Nutthaphon Phattharasupakun

Charge storage mechanisms of electrospun Mn3O4 nanofibres for high-performance supercapacitors

Mixed oxidation states of manganese oxides are widely used as the electrodes in supercapacitors due to their high theoretical pseudocapacitances. However, their charge storage mechanisms are not yet fully understood. In this work, the charge storage mechanism of Mn3O4 or Mn2+(Mn3+)2O4 nanofibres was investigated using a synchrotron-based X-ray absorption spectroscopy (XAS) technique and an in situ electrochemical quartz crystal microbalance (EQCM). The average oxidation state of the Mn in the as-synthesized Mn3O4 is +2.67. After the first charge, the average oxidation states of Mn at the positive and negative electrodes are +2.61 and +2.38, respectively. The significant change in the oxidation state of Mn at the negative electrode is due to phase transformation of Mn3O4 to NaδMnOx·nH2O. Meanwhile, the charge storage mechanism at the positive electrode mainly involves the adsorption of counter ions or solvated SO42−. After the first discharge, the calculated Mn average oxidation numbers are +2.51 and +2.53 at the positive and negative electrodes, respectively. At the negative electrode, the solvated Na+ is desorbed from the electrode surface. At the same time, the solvated SO42− is desorbed from the positive electrode. The mass change of solvated Na+ during charging/discharging is ca. 80 ng per cm2 of the Mn3O4 electrode. A symmetric supercapacitor constructed from Mn3O4 nanofibres in 0.5 M Na2SO4 provides a working potential of 1.8 V, a specific energy of 37.4 W h kg−1 and a maximum specific power of 11.1 kW kg−1 with 98% capacity retention over 4500 cycles. The understanding of the charge storage mechanism of the mixed oxidation states of Mn2+(Mn3+)2O4 presented in this work could lead to further development of metal oxide-based pseudocapacitors.

Chemical Adsorption and Physical Confinement of Polysulfides with the Janus-faced Interlayer for High-performance Lithium-Sulfur Batteries

We design the Janus-like interlayer with two different functional faces for suppressing the shuttle of soluble lithium polysulfides (LPSs) in lithium-sulfur batteries (LSBs). At the front face, the conductive functionalized carbon fiber paper (f-CFP) having oxygen-containing groups i.e., -OH and -COOH on its surface was placed face to face with the sulfur cathode serving as the first barrier accommodating the volume expansion during cycling process and the oxygen-containing groups can also adsorb the soluble LPSs via lithium bonds. At the back face, a crystalline coordination network of [Zn(H2PO4)2(TzH)2]n (ZnPTz) was coated on the back side of f-CFP serving as the second barrier retarding the left LPSs passing through the front face via both physical confinement and chemical adsorption (i.e. Li bonding). The LSB using the Janus-like interlayer exhibits a high reversible discharge capacity of 1,416 mAh g−1 at 0.1C with a low capacity fading of 0.05% per cycle, 92% capacity retention after 200 cycles and ca. 100% coulombic efficiency. The fully charged LSB cell can practically supply electricity to a spinning motor with a nominal voltage of 3.0 V for 28 min demonstrating many potential applications.

Antifungal activity of water-stable copper-containing metal-organic frameworks

Although metal-organic frameworks (MOFs) or porous coordination polymers have been widely studied, their antimicrobial activities have not yet been fully investigated. In this work, antifungal activity of copper-based benzene-tricarboxylate MOF (Cu-BTC MOF), which is water stable and industrially interesting, is investigated against Candida albicans, Aspergillus niger, Aspergillus oryzae and Fusarium oxysporum. The Cu-BTC MOF can effectively inhibit the growth rate of C. albicans and remarkably inhibit the spore growth of A. niger, A. oryzae and F. oxysporum. This finding shows the potential of using Cu-BTC MOF as a strong biocidal material against representative yeasts and moulds that are commonly found in the food and agricultural industries.

Turning Carbon Black to Hollow Carbon Nanospheres for Enhancing Charge Storage Capacities of LiMn2O4, LiCoO2, LiNiMnCoO2, and LiFePO4 Lithium-Ion Batteries

Carbon black nanospheres were turned to hollow carbon nanospheres (HCNs) and were used as the conductive additive in the cathodes of Li-ion batteries (LIBs). The results show that 10 wt % HCN added to the LIB cathodes, such as LiMn2O4, LiCoO2, LiNiMnCoO2, and LiFePO4, can provide significantly higher specific capacity than those using spherical carbon black. For example, a specific capacity of the LiMn2O4/HCN/PVDF cathode at 80:10:10 wt % with a bulk electrical conductivity of 1.07 Ω cm–2 is 125 mA h g–1 at 0.1 C from 3.0 to 4.3 V versus Li+/Li, which is 3.85-fold higher than that using Super P. The stability tested at 1 C remains over 95% after 800 charge/discharge cycles with 100% Coulombic efficiency. Replacing the present carbon black conductive additive with HCN in this work may be one of the best choices to increase the charge storage performance of LIBs rather than only focusing on the development of active cathode materials.

