Classifying Error States of PEMFCs by Current Mapping and Cell Voltage Monitoring

Error states in PEMFC stacks typically cause distortions of the local current distribution and the cell voltage. Measuring those properties can be used for identification of those error states, e.g., membrane dry-out, channel blockage, reactant media contamination, local starvation, gross starvation, overall stack starvation and pinholes. Two techniques for online diagnosis are introduced, measuring the current density distribution by a printed circuit board, and measuring the local cell voltage by a multipoint cell voltage monitoring. A non-invasive experimental setup is proposed for both techniques to gain reliable measurement data. The relationship of the cell voltage distribution over the stack and the current density distribution within the cells is discussed and used to discriminate different error states. Experimental measurement data of those techniques is shown for several common error states. Finally, a categorization of error states is proposed, based on their characteristic patterns of disturbed local current density and cell voltage

Meeting the support needs of patients with complex regional pain syndrome through innovative use of wiki technology: a mixed-methods study

Background: Using online discussion forums can have a positive impact on psychological well-being through development of shared group identity and validation of thoughts, feelings and experiences. This may be particularly beneficial to people with complex regional pain syndrome (CRPS), who often become socially isolated, lack mobility and face threats to their sense of identity. We set up a peer-support online forum to identify the nature of support provided and to explore its development over time. We then introduced a collaborative writing task to facilitate further the development of social processes implicated in psychological support. Research questions: (1) What constitutes support in newly developed online interactions? (2) How does the process of giving and receiving support online evolve? (3) Can the combination of an online forum and a collaborative writing task increase support relative to an online forum alone? Design: This is a three-phase mixed-methods research design. Phase 1: an online forum was launched. Phase 2: forum members were invited to cowrite a patient-centred CRPS information resource. Phase 3: the resource was shared and feedback was sought. Participants: Posts from 26 members (seven males, 19 females) were analysed. The mean age of members was 35.6 years. The number of years since diagnosis was available for 14 members (ranging from 5 months to 10 years with a mean duration of 3.9 years). Data analysis: In order to explore what constitutes support in newly developed online interactions, an inductive thematic analysis was conducted on all ‘introductory posts’ posted during phase 1. In order to explore how the process of giving and receiving support online evolved, a deductive content analysis using the Social Support Behavior Code was conducted on all forum posts posted during the first 12 months. Results: Five themes were identified in members’ first posts. Three of these themes contributed to the development of a ‘common-identity’ community, while the remaining two established a positive tone, consistent with that of a ‘common-bond’ community. Content analysis revealed that support requests were present in 15.5% of posts: predominantly informational support (8.6%) with the remaining support categories ranging from 1.3% to 2.6%. Social support was present in 88.8% of posts; predominantly emotional support (72.8%) followed by informational (36.2%) and esteem (30.2%) support. For a variety of reasons, we were unable to address the third question fully; we gave all members the option of contributing to the collaborative writing task and anticipated comparing those who accepted the invitation with those who did not. However, either participants continued to take part in the forum and contributed to the writing task, or they ceased to interact with the forum altogether, thereby limiting our ability to compare across time and task. Conclusions: Few members of the forum explicitly requested social support, but many offered it (emotional support was the most prevalent). There was evidence of both common-identity and common-bond community development from the outset. This continued to shape forum interactions throughout the 12 months of the study and set up a space that had an over-riding positive and supportive tone which enabled the members to reach out and offer support to similar others, in effect helping them to re-engage with the wider world. Future work that examines support across networked online communities is necessary. Funding: The National Institute for Health Research Health Services and Delivery Research programme

Influence of Cell Reversals on Cr/a-C Pre-coated vs Post-coated Metallic Bipolar Plates in Automotive PEMFC Systems

