Conducting Polymer Electrodes for Thermogalvanic Cells

Fossil fuels are still the dominant (ca. 80%) energy source in our society. A significant fraction is used to generate electricity with a heat engine possessing an efficiency of approximately 35%. Therefore, about 65% of fossil fuel energy is wasted in heat. Other primary heat sources include solar and geothermal energies that can heat up solid and fluids up to 150°C. The growing demand and severe environmental impact of energy systems provide an impetus for effective management and harvesting solutions dealing with waste heat. A promising way to use waste heat is to directly convert thermal energy into electrical energy by thermoelectric generators (TEGs). Solid state TEGs are electronic devices that generate electrical power due to the thermo-diffusion of electronic charge carriers in the semiconductor upon application of the thermal field. However, there is another type of thermoelectric device that has been much less investigated; this is the thermogalvanic cell (TGCs). The TGC is an electrochemical device that consists of the electrolyte solution including a reversible redox couple sandwiched between two electrodes. In our study, we focus on iron-based organometallic molecules in aqueous electrolyte. A temperature difference (Δ) between the electrodes promotes a difference in the electrode potentials [Δ()]. Since the electrolyte contains a redox couple acting like electronic shuttle between the two electrodes, power can be generated when the two electrodes are submitted to a temperature difference. The focus of this thesis is (i) to investigate the possibility to use conducting polymer electrodes for thermogalvanic cells as an alternative to platinum and carbon-based electrodes, (ii) to investigate the role of viscosity of the electrolyte in order to consider polymer electrolytes, (iii) to understand the mechanisms limiting the electrical power output in TGCs; and (iv) to understand the fundamentals of the electron transfer taking place at the interface between the polymer electrode and the redox molecule in the electrolyte. These findings provide an essential toolbox for further improvement in conducting polymer thermogalvanic cells and various other emerging electrochemical technologies such as fuel cells, redox flow battery, dye-sensitized solar cells and industrial electrochemical synthesis

Optimization and tuning of the aspect ratio of hydrothermally grown ZnO nanorods by varying the hydrothermal temperature and their electron transport properties

In this investigation, a facile method to synthesize 1-D ZnO nanorod having different aspect ratio by varying the hydrothermal temperature was demonstrated. The hydrothermal reaction temperatures were optimized to obtain high aspect ratio ZnO nanorods with well-defined 1-D structures. The aspect ratio depended electron transport properties, charge recombination, chemical capacitance, life-time and charge diffusion length of 1-D ZnO nanostructures were investigated. It was observed a clear correlation between the aspect ratio and the electron transport properties of ZnO nanorods. The highest aspect ratio of 7.6 was obtained for the ZnO nanorods synthesized at 100–120 °C and was found to have the highest electron transport properties. It was demonstrated the formation of highly crystalline, high-aspect ratio 1-D ZnO nanorods with enhanced electron transport properties at low hydrothermal temperatures which will be beneficial for device applications

Laser-induced graphitization of a forest-based ink for use in flexible and printed electronics

Abstract Laser-induced graphitization (LIG) is a method of converting a carbon-rich precursor into a highly conductive graphite-like carbon by laser scribing. This method has shown great promise as a versatile and low-cost patterning technique. Here we show for the first time how an ink based on cellulose and lignin can be patterned using screen printing followed by laser graphitization. Screen printing is one of the most commonly used manufacturing techniques of printed electronics, making this approach compatible with existing processing of various devices. The use of forest-based materials opens the possibility of producing green and sustainable electronics. Pre-patterning of the ink enables carbon patterns without residual precursor between the patterns. We investigated the effect of the ink composition, laser parameters, and additives on the conductivity and structure of the resulting carbon and could achieve low sheet resistance of 3.8 Ω sq−1 and a high degree of graphitization. We demonstrated that the process is compatible with printed electronics and finally manufactured a humidity sensor which uses lignin as the sensing layer and graphitized lignin as the electrodes

Bulk electronic transport impacts on electron transfer at conducting polymer electrode-electrolyte interfaces.

Electrochemistry is an old but still flourishing field of research due to the importance of the efficiency and kinetics of electrochemical reactions in industrial processes and (bio-)electrochemical devices. The heterogeneous electron transfer from an electrode to a reactant in the solution has been well studied for metal, semiconductor, metal oxide, and carbon electrodes. For those electrode materials, there is little correlation between the electronic transport within the electrode material and the electron transfer occurring at the interface between the electrode and the solution. Here, we investigate the heterogeneous electron transfer between a conducting polymer electrode and a redox couple in an electrolyte. As a benchmark system, we use poly(3,4-ethylenedioxythiophene) (PEDOT) and the Ferro/ferricyanide redox couple in an aqueous electrolyte. We discovered a strong correlation between the electronic transport within the PEDOT electrode and the rate of electron transfer to the organometallic molecules in solution. We attribute this to a percolation-based charge transport within the polymer electrode directly involved in the electron transfer. We show the impact of this finding by optimizing an electrochemical thermogalvanic cell that transforms a heat flux into electrical power. The power generated by the cell increased by four orders of magnitude on changing the morphology and conductivity of the polymer electrode. As all conducting polymers are recognized to have percolation transport, we believe that this is a general phenomenon for this family of conductors.Funding agencies: Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University Faculty Grant [SFO-Mat-LiU 2009-00971]</p

