David Aradilla

3D hierarchical assembly of ultrathin MnO2 nanoflakes on silicon nanowires for high performance micro-supercapacitors in Li- doped ionic liquid

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 2.2u2009V and exhibits a high areal capacitance of 13u2009mFcm−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.

Vertically aligned graphene nanosheets on silicon using an ionic liquid electrolyte: towards high performance on-chip micro-supercapacitors

Vertically oriented graphene nanosheets were synthesized by an alternative and simple approach based on electron cyclotron resonance-plasma enhanced chemical vapor deposition (ECR-CVD) onto highly doped silicon substrates. The as-grown graphene electrodes were employed in a symmetric micro-supercapacitor using an aprotic ionic liquid [N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonylimide); PYR13TFSI] as electrolyte. The device was able to deliver an outstanding specific capacitance value of 2 mF cm−2, a power density value of 4 mW cm−2 and an energy density value of 4 μW h cm−2 operating at a large and stable cell voltage of 4 V with a quasi-ideal capacitive behaviour. Moreover, the lifetime of the device exhibited a remarkable electrochemical stability retaining 80% of the initial capacitance after 150u2006000 galvanostatic charge–discharge cycles at a high current density of 1 mA cm−2. This excellent electrochemical performance results from the obtained channel-based 3-D graphene network promoting rapid electrolyte ion-transport and short diffusion paths.

An innovative 3-D nanoforest heterostructure made of polypyrrole coated silicon nanotrees for new high performance hybrid micro-supercapacitors

In this work, an innovative 3-D symmetric micro-supercapacitor based on polypyrrole (PPy) coated silicon nanotree (SiNTr) hybrid electrodes has been fabricated. First, SiNTrs were grown on silicon substrates by chemical vapor deposition (CVD) and then via an electrochemical method, the conducting polymer coating was deposited onto the surface of SiNTr electrodes. This study illustrates the excellent electrochemical performance of a hybrid micro-supercapacitor device using the synergistic combination of both PPy as the electroactive pseudo-capacitive material and branched SiNWs as the electric double layer capacitive material in the presence of an aprotic ionic liquid (N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide; PYR 13 TFSI) as the electrolyte. The hybrid device exhibited a specific capacitance as high as ∼14 mF cm-2 and an energy density value of ∼15 mJ cm-2 at a wide cell voltage of 1.5 V using a high current density of 1 mA cm-2. Furthermore, a remarkable cycling stability after thousands of galvanostatic charge-discharge cycles with a loss of approximately 30% was obtained. The results reported in this investigation demonstrated that PPy coated SiNTr-based micro-supercapacitors exhibit the best performances among hybrid micro-supercapacitors made of silicon nanowire electrodes grown by CVD in terms of specific capacitance and energy density.

Novel hybrid micro-supercapacitor based on conducting polymer coated silicon nanowires for electrochemical energy storage

The development of a novel hybrid symmetric micro-supercapacitor based on poly(3,4-ethylenedioxythiophene) coated silicon nanowires using an ionic liquid (N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide) as an electrolyte has been demonstrated. The hybrid supercapacitor device was able to deliver a specific energy of 10 W h kg−1 and a maximal power density of 85 kW kg−1 at a cell voltage of 1.5 V. The hybrid device exhibited long lifetime and an outstanding electrochemical stability retaining 80% of the initial capacitance after thousands of galvanostatic charge–discharge cycles at a high current density of 1 mA cm−2. The improvement of the capacitive properties compared with the bare SiNWs was attributed to the pseudo-capacitive behavior induced by the conducting polymer coating.

