Nitrogen Blanketing and Hydrogen Starvation in Dead-Ended-Anode Polymer Electrolyte Fuel Cells Revealed by Hydro-Electro-Thermal Analysis

Dead-ended anode operation has a number of practical advantages that simplify system complexity and lower cost for polymer electrolyte fuel cells. However, dead-ended mode leads to performance loss over time which can only be reversed by performing intermittent purge events. This work applies a combined hydro-electro-thermal analysis to an air-cooled open-cathode fuel cell, presenting experimental functional maps of water distribution, current density and temperature. This approach has allowed the identification of a 'nitrogen blanketing' effect due to nitrogen cross-over from the cathode and a 'bypass' effect where a peripheral gap between the gasket and the GDL offers a hydrogen flow 'short circuit' to the border of the electrode. A consequence of high local current density at the margin of the electrode, and resulting high temperatures, may impact the lifetime of the cell in dead-end mode

The practice of crime prevention: Design principles for more effective security governance

South Africa has had a comprehensive crime prevention policy agenda for some time in the form of the 1996 National Crime Prevention Strategy and the 1998 White Paper on Safety and Security. Despite this, prevention has remained very much a second cousin within the South African criminal justice family, notwithstanding the fact that there is widespread agreement that it warrants far more attention. In this article we briefly review some of the principal obstacles to effective crime prevention. Our understanding of ‘crime prevention’ is a broad one – it involves simply asking the question: How can we reduce the likelihood of this happening again? This question opens up a range of preventative possibilities. Whether they are of a socio-economic, environmental or law enforcement nature depends on the nature of the (crime) problem. On the basis of our analysis, we propose three design principles to be followed if we, South Africans are to establish crime prevention as a central focus of our security governance. These design principles articulate what might be thought of as ‘best thinking’ rather than ‘best practice’

A novel molten-salt electrochemical cell for investigating the reduction of uranium dioxide to uranium metal by lithium using in situ synchrotron radiation

A novel electrochemical cell has been designed and built to allow for in situ energy-dispersive X-ray diffraction measurements to be made during reduction of UO2 to U metal in LiCl-KCl at 500C. The electrochemical cell contains arecessed well at the bottom of the cell into which the working electrode sits, reducing the beam path for the X-rays through the molten-salt and maximizing the signal-to-noise ratio from the sample. Lithium metal was electrodeposited onto the UO2 working electrode by exposing the working electrode to more negative potentials than the Li deposition potential of the LiCl-KCl eutectic electrolyte. The Li metal acts as a reducing agent for the chemical reduction of UO2 to U, which appears to proceed to completion. All phases were fitted using Le Bail refinement. The cell is expected to be widely applicable to many studies involving molten-salt systems

Direct observation of active material concentration gradients and crystallinity breakdown in LiFePO4 electrodes during charge/discharge cycling of lithium batteries

The phase changes that occur during discharge of an electrode comprised of LiFePO4, carbon, and PTFE binder have been studied in lithium half cells by using X-ray diffraction measurements in reflection geometry. Differences in the state of charge between the front and the back of LiFePO4 electrodes have been visualized. By modifying the X-ray incident angle the depth of penetration of the X-ray beam into the electrode was altered, allowing for the examination of any concentration gradients that were present within the electrode. At high rates of discharge the electrode side facing the current collector underwent limited lithium insertion while the electrode as a whole underwent greater than 50% of discharge. This behavior is consistent with depletion at high rate of the lithium content of the electrolyte contained in the electrode pores. Increases in the diffraction peak widths indicated a breakdown of crystallinity within the active material during cycling even during the relatively short duration of these experiments, which can also be linked to cycling at high rate

Community-centred disaster recovery: A call to change the narrative

This paper challenges current approaches to undertaking community-centred disaster recovery. Community-centred approaches are widely recognised as ‘the gold standard’ for effective recovery from disasters. Yet, they are rarely applied well enough in practice. Challenges include the ‘authority’ culture of command-and-control agencies, the emphasis on discrete recovery time frames, and the reluctance to relinquish centralised control. The paper focuses on people's experiences of community-centred recovery in New South Wales, Australia, which has experienced severe fires and floods since 2019. We undertook key informant interviews and an online survey to inquire into how community-centred recovery is enacted. Our work uncovered widespread dissatisfaction with current practices. The paper discusses key themes emerging from the research and ends with a call to change how community-centred recovery is framed and conducted by responding organisations, to include the underlying causes of vulnerability in recovery, to measure success differently, and to alter the narrative of who ‘owns’ disasters

