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The magnesium chalcogenide spinel MgSc2Se4 with high Mg‐ion room‐temperature conductivity has recently attracted interest as solid electrolyte for magnesium ion batteries. Its ionic/electronic mixed‐conducting nature and the influence of the spinel composition on the conductivity and Mg2+ migration barrier are yet not well understood. Here, results from a combined experimental and computational study on four MgB2Se4 spinels (B = Sc, Y, Er, Tm) are presented. The room‐temperature ionic conductivities (σion = 2 × 10−5–7 × 10–5 S cm−1) of the spinels are accurately measured, as electron transport is effectively suppressed by purely Mg‐ion conducting electrode interlayers. Using the same approach, reversible Mg plating/stripping as well as good electrochemical stability are achieved. Driven by the good accordance of the computationally and experimentally obtained Mg2+ migration barriers Ea(th) and Ea, respectively, further periodic density functional calculations are performed on the MgB2Se4 spinel system, revealing the role of trigonal distortion on the migration path geometry and Ea(th). These findings provide deeper understanding how to reach small Mg2+ migration barriers Ea in the MgB2Se4 spinels. [ABSTRACT FROM AUTHOR]

Hyporheic exchange processes (HEP) play a critical role in controlling riverine biogeochemical turnover and ecological functioning. Despite the expected scaling of HEP across stream networks, only limited knowledge exists about how HEP changes over the hydrological year and across the stream network. This study investigates spatial and temporal changes in HEP in a second‐ to fourth‐order stream network in southern Germany. We employed radon, an environmental tracer commonly used for quantifying HEP, to study the relationships between HEP and discharge. Numerical mass‐balance modelling was applied to quantify HEP, and we specifically focused on the hyporheic area (As) and the stream's cross‐sectional area (A). Our findings showed a decrease in As/A with increasing stream order, indicating changes of HEP across the stream network. The absence of a correlation of As with discharge implies that the scaling of HEP may be influenced by a combination of discharge and local heterogeneities in stream geomorphology. Temporal variability in HEP was observed over the hydrological year, with the highest variability in headwater streams. Lower As values were noted in headwaters during summer compared to the other seasons and coincided with an increased groundwater contribution to the streamflow and decreased stream discharge. Although neither stream or groundwater discharge were identified as driving factors for reduced HEP in the headwaters during summer, our findings suggest that hydrological processes that lead to decreased streamflow in headwaters may have influenced HEP further downstream in the stream network. This is evidenced by the larger As/A ratios observed in higher‐order streams during summer compared to other seasons. These findings highlight the necessity for comprehensive investigations of HEP processes over the hydrological year and across the whole stream network. [ABSTRACT FROM AUTHOR]

Magnesium batteries offer promising potential as next‐generation sustainable energy‐storage solutions due to the high theoretical capacity of the magnesium metal anode. Facilitating dendrite‐free operation of metal anodes necessitates the development of solid electrolytes with high magnesium‐ion conductivity. While the chalcogenide spinel MgSc2Se4 is predicted to exhibit high magnesium ion mobility, unequivocal experimental evidence for magnesium ion conduction beyond short‐range motion is still missing. This study confirms magnesium‐ion transport in MgSc2Se4 through two independent electrochemical methods: electrochemical deposition of magnesium metal and reversible magnesium plating/stripping cycling. To overcome the difficulty of measuring the ionic conductivity of the mixed conducting MgSc2Se4 spinel, a pure ion conducting interlayer is employed in a symmetric transference cell. This approach effectively suppresses the electron transport, allowing accurate characterization of the ionic conductivity. The experimental results confirm a low migration barrier of (386 ± 24) meV for magnesium ion transport in MgSc2Se4 and demonstrate one of the best performances at room temperature among the reported inorganic magnesium solid electrolytes. The findings open a new door for exploring additional mixed magnesium ion conductors and highlight the potential of magnesium chalcogenide spinels as a promising class of magnesium solid electrolytes. [ABSTRACT FROM AUTHOR]