A new energy conversion and storage device of cobalt oxide nanosheets

A new design of a single hybrid energy conversion and storage cell of cobalt oxide (Co3O4) nanosheets, which can absorb the whole visible spectrum, exhibits the highest volumetric capacitance of 80.8 F cm−3 under light illumination (white LED), which is 2.2-fold higher than that under dark conditions at 1.5 A cm−3.

Collaborative design of Li–S batteries using 3D N-doped graphene aerogel as a sulfur host and graphitic carbon nitride paper as an interlayer

Lithium–sulfur batteries (LSBs) have been widely investigated due to their high energy densities; however, their practical applications have still been limited by their poor cycling stability owing to the shuttle mechanism effect, volume expansion, soluble polysulfides, and the poor electrical conductivity of sulfur and Li2S. To address these issues, sulfur was loaded into a conductive 3D nitrogen-doped reduced graphene oxide aerogel (NGae) host with a finely tuned nitrogen doping content. In addition, an interlayer of graphitic carbon nitride coated on flexible and conductive carbon fiber paper (g-C3N4/CFP) was inserted between the cathode and the polymer separator to trap the soluble polysulfides. It was found that the as-fabricated LSB using the NGae host with 4.2% N doping content and the g-C3N4/CFP interlayer can provide a specific capacity of 1271 mA h g−1 at 0.1C with excellent stability over 400 cycles. The capacity fading is rather small (only 0.068% per cycle) while the coulombic efficiency is rather high (ca. 100%). This battery may be practically used in high-energy applications.

Oxidative chemical vapour deposition of a graphene oxide carbocatalyst on 3D nickel foam as a collaborative electrocatalyst towards the hydrogen evolution reaction in acidic electrolyte

In this study, a graphene oxide (GO) carbocatalyst was synthesized as a thin film on a 3D Ni foam substrate (GO@Ni) by oxidative chemical vapour deposition (CVD) using methanol and water as precursors. The GO@Ni was used as a collaborative electrocatalyst towards the hydrogen evolution reaction (HER) in an acidic electrolyte. Notably, pure Ni metal cannot be used as an electrocatalyst in acidic media due to corrosion. The amount of water in the methanol was finely tuned to optimize the electrochemical activity of the GO@Ni for HER. The optimized GO@Ni catalyst, with a sheet resistivity of 133.48 Ω square−1, an optical band gap of 1.52 eV, and a C : O ratio of 3.89 produced using 90 : 10 V% of methanol : water, exhibits excellent and stable HER activity with an overpotential of 137 mV vs. RHE, reaching a high current density of 10 mA cm−2 and prominent electrochemical stability for up to 12 h in 0.5 M H2SO4. In addition, the CVD GO layer on the Ni foam acts as an anti-corrosion material protecting the Ni HER catalyst in the acidic environment. As a result, the GO@Ni may be a promising electrode for HER, replacing expensive Pt catalysts.

Transparent supercapacitors of 2 nm ruthenium oxide nanoparticles decorated on a 3D nitrogen-doped graphene aerogel

Although ruthenium oxide nanoparticles (RuO2), graphene, and their composites have been widely used as supercapacitor electrode materials, transparent supercapacitors of these materials have been rarely investigated. In this work, we fabricated high-performance transparent solid-state supercapacitors of 2 nm RuO2 decorated on a 3D nitrogen-doped reduced graphene oxide aerogel (NGA) with 27–54% transparency. The as-fabricated symmetric supercapacitor of RuO2/NGA at a finely tuned mass loading of 16.3 μg cm−2 with a finely tuned transmittance of 34.1% at a wavelength of 550 nm exhibits a maximum areal energy of 0.074 μW h cm−2 and a maximum areal power of 64 μW cm−2. The cycling stability of the device can also be maintained at 100% over 2000 cycles. The high transparent supercapacitor in this work may practically be used in many advanced transparent electrical devices.

Novel Hybrid Energy Conversion and Storage Cell with Photovoltaic and Supercapacitor Effects in Ionic Liquid Electrolyte

A single hybrid energy conversion and storage (HECS) cell of alpha-cobalt hydroxide (α-Co(OH)2) in ionic liquid was fabricated and operated under light illumination. The α-Co(OH)2, which is unstable in an aqueous electrolyte (i.e. KOH), is surprisingly stable in 1-butyl-1-methyl-pyrrolidinium dicyanamide ionic liquid. The as-fabricated HECS cell provides 100% coulombic efficiency and 99.99% capacity retention over 2000 cycles. Under a photo-charging condition, the dicyanamide anion of ionic liquid can react with a generated α-Co(OH)2+ hole at the positive electrode since the HOMO energy level of the anion is close to the valence band of α-Co(OH)2. The excited photoelectron will transfer to the current collector and move to the negative electrode. At the negative electrode, the 1-butyl-1-methyl-pyrrolidinium cations of ionic liquid do electrostatically adsorb on the surface and intercalate into the interlayer of active material stabilizing the whole cell. The HECS cell having both energy conversion (photovoltaic effect) and energy storage (supercapacitor) properties may be an ideal device for future renewable energy.

Author Correction: Chemical Adsorption and Physical Confinement of Polysulfides with the Janus-faced Interlayer for High-performance Lithium-Sulfur Batteries

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.