• Energy Research
• 2021-2025close
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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.

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

M.S.S. Santos is grateful to Portuguese Foundation for Science and Technology (FCT) for her PhD fellow (reference: SFRH/BD/104087/ 2014). Kashif Mushtaq is grateful to MIT Portugal Program for his doctoral grant (PD/BD/128041/2016) under the scope of the FCT. The authors would like to acknowledge to the FCT under the scope of the strategic funding of UID/BIO/04469 unit and COMPETE 2020 (POCI 01-0145-FEDER-006684) and BioTecNorte operation (NORTE-01-0145- FEDER-000004) funded by the European Regional Development Fund (ERDF), under the scope of Norte2020 - Programa Operacional Regional do Norte. The authors also acknowledge the Projects: i) POCI-01-0145- FEDER-006939 (LEPABE - Laboratory for Process Engineering, Environment, Biotechnology and Energy – UID/EQU/00511/2013), funded by the ERDF, through COMPETE2020 – Programa Operacional Competitividade e Internacionalizacao (POCI) and by nationals funds through FCT, ii) by the Project SunStorage - Harvesting and storage of solar energy”, with reference POCI-01-0145-FEDER-016387, funded by ERDF, through COMPETE 2020 –POCI), and by national funds, through FCT; (iii) Project PTDC/EQU-EQU/30510/2017 - POCI-01-0145- FEDER-030510 – Sunflow “Solar energy storage into redox flow batteries” funded by FEDER funds through COMPETE2020 - Programa Operacional Competitividade e Internacionalizacao (POCI) and by national funds (PIDDAC) through FCT/MCTES and iV) NORTE-01-0145- FEDER-000005 – LEPABE-2-ECO-INNOVATION, supported by North Portugal Regional Operational Programme (Norte 2020), under the Portugal 2020 Partnership Agreement, through the ERDF. The authors are indebted with all the colleagues who assisted in the laboratory work.

Abstract The development of clean, renewable, and affordable energy sources such as wind or sun has become a necessity for a sustainable energy society. Consequently, it is highly required the development of energy storage systems capable of efficiently storing the energy generated by these intermittent sources. In recent years, hydrogen-based technologies have emerged as a way of mitigating the environmental footprint left by the fossil fuels-based ones. In this paper we report new insights into the performance of an environmentally friendly Acid-Base Electrochemical Flow Battery (ABEFB), using an electrolyte consisting of high NaCl concentration. Energy is obtained from the neutralization of two acid and alkaline solutions through hydrogen evolution and oxidation reactions. Different parameters such as the nature of the cationic membrane and the electrolyte concentration have been systematically evaluated. Under optimal conditions, this battery can provide a maximum power density of about 73.5 W m-2 at 215 A m−2, a coulombic efficiency of around 80%, and a round-trip efficiency of 52%.

Polycrystalline lanthanum hexaboride (LaB) discs were sintered by hot pressing of commercial powders and successively polished, in order to investigate their thermionic emission capability. LaB samples presented values of work function in the range 2.55-2.61 eV. Discs with polished surface, independently from the composition and density, demonstrated to provide a Richardson constant around 45 A cm2K2. These results are promising for the use of sintered LaB discs in thermionic energy converters operating at temperatures in the 1400-1700 °C range. Moreover, since the properties of solar absorption and spectral selectivity of LaB make them appealing for the conversion of concentrated solar radiation, a modelling study to estimate the energy conversion efficiency was performed, aimed at identifying the proper engineering strategies able to make the resulting devices competitive for electrical conversion of concentrated solar radiation.

Electrochemical Energy Storage (EES) technologies are playing a significant role in the aspirations to decrease the usage of fossil fuels and move toward an environmentally conscious society. Due to the importance of EES technologies, more researchers are looking for an efficient and effective electrode material, which is the most important part of the EES system that possibly could result in much-needed advancements in the field. However, incoming researchers have a diverse backgrounds and as newcomers to the electrochemical community, they sometimes lack familiarity with the core concepts, well-established procedures, and methodologies that define the standards of the discipline. This issue's importance has been acknowledged, and various publications have been written to guide researchers in doing accurate evaluations. However, to the best of our knowledge, even though these publications demonstrate the methodologies and procedures for approaching the existing challenges none of them address the offered topic with an actual example. To address this gap, we present a step-by-step procedure for the electrochemical analysis of polypyrrole, a widely utilized conducting polymer with significant potential as an electrode material for supercapacitors and batteries.

Current prospective in the liquid fuels synthesis is prefiguring a greater integration of eco-friendly technologies based on the use of "non-fossil" hydrogen and CO. Therefore, a series of MO@CeO catalysts (i.e. M = Cu, Fe and Zn), at different MO-to-CeO ratio (ca. 0.2-1.5 wt./wt.), were prepared and performed in the in the CO hydrogenation reactions at 20 bar and 200-300 °C, (GHSV; 4,400NL?kg?cat h). Depending on catalyst composition, the CO conversion proceeds according to a "volcano shaped" profiles, resulting more effective at an optimal value of interfacial area (i.e. ? = 0.25). This also substantiate that the occurrence of structural-electronic synergistic effects plays a key role in the catalytic properties. The different catalytic pathway of CuZnO@CeO and CuFeZnO@CeO catalysts prove "dual-sites" and "triple-sites" mechanisms in the CO hydrogenation reactions, respectively.

The production of high-value products from lignocellulosic biomass is carried out through the selective scission of crosslinked CC/CO bonds. Nowadays, several techniques are applied to optimize biomass conversion into desired products with high yields. Photocatalytic technology has been proven to be a valuable tool for valorizing biomass at mild conditions. The photoproduced reactive oxygen species (ROSs) can initiate the scission of crosslinked bonds and form radical intermediates. However, the low mass transfer of the photocatalytic process could limit the production of a high yield of products. The incorporation of ultrasonic cavitation in the photocatalytic system provides an exceptional condition to boost the fragmentation and transformation of biomass into the desired products within a lesser reaction time. This review critically discusses the main factors governing the application of photocatalysis for biomass valorization and tricks to boost the selectivity for enhancing the yield of desired products. Synergistic effects obtained through the combination of sonolysis and photocatalysis were discussed in depth. Under ultrasonic vibration, hot spots could be produced on the surface of the photocatalysts, improving the mass transfer through the jet phenomenon. In addition, shock waves can assist the dissolution and mixing of biomass particles.