The results of the measurements presented in this manuscript show that none of the coatings has a significant impact on the performance degradation over the course of cell reversal cycling. However, for the EOL polarization curves, the voltage is significantly decreased for the carbon coatings compared to the Au coating. Further experiments should be performed here to determine if these are measurement inaccuracies or if the trend is confirmed. The BIP coatings Cr/a-C also perform worse in the resistance measurements of the HFR and ICR, with the pre-coat variant having the highest values after the tests. The surface changes, which can be seen in the area of the BIP deflections, probably also have an influence here. These appear to be more distinct for the BIP coating Cr/a-C pre-coat. Here, it should be analyzed in more detail how the surface changes and whether metal ions can emerge. The use of the BIP coatings Cr/a-C post- and pre-coat offers a lot of potential, both economically and technically, but cannot be recommended without reservation, as further investigations are still required.Die Ergebnisse der in diesem Manuskript vorgestellten Messungen zeigen, dass keine der Beschichtungen einen signifikanten Einfluss auf die Leistungsverschlechterung im Verlauf der Cell Reversal Zyklen hat. Bei den EOL Polarisationskurven ist die Spannung bei den Kohlenstoffbeschichtungen jedoch deutlich niedriger als bei der Au-Beschichtung. Hier sollten weitere Experimente durchgeführt werden, um festzustellen, ob es sich um Messungenauigkeiten handelt oder ob der Trend bestätigt wird. Die BIP-Beschichtungen Cr/a-C schneiden auch bei den Widerstandsmessungen des HFR und ICR schlechter ab, wobei die pre-coat nach den Tests die höchsten Werte aufweist. Wahrscheinlich haben auch hier die Oberflächenveränderungen, die im Bereich der BIP Umlenkungen zu sehen sind, einen Einfluss. Diese scheinen bei der BIP Beschichtung Cr/a-C pre-coat deutlicher ausgeprägt zu sein. Hier sollte noch genauer analysiert werden, wie sich die Oberfläche verändert und ob Metallionen austreten können. Der Einsatz der BIP Beschichtungen Cr/a-C post- und pre-coat bietet sowohl wirtschaftlich als auch technisch viel Potenzial, kann aber nicht uneingeschränkt empfohlen werden, da noch weitere Untersuchungen erforderlich sind

Influence of Cell Reversals on Cr/a-C Pre-coated vs Post-coated Metallic Bipolar Plates in Automotive PEMFC Systems

The results of the measurements presented in this manuscript show that none of the coatings has a significant impact on the performance degradation over the course of cell reversal cycling. However, for the EOL polarization curves, the voltage is significantly decreased for the carbon coatings compared to the Au coating. Further experiments should be performed here to determine if these are measurement inaccuracies or if the trend is confirmed. The BIP coatings Cr/a-C also perform worse in the resistance measurements of the HFR and ICR, with the pre-coat variant having the highest values after the tests. The surface changes, which can be seen in the area of the BIP deflections, probably also have an influence here. These appear to be more distinct for the BIP coating Cr/a-C pre-coat. Here, it should be analyzed in more detail how the surface changes and whether metal ions can emerge. The use of the BIP coatings Cr/a-C post- and pre-coat offers a lot of potential, both economically and technically, but cannot be recommended without reservation, as further investigations are still required.Die Ergebnisse der in diesem Manuskript vorgestellten Messungen zeigen, dass keine der Beschichtungen einen signifikanten Einfluss auf die Leistungsverschlechterung im Verlauf der Cell Reversal Zyklen hat. Bei den EOL Polarisationskurven ist die Spannung bei den Kohlenstoffbeschichtungen jedoch deutlich niedriger als bei der Au-Beschichtung. Hier sollten weitere Experimente durchgeführt werden, um festzustellen, ob es sich um Messungenauigkeiten handelt oder ob der Trend bestätigt wird. Die BIP-Beschichtungen Cr/a-C schneiden auch bei den Widerstandsmessungen des HFR und ICR schlechter ab, wobei die pre-coat nach den Tests die höchsten Werte aufweist. Wahrscheinlich haben auch hier die Oberflächenveränderungen, die im Bereich der BIP Umlenkungen zu sehen sind, einen Einfluss. Diese scheinen bei der BIP Beschichtung Cr/a-C pre-coat deutlicher ausgeprägt zu sein. Hier sollte noch genauer analysiert werden, wie sich die Oberfläche verändert und ob Metallionen austreten können. Der Einsatz der BIP Beschichtungen Cr/a-C post- und pre-coat bietet sowohl wirtschaftlich als auch technisch viel Potenzial, kann aber nicht uneingeschränkt empfohlen werden, da noch weitere Untersuchungen erforderlich sind

