Dynamics of SARS-CoV-2 variants during the XBB wave in the Republic of Korea.

As COVID-19 has become endemic, SARS-CoV-2 variants are becoming increasingly diverse, underscoring the escalating importance of global genomic surveillance. This study analyzed 86,762 COVID-19 samples identified in the Republic of Korea from September 2022 to November 2023. The results revealed a consistent increase in the prevalence of the XBB variants following the dominance of BN.1, with various XBB sub-lineages co-circulating in the Republic of Korea. The overall nucleotide diversity (π) among the SARS-CoV-2 genomes was 0.00155. Evolutionary analysis revealed that the average time interval between the first detection and estimated date of the most recent common ancestor of Korean XBB sub-lineages was 47 d, suggesting that the novel variants were efficiently identified in the Korean surveillance system. The mutation rate was determined to be in the range of 5.6 × 10-4 to 9.1 × 10-4 substitutions/site/year. In conclusion, this study provides insights into the genetic diversity and evolutionary interpretation of the XBB sub-lineages during the XBB wave in the Republic of Korea, highlighting the importance of continued genomic surveillance for emerging variants.

The association of emotional labour and workplace violence with health-related productivity loss.

OBJECTIVES: This study explored the association between emotional labour and workplace violence with health-related productivity loss (HRPL). METHODS: We used the initial dataset from a survey known as the Korean Work, Sleep, and Health Study, an ongoing nationwide panel study initiated in 2022. To assess emotional labour, the study included 2386 workers who worked in customer service. The Korean Workplace Violence Scale-13 and the Korean Emotional Labour Scale-11 were used to assess the level of exposure to workplace violence, and the intensity of emotional labour, respectively. The Work Productivity and Activity Impairment Questionnaire was used to measure HRPL, including absenteeism and presenteeism. We examined differences in HRPL based on workplace violence and emotional labour using generalised linear regression models. RESULTS: HRPL increased with an increase in workplace violence and emotional labour scores. Notably, the mean HRPL was highest in high-risk group of both workplace violence and emotional labour. The mean HRPL increased as the number of 'high-risk' components for workplace violence and emotional labour increased. All the workplace violence and emotional labour components exhibited higher HRPL in the 'high-risk' groups compared to the 'low-risk' groups. CONCLUSIONS: Our study showed that both emotional labour and workplace violence are associated with reduced productivity.

Association between phthalate exposure and sleep quality in pregnant women: Results from the Korean Children's Environmental Health Study with repeated assessment of exposure.

Background: Evidence linking environmental toxicants to sleep quality is growing; however, these associations during pregnancy remain unclear. We examined the associations of repeated measures of urinary phthalates in early and late pregnancy with multiple markers of sleep quality among pregnant women. Methods: The study population included 2324 pregnant women from the Korean Children's Environmental Health Study. We analyzed spot urine samples collected at two time points during pregnancy for exposure biomarkers of eight phthalate metabolites. We investigated associations between four summary phthalates (all phthalates: ∑Phthalates; di-(2-ethylhexyl) phthalate: ∑DEHP; phthalates from plastic sources: ∑Plastic; and antiandrogenic phthalates: ∑AA) and eight individual phthalates and self-reported sleep measures using generalized ordinal logistic regression and generalized estimating equations models that accounted for repeated exposure measurements. The models were adjusted for age, body mass index, education, gestational age, income, physical activity, smoking, occupation, chronic diseases, depression, and urinary cotinine levels. Results: Multiple individual phthalates and summary measures of phthalate mixtures, including ∑Plastic, ∑DEHP, ∑AA, and ∑Phthalates, were associated with lower sleep efficiency. To illustrate, every 1-unit log increase in ∑AA was associated with a reduction of sleep efficiency by 1.37 % (95% confidence interval [CI] = -2.41, -0.32). ∑AA and ∑Phthalates were also associated with shorter sleep duration and longer sleep latency. Associations between summary phthalate measures and sleep efficiency differed by urinary cotinine levels (P for subgroup difference < 0.05). Conclusions: Findings suggest that higher phthalate exposure may be related to lower sleep efficiency, shorter sleep duration, and prolonged sleep latency during pregnancy.

