Search

The open circuit voltage (OCV) in a proton exchange membrane fuel cell (PEMFC) is typically recorded as being approximately 300 mV lower than the equilibrium voltage computed by the Nernst equation. While a number of causes have been proposed, the voltage drop is generally attributed to the oxidation of crossover hydrogen in the cathode. A single phase, through-the-channel model is presented that includes hydrogen transport across the membrane, an empirical model for the hydrogen oxidation reaction (HOR) fit to experimental data obtained at high potentials and a multi-step kinetic model to describe the oxygen reduction reaction (ORR). Model predictions were compared to experimentally obtained OCVs and the results show that the model is capable of capturing the experimentally observed changes in OCV with platinum loading, as well as fuel cell performance; and that, at low Pt loadings, small quantities of unreacted hydrogen leave the cathode because the HOR is kinetically limited by oxide blocking and anion adsorption. A parametric study is used to show that a minimum OCV is achieved at ultra-low loadings. Results also show that only a multi-step ORR model can simultaneously capture polarization data and the OCV.

The open-circuit voltage (OCV) is the measured potential when no current is drawn from a cell. Theoretically this potential is given by the equilibrium potential, which is determined from thermodynamics based on the operating conditions. In practice, the actual potential at zero current is measured to be approximately 300 mV lower than the theoretical value. There are a number of possible causes for the lower OCV [1,2], however the most commonly accepted is that hydrogen crossing from the anode to the cathode will react in the presence of the platinum catalyst, thereby developing a mixed potential [2,3,4]. The OCV will therefore depend on the relative kinetics of the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) in the cathode such that when the ORR is equal to the HOR in the cathode, the OCV is reached, see Figure 1A. The overpotential required to achieve the required ORR will determine the potential at which OCV occurs and the overpotential required will be impacted by the platinum loading in the cathode. This effect is shown experimentally, where the OCV is seen to drop significantly at loadings less than 0.05mg/cm2 , as shown in Figure 1B. The two-dimensional, macro-homogeneous model in OpenFCST [5] is extended to allow multiple reactions in an electrode and used to study the impact of platinum loading on OCV. The model accounts for the transport of oxygen, hydrogen, water vapour and solved water, as well as the potentials of both the solid and electrolyte phases. Both the ORR and HOR are considered in the cathode, and as the hydrogen crossover rate is only of the order of 1 mA/cm2, the accuracy of the kinetic models used for the ORR and HOR are studied. Furthermore, the impact of the HOR kinetics is examined by considering recent experimental studies [7,8] that have shown the HOR is severely limited at high overpotentials by anion adsorption and oxide formation. This work shows that the double-trap kinetic model [6] for the ORR is able to match the polarization data in the kinetic region as well as correctly predict the OCVs for platinum loadings of 0.014-0.113 mg/cm2 . The commonly used Tafel equation, in contrast, cannot simultaneously fit both the kinetic region of the polarisation curve and the OCVs. Using a HOR model that reproduces the kinetic data showing limited activity at high overpotentials does not accurately capture the OCV and predicts that hydrogen would escape through the cathode. The impact of microscale transport is studied using the ionomer covered carbon particle (ICCP) model. A parametric study on the parameters controlling the dissolution of hydrogen into the ionomer thin film and its diffusion to the reaction site indicate that hydrogen transport is not limiting at these scales for the cell structural parameters used in this study, but may be important at higher ionomer film thicknesses. Changing the operating oxygen partial pressure shows that the double trap model in ref. [6] does not accurately capture the change in reaction rate with the change in oxygen concentration. This work demonstrates that modeling the OCV is helpful in fitting the kinetic region of the polarisation curve, as an accurate fit here and at OCV means that the kinetic model is accurate over several orders of magnitude in current and approximately 100mV of potential. References: [1] J. J. Giner-Sanz et al., Int. J. Hydrogen Energ., 39 (2014) 13206-13216 [2] S. A. Vilekar et al., J. Power Sources, 195 (2010) 2241–2247 [3] V. M. Ehlinger et al., J. Electrochem. Soc., 166, (7) F3255-F3267 (2019) [4] A. A. Kulikovsky, Electrochimica Acta, 247 (2017) 730–735 [5] M. Secanell et al., Electrochem. Soc. Trans., 64 (3) 655-680 (2014) [6] M. Moore et al., J. Electrochem. Soc., 160 (6) F670-F681 (2013) [7] J. Durst et al., J. Electrochem. Soc., 162 (1) F190-F203 (2015) [8] C. M. Zalitis et al., Phys. Chem. Chem. Phys., 2013, 15, 4329 Figure 1

