authors contributed equally to this work. One Sentence Summary: Lewis acidic molten salts etching is an effective and promising route for producing MXenes with superior electrochemical performance in non-aqueous electrolyte. Abstract: Two-dimensional carbides and nitrides of transition metals, known as MXenes, are a fast-growing family of 2D materials that draw attention as energy storage materials. So far, MXenes are mainly prepared from Al-containing MAX phases (where A = Al) by Al dissolution in F-containing solution, but most other MAX phases have not been explored. Here, a redox-controlled A-site-etching of MAX phases

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The exponential growth of the market for portable electronic devices together with the development of electric vehicles have created an ever-increasing demand for light-weight and compact electric power sources of high energy and power density. Among them, rechargeable batteries can store energy in large amounts, but with low specific power. On the contrary, electrochemical capacitors can supply higher power than most batteries, but the energy density is relatively low. [1][2][3] Therefore, a number of strategies are under development for optimizing the energy density of capacitors while keeping a high specific power. The amount of electrical energy (E) accumulated in a capacitor is related to the capacitance (C) and voltage (V) according to the formulaThe capacitance depends essentially on the electrode material used, whereas the operating voltage is determined by the stability window of the electrolyte. The use of high-capacitance materials is a key factor for the optimization of energy density. Power density (P) itself is given bywhere ESR and M represent the equivalent series resistance and the total mass of the two electrodes, respectively. Since ESR is mainly dependent on the resistance of the electrodes, it is necessary to develop materials of high electrical conductivity. Activated carbons are the most widely used electrode material for supercapacitors because of their high surface area and relatively good electrical conductivity. The energy storage mechanism in this case is mainly based on an accumulation of charge in the double layer formed at the electrode/electrolyte interface. In general, the specific capacitance is in the range of 10-30 lF cm -2 . However, the performance of electrical double-layer capacitors (EDLCs) is only slightly correlated with the specific surface area of activated carbons, being also influenced by other parameters, such as the pore size.

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The sea provides a large variety of seaweeds that, because of their chemical composition, are fantastic precursors of nanotextured carbons. The carbons are obtained by the simple pyrolysis of the seaweeds under a nitrogen atmosphere between 600 and 900 °C, followed by rinsing the product in slightly acidic water. Depending on the origin of the seaweed and on the pyrolysis conditions, the synthesis may be oriented to give an oxygen‐enriched carbon or to give a tuned micro/mesoporous carbon. The samples with a rich oxygenated surface functionality are excellent as supercapacitor electrodes in an aqueous medium whereas the perfectly tuned porous carbons are directly applicable for organic media. In both cases, the specific surface area of the attained carbons does not exceed 1300 m2 g−1, which results in high‐density materials. As a consequence, the volumetric capacitance is very high, making these materials more interesting than activated carbons from the point of view of developing small and compact electric power sources. Such versatile carbons, obtained by a simple, ecological, and cheap process, could be well used for environment remediation such as water and air treatment.

A novel microporous templated carbon material doped with nitrogen is synthesized by using a two‐step nanocasting process using acrylonitrile (AN) and propylene as precursors, and Na–Y zeolite as a scaffold. Liquid‐phase impregnation and in situ polymerization of the nitrogenated precursor inside the nanochannels of the inorganic scaffold, followed by gas‐phase impregnation with propylene, enables pore‐size control and functionality tuning of the resulting carbon material. The material thereby obtained has a narrow pore‐size distribution (PSD), within the micropore range, and a large amount of heteroatoms (i.e., oxygen and nitrogen). In addition, the carbon material inherits the ordered structure of the inorganic host. Such features simultaneously present in the carbon result in it being ideal for use as an electrode in a supercapacitor. Although presenting a moderately developed specific surface area (SBET = 1680 m2 g–1), the templated carbon material displays a large gravimetric capacitance (340 F g–1) in aqueous media because of the combined electrochemical activity of the heteroatoms and the accessible porosity. This material can operate at 1.2 V in an aqueous medium with good cycleability—‐beyond 10 000 cycles—and is extremely promising for use in the development of high‐energy‐density supercapacitors.

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