Anthropogenic activities increase the contributions of inland waters to global greenhouse gas (GHG; CO 2 , CH 4 , and N 2 O) budgets, yet the mechanisms driving these increases are still not well constrained. In this study, we quantified year-long GHG concentrations, fluxes, and water physico-chemical variables from 28 sites contrasted by land use across five headwater catchments in Germany. Based on linear mixed-effects models, we showed that land use was more significant than seasonality in controlling the intra-annual variability of the GHGs. Streams in agriculture-dominated catchments or with wastewater inflows had up to 10 times higher daily CO 2 , CH 4 , and N 2 O emissions and were also more temporally variable (CV > 55 %) than forested streams. Our findings also suggested that nutrient, labile carbon, and dissolved GHG inputs from the agricultural and settlement areas may have supported these hotspots and hot-moments of fluvial GHG emissions. Overall, the annual emission from anthropogenic-influenced streams in CO 2 equivalents was up to 20 times higher (∼ 71 kg CO 2 m -2 yr -1) than from natural streams (∼ 3 kg CO 2 m -2 yr -1), with CO 2 accounting for up to 81 % of these annual emissions, while N 2 O and CH 4 accounted for up to 18 % and 7 %, respectively. The positive influence of anthropogenic activities on fluvial GHG emissions also resulted in a breakdown of the expected declining trends of fluvial GHG emissions with stream size. Therefore, future studies should focus on anthropogenically perturbed streams, as their GHG emissions are much more variable in space and time and can potentially introduce the largest uncertainties to fluvial GHG estimates. [ABSTRACT FROM AUTHOR]

Anthropogenic activities increase the contributions of inland waters to global greenhouse gas (GHG; CO2, CH4, and N2O) budgets, yet the mechanisms driving these increases are still not well constrained. In this study, we quantified year-long GHG concentrations and fluxes, as well as water physico-chemical variables from 23 streams, 3 ditches, and 2 wastewater inflow sites across five headwater catchments in Germany contrasted by land use. Using mixed-effects models, we determined the overall impact of land use and seasonality on the intra-annual variabilities of these parameters. We found that land use was more significant than seasonality in controlling the intra-annual variability of GHG concentrations and fluxes. Agricultural land use and wastewater inflows in settlement areas resulted in up to 10 times higher daily riverine CO2, CH4, and N2O emissions than forested areas, as substrate inputs by these sources appeared to favor in situ GHG production processes. Dissolved GHG inputs directly from agricultural runoff and waste-water inputs also contributed substantially to the annual emissions from these sites. Drainage ditches were hotspots for CO2 and CH4 fluxes due to high dissolved organic matter concentrations, which appeared to favor in situ production via respiration and methanogensis. Overall, the annual emission from anthropogenic-influenced streams in CO2-equivalents was up to 20 times higher (~71 kg CO2 m-2 yr-1) than from natural streams (~3 kg CO2 m-2 yr-1). Future studies aiming to estimate the contribution of lotic ecosystems to GHG emissions should therefore focus on anthropogenically perturbed streams, as their GHG emission are much more variable in space and time. [ABSTRACT FROM AUTHOR]

Enabling high Mg ion mobility, spinel‐type materials are promising candidates for cathode or solid electrolyte applications. To elucidate the factors governing the observed high mobility of multivalent ions, periodic DFT calculations of various charge carriers (A=Li, Na, K, Mg, Ca, Zn and Al) in the ASc2S4 and ASc2Se4 spinel compounds were performed, resulting in the identification of a Brønsted‐Evans‐Polanyi‐type scaling relation for the migration barriers of the various charge carriers. Combining this scaling relation with the derivation of a descriptor, solely based on easily accessible observables, constitutes a conceptual framework to investigate ion mobility in d0‐metal‐based spinel chalcogenides with significantly reduced computational effort. This approach was exemplarily verified for various d0‐metal‐based spinel chalcogenide compounds AB2X4 (B=Sc, Y, Ga, In, Er and Tm; X=O, S and Se) and led to the identification of d0‐metal‐based CaB2O4 spinels as promising compounds possibly enabling high Ca ion mobility. [ABSTRACT FROM AUTHOR]

The precise detection of the toxic gas H2S requires reliable sensitivity and specificity of sensors even at minute concentrations of as low as 10 ppm, the value corresponding to typical exposure limits. CuO can be used for H2S dosimetry, based on the formation of conductive CuS and the concomitant significant increase in conductance. In theory, at elevated temperature the reaction is reversed and CuO is formed, ideally enabling repeated and long‐term use of one sensor. Yet, the performance of CuO tends to drop upon cycling. Utilizing defined CuO nanorods we thoroughly elucidated the associated detrimental chemical changes directly on the sensors, by Raman and electron microscopy analysis of each step during sensing (CuO→CuS) and regeneration (CuS→CuO) cycles. We find the decrease in the sensing performance is mainly caused by the irreversible formation of CuSO4 during regeneration. The findings allowed us to develop strategies to reduce CuSO4 formation and thus to substantially maintain the sensing stability even for repeated cycles. We achieved CuO‐based dosimeters possessing a response time of a few minutes only, even for 10 ppm H2S, and prolonged life‐time. [ABSTRACT FROM AUTHOR]

