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[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

Transition metal carbides and nitrides (MXenes), a family of two-dimensional (2D) inorganic compounds, are materials composed of a few atomic layers of transition metal carbides, nitrides, or carbonitrides. Ti3C2, the first 2D layered MXene, was isolated in 2011. This material, which is a layered bulk material analogous to graphite, was derived from its 3D phase, Ti3AlC2 MAX. Since then, material scientists have either determined or predicted the stable phases of >200 different MXenes based on combinations of various transition metals such as Ti, Mo, V, Cr, and their alloys with C and N. Extensive experimental and theoretical studies have shown their exciting potential for energy conversion and electrochemical storage. To this end, we comprehensively summarize the current advances in MXene research. We begin by reviewing the structure types and morphologies and their fabrication routes. The review then discusses the mechanical, electrical, optical, and electrochemical properties of MXenes. The focus then turns to their exciting potential in energy storage and conversion. Energy storage applications include electrodes in rechargeable lithium- and sodium-ion batteries, lithium-sulfur batteries, and supercapacitors. In terms of energy conversion, photocatalytic fuel production, such as hydrogen evolution from water splitting, and carbon dioxide reduction are presented. The potential of MXenes for the photocatalytic degradation of organic pollutants in water, such as dye waste, is also addressed, along with their promise as catalysts for ammonium synthesis from nitrogen. Finally, their application potential is summarized.

Applications of 2D MXenes in energy conversion and storage systems

A decade after the first report, the family of two-dimensional (2D) carbides and nitrides (MXenes) includes structures with three, five, seven, or nine layers of atoms in an ordered or solid solution form. Dozens of MXene compositions have been produced, resulting in MXenes with mixed surface terminations. MXenes have shown useful and tunable electronic, optical, mechanical, and electrochemical properties, leading to applications ranging from optoelectronics, electromagnetic interference shielding, and wireless antennas to energy storage, catalysis, sensing, and medicine. Here we present a forward-looking review of the field of MXenes. We discuss the challenges to be addressed and outline research directions that will deepen the fundamental understanding of the properties of MXenes and enable their hybridization with other 2D materials in various emerging technologies.

The world of two-dimensional carbides and nitrides (MXenes)

Ti3C2Tx is a 2-dimensional titanium carbide material featuring outstanding electrochemical properties. In spite of this, application of Ti3C2Tx as co-catalyst in photo-catalysis is rarely explored, probably because of its metallic nature and hydrophilic surface. Given that Ti3C2Tx with different surface terminations exhibits large differences in catalytic, electrochemical and chemical properties, we demonstrate an improvement of the photocatalytic activity of Ti3C2Tx as a co-catalyst by annealing a composite of carbon nitride and Ti3C2Tx. Ti3C2Tx with an oxygen terminated surface improved the separation of electron–hole pairs and resulted in a 105% enhancement in the production ratio of hydrogen evolution compared to control samples. The best hydrogen production performance reached as high as 88 μmol h−1 gcat−1. The apparent quantum yield (AQY) reached as high as 1.27%. The DFT calculations also demonstrate a better hydrogen evolution on Ti3C2 with oxygen surface termination.

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g-C3N4/Ti3C2Tx (MXenes) composite with oxidized surface groups for efficient photocatalytic hydrogen evolution

Efficient Nondoped Blue Fluorescent Organic Light‐Emitting Diodes (OLEDs) with a High External Quantum Efficiency of 9.4% @ 1000 cd m−2 Based on Phenanthroimidazole−Anthracene Derivative

Yu Gao

Papers

g-C3N4/Ti3C2Tx (MXenes) composite with oxidized surface groups for efficient photocatalytic hydrogen evolution

Efficient Nondoped Blue Fluorescent Organic Light‐Emitting Diodes (OLEDs) with a High External Quantum Efficiency of 9.4% @ 1000 cd m−2 Based on Phenanthroimidazole−Anthracene Derivative

Hierarchical flower-like VS2 nanosheets – A high rate-capacity and stable anode material for sodium-ion battery

Porous carbon made from rice husk as electrode material for electrochemical double layer capacitor

Two-dimensional vanadium carbide (V2C) MXene as electrode for supercapacitors with aqueous electrolytes