Dr Jessica Allen

Here graphite was found to undergo carbon/carbonate gasification at 800 °C, resulting in exfoliation of graphite to form turbostratic carbon. The lattice distance of graphene sheets in graphite are shown to undergo marked changes following treatment with molten ternary eutectic carbonate (Li2CO3: 43.5%, Na2CO3: 31.5%, K2CO3: 25%) during slow temperature ramping rates (5 °C/min) under N2 at temperatures above 750 °C. Initial findings suggest that approximately 50 wt% of graphite experiences interlayer expansion. The conventional d spacing of 0.34 nm is modified to a range of intervals between 0.41 nm and 1.22 nm. As a consequence of high operational temperature (800 °C), cations (Li+, Na+ and K+) as well as potentially the anion (CO32¿) intercalate between graphitic layers and overcome Van der Waal force between layers. Employing a pressurized N2 environment of 5 bar and 10 bar successfully controls carbonate vaporization and decomposition, as well as inducing ordered layer manipulation to exfoliate more graphite planes from the edges towards deeper levels of the particles. Exploring parameters of both carbonate loading and treatment time in addition to pressure demonstrate that this work opens up a rich selection of parameters that can be used to produce carbons with tuned properties from graphite.

This paper investigates the impact of kaolin, a dominant coal mineral, on the thermal and electrochemical behaviour of the molten ternary carbonate eutectic ((Li,Na,K)2CO3) in the direct carbon fuel cell (DCFC) as a means to simulate long-term operation with a continuous coal feed. Thermogravimetric and differential thermal analysis, coupled with kinetic modelling using the Friedman method, shows a substantial decrease in activation energy for eutectic melting with the addition of kaolin. Electro-oxidation of carbon (graphite) is also enhanced with kaolin in the electrolyte, increasing from 17.68 mA/cm2 at 0 wt% kaolin to the highest value of 162 mA/cm2 with 15 wt% kaolin added. It is shown that the improvement is due to increasing oxide concentration resulting from kaolin dissolution in the electrolyte.

Empirical correlations over a diverse range of biomass feedstocks have been developed for prediction of resultant biochar properties using experimental data of more than thirty slow-pyrolysis batch reactions. Biochar was produced under a standard set of conditions; including 550 °C higher heating temperature (HHT), 7 °C/min heating rate, atmospheric pressure, and 40 min residence time. Analysis of the experimental results complimented with literature data showed that calculating biochar yields based on a conservation of the ash method was a valid approach to estimating solid yields in cases where gravimetry is difficult or inconvenient. Increasing the proportion of feedstock ash is observed to increase the biochar yield semilinearly, with the greatest deviation from this observation in low-ash feedstocks. The developed empirical correlation is provided here. When considering highly diverse feedstocks of varying origins, including extensive literature data, the dominating influence of feedstock ash content on the biochar produced is clearly observed in this work. A second-order polynomial relationship between the starting feedstock ash and final biochar ash content was observed, even when including literature results for biochar obtained under widely varied experimental programs. This result suggests a dependency between the amount of the organic material removed from a feedstock and the amount of feedstock ash initially present. This dependency appears to overshadow expected reliance on the heating rate or HHT (within the range of 1-15 °C/min and 450-800 °C respectively). Empirical correlations have been developed and verified and will be of use to the ones doing greenhouse gas, mass and energy balances, or business case modeling for slow-pyrolysis processes utilizing a range of feedstocks, particularly in the case of high-ash and waste-derived sources.

The electrochemical conversion of CO<inf>2</inf> to carbon through the reductive electrolysis of molten carbonate-containing salts has been studied by a range of groups. These groups have examined the yields, mechanisms of deposition and physical characteristics of carbon synthesized through electrolysis using a variety of electrolytes, substrates, temperatures, current densities and deposition potentials. The findings of these research groups have been compiled and compared, with particular significance being placed on findings relating to the influence of variables on the physical properties of carbon obtained in this manner. Research on potential applications of carbon derived from the electrolysis of molten carbonate-containing salts has been presented and the energetics of these carbons have been discussed. The possibility of using this form of carbon synthesis as a manner of permanent waste CO<inf>2</inf> sequestration has been considered.