Cover Feature: Unravelling Charge Carrier Mobility in d0-Metal-based Spinels (Batteries & Supercaps 7/2022) Descriptor, scaling relation, solid electrolyte, spinel, ion mobility Keywords: descriptor; ion mobility; scaling relation; solid electrolyte; spinel EN descriptor ion mobility scaling relation solid electrolyte spinel 1 1 1 07/11/22 20220701 NES 220701 B The Cover Feature b illustrates properties of the potential energy surface for charge carriers in spinel solid electrolyte and electrode materials that yield a descriptor for the ion mobility. [Extracted from the article]

Characterization of groundwater-surface water interactions remains challenging,especially in anthropogenically affected and geologically complex river systems. In thisstudy, groundwater inflow into the Ammer River was quantified by optimizingexfiltration rates in an implicit numerical model (FINIFLUX) to measured data ofseveral environmental tracers (e.g., sulfate (SO42−), radon (222Rn)) and organicconservative pollutants like carbamazepine and sulfamethoxazole emitted via awastewater treatment plant (WWTP). Modelling results of the selected tracers werecompared. The investigated Ammer River is strongly karstified and anthropogenically modified (millcanals, weirs, numerous artificial inputs) but representative for many small river systems inEurope. 222Rn activities in the river ranged from 500 to 3300 Bq m−3 and SO42−concentrations from 224 to 291 mg L−1. Concentrations of carbamazepine (90-130 ng L−1)and sulfamethoxazole (55-100 ng L−1) in the river water result from effluents of aWWTP. All tracers indicate major local groundwater inflows over the 6 km riverreach. Additional high peaks mainly observed in 222Rn activities indicate inputsalong geological fault lines, whereby increasing concentrations of carbamazepineand sulfamethoxazole may be attributed to inputs of groundwater contaminated byinfiltration of wastewater from a nearby WWTP. 222Rn-based calculations showed thebest optimization performance (R2=0.90) and result in a reasonable cumulativegroundwater inflow of 0.274 m3 s−1 (28.5% of total discharge) for the investigated reach.Poor optimizations for the other tracers may be due to the diurnal pattern of ionconcentrations induced by the WWTP and measurement uncertainties and the smallconcentration differences between river water and groundwater for carbamazepine andsulfamethoxazole. In our case study, 222Rn seems to be the most suitable environmental tracer despiteuncertainties in degassing and determination of the groundwater endmember concentration.However, only a multi tracer approach can account for the complexity of the investigatedriver system and may thus be indispensable for future investigations aiming to understandgroundwater-surface water interactions. [ABSTRACT FROM AUTHOR]

Anthropogenic organic micropollutants enter river systems mainly via wastewater treatment plants (WWTP). Characterization of turnover processes and fate of these compounds including temporal and spatial resolution at the same time remains challenging. Still, published results rely frequently on grab samples that do not account adequately for advection, dispersion and transformation along the studied reach. This study aims to compare degradation rates calculated from a Lagrangian Sampling concept in two different sequential reaches with calculations from arbitrary grab samples.Field investigations took place at two sequential reaches at the Ammer River close to Tübingen in the southwest of Germany that differ in (hydro-) morphology, slope and amount of groundwater inflow. Time-series measurements of organic chemical compounds (target screening), accompanied by electrical conductivity (EC), and conservative ions were conducted over a period of 24 hours. A lumped parameter model approach accounting for advection and dispersion was applied to the time-series measurements to calculate degradation rate constants affecting water parcels entering and leaving the same reach. In an alternative approach, degradation rate constants were calculated from arbitrary grab samples of the time series, representative for samples not properly considering travel time of water in the river. The influence of dilution caused by tributary and groundwater inflow was included for the overall attenuation rate in both approaches. The Lagrangian sampling approach integrates temporal dynamics such as the changed solar radiation or input of the WWTP into the river throughout the whole day and thus leads to representative degradation rates and characterization of turnover processes. In contrast, results from arbitrary grab samples may be misleading and indicating unrealistic processes and rates.The different results of the tested approaches show the relevance of identifying and including temporal and spatial aspects of river systems for characterization of the fate of organic micropollutants. They highlight the need to consider hydrological processes in the river for future field-based attenuation investigations. [ABSTRACT FROM AUTHOR]