Alexander J. Roberts

Factors affecting the performance of microbial fuel cells for sulfur pollutants removal

A microbial fuel cell (MFC) has been developed for removal of sulfur-based pollutants and can be used for simultaneous wastewater treatment and electricity generation. This fuel cell uses an activated carbon cloth+carbon fibre veil composite anode, air-breathing dual cathodes and the sulfate-reducing species Desulfovibrio desulfuricans. 1.16gdm(-3) sulfite and 0.97gdm(-3) thiosulfate were removed from the wastewater at 22 degrees C, representing sulfite and thiosulfate removal conversions of 91% and 86%, respectively. The anode potential was controlled by the concentration of sulfide in the compartment. The performance of the cathode assembly was affected by the concentration of protons in the cation-exchanging ionomer with which the electrocatalyst is co-bound at the three-phase (air, catalyst and support) boundary.

Controlled synthesis of ε-MnO2 and its application in hybrid supercapacitor devices

A controlled interfacial synthesis using a permeable membrane has been used to obtain e-MnO2 of a globular morphology, with a mechanism of formation inferred from SEM results. Specific surface areas of 50–160 m2 g−1 have been obtained through simple variation of the permeable membrane used in synthesis. This has been shown to have a marked effect on both particle size and pore size distributions. After assembly in supercapacitor test cells with aqueous neutral electrolyte, specific capacitances have been determined through galvanostatic cycling giving initial values as high as 240 F g−1, which drop to 160 F g−1 after 200 cycles at low discharge rates. Excellent cycling behavior is observed at higher discharge rates.

High electrochemical performance in asymmetric supercapacitors using MWCNT/nickel sulfide composite and graphene nanoplatelets as electrodes

The electrochemical performance of asymmetric supercapacitors (ASCs) using MWCNT/NiS and graphene nanoplatelets as the positive and negative electrode, respectively, are reported. Nickel sulfide nanoparticles can be decorated on multiwall carbon nanotubes using a hydrothermal synthesis process, with graphene nanoplatelets obtained via a chemical route. The fabricated ACSs were operated over a potential window of 1.4 V with a specific capacitance of 181 F g−1 observed at 1 A g−1. The ASCs were cycled at 2 A g−1 showing 92% retention of initial capacitance after 1000 cycles.

Alkaline ionomer with tuneable water uptakes for electrochemical energy technologies

A simple aqueous-processable alkaline ionomer (amenable to scale-up) has been developed for enhancing electrode/electrolyte interfaces in clean energy devices (e.g. alkaline polymer electrolyte membrane fuel cells). The water uptake of the alkaline ionomer is tuneable allowing its use as a tool for fundamental studies into these interfaces.

Birnessite nanotubes for electrochemical supercapacitor electrodes

Birnessite nanotubes have been made through a templated hydrothermal route. Variations in experimental conditions have resulted in differing morphologies of high specific surface area. After forming into electrodes in supercapacitor test cells, good cycleability was observed with specific capacitances approaching 350 F g−1 at low discharge current densities.

Electric field assisted chemical vapour deposition – a new method for the preparation of highly porous supercapacitor electrodes

Nanostructured thin films of vanadium oxides were deposited using electric field assisted chemical vapour deposition. The films were characterised using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. It was found that the films had open and porous morphologies with extremely small (5 nm) surface features. The films were made into supercapacitor cells and tested using cyclic voltammetry. It was found that stable asymptotic values specific capacitance values as high as 3700 μF cm−2 could be obtained with good cycling behaviour. Electrodes synthesized in this way show promise for applications in fields such as supercapacitors.

Nanostructured oxides for energy storage applications in batteries and supercapacitors

Nanostructured materials are extensively investigated for application in energy storage and power generation devices. This paper deals with the synthesis and characterization of nanomaterials based on oxides of vanadium and with their application as electrode materials for energy storage systems viz. supercapacitors. These nano-oxides have been synthesized using a hydrothermal route in the presence of templates: 1-hexadecylamine, Tweens and Brij types. Using templates during synthesis enables tailoring of the particle morphology and physical characteristics of synthesized powders. Broad X-ray diffraction peaks show the formation of nanoparticles, confirmed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations. SEM studies show that a large range of nanostructures such as needles, fibers, particles, etc. can be synthesized. These particles have varying surface areas and electrical conductivity. Enhancement of surface area as much as seven times relative to surface areas of starting parent materials has been observed. These properties make such materials ideal candidates for application as electrode materials in supercapacitors. Assembly and characterization of supercapacitors based on electrodes containing these active nano-oxides are discussed. Specific capacitance of >100 F g–1 has been observed. The specific capacitance decreases with cycling: causes of this phenomenon are presented.

Performance loss of aqueous MnO2/carbon supercapacitors at elevated temperature: cycling vs. storage

Birnessite MnO2 nanotubes of high specific surface area have been used as one electrode material in supercapacitors with a commercial-carbon-based second electrode ((NH4)2SO4(aq.) electrolyte). Assembled cells have been subjected to full electrochemical testing at temperatures ≤80 °C. At elevated temperatures, specific capacitance as high as 700 F g−1 has been observed. The increase in specific capacitance with temperature has been found to be at a cost to cycling performance. Furthermore, the time spent at elevated temperatures “at rest” has been shown to have a major effect on device lifetime. It has been found that at 80 °C, without cycling, such devices lose all significant capacitance after 21 days. The findings herein are believed to have major implications for transport, storage lifetime and ultimate utilization of such systems.

Nanostructured vanadium oxide based systems: their applications in supercapacitors

Synthesis and characterisation of nanostructured vanadium oxide based systems and their application in energy storage devices, namely supercapacitors, is presented. Vanadium oxide has been synthesised using a hydrothermal route in presence of various templates. X-ray diffraction studies reveal the formation of vanadium (IV) oxide as majority phase. SEM and TEM results depict presence of different nano-structured morphologies depending upon the template used. BET surface area measurement shows an increase of ∼7 times in the surface area of the synthesised powders in comparison to surface area of the starting raw powders. Conductivity enhancement of ∼3 to 5 orders of magnitude is observed as compared to conductivity of the starting raw material. These properties make this templated system suitable for application as electrode material in energy storage devices such as supercapacitors. Promising results of charge discharge on supercapacitors assembled using templated vanadium oxide based electrodes are reported. It is proposed that such systems can act as a cheap alternative to RuO2.

Temperature Dependence of Key Performance Indicators for Aqueous Supercapacitors Containing Nanostructured Birnessite

In this work, phase pure nanostructured birnessite-type MnO2 has been made through a templated aqueous hydrothermal route at a variety of temperatures between 120–150C for varying time. At lower synthesis temperatures, purely birnessite MnO2 was confirmed by powder XRD studies, but an additional MnOOH phase was present after reaction at 150C. The materials so formed have been shown to have varying pore size distributions with specific surface areas as high as 125 m g. Electron microscopy studies have shown morphologies to depend on synthesis conditions, ranging from simple sheets, through “nanoflowers”, “crown of thorns” (Figure 1), nanotubes and nanowires.