Designing a Schottky Barrier-Free Interface for a Highly Conductive Anode in Proton Exchange Membrane Water Electrolysis.

Iridium, the most widely used anode catalyst in proton exchange membrane water electrolysis (PEMWE), must be used minimally due to its high price and limited supply. However, reducing iridium loading poses challenges due to abnormally large anode polarization. Herein, we present an anode catalyst layer (CL) based on a one-dimensional iridium nanofiber that enables a high current density operation of 3 A cm-2 at 1.86 V, even at an ultralow loading (0.07 mgIr cm-2). The performance is maintained even with a Pt coating-free porous transport layer (PTL) because our nanofiber CL circumvents the interfacial electron transport problem caused by the native oxide on the Ti PTL. We attribute this to the low work function and the low-ionomer-exposed surface of the nanofiber CL, which prevent the formation of Schottky contact at the native oxide interface. These results highlight the significance of optimizing the electronic properties of the CL/PTL interface for low-iridium-loading PEMWE.

Effects of indoor environments and outdoor air pollutants in residential areas on acute exacerbation in patients with severe asthma.

This study aimed to determine the effects of indoor environment (IE) and outdoor air pollutants (OAPs) in residential areas on acute exacerbation (AE) in patients with severe asthma. A total of 115 participants were recruited. To characterize IE, we used structured questionnaires and estimated OAP concentrations using a land-use regression model. Participants who were exposed to passive smoking and lived in houses where the kitchen and living room were not separated showed a significantly higher rate of AE (p = 0.014 and 0.0016, respectively). The mean concentration of PM2.5 in residential areas during the last 3 years was significantly higher in participants with AE than that in those without AE (19.8 ± 3.1 vs. 21.0 ± 2.5 µg/m3, p = 0.033). Moreover, the serum level of 8-hydroxy-2'-deoxyguanosine significantly increased in participants with AE compared to those without AE (56.9 ± 30.0 vs. 94.7 ± 44.5 ng/mL, p = 0.0047) suggesting enhanced oxidative stress in those with AE.

Exploring the impact of age and socioeconomic factors on health-related unemployment using propensity score matching: results from Korea National Health and Nutrition Examination Survey (2015-2017).

Background: Previous reports showed that age and socioeconomic factors mediated health-related unemployment. However, those studies had limitations controlling for confounding factors. This study examines age and socioeconomic factors contributing to health-related unemployment using propensity score matching (PSM) to control for various confounding variables. Methods: Data were obtained from the Korean National Health and Nutrition Examination Survey (KNHANES) from 2015-2017. We applied a 1:1 PSM to align health factors, and examined the association between health-related unemployment and age or socioeconomic factors through conditional logistic regression. The health-related unemployment group was compared with the employment group. Results: Among the 9,917 participants (5,817 women, 4,100 men), 1,182 (853 women, 329 men) were in the health-related unemployment group. Total 911 pairs (629 women pairs and 282 men pairs) were retained after PSM for health factors. The results of conditional logistic regression showed that older age, low individual and household income levels, low education level, receipt of the Basic Livelihood Security Program benefits and longest-held job characteristics were linked to health-related unemployment, despite having similar health levels. Conclusions: Older age and low socioeconomic status can increase the risk of health-related unemployment, highlighting the presence of age discrimination and socioeconomic inequality. These findings underscore the importance of proactive management strategies aimed at addressing these disparities, which are crucial for reducing the heightened risk of health-related unemployment.

Prenatal and early-life air pollutant exposure and epigenetic aging acceleration.

