• Energy Research
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Abstract High power pseudocapacitors are extremely relevant to answer specific needs in the current energy transition arena and to implement an efficient renewable energy society. However, literature shows that are still open gaps concerning improvement of their energy density at high power, conversion efficiency, cost and cycle life. Electrodes based on active transition metal compounds, and in particular metal sulphides, evidence high potential to meet these objectives. This work discusses the dependence on the synthesis route of the charge storage mechanism of manganese sulphide-based materials and relates the pseudocapacitive response of these electrodes with their polycrystalline nature. Results reveal that a manganese oxy-sulphide mixture can achieve a high specific capacitance of 231 F.g−1 at 0.5 A/g in a 0.65 V active window. These values represent a 31.5 % increase compared to pure rambergite, γ-MnS, and 436 % compared to pure hausmannite Mn3O4 prepared under the same conditions. Moreover, the results show that manganese oxy-sulphide electrodes are characterized by good charge retention (73%), and superior long term capacity retention (above 86%) after 5000 cycles, evidencing potential for high power energy storage applications.

Abstract The Mediterranean region is one of the most vulnerable regions to climate change. The majority of climate models forecast a rise in temperatures and less rainfall, which have been observed in recent decades. These changes will affect several vegetation properties, especially phenological dynamics and traits, by increasing drought intensity and recurrence. In this climate change context, the present study aims to assess the evolution of vegetation state and its relation with the climate dynamics in the Mediterranean forest region of northeast Tunisia using Land Surface Phenology (LSP) metrics and the vegetation index (NDVI) analysis from 2000 to 2017. To conduct this work, we used precipitation and temperature data from the two closest weather stations and 16-day NDVI composite images from the MODIS satellite source, with 250-m spatial resolution. Three phenological metrics— start of season (SOS), end of season (EOS), and length of season (LOS) — were obtained and compared for different vegetation types. The LSP variation in response to climatic metrics was also analyzed. The results showed that the LSP in our study area changed significantly during the 2000–2017 period, which includes an average 7.8 days delay in the SOS, an average advance in the EOS by 5 days, and LOS shortened by an average 12.8 days. Autumn (Pr_9) and spring (Pr_3 and P3_4) precipitations, as well as maximum temperature (Tx9+10), represent the best climate parameters to explain the changes in LSP. Both the NDVI and SPEI showed a significant high correlation (p

In recent years, the biomass as a renewable feedstock has been gaining utmost importance in order to meet the global need for fuels and chemicals from sustainability perspectives [1,2]. Principal components of biomass are cellulosic and triglycerides derivatives. The triglyceride part is principally used to obtain biodiesel and liquid alkanes, as alternative fuels [3]. Biomass derived from the lignocellulose part is rich in carbohydrates and furan derivatives, and the presence of oxygen in their structure makes them suitable for further utilization to obtain added-value products. As concern the sustainability of the chemical processes, efforts are being made to turn them into "green" processes, working on the procedures (favorable reagent ratio, catalyst amount and green solvents) and exploiting heterogeneous catalysis. The use of solid catalyst is indeed very favorable from a sustainable point of view, due to its simple separation, regeneration and recycling of the material [4,5]. This implies a high efficiency of the catalysts accompanied by a decrease in the processing cost. This presentation will focus on different types of functionalized silica or titania based materials applied to the biomass exploitation, both to the synthesis of biodiesel and its additives and for the obtainment of added-value products such as GVL, diols or HMF. Biomass can use also for the production of new materials applied in the abatement of aqueous pollutants

Tourism is an important economic sector that has a significant impact on sustainability indicators, such as GHG emissions and cohesion. Local policy makers are increasingly challenged to manage the urban tourism system at large. As part of a EU funded project, the authors have conceptualized sustainable urban tourism as the ‘management of competing values’ represented in a conceptual model of ecology, visitability, livability, equity, economic growth and smart citizenship. A simulation game was designed and implemented to improve social learning about these competing values. The game was played in six European cities, with around 15 local policy-makers and stakeholders in each session. The players indicated a high level of satisfaction with the game and social learning. In order to understand to what extent the game is able to validate and communicate the competing values model, the start and end states of the tourism values of the cities, as logged in the game’s dashboard, were analyzed in a comparative manner. The analysis shows significant differences in how cities manage sustainable tourism, with marked differences in ecology and smart citizenship. The differences in tourism issues and policy making styles demonstrate the value of a simulation approach to support future planning processes.

Abstract Tracers are practical tools to provide insight on reservoir heterogeneity. However, scarce is the variety of available alternatives designed specifically for carbonate oil reservoir. Through application-oriented design, directed ad hoc to carbonate oil reservoirs, a family of cationic fluorinated tracers was developed, aided by computational design. This was done through the microwave assisted, one-step synthesis of fluorinated anilines exhaustively methylated in mild reaction conditions. Stability and aging tests were carried out at reservoir-emulating conditions, confirming the structural integrity of the compounds through 19F NMR and UHPLC-MS. Moreover, the developed tracer showed low adsorption compared to a commercial anionic tracer and did not modify the water-oil-rock physical and interfacial properties, remaining preferably partitioned towards water. Finally, degree of heterogeneity characterization in a packed column of natural mineral rock was obtained with the developed tracer, and its commercially available anionic analogue commonly used in field tracer tests. The comparison showed the potential of developed tracers as prominent candidates to support the design of exploitation processes, environmentally friendly and nontoxic, in carbonate oil reservoirs.

