a power density of 920 W kg−1 (the energy density and power density are calculated based on the total mass of active materials in the anode and cathode).
Advanced Energy Materials - Tập 10 Số 4 - 2020
Selective CO<sub>2</sub> Reduction on 2D Mesoporous Bi Nanosheets Abstract The conversion of CO2 to value‐added products using electrical or solar energy represents an attractive means for the capture and utilization of atmospheric CO2 . Formate is a popular product from CO2 reduction, but its reaction selectivity is usually unsatisfactory. Tin‐based materials have attracted the most attention for formate production at present. Unfortunately, most of them only exhibit moderate selectivity in a narrow and highly cathodic potential window. In this study, it is demonstrated that traditionally under‐explored bismuth has a much greater potential for formate production than tin or other materials. Mesoporous bismuth nanosheets are prepared here by the cathodic transformation of atomic‐thick bismuth oxycarbonate nanosheets. They enable the selective CO2 reduction to formate with large current density, excellent Faradaic efficiency (≈100%) over a broad potential window and great operation stability. Moreover, Bi nanosheets are integrated with an oxygen evolution reaction electrocatalyst in full cells, and achieve efficient and robust solar conversion of CO2 /H2 O to formate/O2 .
Advanced Energy Materials - Tập 8 Số 35 - 2018
Fully Hydrocarbon Membrane Electrode Assemblies for Proton Exchange Membrane Fuel Cells and Electrolyzers: An Engineering Perspective Abstract Perfluorinated‐sulfonic‐acid‐based ionomers (PFSAs) are still the material of choice for electrochemical energy devices such as proton‐exchange membrane fuel cells or water electrolyzers. However, PFSAs show significant drawbacks ranging from a restricted temperature window of operation due to the insufficient thermomechanical stability, high cost, and questionable environmental properties. Recently, novel hydrocarbon‐based ionomers have been introduced, which not only have the potential to overcome these limitations, but also for the first time show promising performance, approaching that of PFSA‐based fuel cells and electrolyzers. This article summarizes the recent developments in this emerging field with a particular focus on the engineering of membrane‐electrode assemblies with hydrocarbon‐based polymer electrolytes. In the final part, the necessary key innovations are discussed, which are required for hydrocarbon ionomers to replace PFSAs in fuel cells and electrolyzers in the future.
Advanced Energy Materials - Tập 12 Số 12 - 2022
Amorphous/Crystalline Heterostructured Cobalt‐Vanadium‐Iron (Oxy)hydroxides for Highly Efficient Oxygen Evolution Reaction Abstract The oxygen evolution reaction (OER) is a key process involved in energy and environment‐related technologies. An ideal OER electrocatalyst should show high exposure of active sites and optimal adsorption energies of oxygenated species. However, earth‐abundant transition‐metal‐based OER electrocatalysts still operate with sluggish OER kinetics. Here, a cation‐exchange route is reported to fabricate cobalt‐vanadium‐iron (oxy)hydroxide (CoV‐Fe0.28 ) nanosheets with tunable binding energies for the oxygenated intermediates. The formation of an amorphous/crystalline heterostructure in the CoV‐Fe0.28 catalyst boosts the exposure of active sites compared to their crystalline and amorphous counterparts. Furthermore, the synergetic interaction of Co, V, and Fe cations in the CoV‐Fe0.28 catalyst subtly regulates the local coordination environment and electronic structure, resulting in the optimal thermodynamic barrier for this elementary reaction step. As a result, the CoV‐Fe0.28 catalyst exhibits superior electrocatalytic activity toward the OER. A low overpotential of 215 mV is required to afford a current density of 10 mA cm−2 with a small Tafel slope of 39.1 mV dec−1 , which outperforms commercial RuO2 (321 mV and 86.2 mV dec−1 , respectively).
Advanced Energy Materials - Tập 10 Số 43 - 2020
Highly Air‐Stable Single‐Crystalline β‐CsPbI<sub>3</sub> Nanorods: A Platform for Inverted Perovskite Solar Cells Abstract The synthesis of single‐crystalline β‐CsPbI3 perovskite nanorods (NRs) using a colloidal process is reported, exhibiting their improved photostability under 45–55% humidity. The crystal structure of CsPbI3 NRs films is investigated using Rietveld refined X‐ray diffraction (XRD) patterns to determine crystallographic parameters and the phase transformation from orthorhombic (γ‐CsPbI3 ) to tetragonal (β‐CsPbI3 ) on annealing at 150 °C. Atomic resolution transmission electron microscopy images are utilized to determine the probable atomic distribution of Cs, Pb, and I atoms in a single β‐phase CsPbI3 NR, in agreement with the XRD structure and selected area electron diffraction pattern, indicating the growth of single crystalline β‐CsPbI3 NR. The calculation of the electronic band structure of tetragonal β‐CsPbI3 using density functional theory (DFT) reveals a direct transition with a lower band gap and a higher absorption coefficient in the solar spectrum, as compared to its γ‐phase. An air‐stable (45–55% humidity) inverted perovskite solar cell, employing β‐CsPbI3 NRs without any encapsulation, yields an efficiency of 7.3% with 78% enhancement over the γ‐phase, showing its potential for future low cost photovoltaic devices.
Advanced Energy Materials - Tập 10 Số 30 - 2020
Grain Boundary Phases in NbFeSb Half‐Heusler Alloys: A New Avenue to Tune Transport Properties of Thermoelectric Materials Abstract Many thermoelectric materials benefit from complex microstructures. Grain boundaries (GBs) in nanocrystalline thermoelectrics cause desirable reduction in the thermal conductivity by scattering phonons, but often lead to unwanted loss in the electrical conductivity by scattering charge carriers. Therefore, modifying GBs to suppress their electrical resistivity plays a pivotal role in the enhancement of thermoelectric performance, zT . In this work, different characteristics of GB phases in Ti‐doped NbFeSb half‐Heusler compounds are revealed using a combination of scanning transmission electron microscopy and atom probe tomography. The GB phases adopt a hexagonal close‐packed lattice, which is structurally distinct from the half‐Heusler grains. Enrichment of Fe is found at GBs in Nb0.95 Ti0.05 FeSb, but accumulation of Ti dopants at GBs in Nb0.80 Ti0.20 FeSb, correlating to the bad and good electrical conductivity of the respective GBs. Such resistive to conductive GB phase transition opens up new design space to decouple the intertwined electronic and phononic transport in thermoelectric materials.
Advanced Energy Materials - Tập 13 Số 13 - 2023
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