Electroanalytical applications of carbon electrodes

Carbon materials, such as graphite and conducting diamond, are highly popular for analytical and electrochemical applications, and fundamental knowledge of heterogeneous electron transfer is required to understand and optimise applications. In this thesis, the relationship between the structure of HOPG (Highly Oriented Pyrolytic Graphite) and its electrochemical behaviour has been thoroughly studied from the macroscale to the nanoscale. With the use of data collected from a wide range of techniques, spanning voltammetry, electrochemical imaging and high resolution microscopy, on 5 different grades of basal plane HOPG whose surfaces vary in defect density, the contribution of edge plane vs. basal plane on the electrochemical activity of HOPG has been re-examined. The significant body of work presented herein shows, without doubt, that the basal plane of HOPG is a very active electrode for Ru(NH)6 3+/2+; Fe(CN)6 4-/3-; the oxidation of the neurotransmitter, dopamine (DA), and quinones in aqueous solution. This overturns a well-established (textbook) model that the basal surface is inert, which researchers have assumed for two decades, with implications that carry over to related sp2 carbon materials, such as graphene and carbon nanotubes. A second aspect has considered polycrystalline boron-doped diamond (pBDD) to study neurotransmitters, such as DA and serotonin (5-HT). The electrode surface was found to be resistive towards permanent surface blocking during the electrochemical oxidation of these neurotransmitters. The properties of the film formed by 5-HT oxidative products, was thoroughly investigated using voltammetry and high resolution microscopy. It is shown, for the first time, that electro-oxidation of 5-HT results in an electrically insulating, but charged and porous film, but procedures are demonstrated that allow the pBDD to be renewed in-situ for precise electroanalysis

Nanoscale electrochemical patterning reveals the active sites for catechol oxidation at graphite surfaces

Graphite-based electrodes (graphite, graphene, and nanotubes) are used widely in electrochemistry, and there is a long-standing view that graphite step edges are needed to catalyze many reactions, with the basal surface considered to be inert. In the present work, this model was tested directly for the first time using scanning electrochemical cell microscopy reactive patterning and shown to be incorrect. For the electro-oxidation of dopamine as a model process, the reaction rate was measured at high spatial resolution across a surface of highly oriented pyrolytic graphite. Oxidation products left behind in a pattern defined by the scanned electrochemical cell served as surface-site markers, allowing the electrochemical activity to be correlated directly with the graphite structure on the nanoscale. This process produced tens of thousands of electrochemical measurements at different locations across the basal surface, unambiguously revealing it to be highly electrochemically active, with step edges providing no enhanced activity. This new model of graphite electrodes has significant implications for the design of carbon-based biosensors, and the results are additionally important for understanding electrochemical processes on related sp2-hybridized materials such as pristine graphene and nanotubes

Electrochemistry of Fe3+/2+ at highly oriented pyrolytic graphite (HOPG) electrodes : kinetics, identification of major electroactive sites and time effects on the response

The electrochemistry of the Fe3+/2+ redox couple has been studied on highly oriented pyrolytic graphite (HOPG) samples that differ in step edge density by 2 orders of magnitude to elucidate the effect of surface structure on the electron transfer (ET) kinetics. Macroscopic cyclic voltammetry measurements in a droplet-cell arrangement, highlight that the Fe3+/2+ process is characterised by slow ET kinetics on HOPG and that step edge coverage has little effect on the electrochemistry of Fe3+/2+. A standard heterogeneous ET rate constant of ~5 × 10-5 cm s-1 for freshly cleaved HOPG was derived from simulation of the experimental results, which fell into the range of the values reported for metal eletrodes, e.g. platinum and gold, despite the remarkable difference in density of electronic states (DOS) between HOPG and metal electrodes. This provides further evidence that outer-sphere redox processes on metal and sp2 carbon electrodes appear to be adiabatic. Complementary surface electroactivity mapping of HOPG, using scanning electrochemical cell microscopy, reveal the basal plane to be the predominant site for the Fe3+/2+ redox process. It is found that time after cleavage of the HOPG surface has an impact on the surface wettability (and surface contamination), as determined by contact angle measurements, and that this leads to a slow deterioration of the kinetics. These studies further confirm the importance of understanding and evaluating surface structure and history effects in HOPG electrochemistry, and how high resolution measurements, coupled with macroscopic studies provide a holistic view of electrochemical processes

Molecular functionalization of graphite surfaces : Basal Plane versus Step Edge electrochemical activity

