Spatial distribution and decrease of dye solar cell performance induced by electrolyte filling

The spatial performance variation of dye solar cell with standard liquid electrolyte was examined by dividing the cell into segments. Surprisingly large and permanent performance differences were found in different parts of the cell leading to significant losses in the overall cell efficiency. The decrease of open circuit voltage along the electrolyte filling direction suggests that 4-tert-butylpyridine is adsorbed non-uniformly as the electrolyte passes through the dyed TiO2 layer during the filling process. The result indicates that non-uniform electrolyte adsorption may limit the up-scaling of dye solar cells, which calls for the examination of electrolyte filling techniques and electrolyte compositions less prone to this effect.Peer reviewe

Segmented Cell Design for Improved Factoring of Aging Effects in Dye Solar Cells

A new segmented cell design was applied to study the aging of dye solar cell with stainless steel (StS) photoelectrode substrate, in particular the role of electrolyte in the degradation. Photovoltaic characterization indicated that StS photoelectrode cells are subjected to rapid (within hours or days) performance degradation that did not occur in the StS counter electrode cells. Other complementary techniques, open circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS), showed changes in the recombination at the photoelectrode/electrolyte interface. With the segmented cell method, we confirmed that the electrolyte was not contaminated by the StS nor was it subject to other significant changes related to the rapid degradation.Peer reviewe

Physical Modeling of Photoelectrochemical Hydrogen Production Devices

Solar-powered water splitting with photoelectrochemical (PEC) devices is a promising method to simultaneously harvest and store solar energy at a large scale. Highly efficient small prototype PEC devices reported recently demonstrate a move from basic material research toward design and engineering of complete devices and systems. The increased interest in engineering calls for a better understanding about the operational details of PEC devices at different length scales. The relevant physical phenomena and the properties of typical materials are well-known for separate device components, but their interaction in a complete PEC cell has received less attention. Coupled physical models are useful for studying these interactions and understanding the device operation as a whole and for optimizing the devices. We review the central physical processes in solar-powered water splitting cells and the physical models used in their theoretical simulations. Our focus is in particular on how different physical processes have been coupled together to construct device models and how different electrode and device geometries have been taken into account in them. Reflecting on the literature we discuss future opportunities and challenges in the modeling of PEC cells.Peer reviewe

Metallic and plastic dye solar cells

Dye solar cells (DSCs) are quite a new technology in photovoltaics. The traditional DSCs are prepared on conductively coated glass substrates in high temperature using a batch process. Manufacturing the cells on low-cost metal and plastic substrates would enable significant cost reductions as well as roll-to-roll mass production. There is a selection of metals and possible conducting coatings for plastics with varying electrical, optical, and chemical properties and price. The substrate has a dominant impact on the methods and materials that can be applied to make the cell and consequently on the resulting performance of the device. Furthermore, the substrates influence significantly the stability of the device. The main issue with plastics is their permeability whereas with metals, chemical stability in the electrolyte is themain concern. The leakage of electrolyte and the impact of water intake through the plastics can be affected by the material choices in particular with the electrolyte and dye composition. In the case of the metallic electrodes, the chemical stability can be improved by choosing a corrosion-resistant metal, applying a blocking layer or changing to a less aggressive electrolyte. One major focus of the current research of the flexible DSCs is increasing the efficiency by improved low-temperature preparation methods and materials especially for the photoelectrode. Another significant challenge is the development of noncorrosive electrolyte and dye combinations that work well even in the presence of significant amounts of water.Peer reviewe

Hverdag og verden er unge jenters psyke. En kontekstualisert forståelse av psykososiale helseplager blant unge jenter

Psychosocial health among girls implies that girls’ perception of themselves is related to both their close surroundings and their more distant surroundings. Selfreported mental health problems among adolescents have increased and this is specifically evident for girls. Challenges related to mental health have received great emphasis throughout recent years in research, media and preventive mental health work. Regarding these issues, it is relevant to seek a contextualized understanding that explores the psychosocial health connected to everyday life and to broader societal structures among young girls.publishedVersio