Designing 3D Multihierarchical Heteronanostructures for High-Performance On-Chip Hybrid Supercapacitors: Poly(3,4-(ethylenedioxy)thiophene)-Coated Diamond/Silicon Nanowire Electrodes in an Aprotic Ionic Liquid

A versatile and robust hierarchically multifunctionalized nanostructured material made of poly(3,4-(ethylenedioxy)thiophene) (PEDOT)-coated diamond@silicon nanowires has been demonstrated to be an excellent capacitive electrode for supercapacitor devices. Thus, the electrochemical deposition of nanometric PEDOT films on diamond-coated silicon nanowire (SiNW) electrodes using N-methyl-N-propylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide ionic liquid displayed a specific capacitance value of 140 F g(-1) at a scan rate of 1 mV s(-1). The as-grown functionalized electrodes were evaluated in a symmetric planar microsupercapacitor using butyltrimethylammonium bis((trifluoromethyl)sulfonyl)imide aprotic ionic liquid as the electrolyte. The device exhibited extraordinary energy and power density values of 26 mJ cm(-2) and 1.3 mW cm(-2) within a large voltage cell of 2.5 V, respectively. In addition, the system was able to retain 80% of its initial capacitance after 15u2009000 galvanostatic charge-discharge cycles at a high current density of 1 mA cm(-2) while maintaining a Coulombic efficiency around 100%. Therefore, this multifunctionalized hybrid device represents one of the best electrochemical performances concerning coated SiNW electrodes for a high-energy advanced on-chip supercapacitor.

Silicon nanowires and nanotrees: elaboration and optimization of new 3D architectures for high performance on-chip supercapacitors

Micro-supercapacitors are increasingly foreseen as future energy storage or power buffer solutions for small scale integration on-chip. However, widely used electrode materials or electrolytes often proved to be incompatible with microelectronics processes. Although being the material of choice for on-chip integration, nanostructured silicon electrodes only recently caught attention for potential applications, and they displayed promising results especially for bottom-up silicon nanostructures, where the design liberty and fine control of nanostructure morphologies allow considerable improvements. The present work deals with the optimization of highly doped silicon nanowires (Si-NWs) and nanotrees (Si-NTrs) pioneered in the laboratory using an innovative, fast and efficient electroless gold deposition method in order to explore a wide variety of 3D architectures and their physicochemical properties. Through a systematic study of branches and trunks morphologies, the nature inspired nanotrees have been drastically improved compared to previously published works, resulting in excellent electrode properties, showing high energy and power densities, respectively, up to 2.8 mJ cm−2 and 235 mW cm−2. In addition, a cyclability of over a million charge–discharge galvanostatic cycles was determined using an enlarged electrochemical window of 4 V in an ionic liquid electrolyte.

SiNWs-based electrochemical double layer micro-supercapacitors with wide voltage window (4 V) and long cycling stability using a protic ionic liquid electrolyte*

The present work reports the use and application of a novel protic ionic liquid (triethylammonium bis(trifluoromethylsulfonyl)imide; NEt3H TFSI) as an electrolyte for symmetric planar micro-supercapacitors based on silicon nanowire electrodes. The excellent performance of the device has been successfully demonstrated using cyclic voltammetry, galvanostatic charge-discharge cycles and electrochemical impedance spectroscopy. The electrochemical characterization of this system exhibits a wide operative voltage of 4 V as well as an outstanding long cycling stability after millions of galvanostatic cycles at a high current density of 2 mA cm−2. In addition, the electrochemical double layer micro-supercapacitor was able to deliver a high power density of 4 mW cm−2 in a very short time pulses (a few ms). Our results could be of interest to develop prospective on-chip micro-supercapacitors using protic ionic liquids as electrolytes with high performance in terms of power and energy densities.

Diamond-coated silicon nanowires for enhanced micro-supercapacitor with ionic liquids

Silicon nanowires (SiNWs) and diamond-coated SiNWs (D@SiNWs) on highly n-doped silicon wafer substrates were prepared through standard chemical vapor deposition (CVD) method as electrodes for micro-supercapacitors. The surface of electrodes exhibited uniform distribution of SiNWs on silicon wafer and continuous diamond coating on SiNWs. Electrochemical measurements were carried out in order to test the combined effect of using Ionic Liquid electrolytes and diamond coating on SiNWs on energy storage performance. Optimal values of areal capacitance, energy density and power densities were 317 μF cm-2, 0.13 μWh cm-2 and 150 μW cm-2, respectively. So, the work reported here confirms the suitability and compatibility of D@SiNWs electrode materials and ionic liquid electrolytes for the fabrication of high-performing and robust micro-supercapacitors.