Multi-heteroatom self-doped porous carbon is synthesized via carbonization and activation of amino-acid-rich swim bladders. It shows a large capacitance when applied in supercapacitors.
Supercapacitors deliver exceptional power densities, high cycling stability, and inherent safety but suffer from low energy densities. Many methods to enhance the energy density are based on exploring electrode materials with well‐developed structures and designing asymmetric systems with wide voltage windows. The energy density is substantially enhanced at the compromise of power density by utilizing the sluggish kinetics of pseudocapacitive materials. Redox‐active electrolytes can contribute additional pseudocapacitance from the reactions of redox mediators at the interface, which have attracted increasing attention of researchers. Redox‐mediator‐enhanced supercapacitors deliver high energy densities while retaining high power densities. This Minireview highlights the recently prominent progresses of single‐, dual‐, and ambipolar‐redox‐mediator‐enhanced supercapacitors, the challenges they face, and approaches to suppress self‐discharge and develop high‐concentration redox‐active electrolytes for performance promotion.
Scattered Au 3D nanoparticles form distinct functional regions with an uncovered internal surface in confined channels, named the "Janus" annulus. Electrochemical impedance spectroscopy responses to the variations in DNA self-assembly and hybridization in the channels decorated by the "Janus" annulus are presented. Single nucleotide mutations are further detected in a linear DNA chain, including terminal base polymorphisms.
Highly porous carbon (3047 m2 g−1) with a graphene nanoplatelet microstructure is obtained by using a biomass waste as a new carbon source. Introducing high‐energy ball milling treatment during the synthesis procedure can greatly improve the surface wettability of carbon and ensure the homogenously contact between carbon and KOH, thus leading to high reactivity of the KOH activation. The highly efficient activation endows this carbon with favorable features for supercapacitors, such as high surface area with coexistence of rich micropores and mesopores, unique graphene nanoplatelet microstructure with good conductivity and many capacitive active sites. The as‐prepared carbon exhibits high specific capacitances of 329 and 311 F g−1 in 2 m KOH and 1 m H2SO4 electrolyte at 1.0 A g−1, respectively. In 1 m TEABF4/AN electrolyte, a high working voltage of 3 V and excellent rate performance can be obtained based on a two‐electrode full cell. The energy density of the carbon/carbon symmetric capacitor reaches 49.5 W h kg−1 and the extreme power density can reach 10.8 kW kg−1. The results suggest this biomass‐waste‐derived carbon can serve as a low‐cost and high‐performance electrode material for supercapacitors with universal electrolytes.
A new phase Na 2 Ti 3 O 7 compound is synthesized by solid-state method for the first time, which is verified to belong to the triclinic structure in P-1 space group. Compared to the conventional monoclinic Na 2 Ti 3 O 7 (m-NTO), in P2 1 /m1 space group, the triclinic Na 2 Ti 3 O 7 (t-NTO) possesses a shorter O-O band in the distorted TiO 6 octahedron, which accounts for more smooth Na + transport channels and a more stable layered structure with smaller fluctuation. The experimental results show that the t-NTO keeps a low charge potential plateau at 0.3 V compared to the m-NTO, but with much promoted structure resilience. It delivers a capacity retention of 94.7%, far exceeding the 25.7% of the m-NTO upon decades of cycles. In situ X-ray diffraction reveals that the conventional m-NTO experiences an irreversible phase transition during insertion/de-insertion of Na + , while the new t-NTO can recover its structure reversibly after discharge and charge, which is consistent with its improved cycling performance. The results demonstrate a new t-NTO anode and provide a new understanding for the phase diversity of sodium-ion battery materials.
Carbon-based electrochemical double-layer capacitors (EDLCs) generally exhibit high power and long life, but low energy density/capacitance. Pore/morphology optimization and pseudo-capacitive materials modification of carbon materials have been used to improve electrode capacitance, but leading to the consumption of tap density, conductivity and stability. Introducing soluble redox mediators into electrolyte is a promising alternative to improve the capacitance of electrode. However, it is difficult to find one redox mediator that can provide additional capacitance for both positive and negative electrodes simultaneously. Here, an ambipolar organic radical, 2, 2, 6, 6-tetramethylpiperidinyloxyl (TEMPO) is first introduced to the electrolyte, which can substantially contribute additional pseudo-capacitance by oxidation at the positive electrode and reduction at the negative electrode simultaneously. The EDLC with TEMPO mediator delivers an energy density as high as 51 Wh kg , 2.4 times of the capacitor without TEMPO, and a long cycle stability over 4000 cycles. The achieved results potentially point a new way to improve the energy density of EDLCs.
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