The chemical functionalization of carbon surfaces has myriad applications, from tailored sensors to electrocatalysts. Here, the adsorption and electrochemistry of anthraquinone-2,6-disulfonate (AQDS) is studied on highly oriented pyrolytic graphite (HOPG) as a model sp2 surface. A major focus is to elucidate whether adsorbed electroactive AQDS can be used as a marker of step edges, which have generally been regarded as the main electroactive sites on graphite electrode surfaces. First, the macroscopic electrochemistry of AQDS is studied on a range of surfaces differing in step edge density by more than 2 orders of magnitude, complemented with ex situ tapping mode atomic force microscopy (AFM) data. These measurements show that step edges have little effect on the extent of adsorbed electroactive AQDS. Second, a new fast scan cyclic voltammetry protocol carried out with scanning electrochemical cell microscopy (SECCM) enables the evolution of AQDS adsorption to be followed locally on a rapid time scale. Subsequent AFM imaging of the areas probed by SECCM allows a direct correlation of the electroactive adsorption coverage and the actual step edge density of the entire working area. The amount of adsorbed electroactive AQDS and the electron transfer kinetics are independent of the step edge coverage. Last, SECCM reactive patterning is carried out with complementary AFM measurements to probe the diffusional electroactivity of AQDS. There is essentially uniform and high activity across the basal surface of HOPG. This work provides new methodology to monitor adsorption processes at surfaces and shows unambiguously that there is no correlation between the step edge density of graphite surfaces and the observed coverage of electroactive AQDS. The electroactivity is dominated by the basal surface, and studies that have used AQDS as a marker of steps need to be revised

Lithium-ion battery second life:pathways, challenges and outlook

Net zero targets have resulted in a drive to decarbonise the transport sector worldwide through electrification. This has, in turn, led to an exponentially growing battery market and, conversely, increasing attention on how we can reduce the environmental impact of batteries and promote a more efficient circular economy to achieve real net zero. As these batteries reach the end of their first life, challenges arise as to how to collect and process them, in order to maximise their economical use before finally being recycled. Despite the growing body of work around this topic, the decision-making process on which pathways batteries could take is not yet well understood, and clear policies and standards to support implementation of processes and infrastructure are still lacking. Requirements and challenges behind recycling and second life applications are complex and continue being defined in industry and academia. Both pathways rely on cell collection, selection and processing, and are confronted with the complexities of pack disassembly, as well as a diversity of cell chemistries, state-of-health, size, and form factor. There are several opportunities to address these barriers, such as standardisation of battery design and reviewing the criteria for a battery’s end-of-life. These revisions could potentially improve the overall sustainability of batteries, but may require policies to drive such transformation across the industry. The influence of policies in triggering a pattern of behaviour that favours one pathway over another are examined and suggestions are made for policy amendments that could support a second life pipeline, while encouraging the development of an efficient recycling industry. This review explains the different pathways that end-of-life EV batteries could follow, either immediate recycling or service in one of a variety of second life applications, before eventual recycling. The challenges and barriers to each pathway are discussed, taking into account their relative environmental and economic feasibility and competing advantages and disadvantages of each. The review identifies key areas where processes need to be simplified and decision criteria clearly defined, so that optimal pathways can be rapidly determined for each end-of-life battery

Mother-to-mother therapy in India and Pakistan: adaptation and feasibility evaluation of the peer-delivered Thinking Healthy Programme.

BACKGROUND: Perinatal depression is highly prevalent in South Asia. Although effective and culturally feasible interventions exist, a key bottleneck for scaled-up delivery is lack of trained human resource. The aim of this study was to adapt an evidence-based intervention so that local women from the community (peers) could be trained to deliver it, and to test the adapted intervention for feasibility in India and Pakistan. METHODS: The study was conducted in Rawalpindi, Pakistan and Goa, India. To inform the adaptation process, qualitative data was collected through 7 focus groups (four in Pakistan and three in India) and 61 in-depth interviews (India only). Following adaptation, the intervention was delivered to depressed mothers (20 in Pakistan and 24 in India) for six months through 8 peers in Pakistan and nine in India. Post intervention data was collected from depressed mothers and peers through 41 in-depth interviews (29 in Pakistan and 12 in India) and eight focus groups (one in Pakistan and seven in India). Data was analysed using Framework Analysis approach. RESULTS: Most mothers perceived the intervention to be acceptable, useful, and viewed the peers as effective delivery-agents. The simple format using vignettes, pictures and everyday terms to describe distress made the intervention easy to understand and deliver. The peers were able to use techniques for behavioural activation with relative ease. Both the mothers and peers found that shared life-experiences and personal characteristics greatly facilitated the intervention-delivery. A minority of mothers had concerns about confidentiality and stigma related to their condition, and some peers felt the role was emotionally challenging. CONCLUSIONS: The study demonstrates the feasibility of using peers to provide interventions for perinatal depression in two South Asian settings. Peers can be a potential resource to deliver evidence-based psychosocial interventions. TRIAL REGISTRATION: Pakistan Trial: ClinicalTrials.gov Identifier: NCT02111915 (9 April 2014), India Trial: ClinicalTrials.gov Identifier: NCT02104232 (1 April 2014)

Towards Optimised Cell Design of Thin Film Silicon-Based Solid-State Batteries via Modelling and Experimental Characterisation