BACKGROUND: This study investigated the association of prenatal and early childhood exposure to air pollution with epigenetic age acceleration (EAA) at six years of age using the Environment and Development of Children Cohort (EDC Cohort) MATERIALS & METHODS: Air pollution, including particulate matter [< 2.5 µm (PM2.5) and < 10 µm (PM10) in an aerodynamic diameter], nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO), and sulfur dioxide (SO2) were estimated based on the residential address for two periods: 1) during the whole pregnancy, and 2) for one year before the follow-up in children at six years of age. The methylation levels in whole blood at six years of age were measured, and the methylation clocks, including Horvath's clock, Horvath's skin and blood clock, PedBE, and Wu's clock, were estimated. Multivariate linear regression models were constructed to analyze the association between EAA and air pollutants. RESULTS: A total of 76 children in EDC cohort were enrolled in this study. During the whole pregnancy, interquartile range (IQR) increases in exposure to PM2.5 (4.56 µg/m3) and CO (0.156 ppm) were associated with 0.406 years and 0.799 years of EAA (Horvath's clock), respectively. An IQR increase in PM2.5 (4.76 µg/m3) for one year before the child was six years of age was associated with 0.509 years of EAA (Horvath's clock) and 0.289 years of EAA (Wu's clock). PM10 (4.30 µg/m3) and O3 (0.003 ppm) exposure in the period were also associated with EAA in Horvath's clock (0.280 years) and EAA in Horvath's skin and blood clock (0.163 years), respectively. CONCLUSION: We found that prenatal and childhood exposure to ambient air pollutants is associated with EAA among children. The results suggest that air pollution could induce excess biological aging even in prenatal and early life.

Advances in self-expandable metal stents for endoscopic ultrasound-guided interventions.

Endoscopic ultrasound (EUS)-guided interventions have evolved rapidly in recent years, with dedicated metal stents playing a crucial role in this process. Specifically, the invention of biflanged short metal-covered stents, including lumen-apposing metal stents (LAMS), and modifications in a variety of tubular self-expandable metal stents (SEMS), have led to innovations in EUS-guided interventions. LAMS or non-LAMS stents are commonly used in the EUS-guided drainage of pancreatic fluid collections, especially in cases of walled-off necrosis. Additionally, LAMS is commonly considered for drainage of the EUS-guided gallbladder or dilated common bile duct and EUS-guided gastroenterostomy. Fully or partially covered tubular SEMS with several new designs are being considered for EUS-guided biliary drainage. This review focuses on advances in SEMS for EUS-guided interventions and discusses related research results.

A comparison of novel electrocautery-enhanced lumen-apposing metal stents and plastic stents in endoscopic ultrasound-guided drainage of infected walled-off necrosis: a multicenter randomized study.

BACKGROUND: Although lumen-apposing metal stents (LAMSs) have been increasingly used for walled-off necrosis (WON), their advantages over plastic stents in infected WON are unclear. We investigated the safety and efficacy of a novel electrocautery-enhanced LAMS for managing infected WON. METHODS: Patients who required endoscopic ultrasound-guided WON drainage were randomly assigned to LAMS or plastic stent groups. The primary outcome was total number of direct endoscopic necrosectomy (DEN) procedures required to achieve clinical success. Secondary outcomes included rates of technical success, clinical success, and adverse events. RESULTS: 46 patients were included in the LAMS (n = 23) and plastic stent (n = 23) groups. The median total number of DEN procedures did not differ significantly between the plastic stent group (4 procedures, interquartile range [IQR] 2.5-5.0) and LAMS group (9 procedures, IQR 8.0-9.0) (P = 0.07). The LAMS group demonstrated a significantly higher clinical success rate than the plastic stent group based on intention-to-treat analysis (100% vs. 73.9%, P =0.03) at 8 weeks but not at 4 weeks. Significant bleeding occurred in one patient in the plastic stent group and no patients in the LAMS group. CONCLUSIONS: We found no significant difference in the total number of DEN procedures between LAMSs and plastic stents for managing infected WON. The only statistically significant finding was a higher clinical success rate at 8 weeks for patients treated with LAMS. The use of LAMS did not result in any adverse events, such as bleeding or buried LAMS syndrome, within the study duration.

Association between work from home and health-related productivity loss among Korean employees.

