Thermal conductivity enhancement in gold decorated graphene nanosheets in ethylene glycol based nanofluid.

We report on the synthesis and thermal conductivity of gold nanoparticles (AuNPs) decorated graphene nanosheets (GNs) based nanofluids. The GNs-AuNPs nanocomposites were synthesised using a nanosecond pulsed Nd:YAG laser (wavelength = 1,064 nm) to ablate graphite target followed by Au in ethylene glycol (EG) base fluid to obtain GNs-AuNPs/EG hybrid nanofluid. The characterization of the as-synthesised GNs-AuNPs/EG hybrid nanofluid confirmed a sheet-like structure of GNs decorated with crystalline AuNPs with an average particle diameter of 6.3 nm. Moreover, the AuNPs appear smaller in the presence of GNs which shows the advantage of ablating AuNPs in GNs/EG. The thermal conductivity analysis in the temperature range 25-45 °C showed that GNs-AuNPs/EG hybrid nanofluid exhibits an enhanced thermal conductivity of 0.41 W/mK compared to GNs/EG (0.35 W/mK) and AuNPs/EG (0.39 W/mK) nanofluids, and EG base fluid (0.33 W/mK). GNs-AuNPs/EG hybrid nanofluid displays superior enhancement in thermal conductivity of up to 26% and this is due to the synergistic effect between AuNPs and graphene sheets which have inherent high thermal conductivities. GNs-AgNPs/EG hybrid nanofluid has the potential to impact on enhanced heat transfer technological applications. Also, this work presents a green synthesis method to produce graphene-metal nanocomposites for various applications.

Remarkable thermal conductivity enhancement in Ag-decorated graphene nanocomposites based nanofluid by laser liquid solid interaction in ethylene glycol.

We report on the synthesis and enhanced thermal conductivity of stable Ag-decorated 2-D graphene nanocomposite in ethylene glycol based nanofluid by laser liquid solid interaction. A surfactant free nanofluid of Ag nanoparticles anchored onto the 2-D graphene sheets were synthesized using a two-step laser liquid solid interaction approach. In order to understand a pulsed Nd:YAG laser at the fundamental frequency (λ = 1,064 nm) to ablate Ag and graphite composite target submerged in ethylene glycol (EG) to form AgNPs decorated 2-D GNs-EG based nanofluid. From a heat transfer point of view, it was observed that the thermal conductivity of this stable Ag-graphene/EG is significantly enhanced by a factor of about 32.3%; this is highest reported value for a graphene based nanofluid.

Effect of porosity enhancing agents on the electrochemical performance of high-energy ultracapacitor electrodes derived from peanut shell waste.

In this study, the synthesis of porous activated carbon nanostructures from peanut (Arachis hypogea) shell waste (PSW) was described using different porosity enhancing agents (PEA) at various mass concentrations via a two-step process. The textural properties obtained were depicted with relatively high specific surface area values of 1457 m2 g-1, 1625 m2 g-1 and 2547 m2 g-1 for KHCO3, K2CO3 and KOH respectively at a mass concentration of 1 to 4 which were complemented by the presence of a blend of micropores, mesopores and macropores. The structural analyses confirmed the successful transformation of the carbon-containing waste into an amorphous and disordered carbonaceous material. The electrochemical performance of the material electrodes was tested in a 2.5 M KNO3 aqueous electrolyte depicted its ability to operate reversibly in both negative and positive potential ranges of 0.90 V. The activated carbon obtained from the carbonized CPSW:PEA with a mass ratio of 1:4 yielded the best electrode performance for all featured PEAs. The porous carbons obtained using KOH activation displayed a higher specific capacitance and the lower equivalent series resistance as compared to others. The remarkable performance further corroborated the findings linked to the textural and structural properties of the material. The assembled device operated in a neutral electrolyte (2.5 M KNO3) at a cell potential of 1.80 V, yielded a ca. 224.3 F g-1 specific capacitance at a specific current of 1 A g-1 with a corresponding specific energy of 25.2 Wh kg-1 and 0.9 kW kg-1 of specific power. This device energy was retained at 17.7 Wh kg-1 when the specific current was quadrupled signifying an excellent supercapacitive retention with a corresponding specific power of 3.6 kW kg-1. These results suggested that peanut shell waste derived activated carbons are promising candidates for high-performance supercapacitors.

A high energy density asymmetric supercapacitor utilizing a nickel phosphate/graphene foam composite as the cathode and carbonized iron cations adsorbed onto polyaniline as the anode.

This work presents the effect of different contents of graphene foam (GF) on the electrochemical capacitance of nickel phosphate Ni3(PO4)2 nano-rods as an electrode material for hybrid electrochemical energy storage device applications. Pristine Ni3(PO4)2 nano-rods and Ni3(PO4)2/GF composites with different GF mass loadings of 30, 60, 90 and 120 mg were synthesised via a hydrothermal method. The electrochemical behavior of pristine Ni3(PO4)2 and Ni3(PO4)2/GF composites were analysed in a three-electrode cell configuration using 6 M KOH electrolyte. The Ni3(PO4)2/90 mg GF composite sample exhibited the highest specific capacity of 48 mA h g-1 at a current density of 0.5 A g-1. The electrochemical behavior of the Ni3(PO4)2/90 mg GF composite was further analysed in a two-electrode hybrid asymmetric device. A hybrid asymmetric device was fabricated with Ni3(PO4)2/90 mg GF as the cathode and carbonized iron cations (Fe3+) adsorbed onto polyaniline (PANI) (C-FP) as the anode material (Ni3(PO4)2/90 mg GF//C-FP) and tested in a wide potential window range of 0.0-1.6 V using 6 M KOH. This hybrid device achieved maximum energy and power densities of 49 W h kg-1 and 499 W kg-1, respectively, at 0.5 A g-1 and had long-term cycling stability.

Correction: A high energy density asymmetric supercapacitor utilizing a nickel phosphate/graphene foam composite as the cathode and carbonized iron cations adsorbed onto polyaniline as the anode.

[This corrects the article DOI: 10.1039/C7RA12028A.].