Social, cultural and economical determinants of diabetes mellitus in Kalutara district, Sri Lanka: a cross sectional descriptive study

<p>Abstract</p> <p>Introduction</p> <p>Sri Lanka is a country that is expected to face a high burden of diabetes mellitus (DM). There is a paucity of data on social and demographic determinants of DM, especially in the plantation sector.</p> <p>Aims</p> <p>To describe social and economic correlates and inequalities of DM in Kalutara District.</p> <p>Methods</p> <p>A cross sectional descriptive study was carried out among adults over the age of 35 years. A sample of 1300 individuals was selected using stratified random cluster sampling method from 65 Grama Niladari Divisions (GND), which were representative of urban, rural and plantation sectors. Twenty households were randomly selected from each division and one adult was randomly selected from each household. Data were collected using a pre-tested questionnaire. Fasting plasma blood sugar of ≥126mg/dl was used to define DM. Significance of prevalence of diseases and risk factors across different socio-economic strata were determined by chi square test for trend.</p> <p>Results</p> <p>Of 1234 adults who were screened (628 males), 202 (14.7%) had DM. Higher DM proportions (16.1%) were seen in the highest income quintile and in those educated up to Advanced Levels (AL) and above (17.3%). Prevalence in the urban, rural and plantation sectors were 23.6%, 15.5% and 8.5% respectively. Prevalence among Sinhalese, Tamils and Muslims were 14.4%, 29.0% and 20.0% respectively. There was a gradient in prevalence according to the unsatisfactory basic needs index of the GND with the highest proportion (20.7%) observed in the richest GND. The highest social status quintile demonstrated the highest proportion (17.4%) with diabetes mellitus.</p> <p>Conclusion</p> <p>There is a higher prevalence of diabetes mellitus in the more affluent and educated segments of society. There is also a higher prevalence among urban compared to rural and estates. Sri Lanka is in an early stage of the epidemic where the wealthy people are at a higher risk of DM.</p

Unconventional Thermoelectric Materials for Energy Harvesting and Sensing Applications

Heat is an abundant but often wasted source of energy. Thus, harvesting just a portion of this tremendous amount of energy holds significant promise for a more sustainable society. While traditional solid-state inorganic semiconductors have dominated the research stage on thermal-to-electrical energy conversion, carbon-based semiconductors have recently attracted a great deal of attention as potential thermoelectric materials for low-temperature energy harvesting, primarily driven by the high abundance of their atomic elements, ease of processing/manufacturing, and intrinsically low thermal conductivity. This quest for new materials has resulted in the discovery of several new kinds of thermoelectric materials and concepts capable of converting a heat flux into an electrical current by means of various types of particles transporting the electric charge: (i) electrons, (ii) ions, and (iii) redox molecules. This has contributed to expanding the applications envisaged for thermoelectric materials far beyond simple conversion of heat into electricity. This is the motivation behind this review. This work is divided in three sections. In the first section, we present the basic principle of the thermoelectric effects when the particles transporting the electric charge are electrons, ions, and redox molecules and describe the conceptual differences between the three thermodiffusion phenomena. In the second section, we review the efforts made on developing devices exploiting these three effects and give a thorough understanding of what limits their performance. In the third section, we review the state-of-the-art thermoelectric materials investigated so far and provide a comprehensive understanding of what limits charge and energy transport in each of these classes of materials.Funding Agencies|Knut and Alice Wallenberg foundationKnut &amp; Alice Wallenberg Foundation; Swedish Research CouncilSwedish Research CouncilEuropean Commission [201603979, 2020-03243]; AForsk [18-313, 19-310]; Olle Engkvists Stiftelse [204-0256]; European CommissionEuropean CommissionEuropean Commission Joint Research Centre [GA-955837]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]; U.S. Department of Energy (DOE)United States Department of Energy (DOE) [DE-AC36-08GO28308]</p

Global age-sex-specific mortality, life expectancy, and population estimates in 204 countries and territories and 811 subnational locations, 1950–2021, and the impact of the COVID-19 pandemic: a comprehensive demographic analysis for the Global Burden of Disease Study 2021