Background: After the coronavirus disease 2019 pandemic, the widespread adoption of working from home, or teleworking, has prompted extensive research regarding its effects on work productivity and the physical and mental health of employees. In this context, our study aimed to investigate the association between working from home and health-related productivity loss (HRPL). Methods: An online survey was conducted with a sample of 1,078 workers. HRPL was estimated by the Work Productivity and Activity Impairment Questionnaire: General Health version. Workers that have been working from home in the last 6 months were categorized into the "work from home" group. Generalized linear models were used to compare the mean difference of HRPL between "work from home" and "commuters" group. Stratified analyses were conducted based on various factors including gender, age, income level, occupation, education level, previous diagnosis of chronic disease, presence of preschool children, living in studio apartment, living alone, commuting time, working hours and regular exercise. Results: The overall HRPL was higher in the "work from home" group than in the "commuters" group with a mean difference of 4.05 (95% confidence interval [CI]: 0.09-8.01). In the stratified analyses, significant differences were observed in workers with chronic diseases (mean difference: 8.23, 95% CI: 0.38-16.09), who do not live alone (mean difference: 4.84, 95% CI: 0.35-9.33), and workers that do not exercise regularly (mean difference: 4.96, 95% CI: 0.12-9.80). Conclusions: Working from home is associated with an increased HRPL in the Korean working population, especially among those with chronic diseases, those who do not live alone, and those who do not exercise regularly.

SupporTive Care At Home Research (STAHR) for patients with advanced cancer: Protocol for a cluster non-randomized controlled trial.

Advancements in the treatment and management of patients with cancer have extended their survival period. To honor such patients' desire to live in their own homes, home-based supportive care programs have become an important medical practice. This study aims to investigate the effects of a multidimensional and integrated home-based supportive care program on patients with advanced cancer. SupporTive Care At Home Research is a cluster non-randomized controlled trial for patients with advanced cancer. This study tests the effects of the home-based supportive care program we developed versus standard oncology care. The home-based supportive care program is based on a specialized home-based medical team approach that includes (1) initial assessment and education for patients and their family caregivers, (2) home visits by nurses, (3) biweekly regular check-ups/evaluation and management, (4) telephone communication via a daytime access line, and (5) monthly multidisciplinary team meetings. The primary outcome measure is unplanned hospitalization within 6 months following enrollment. Healthcare service use; quality of life; pain and symptom control; emotional status; satisfaction with services; end-of-life care; advance planning; family caregivers' quality of life, care burden, and preparedness for caregiving; and medical expenses will be surveyed. We plan to recruit a total of 396 patients with advanced cancer from six institutions. Patients recruited from three institutions will constitute the intervention group, whereas those recruited from the other three institutions will comprise the control group.

Mortality Burden Due to Short-term Exposure to Fine Particulate Matter in Korea.

OBJECTIVES: Excess mortality associated with long-term exposure to fine particulate matter (PM2.5) has been documented. However, research on the disease burden following short-term exposure is scarce. We investigated the cause-specific mortality burden of short-term exposure to PM2.5 by considering the potential non-linear concentration-response relationship in Korea. METHODS: Daily cause-specific mortality rates and PM2.5 exposure levels from 2010 to 2019 were collected for 8 Korean cities and 9 provinces. A generalized additive mixed model was employed to estimate the non-linear relationship between PM2.5 exposure and cause-specific mortality levels. We assumed no detrimental health effects of PM2.5 concentrations below 15 µg/m3. Overall deaths attributable to short-term PM2.5 exposure were estimated by summing the daily numbers of excess deaths associated with ambient PM2.5 exposure. RESULTS: Of the 2 749 704 recorded deaths, 2 453 686 (89.2%) were non-accidental, 591 267 (21.5%) were cardiovascular, and 141 066 (5.1%) were respiratory in nature. A non-linear relationship was observed between all-cause mortality and exposure to PM2.5 at lag0, whereas linear associations were evident for cause-specific mortalities. Overall, 10 814 all-cause, 7855 non-accidental, 1642 cardiovascular, and 708 respiratory deaths were attributed to short-term exposure to PM2.5. The estimated number of all-cause excess deaths due to short-term PM2.5 exposure in 2019 was 1039 (95% confidence interval, 604 to 1472). CONCLUSIONS: Our findings indicate an association between short-term PM2.5 exposure and various mortality rates (all-cause, non-accidental, cardiovascular, and respiratory) in Korea over the period from 2010 to 2019. Consequently, action plans should be developed to reduce deaths attributable to short-term exposure to PM2.5.