Background: Pregabalin, approved for various medical conditions, has shown increasing misuse potential globally. However, limited research exists on pregabalin dependence in India. This study aimed to investigate the prevalence and characteristics of pregabalin dependence among individuals seeking substance use disorder (SUD) treatment in North India. Methods: A cross-sectional, analytical study was conducted on patients enrolled between August 2022 and July 2023 at an academic institution-based addiction treatment center. Case records of patients with pregabalin dependence were retrieved and compared with controls with opioid dependence but no history of pregabalin use. Results: Among 3766 registered patients, 135 had pregabalin dependence (prevalence: 3.58 per 100 registered patients). Pregabalin-dependent patients were male, with a median usage duration of eight months and a median daily dose of 1200 mg. Most had concurrent opioid dependence, primarily heroin, used via the injection route. The odds of pregabalin dependence among those with opioid dependence were significantly higher than those with other substance dependence (OR 1.44, 95% CI 1.13-1.85). Reasons for pregabalin use included opioid craving reduction, sedation, and euphoria. Patients with pregabalin dependence were more likely to have lower socioeconomic status (P < 0.0001) and urban residence (P = 0.032), an earlier age of substance use initiation (P = 0.02) and treatment seeking (P < 0.0001), and a higher co-occurrence of psychiatric disorders (P = 0.007) and less occurrence of alcohol dependence (P = 0.03). Conclusion: Findings underscore the need for heightened awareness, screening, and intervention efforts targeting pregabalin misuse within SUD treatment. Further research should focus on longitudinal studies to elucidate pregabalin dependence's trajectory. [ABSTRACT FROM AUTHOR]

Background: Craving is the subjective experience of desire for specific drugs. Lack of reliability and untested construct validity are limiting factors for the existing questionnaires to assess craving. Aim: The aim of the study was to design and test the validity and reliability of an instrument to assess visual cue-induced craving for heroin dependence. Materials and Methods: In the first stage of the study, a set of forty images (twenty each of heroin and neutral cues-) were captured and validated by expert consensus. Thirty male participants with heroin dependence rated their cue-induced craving on a six-point Likert scale while viewing this image-set. In the next stage, putative construct validity was examined using a pilot cue-reactivity functional magnetic resonance imaging paradigm with ten additional heroin-dependent patients. Results: Cronbach's alpha for the instrument for visual cue-associated craving of HEroin (IV-CACHE) was 0.9, suggestive of high internal consistency. There were modest and significant correlations of IV-CACHE with the drug desire questionnaire (r = 0.43), and obsessive-compulsive drug use scale (r = 0.37), supporting concurrent validity. Patients with heroin dependence exhibited cue reactivity in the left fusiform area, right lingual gyrus, right precuneus region, right inferior frontal, inferior temporal gyri, and middle occipital gyri. The activated brain areas were largely aligned to the underlying neurobiological substrates of craving but might also have depicted nondrug-specific factors (aberrant face processing and attentional bias). Conclusion: The present cue-task is a promising tool for the examination of cue-related craving for heroin in the Indian setting. [ABSTRACT FROM AUTHOR]

The volatile alkylpyrazines methyl‐ and methoxypyrazines (MPs) present in the reflex bleeds of coccinellid beetles such as the harlequin ladybird beetle Harmonia axyridis are important semiochemicals that function in antipredatory defense behavior. Pyrazines have also been coadapted from a primarily defensive role into pheromones that function in intraspecific communication, attraction, and aggregation behavior. However, the biosynthesis of MPs in ladybird beetles is poorly understood. Here, we tested the hypothesis that MPs could be produced by microbial symbionts in H. axyridis, which generates four different MPs. The evaluation of tissue‐specific MP production showed that MP concentrations were highest in the gut tissue and hemolymph of the beetles rather than the fat body tissue as the presumed site of MP biosynthesis. Furthermore, manipulation of gut microbiota by antibiotic‐containing diets resulted in a lower MP content in adult beetles. The analysis of the bacterial community of the digestive tract revealed the presence of bacteria of the genera Serratia and Lactococcus which are reportedly able to produce MPs. In line with the known diet‐dependent production of MP in H. axyridis, we determined that the presence or relative abundance of some of the potential MP producers (Enterococcus and Staphylococcus) is also diet‐dependent. We hypothesize a potential role of the microbiota in MP production in H. axyridis as a possible example for outsourcing the synthesis of ecologically important semiochemicals to its gut bacteria. Methoxypyrazines in the reflex bleeds of ladybirds function in defense, aggregation and as warning signals. Our study implicates that methoxypyrazines are synthesized by the gut microbiota of the invasive ladybird Harmonia axyridis implicating outsourcing the synthesis of these ecologically important semiochemicals. [ABSTRACT FROM AUTHOR]

Abstract: Necrophagous beetles utilize carrion, a highly nutritious resource that is susceptible to intense microbial competition, by treating it with antimicrobial anal and oral secretions. However, how this regulates the carcass microbiota remains unclear. Here, we show that carcasses prepared by the burying beetle Nicrophorus vespilloides undergo significant changes in their microbial communities subsequent to their burial and “preparation.” Prepared carcasses hosted a microbial community that was more similar to that of beetles’ anal and oral secretions than to the native carcass community or the surrounding soil, indicating that the beetles regulated the carcass microbiota. A core microbial community (Xanthomonadaceae, Enterococcaceae, Enterobacteriaceae and Yarrowia yeasts) was transmitted by the beetles to the larvae via the anal and oral secretions and the carcass surface. These core taxa proliferated on the carcass, indicating a growth conducive environment for these microbes when associated with beetles. However, total bacterial loads were higher on decomposing carcasses without beetles than on beetle‐prepared carcasses, indicating that the beetles and/or their associated symbionts suppress the growth of competing microbes. Thus, apart from being a nutritional resource, the carcass provides a medium for vertical transmission of a tightly regulated symbiotic microbiota, whose activity on the carcass and in the larval gut may involve carcass preservation as well as digestion. [ABSTRACT FROM AUTHOR]