Powering electrodes for high performance aqueous micro-supercapacitors: Diamond-coated silicon nanowires operating at a wide cell voltage of 3 V

Abrupt degenerately-doped silicon nanowire tunnel junctions

We have confirmed the presence of narrow, degenerately-doped axial silicon nanowire (SiNW) p-n junctions via off-axis electron holography (EH). SiNWs were grown via the vapor-solid-liquid (VLS) mechanism using gold (Au) as the catalyst, silane (SiH₄), diborane (B₂H₆) and phosphine (PH₃) as the precursors, and hydrochloric acid (HCl) to stabilize the growth. Two types of growth were carried out, and in each case we explored growth with both n/p and p/n sequences. In the first type, we abruptly switched the dopant precursors at the desired junction location, and in the second type we slowed the growth rate at the junction to allow the dopants to readily leave the Au catalyst. We demonstrate degenerately-doped p/n and n/p nanowire segments with abrupt potential profiles of 1.02 ± 0.02 and 0.86 ± 0.3 V, and depletion region widths as narrow as 10 ± 1 nm via EH. Low temperature current-voltage measurements show an asymmetric curvature in the forward direction that resemble planar gold-doped tunnel junctions, where the tunneling current is hidden by a large excess current. The results presented herein show that the direct VLS growth of degenerately-doped axial SiNW p-n junctions is feasible, an essential step in the fabrication of more complex SiNW-based devices for electronics and solar energy.

Boron-doped Nanodiamond as an Electrode Material for Aqueous Electric Double-layer Capacitors

Herein, a conductive boron-doped nanodiamond (BDND) particle is prepared as an electrode material for an aqueous electric double-layer capacitor with high power and energy densities. The BDND is obtained by depositing a boron-doped diamond (BDD) on a nanodiamond particle substrate with a primary particle size of 4.7 nm via microwave plasma-assisted chemical vapor deposition, followed by heat treatment in air. The BDND comprises BDD and sp² carbon components, and exhibits a conductivity above 10⁻² S cm⁻¹ and a specific surface area of 650 m² g⁻¹. Cyclic voltammetry measurements recorded in 1 M H₂SO₄ at a BDND electrode in a two-electrode system shows a capacitance of 15.1 F g⁻¹ and a wide potential window (cell voltage) of 1.8 V, which is much larger than that obtained at an activated carbon electrode, i.e., 0.8 V. Furthermore, the cell voltage of the BDND electrode reaches 2.8 V when using saturated NaClO₄ as electrolyte. The energy and power densities per unit weight of the BDND for charging–discharging in 1 M H₂SO₄ at the BDND electrode cell are 10 Wh kg⁻¹ and 10⁴ W kg⁻¹, respectively, and the energy and power densities per unit volume of the BDND layer are 3–4 mWh cm⁻³ and 10 W cm⁻³, respectively. Therefore, the BDND is a promising candidate for the development of a compact aqueous EDLC device with high energy and power densities.

Understanding the Thermal Treatment Effect of Two-Dimensional Siloxene Sheets and the Origin of Superior Electrochemical Energy Storage Performances

Two-dimensional siloxene sheets are an emerging class of materials with an eclectic range of potential applications including electrochemical energy conversion and storage sectors. Here, we demonstrated the dehydrogenation/dehydroxylation of siloxene sheets by thermal annealing at high temperature (HT) and investigated their supercapacitive performances using ionic liquid electrolyte. The X-ray diffraction analysis, spectroscopic (Fourier transform infrared, laser Raman, and X-ray photoelectron spectroscopy) studies, and morphological analysis of HT-siloxene revealed the removal of functional groups at the edges/basal planes of siloxene, and preservation of oxygen-interconnected Si₆ rings with sheet-like structures. The HT-siloxene symmetric supercapacitor (SSC) operates over a wide potential window (0-3.0 V), delivers a high specific capacitance (3.45 mF cm^-2), high energy density of about 15.53 mJ cm^-2 (almost 2-fold higher than that of the as-prepared siloxene SSC), and low equivalent series resistance (compared to reported silicon-based SSCs) with excellent rate capability and long cycle life over 10 000 cycles.

Enhanced electrochemical supercapacitor performance with a three-dimensional porous boron-doped diamond film

A three-dimensional porous boron-doped diamond film is developed to enhance the electrochemical performance of supercapacitors in a wide potential window.

Boron Doped Diamond: A Designer Electrode Material for the Twenty-First Century

Boron doped diamond (BDD) is continuing to find numerous electrochemical applications across a diverse range of fields due to its unique properties, such as having a wide solvent window, low capacitance, and reduced resistance to fouling and mechanical robustness. In this review, we showcase the latest developments in the BDD electrochemical field. These are driven by a greater understanding of the relationship between material (surface) properties, required electrochemical performance, and improvements in synthetic growth/fabrication procedures, including material postprocessing. This has resulted in the production of BDD structures with the required function and geometry for the application of interest, making BDD a truly designer material. Current research areas range from in vivo bioelectrochemistry and neuronal/retinal stimulation to improved electroanalysis, advanced oxidation processes, supercapacitors, and the development of hybrid electrochemical-spectroscopic- and temperature-based technology aimed at enhancing electrochemical performance and understanding.