The associations between maternal and fetal exposure to endocrine-disrupting chemicals and asymmetric fetal growth restriction: a prospective cohort study.

Recent evidence has revealed associations between endocrine-disrupting chemicals (EDCs) and placental insufficiency due to altered placental growth, syncytialization, and trophoblast invasion. However, no epidemiologic study has reported associations between exposure to EDCs and asymmetric fetal growth restriction (FGR) caused by placenta insufficiency. The aim of this study was to evaluate the association between EDC exposure and asymmetric FGR. This was a prospective cohort study including women admitted for delivery to the Maternal Fetal Center at Seoul St. Mary's Hospital between October 2021 and October 2022. Maternal urine and cord blood samples were collected, and the levels of bisphenol-A (BPA), monoethyl phthalates, and perfluorooctanoic acid in each specimen were analyzed. We investigated linear and non-linear associations between the levels of EDCs and fetal growth parameters, including the head circumference (HC)/abdominal circumference (AC) ratio as an asymmetric parameter. The levels of EDCs were compared between fetuses with and without asymmetric FGR. Of the EDCs, only the fetal levels of BPA showed a linear association with the HC/AC ratio after adjusting for confounding variables (ß = 0.003, p < 0.05). When comparing the normal growth and asymmetric FGR groups, the asymmetric FGR group showed significantly higher maternal and fetal BPA levels compared to the normal growth group (maternal urine BPA, 3.99 µg/g creatinine vs. 1.71 µg/g creatinine [p < 0.05]; cord blood BPA, 1.96 µg/L vs. -0.86 µg/L [p < 0.05]). In conclusion, fetal exposure levels of BPA show linear associations with asymmetric fetal growth patterns. High maternal and fetal exposure to BPA might be associated with asymmetric FGR.

Genomic epidemiology of highly pathogenic avian influenza A (H5N1) virus in wild birds in South Korea during 2021-2022: Changes in viral epidemic patterns.

Clade 2.3.4.4b highly pathogenic avian influenza A (HPAI) viruses have been detected in wild birds worldwide, causing recurrent outbreaks since 2016. During the winter of 2021-2022, we detected one H5N8 and forty-three H5N1 clade 2.3.4.4b HPAI viruses from wild birds in South Korea. Phylogenetic analysis revealed that HA gene of H5N1 viruses was divided into two genetically distinct groups (N1.G1 and N1.G2). Bayesian phylodynamic analysis demonstrated that wild birds play a vital role in viral transmission and long-term maintenance. We identified five genotypes (N1.G1.1, N1.G2, N1.G2.1, N1.G2.2, and N1.G2.2.1) having distinct gene segment constellations most probably produced by reassortments with low-pathogenic avian influenza viruses. Our results suggest that clade 2.3.4.4b persists in wild birds for a long time, causing continuous outbreaks, compared with previous clades of H5 HPAI viruses. Our study emphasizes the need for enhancing control measures in response to the changing viral epidemiology.

Comparative study between biliary covered self-expandable metal stent and conventional endoscopic bile drainage treatment in endoscopic retrograde cholangiopancreatography-related Stapfer type II retroperitoneal perforations.