Influence of Cell Reversals on Cr/a-C Pre-coated vs Post-coated Metallic Bipolar Plates in Automotive PEMFC Systems

The results of the measurements presented in this manuscript show that none of the coatings has a significant impact on the performance degradation over the course of cell reversal cycling. However, for the EOL polarization curves, the voltage is significantly decreased for the carbon coatings compared to the Au coating. Further experiments should be performed here to determine if these are measurement inaccuracies or if the trend is confirmed. The BIP coatings Cr/a-C also perform worse in the resistance measurements of the HFR and ICR, with the pre-coat variant having the highest values after the tests. The surface changes, which can be seen in the area of the BIP deflections, probably also have an influence here. These appear to be more distinct for the BIP coating Cr/a-C pre-coat. Here, it should be analyzed in more detail how the surface changes and whether metal ions can emerge. The use of the BIP coatings Cr/a-C post- and pre-coat offers a lot of potential, both economically and technically, but cannot be recommended without reservation, as further investigations are still required.Die Ergebnisse der in diesem Manuskript vorgestellten Messungen zeigen, dass keine der Beschichtungen einen signifikanten Einfluss auf die Leistungsverschlechterung im Verlauf der Cell Reversal Zyklen hat. Bei den EOL Polarisationskurven ist die Spannung bei den Kohlenstoffbeschichtungen jedoch deutlich niedriger als bei der Au-Beschichtung. Hier sollten weitere Experimente durchgeführt werden, um festzustellen, ob es sich um Messungenauigkeiten handelt oder ob der Trend bestätigt wird. Die BIP-Beschichtungen Cr/a-C schneiden auch bei den Widerstandsmessungen des HFR und ICR schlechter ab, wobei die pre-coat nach den Tests die höchsten Werte aufweist. Wahrscheinlich haben auch hier die Oberflächenveränderungen, die im Bereich der BIP Umlenkungen zu sehen sind, einen Einfluss. Diese scheinen bei der BIP Beschichtung Cr/a-C pre-coat deutlicher ausgeprägt zu sein. Hier sollte noch genauer analysiert werden, wie sich die Oberfläche verändert und ob Metallionen austreten können. Der Einsatz der BIP Beschichtungen Cr/a-C post- und pre-coat bietet sowohl wirtschaftlich als auch technisch viel Potenzial, kann aber nicht uneingeschränkt empfohlen werden, da noch weitere Untersuchungen erforderlich sind

Fuel starvation in automotive PEMFC stacks: hydrogen stoichiometry and electric cell-to-cell interaction

Fuel gross starvation (FGS) in a polymer electrolyte membrane fuel cell is an error state, during which the supplied amount of fuel is insufficient to sustain the requested electrical current. A novel experimental technique was developed to intentionally provoke well-controlled fuel starvation situations of one single cell in a multi-cell fuel cell stack. This modification was implemented in a 20 cell stack of automotive-sized cell geometry and carbon composite bipolar plates (BP). The intentional fuel starvation situation was analyzed using a printed circuit board to measure the current density distribution (CDD) in addition to a multipoint cell voltage monitoring (CVM) to measure local cell voltages. The provoked detrimental subsidiary reactions of the anode were found to take place spatially separated from the normal hydrogen oxidation reaction. It was therefore possible to determine and intentionally vary the hydrogen stoichiometry of the fuel starved cell. This error state caused intense distortions of the starved cells CDD and local cell voltages. The maximum difference obtained between outlet and inlet voltage of the modified cell was 1.4 V. Compared to the average current density, a more than 4-times higher maximum local current density was measured in the affected cell. Adjacent cells were also affected via electric cell-to-cell interaction. Characteristic patterns therefore became visible in the cell voltage distribution, measured by the inlet and outlet CVM. The use of carbon composite BP is favoring the occurrence of these patterns due to their relatively high electric sheet resistance. Using the new hardware setup, we could investigate the relation between the hydrogen stoichiometry of the affected cell during FGS and the observed irregular redistribution of current density and local cell voltages