BackgroundEstimates of demographic metrics are crucial to assess levels and trends of population health outcomes. The profound impact of the COVID-19 pandemic on populations worldwide has underscored the need for timely estimates to understand this unprecedented event within the context of long-term population health trends. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 provides new demographic estimates for 204 countries and territories and 811 additional subnational locations from 1950 to 2021, with a particular emphasis on changes in mortality and life expectancy that occurred during the 2020–21 COVID-19 pandemic period.Methods22 223 data sources from vital registration, sample registration, surveys, censuses, and other sources were used to estimate mortality, with a subset of these sources used exclusively to estimate excess mortality due to the COVID-19 pandemic. 2026 data sources were used for population estimation. Additional sources were used to estimate migration; the effects of the HIV epidemic; and demographic discontinuities due to conflicts, famines, natural disasters, and pandemics, which are used as inputs for estimating mortality and population. Spatiotemporal Gaussian process regression (ST-GPR) was used to generate under-5 mortality rates, which synthesised 30 763 location-years of vital registration and sample registration data, 1365 surveys and censuses, and 80 other sources. ST-GPR was also used to estimate adult mortality (between ages 15 and 59 years) based on information from 31 642 location-years of vital registration and sample registration data, 355 surveys and censuses, and 24 other sources. Estimates of child and adult mortality rates were then used to generate life tables with a relational model life table system. For countries with large HIV epidemics, life tables were adjusted using independent estimates of HIV-specific mortality generated via an epidemiological analysis of HIV prevalence surveys, antenatal clinic serosurveillance, and other data sources. Excess mortality due to the COVID-19 pandemic in 2020 and 2021 was determined by subtracting observed all-cause mortality (adjusted for late registration and mortality anomalies) from the mortality expected in the absence of the pandemic. Expected mortality was calculated based on historical trends using an ensemble of models. In location-years where all-cause mortality data were unavailable, we estimated excess mortality rates using a regression model with covariates pertaining to the pandemic. Population size was computed using a Bayesian hierarchical cohort component model. Life expectancy was calculated using age-specific mortality rates and standard demographic methods. Uncertainty intervals (UIs) were calculated for every metric using the 25th and 975th ordered values from a 1000-draw posterior distribution.FindingsGlobal all-cause mortality followed two distinct patterns over the study period: age-standardised mortality rates declined between 1950 and 2019 (a 62·8% [95% UI 60·5–65·1] decline), and increased during the COVID-19 pandemic period (2020–21; 5·1% [0·9–9·6] increase). In contrast with the overall reverse in mortality trends during the pandemic period, child mortality continued to decline, with 4·66 million (3·98–5·50) global deaths in children younger than 5 years in 2021 compared with 5·21 million (4·50–6·01) in 2019. An estimated 131 million (126–137) people died globally from all causes in 2020 and 2021 combined, of which 15·9 million (14·7–17·2) were due to the COVID-19 pandemic (measured by excess mortality, which includes deaths directly due to SARS-CoV-2 infection and those indirectly due to other social, economic, or behavioural changes associated with the pandemic). Excess mortality rates exceeded 150 deaths per 100 000 population during at least one year of the pandemic in 80 countries and territories, whereas 20 nations had a negative excess mortality rate in 2020 or 2021, indicating that all-cause mortality in these countries was lower during the pandemic than expected based on historical trends. Between 1950 and 2021, global life expectancy at birth increased by 22·7 years (20·8–24·8), from 49·0 years (46·7–51·3) to 71·7 years (70·9–72·5). Global life expectancy at birth declined by 1·6 years (1·0–2·2) between 2019 and 2021, reversing historical trends. An increase in life expectancy was only observed in 32 (15·7%) of 204 countries and territories between 2019 and 2021. The global population reached 7·89 billion (7·67–8·13) people in 2021, by which time 56 of 204 countries and territories had peaked and subsequently populations have declined. The largest proportion of population growth between 2020 and 2021 was in sub-Saharan Africa (39·5% [28·4–52·7]) and south Asia (26·3% [9·0–44·7]). From 2000 to 2021, the ratio of the population aged 65 years and older to the population aged younger than 15 years increased in 188 (92·2%) of 204 nations.InterpretationGlobal adult mortality rates markedly increased during the COVID-19 pandemic in 2020 and 2021, reversing past decreasing trends, while child mortality rates continued to decline, albeit more slowly than in earlier years. Although COVID-19 had a substantial impact on many demographic indicators during the first 2 years of the pandemic, overall global health progress over the 72 years evaluated has been profound, with considerable improvements in mortality and life expectancy. Additionally, we observed a deceleration of global population growth since 2017, despite steady or increasing growth in lower-income countries, combined with a continued global shift of population age structures towards older ages. These demographic changes will likely present future challenges to health systems, economies, and societies. The comprehensive demographic estimates reported here will enable researchers, policy makers, health practitioners, and other key stakeholders to better understand and address the profound changes that have occurred in the global health landscape following the first 2 years of the COVID-19 pandemic, and longer-term trends beyond the pandemic