BACKGROUND: Perforation is one of the most serious complications of endoscopic retrograde cholangiopancreatography (ERCP). Conventional nonsurgical endoscopic treatments including intravenous antibiotic administration and plastic endoscopic biliary drainage are generally approved for the treatment of ERCP-related Stapfer type II perforation (perivaterian type). Biliary covered metal stent placement has recently been reported to have favorable outcomes in ERCP-related Stapfer type II perforations. We aimed to compare the outcomes of conventional endoscopic bile drainage and biliary covered self-expandable metal stent (SEMS) insertion in patients with Stapfer type II perforation. METHODS: Medical records of patients who underwent ERCP at Kyungpook National University Hospital in Daegu from 2011 to 2022 were retrospectively reviewed. RESULTS: A total of 8,402 ERCP procedures were performed in our hospital. Sixty-six ERCP-related perforations (0.78%) were identified. Among them, 37 patients (56.1%) who had Stapfer type II perforations were enrolled. Thirteen and twenty-four patients received biliary covered SEMS insertion and conventional endoscopic bile drainage treatments, respectively. No significant differences were observed in the clinical success rate (92.3% vs. 91.7%, p = 1.000), hospital stay (9.46 ± 5.97 vs. 13.9 ± 13.2 days, p = 0.258), and post-ERCP-related fasting time (5.4 ± 3.4 vs 4.3 ± 3.0 days, p = 0.305). Complications including bleeding, post-ERCP pancreatitis, fever, and death were not significantly different between the two groups. The conventional endoscopic bile drainage group took less time for ERCP than the SEMS group (11.5 ± 5.2 vs. 18.5 ± 11.2 min, p = 0.013). CONCLUSIONS: Compared with the conventional endoscopic bile drainage treatment method, biliary covered SEMS did not improve patient outcomes in ERCP-related Stapfer type II perforations.

Ambient particulate matter and surrounding greenness in relation to sleep quality among pregnant women: A nationwide cohort study.

Background: Particulate air pollution and residential greenness are associated with sleep quality in the general population; however, their influence on maternal sleep quality during pregnancy has not been assessed. Objective: This cross-sectional study investigated the individual and interactive effects of exposure to particulate matter (PM) air pollution and residential greenness on sleep quality in pregnant women. Methods: Pregnant women (n = 4933) enrolled in the Korean Children's Environmental Health Study with sleep quality information and residential address were included. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). The average concentrations of PM (PM2.5 and PM10) during pregnancy were estimated through land use regression, and residential greenness in a 1000 m buffer area around participants' residences was estimated using the Normalized Difference Vegetation Index (NDVI1000-m). Modified Poisson regression models were used to estimate the associations between PM and NDVI and poor sleep quality (PSQI >5) after controlling for a range of covariates. A four-way mediation analysis was conducted to examine the mediating effects of PM. Results: After adjusting for confounders, each 10 µg/m3 increase in PM2.5 and PM10 exposure was associated with a higher risk of poor sleep quality (relative risk [RR]: 1.06; 95% confidence interval [CI]: 1.01, 1.11; and RR: 1.09; 95% CI: 1.06, 1.13, respectively), and each 0.1-unit increase in NDVI1000-m was associated with a lower risk of poor sleep quality (RR: 0.97; 95% CI: 0.95, 0.99). Mediation analysis showed that PM mediated approximately 37%-56% of the association between residential greenness and poor sleep quality. Conclusions: This study identified a positive association between residential greenness and sleep quality. Furthermore, these associations are mediated by a reduction in exposure to particulate air pollution and highlight the link between green areas, air pollution control, and human health.

Quality Indicators of Endoscopic Retrograde Cholangiopancreatography in Korea.

Endoscopic retrograde cholangiopancreatography (ERCP) is a procedure that requires significant experiences and skills and has various procedure-related complications, some of which can be severe and even result in the death of patients. Expanding ERCP availability has the advantage of increasing accessibility for patients. However, ERCP poses a substantial risk if performed without proper quality management. ERCP quality management is essential for both ensuring safe and successful procedures and meeting the social demands for enhanced healthcare competitiveness and quality assurance. To address these concerns, the Korean Pancreatobiliary Association established a task force to develop ERCP quality indicators (QIs) tailored to the Korean medical environment. Key questions for five pre-procedure, three intra-procedure, and four post-procedure measures were formulated based on a literature search related to ERCP QIs and a comprehensive clinical review conducted by experts. The statements and recommendations regarding each QI item were selected through peer review. The developed ERCP QIs were reviewed by external experts based on the latest available evidence at the time of development. These domestically tailored ERCP QIs are expected to contribute considerably to improving ERCP quality in Korea.