Vannhumler og andre humler: Barns fantasiuttrykk i en norsk barnehage

I denne artikkelen presenteres barns fantasi både som en felles aktivitet og som en individuell evne. Artikkelen er basert på et studie som er gjennomført i en norsk barnehage. Datamaterialet ble samlet inn ved hjelp av deltakende observasjon, videofilming og samtaler med barn. Det ble også gjennomført observasjon av møter blant pedagogene i barnehagen. Barn uttrykker fantasi på ulike måter og de kan lære fantasi av hverandre idet de inngår i felles fantasiaktiviteter. I tillegg viser det seg i studiet at de voksne deltar i kollektiv fantasi sammen med barna ved å anerkjenne fantasien og ved å skape rammer der fantasien får spillerom. Samtidig er det et økende fokus på basisferdigheter og kunnskapstilegnelse i norske barnehager, noe som utgjør en fare for om man evner å gjøre fantasi til et eksplisitt og verdsatt tema eller om den skyves til side som noe mindre viktig i barns liv, oppvekst og utvikling

An analytical model of hydrogen evolution and oxidation reactions on electrodes partially covered with a catalyst

Our previous theoretical study on the performance limits of the platinum (Pt) nanoparticle catalyst for the hydrogen evolution reaction (HER) had shown that the mass transport losses at a partially catalyst-covered planar electrode are independent of the catalyst loading. This suggests that the two-dimensional (2D) numerical model used could be simplified to a one-dimensional (1D) model to provide an easier but equally accurate description of the operation of these HER electrodes. In this article, we derive an analytical 1D model and show that it indeed gives results that are practically identical to the 2D numerical simulations. We discuss the general principles of the model and how it can be used to extend the applicability of existing electrochemical models of planar electrodes to low catalyst loadings suitable for operating photoelectrochemical devices under unconcentrated sunlight. Since the mass transport losses of the HER are often very sensitive to the H2 concentration, we also discuss the limiting current density of the hydrogen oxidation reaction (HOR) and how it is not necessarily independent of the reaction kinetics. The results give insight into the interplay of kinetic and mass-transport limitations at HER/HOR electrodes with implications for the design of kinetic experiments and the optimization of catalyst loadings in the photoelectrochemical cells.Peer reviewe

Contrasting snus and NRT as methods to quit smoking. an observational study

Background: Snus is considerably less hazardous to health than cigarettes. Recent data from Scandinavia have indicated that many smokers use snus as a method for quitting smoking. Methods: Data from five repeated cross-sectional surveys of Norwegian men and women aged 16-74 were pooled (N = 6 262). Respondents were asked about current and former smoking and snus use. Former daily smokers (N = 1219) and current daily smokers who had tried to quit at least once (N = 1118) were asked about the method they had used at their latest quit attempt and how many quit attempts they had made. Former smokers were also requested to report what year they had made their final quit attempt. Results: Snus was the most common method used for quitting smoking among men, while NRT was most often used among women. Stratifying the data according to year of quitting smoking (1945-2007) indicated a significant increase in use of the methods for quitting asked about over time. Among men, this was largely due to an increase in the use of snus. Among male quitters under the age of 45 years, 45.8 % of those who had used snus on their last attempt to quit were current non-smokers (OR = 1.61, CI 1.04-2.29), while 26,3 % of those who had used NRT were current non-smokers. 59.6 % of successful quitters and 19.5 % of unsuccessful quitters who had used snus as a method for quitting smoking had continued to use snus on a daily basis after quitting. Conclusion: Norwegian men frequently use snus as a method for quitting smoking whereas women are more likely to use NRT. The findings indicate that switching to snus can be an effective method for quitting smoking

Two-Dimensional Time-Dependent Numerical Modeling of Edge Effects in Dye Solar Cells

A two-dimensional transient model of dye solar cells (DSC) describing the electrochemical reactions in the cell has been prepared. The model includes the relevant components of DSCs: the photoelectrode, the electrolyte, and the counter electrode. The solved variables are potential and the concentrations of the different ion species, which can be used to determine, e.g., the current−voltage characteristics of the cell. The largest benefit of this model is its 2D features which enable the study of lateral inhomogeneity. Using the model, a new phenomenon was described: lateral current density distribution caused by a small difference in the size between photoelectrode and counter electrode, typical of laboratory test cells, causes tri-iodide to move from the edge region to the active area of the cell. This process takes a relatively long time (8 min) and can be important for performance characterization and design of DSCs.Peer reviewe