To realise the promise of solid-state batteries, negative electrode materials exhibiting large volumetric expansions, such as Li and Si, must be used. These volume changes can cause significant mechanical stresses and strains that affect cell performance and durability, however their role and nature in SSBs are poorly understood. Here, a 2D electro-chemo-mechanical model is constructed and experimentally validated using steady-state, transient and pulsed electrochemical methods. The model geometry is taken as a representative cross-section of a non-porous, thin-film solid-state battery with an amorphous Si (a-Si) negative electrode, lithium phosphorous oxynitride (LiPON) solid electrolyte and LiCoO2 (LCO) positive electrode. A viscoplastic model is used to predict the build-up of strains and plastic deformation of a-Si as a result of (de)lithiation during cycling. A suite of electrochemical tests, including electrochemical impedance spectroscopy, the galvanostatic intermittent titration technique and hybrid pulse power characterisation are carried out to establish key parameters for model validation. The validated model is used to explore the peak interfacial (a-Si∣LiPON) stress and strain as a function of the relative electrode thickness (up to a factor of 4), revealing a peak volumetric expansion from 69% to 104% during cycling at 1C. The validation of this electro-chemo-mechanical model under load and pulsed operating conditions will aid in the cell design and optimisation of solid-state battery technologies

Increasing the Availability and Consumption of Drinking Water in Middle Schools: A Pilot Study

Introduction: Although several studies suggest that drinking water may help prevent obesity, no US studies have examined the effect of school drinking water provision and promotion on student beverage intake. We assessed the acceptability, feasibility, and outcomes of a school-based intervention to improve drinking water consumption among adolescents. Methods: The 5-week program, conducted in a Los Angeles middle school in 2008, consisted of providing cold, filtered drinking water in cafeterias; distributing reusable water bottles to students and staff; conducting school promotional activities; and providing education. Self-reported consumption of water, nondiet soda, sports drinks, and 100% fruit juice was assessed by conducting surveys among students (n = 876), preintervention and at 1 week and 2 months postintervention, from the intervention school and the comparison school. Daily water (in gallons) distributed in the cafeteria during the intervention was recorded. Results: After adjusting for sociodemographic characteristics and baseline intake of water at school, the odds of drinking water at school were higher for students at the intervention school than students at the comparison school. Students from the intervention school had higher adjusted odds of drinking water from fountains and from reusable water bottles at school than students from the comparison school. Intervention effects for other beverages were not significant. Conclusion: Provision of filtered, chilled drinking water in school cafeterias coupled with promotion and education is associated with increased consumption of drinking water at school. A randomized controlled trial is necessary to assess the intervention's influence on students' consumption of water and sugar-sweetened beverages, as well as obesity-related outcomes

The effectiveness and cost-effectiveness of the peer-delivered Thinking Healthy Programme for perinatal depression in Pakistan and India: the SHARE study protocol for randomised controlled trials.

BACKGROUND: Rates of perinatal depression (antenatal and postnatal depression) in South Asia are among the highest in the world. The delivery of effective psychological treatments for perinatal depression through existing health systems is a challenge due to a lack of human resources. This paper reports on a trial protocol that aims to evaluate the effectiveness and cost-effectiveness of the Thinking Healthy Programme delivered by peers (Thinking Healthy Programme Peer-delivered; THPP), for women with moderate to severe perinatal depression in rural and urban settings in Pakistan and India. METHODS/DESIGN: THPP is evaluated with two randomised controlled trials: a cluster trial in Rawalpindi, Pakistan, and an individually randomised trial in Goa, India. Trial participants are pregnant women who are registered with the lady health workers in the study area in Pakistan and pregnant women attending outpatient antenatal clinics in India. They will be screened using the patient health questionnaire-9 (PHQ-9) for depression symptoms and will be eligible if their PHQ-9 is equal to or greater than 10 (PHQ-9 ≥ 10). The sample size will be 560 and 280 women in Pakistan and India, respectively. Women in the intervention arm (THPP) will be offered ten individual and four group sessions (Pakistan) or 6-14 individual sessions (India) delivered by a peer (defined as a mother from the same community who is trained and supervised in delivering the intervention). Women in the control arm (enhanced usual care) will receive health care as usual, enhanced by providing the gynaecologist or primary-health facilities with adapted WHO mhGAP guidelines for depression treatment, and providing the woman with her diagnosis and information on how to seek help for herself. The primary outcomes are remission and severity of depression symptoms at the 6-month postnatal follow-up. Secondary outcomes include remission and severity of depression symptoms at the 3-month postnatal follow-up, functional disability, perceived social support, breastfeeding rates, infant height and weight, and costs of health care at the 3- and 6-month postnatal follow-ups. The primary analysis will be intention-to-treat. DISCUSSION: The trials have the potential to strengthen the evidence on the effectiveness and cost-effectiveness of an evidence-based psychological treatment recommended by the World Health Organisation and delivered by peers for perinatal depression. The trials have the unique opportunity to overcome the shortage of human resources in global mental health and may advance our understanding about the use of peers who work in partnership with the existing health systems in low-resource settings. TRIAL REGISTRATION: Pakistan Trial: ClinicalTrials.gov Identifier: NCT02111915 (9 April 2014) India Trial: ClinicalTrials.gov Identifier: NCT02104232 (1 April 2014)