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Highlights • Vertical silicon, diamond and graphene structures for supercapacitor applications. • Electrochemical synthesis of conducting polymers onto 3D nanostructures. • Electrochemical performances of supercapacitor devices using ionic liquids. • Multi-hierarchized 3D nanostructures (PEDOT-D@SiNWs) showed the best performances. • Supercapacitive graphene and diamond nanostructures for new perspectives using ILs. Abstract The potential of electroactive conducting polymers (ECPs), as innovative pseudocapacitive materials, has recently emerged as a promising strategy to design new and advanced concepts in the field of electrochemical energy storage devices. From this point of view, the synergistic effect produced between high electroactivity ECPs (faradaic behaviour) and large active surface 3D nanostructured materials (electrochemical double layer behaviour) in terms of their high specific capacitance, high energy and power density as well as long lifetime, has awakened an enormous interest in the domain of (micro)-supercapacitors. Accordingly, in this work, we have originally analyzed the conformal electrochemical deposition of three different π-conjugated heterocyclic polymers [poly(3,4-ethylenedioxythiophene, polypyrrole and polyaniline] onto various vertically-oriented 3D nanoarchitectures, as for example silicon nanowires (SiNWs), diamond nanowires (DiNWs) or graphene nanosheets (GNs) among others. Next, the resulting as-grown hybrid materials were evaluated as attractive electrodes in symmetric supercapacitors (sandwich configuration) in presence of organic, aqueous, aprotic and protic ionic liquid (IL) electrolytes respectively. An exhaustive characterization of their corresponding electrochemical performances was investigated according to our previously reported works, confirming the remarkable cycling stability of ECPs in ILs. In addition, a detailed state-of-the-art dealing with other types of (micro)-supercapacitors in the literature was reported to corroborate the great impact of such devices to pave the way towards the elaboration of next generation high performance supercapacitors in the coming years. [ABSTRACT FROM AUTHOR]

Silicon nanowires (SiNWs) were successfully coated by uniform, adherent and homogenous ultra-thin crystalline diamond films through microwave enhanced chemical vapor deposition (MWCVD). The as-grown functionalized nanowires were employed as electrodes in a symmetric micro-supercapacitor (MSC) using a protic ionic liquid electrolyte [triethylammonium bis(trifluoromethylsulfonyl)imide; Et 3 NH TFSI]. The electrochemical performance of the device delivered a specific capacitance of 1.5 mF cm − 2 and a power density of 25 mW cm − 2 using an enlarged cell voltage of 4 V. Furthermore, a remarkable cycling stability was evaluated after 1 · 10 6 galvanostatic cycles at a high current density of 10 mA cm − 2 with an excellent capacitive behavior. These results confirm that diamond-coated SiNW micro-supercapacitors exhibit very promising performances dealing with MSCs based on CVD-grown SiNWs. [ABSTRACT FROM AUTHOR]

Silicon nanotrees (SiNTrs) have been grown by Chemical Vapor Deposition (CVD) via gold catalysis and a three steps process: trunks and branches growth are separated by a new gold catalyst deposition. The influence of growth conditions and the second gold catalyst deposition method on SiNTrs morphology are investigated. SiNTrs based electrodes show a capacitive behavior and better capacitance than the corresponding silicon nanowires (SiNWs) electrode. Electrode capacitance is increased up to 900 µF cm-2, i.e. 150 fold higher than for bulk silicon. Micro-supercapacitors with SiNTrs electrodes have a remarkable stability (only 1.2% loses of their initial capacitance after more than one million cycles). The use of an ionic liquid based electrolyte leads to a high maximum power density (around 225 mW cm-2) which is competitive with Onion Like Carbon based micro-supercapacitors. [ABSTRACT FROM AUTHOR]

Building of hierarchical core-shell hetero-structures is currently the subject of intensive research in the electrochemical field owing to its potential for making improved electrodes for high-performance micro-supercapacitors. Here we report a novel architecture design of hierarchical MnO2@silicon nanowires (MnO2@SiNWs) hetero-structures directly supported onto silicon wafer coupled with Li-ion doped 1-Methyl-1-propylpyrrolidinium bis(trifluromethylsulfonyl)imide (PMPyrrBTA) ionic liquids as electrolyte for micro-supercapacitors. A unique 3D mesoporous MnO2@SiNWs in Li-ion doped IL electrolyte can be cycled reversibly across a voltage of 2.2 V and exhibits a high areal capacitance of 13 mFcm−2. The high conductivity of the SiNWs arrays combined with the large surface area of ultrathin MnO2 nanoflakes are responsible for the remarkable performance of these MnO2@SiNWs hetero-structures which exhibit high energy density and excellent cycling stability. This combination of hybrid electrode and hybrid electrolyte opens up a novel avenue to design electrode materials for high-performance micro-supercapacitors. [ABSTRACT FROM AUTHOR]