A systematic assessment of the electrochemical activity of two different parent coal types, pyrolysed at temperatures between 500 and 900 °C higher heating temperature (HHT), is presented in this work. Analysis shows that certain coal chars are catalytically activated in molten carbonate media at 600 °C, however activity does not appear to follow trends established for ashless carbon sources. It is seen here that it is not possible to predict activity based solely on electrical resistance, surface functionalization, or the BET surface area of pyrolysed coals. Instead, it is suggested that coal ash type, abundance and distribution plays a pivotal role in activating the coal char to allow fast electrochemical oxidation through a catalytically enhanced pathway. Activation from ash influence is discussed to result from wetting of the molten carbonate media with the carbon surface (change in polarity of electrode surface), through ash mediated oxide adsorption and transfer to carbon particles, or possibly through another catalytic pathway not yet able to be predicted from current results.

The carbonate eutectic mixture of Li<inf>2</inf>CO<inf>3</inf>, K<inf>2</inf>CO<inf>3</inf>, and Na<inf>2</inf>CO<inf>3</inf> is commonly used as an electrolyte within the direct carbon fuel cell. Here, seven different minerals common to the ash content of Australian bituminous coals (anatase TiO<inf>2</inf>, SiO<inf>2</inf>, CaCO<inf>3</inf>, CaSO<inf>4</inf>, Fe<inf>2</inf>O<inf>3</inf>, FeS, and kaolin) were used to modify the ternary carbonate eutectic to explore the thermodynamics of the carbonate melting process. Thermal effects were examined using differential thermal analysis, where it has been shown that dissolution of the contaminant leads to liquid-phase disruption, the extent of which varies with dopant type. Furthermore, modeling of the melting process carried out using different heating rates allowed determination of the activation energy for melting in the presence of the various contaminants, where it was shown that the contaminants can dramatically affect the activation energy and, subsequently, the kinetics of the melting process.

Biochars are complex heterogeneous materials that consist of mineral phases, amorphous C, graphitic C, and labile organic molecules, many of which can be either electron donors or acceptors when placed in soil. Biochar is a reductant, but its electricaland electrochemical properties are a function of both the temperature of production and the concentration and composition of the various redox active mineral and organic phases present. When biochars are added to soils, they interact with plant roots and root hairs, micro-organisms, soil organic matter, proteins and the nutrient-rich water to form complex organo-mineral-biochar complexes Redox reactions can play an important role in the development of these complexes, and can also result in significant changes in the original C matrix. This paper reviews the redox processes that take place in soil and how they may be affected by the addition of biochar. It reviews the available literature on the redox properties of different biochars. It also reviews how biochar redox properties have been measured and presents new methods and data for determining redox properties of fresh biochars and for biochar/soil systems.

The oxidation mechanism for carbon in a carbonate melt was modelled using an electrochemical kinetic approach. Through the Butler-Volmer equation for electrode kinetics, a series of expressions was derived assuming each step of the proposed carbon oxidation mechanism is in turn the rate determining step (RDS). Through the derived expressions the transfer coefficient and Tafel slope were calculated for each possible RDS of the proposed mechanism and these were compared with real data collected on carbon based electrodes including graphite and coal. It was established that the RDS of the electrochemical oxidation process is dependent on both the carbon type and the potential region of oxidation. The simplified kinetic analysis suggested that the RDS in the main oxidation region is likely to be the first or second electron transfer on a graphite electrode surface, which occurs following initial adsorption of an oxygen anion to an active carbon site. This is contrary to previous suggestions that adsorption of the second anion to the carbon surface will be rate determining. It was further shown that use of a coal based carbon introduces a change in mechanism with an additional reaction region where a different mechanism is proposed to be operating. ©2014 Published by Elsevier Ltd.

The Hybrid Sulfur Cycle is a thermo-electrochemical process designed for the large scale production of hydrogen. The two-step process is essentially based on water splitting using various sulfur species as intermediates. The limiting step in the overall process is the electrochemical oxidation of sulfur dioxide to form sulphuric acid, which suffers from a substantial (~0.4V) anodic overpotential. Here we report on various aspects of sulfur dioxide oxidation in an acidic media including the effects of electrode preconditioning, the electrode substrate and electrolyte effects, the combination of which has allowed development of a sulfur dioxide oxidation mechanism which is described and discussed. Additionally, the electrochemical oxidation of sulfur dioxide has been shown to be an oscillating reaction, which is also a novel finding. © 2014 Hydrogen Energy Publications, LLC.