Reshaping disaster management: An integrated community-led approach

The management of disasters has traditionally involved public, private, and nongovernmental organisations working together. While scholars have examined the value of collaborations among these entities, less is known about how to successfully engage and empower communities in disaster management. Based on network governance theory, this article contributes to the growing body of public management literature on community engagement by presenting findings from an Australian research initiative conducted after the 2019/20 Black Summer bushfires in New South Wales. Through workshops and semi-structured interviews with a total of 58 members from local communities and emergency agencies, this paper identifies differing perspectives on power distribution among stakeholders, indicating complexities in achieving an integrated and community-led disaster management approach. The findings underscore the need to shift from exclusively centralised to more inclusive systems, recognising the unique contributions of nonofficial community-based groups. To address this, the study suggests: a funded community consultation committee, ensuring government and local community representation; collaborative debriefing sessions, leveraging technology for knowledge capture; and the adoption of different leadership styles able to identify, include, and integrate communities as both steerers and rowers within established hierarchical arrangements. Points for practitioners: The current centralised emergency management system, which relies on recognised experts and state-controlled facilities, limits the integration of nonofficial resources and community-based knowledge. A shift towards a more community-centric and integrated approach (collaborative polycentric governance) is needed to enhance disaster resilience and response in Australia. Different stages of disaster reduction could and should have different leadership styles: a transformational, collaborative community-based style should be implemented before and after the disaster, while a transactional leadership style, more focused on restructuring the system or how it is applied, should be adopted during the disaster

Developments in X-ray tomography characterization for electrochemical devices

Over the last century, X-ray imaging instruments and their accompanying tomographic reconstruction algorithms have developed considerably. With improved tomogram quality and resolution, voxel sizes down to tens of nanometers can now be achieved. Moreover, recent advancements in readily accessible lab-based X-ray computed tomography (X-ray CT) instruments have produced spatial resolutions comparable to specialist synchrotron facilities. Electrochemical energy conversion devices, such as fuel cells and batteries, have inherently complex electrode microstructures to achieve competitive power delivery for consideration as replacements for conventional sources. With resolution capabilities spanning tens of microns to tens of nanometers, X-ray CT has become widely employed in the three-dimensional (3D) characterization of electrochemical materials. The ability to perform multiscale imaging has enabled characterization from system-down to particle-level, with the ability to resolve critical features within device microstructures. X-ray characterization presents a favorable alternative to other 3D methods, such as focused ion beam scanning electron microscopy, due to its non-destructive nature, which allows four-dimensional (4D) studies, three spatial dimensions plus time, linking structural dynamics to device performance and lifetime. X-ray CT has accelerated research from fundamental understanding of the links between cell structure and performance, to the improvement in manufacturing and scale-up of full electrochemical cells. Furthermore, this has aided in the mitigation of degradation and cell-level failures, such as thermal runaway. This review presents recent developments in the use of X-ray CT as a characterization method and its role in the advancement of electrochemical materials engineering

Data on the theoretical X-Ray attenuation and transmissions for lithium-ion battery cathodes

This article reports the data required for planning attenuation-based X-ray characterisation e.g. X-ray computed tomography (CT), of lithium-ion (Li-ion) battery cathodes. The data reported here is to accompany a co-submitted manuscript (10.1016/j.matdes.2020.108585 [1]) which compares two well-known X-ray attenuation data sources: Henke et al. and Hubbell et al., and applies methodology reported by Reiter et al. to extend this data towards the practical characterisation of prominent cathode materials. This data may be used to extend beyond the analysis reported in the accompanying manuscript, and may aid in the applications for other materials, not limited to Li-ion batteries

Representative resolution analysis for X-ray CT: A Solid oxide fuel cell case study

A requirement to reduce dependency on high-carbon fuels has resulted in the rapid advancement of electrochemical devices. Considerable research has been applied to improve device performance and lifetime in order to compete with incumbent technologies. Of the portfolio of electrochemical conversion technologies, solid oxide fuel cells (SOFC) offer high fuel versatility and fast reaction kinetics without the requirement of expensive catalysts. However, degradation due to high temperature operation limits cell performance and lifetime, impeding widespread commercialisation. Due to the inherent link between microstructure and electrochemical performance, many three-dimensional (3D) characterisation techniques have been employed in the pursuit of the mitigation of degradation through rational electrode design. Instruments such as lab-based X-ray microscopes are now capable of imaging across multiple length scales, where the highest resolutions (i.e. smallest voxel lengths) are comparable to specialist synchrotron facilities. A widely used metric to describe electrode microstructure is the triple-phase boundary (TPB); the location where reactions occur within the SOFC electrode. The total TPB length is a vital metric in assessing the quality of an SOFC material, and thus many efforts have been made to determine accurate values. In order to map the TPB locations in 3D, the three constituent phases: metal, ceramic, and pore, need to be distinguished and segmented, requiring high resolutions. Although TPB values have been reported and compared extensively in the literature, the influence of the microscopic roughness is yet to be investigated. Using X-ray computed tomography (CT), here, for the first time, the effect of resolution is inspected for several key microstructural parameters. Moreover, the study is extended through the use of multiple instruments for a variety of sample structures. This work introduces the importance of the fractal properties of structures characterised using X-ray CT, which we expect to be influential across a broad range of materials. The choice of resolution when characterising a structure is important and determined by a variety of factors: instrument, feature size, image quality, etc., and should ultimately be chosen in order to efficaciously expose the features under investigation, in addition to this, metrics extracted should only be directly compared at the same resolution and, if possible, should be inspected for fractal properties via a representative resolution analysis. These conclusions are not restricted to SOFCs but should be applied to all fields of microstructural analysis