AbstractRadial tree growth is sensitive to environmental conditions, making observed growth increments an important indicator of climate change effects on forest growth. However, unprecedented climate variability could lead to non‐stationarity, that is, a decoupling of tree growth responses from climate over time, potentially inducing biases in climate reconstructions and forest growth projections. Little is known about whether and to what extent environmental conditions, species, and model type and resolution affect the occurrence and magnitude of non‐stationarity. To systematically assess potential drivers of non‐stationarity, we compiled tree‐ring width chronologies of two conifer species, Picea abies and Pinus sylvestris, distributed across cold, dry, and mixed climates. We analyzed 147 sites across the Europe including the distribution margins of these species as well as moderate sites. We calibrated four numerical models (linear vs. non‐linear, daily vs. monthly resolution) to simulate growth chronologies based on temperature and soil moisture data. Climate–growth models were tested in independent verification periods to quantify their non‐stationarity, which was assessed based on bootstrapped transfer function stability tests. The degree of non‐stationarity varied between species, site climatic conditions, and models. Chronologies of P. sylvestris showed stronger non‐stationarity compared with Picea abies stands with a high degree of stationarity. Sites with mixed climatic signals were most affected by non‐stationarity compared with sites sampled at cold and dry species distribution margins. Moreover, linear models with daily resolution exhibited greater non‐stationarity compared with monthly‐resolved non‐linear models. We conclude that non‐stationarity in climate–growth responses is a multifactorial phenomenon driven by the interaction of site climatic conditions, tree species, and methodological features of the modeling approach. Given the existence of multiple drivers and the frequent occurrence of non‐stationarity, we recommend that temporal non‐stationarity rather than stationarity should be considered as the baseline model of climate–growth response for temperate forests.

Fuel moisture limits the availability of fuel to wildfires in many forest areas worldwide, but the effects of climate change on moisture constraints remain largely unknown. Here we addressed how climate affects fuel moisture in pine stands from Catalonia, NE Spain, and the potential effects of increasing climate aridity on burned area in the Pyrenees, a mesic mountainous area where fire is currently rare. We first quantified variation in fuel moisture in six sites distributed across an altitudinal gradient where the long-term mean annual temperature and precipitation vary by 6-15 °C and 395-933 mm, respectively. We observed significant spatial variation in live (78-162%) and dead (10-15%) fuel moisture across sites. The pattern of variation was negatively linked (r = |0.6|-|0.9|) to increases in vapor pressure deficit (VPD) and in the Aridity Index. Using seasonal fire records over 2006-2020, we observed that summer burned area in the Mediterranean forests of Northeast Spain and Southern France was strongly dependent on VPD (r = 0.93), the major driver (and predictor) of dead fuel moisture content (DFMC) at our sites. Based on the difference between VPD thresholds associated with large wildfire seasons in the Mediterranean (3.6 kPa) and the maximum VPD observed in surrounding Pyrenean mountains (3.1 kPa), we quantified the "safety margin" for Pyrenean forests (difference between actual VPD and that associated with large wildfires) at 0.5 kPa. The effects of live fuel moisture content (LFMC) on burned area were not significant under current conditions, a situation that may change with projected increases in climate aridity. Overall, our results indicate that DFMC in currently fire-free areas in Europe, like the Pyrenees, with vast amounts of fuel in many forest stands, may reach critical dryness thresholds beyond the safety margin and experience large wildfires after only mild increases in VPD, although LFMC can modulate the response.

Abstract Hydrochars produced from agro-industrial wastes contain significant amounts of alkali metals and other inorganic elements that lead to different ash-related issues in energy systems. This work aims to modify the composition of hydrochar ash by adding rice hulls and/or mineral additives (i.e., lime, bentonite and kaolin) to improve their fusion behavior. Two series of samples were prepared to analyze the effect that the use of additives before or after the HTC processing of olive mill waste at 225 °C for 2 h had on the hydrochar properties. Hydrochars were then ashed, in agreement with UNE-EN 18122:2016, and the corresponding ashes subsequently characterized through XRF and ash fusion tests to determine their ash composition and ash characteristic fusion temperatures (AFTs), respectively. Among the studied additives, rice hulls led to the best results, as their use increased the initial ash deformation temperature to >1500 °C and resulted in the lowest hydrochar ash content. Using rice hulls before or after the HTC process did not affect the ash behavior, but it did change the hydrochar properties as a fuel. The joint HTC of rice hulls and feedstock led to a less carbonized solid with 13% higher moisture content and 15% lower energy density. Accordingly, the addition of rice hulls to ready-produced hydrochars is recommended to maintain the energy benefits of HTC as possible. The use of rice hulls as a low-cost additive to improve the fusion behavior of hydrochar ash opens new avenues for hydrochars in energy conversion processes with limited ash-related operational problems.