Detection of multiple recombinations of avian coronavirus in South Korea by whole-genome analysis.

Infectious bronchitis virus (IBV), an avian coronavirus, has caused considerable damage to the poultry industry. In Korea, indigenous KM91-like and newly introduced QX-like lineages belonging to the GI-19 lineage have been prevalent despite constant vaccination. In this study, complete genome sequences of 23 IBV isolates in Korea from 2010 to 2020 were obtained using next-generation sequencing, and their phylogenetic relationship and recombination events were analyzed. Phylogenetic analysis based on the S1 gene showed that all isolates belonged to the GI-19 lineage and were divided into five subgroups (KM91-like, K40/09-like, and QX-like II to IV). Among the 23 isolates, 14 recombinants were found, including frequent recombination between KM91-like and QX-like strains. In addition, it was observed that other lineages, such as GI-1, GI-13, and GI-16, were involved in recombination. Most recombination breakpoints were detected in the ORF1ab gene, particularly nsp3. However, when considering the size of each genome, recombination occurred more frequently in the 3a, E and 5a genes. Taken together, genetic recombination frequently occurred throughout the entire genome between various IBV strains in Korea, including live attenuated vaccine strain. Our study suggests the necessity of further research on the contribution of recombination of genomes outside the spike region to the biological characteristics of IBV.

Potential-Dependent Ionomer Rearrangement on the Pt Surface in Polymer Electrolyte Membrane Fuel Cells.

The interface between the catalyst and the ionomer in the catalyst layer of polymer electrolyte membrane fuel cells (PEMFCs) has been a subject of keen interest, but its effect on durability has not been fully understood due to the complexity of the catalyst layer structure. Herein, we utilize a Pt nanoparticle (NP) array electrode fabricated using a block copolymer template as the platform for a focused investigation of the interfacial change between the Nafion thin film and the Pt NP under a constant potential. A set of analyses for the electrodes treated with various potentials reveals that the Nafion thin film becomes densely packed at the intermediate potentials (0.4 and 0.7 V), indicating an increased ionomer-catalyst interaction due to the positive charges formed at the Pt surface at these potentials. Even for a practical PEMFC single cell, we demonstrate that the potential holding at the intermediate potentials increases ionomer adsorption to the Pt surface and the oxygen transport resistance, negatively impacting its power performance. This work provides fresh insight into the mechanism behind the performance fade in PEMFCs caused by potential-dependent ionomer rearrangement.

Enhanced Electrical and Optical Properties of Bismuth Tantalum Oxide Thin Films through Graphene Oxide Doping.

In this study, a hybrid thin film was fabricated by doping graphene oxide in a bismuth tantalum oxide solution in the sol-gel state. The thin film was produced by a brush-coating process. The graphene oxide doping ratios used were 0, 5, and 15 wt %. In the process of producing the thin film, the prepared sol-gel solution generates contraction forces, owing to the shear stress from the bristles of the brush, forming a microgroove structure. This structure was confirmed through atomic force microscopy, transmission electron microscopy, and energy-dispersive spectroscopy analyses. As a result of line profile analysis in atomic force microscopy, the groove heights of the thin film surface at 0, 5, and 15 wt % doping were 110, 130, and 160 nm, respectively, and the width of all grooves was 1 µm. The width of all thin films was approximately 1 µm, and microgrooves were confirmed. Moreover, the hybrid thin-film formation was confirmed by X-ray photoelectron spectroscopy. By comparing the electrical properties of the bismuth tantalum oxide thin film without graphene oxide doping and the thin film doped with 15 wt % graphene oxide, it was demonstrated that the electro-optical properties increased excellently with graphene oxide doping. Typically, the threshold voltage was reduced by approximately 0.26 V. Based on these observations, graphene oxide doped bismuth tantalum oxide hybrid thin films can be considered as promising candidates for thin-film applications in next-generation displays.