•Description of a new low-temperature synthesis of fluorophosphates.•Titanium doping improves storage capacities of fluorophosphates as positive electrodes do ion-sodium batteries.•Niobium doping ...increase capacity retention of fluorophosphates as positive electrodes do ion-sodium batteries.
Sodium fluorophosphates are among the most promising materials for positive electrodes in sodium-ion batteries; however, their low electronic conductivity, kinetics limitations, and structural instability prevent them from reaching their full potential. We obtained sodium vanadium fluorophosphates (NVPF) doped with Ti4+ (NVTPF) and Nb5+ (NVNPF) via an original low-temperature synthesis. It was observed that Ti4+ doping facilitated access to electrode sites and provided higher capacities at high current densities while Nb5+ provided a 91.7% capacity retention from the 20th to 200th cycle, which was over the 80.1% capacity retention of NVPF. Moreover, both NVTPF and NVNPF provided diffusion coefficients in the range of ~10−10 cm2 s−1, which was better than ~10−12 cm2 s−1 of NVPF. Additionally, electrochemical impedance spectroscopy and ex situ X-ray diffraction measurements confirmed that Ti4+ enhanced the electrode kinetics and stabilized its structure through sodiation/desodiation reactions. The results presented in this paper might provide insights and new directions to enhance the electrochemical storage properties of fluorophosphates.
We have investigated the oxygen reduction reaction (ORR) in the presence of non-aqueous electrolytes in an attempt to overcome the challenges related to lithium-air batteries, such as low ...reversibility, poor rate capability, and electrode/solvent stability. We have used glassy carbon as the working electrode in electrolytes composed of lithium bis(trifluoromethanesulfonyl)imide and 1,2-dimethoxyethane or N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI, ionic liquid). We have employed the kinetic model to treat the electrochemical impedance spectroscopy data. This approach provides the rate constants for each of the elementary steps and allows indirect investigation of the role played by the ionic liquid in the ORR. The ionic liquid shifts the onset potential of the ORR to more positive values. The presence of the large Pyr14+ cation increases the rate-determining step by approximately three orders of magnitude as compared to the ether-based electrolyte. This ionic liquid is chemically resistant to degradation reactions and increases the rate of the ORR, which makes it a promising candidate for use in lithium-air batteries.
This study proposes a power source that operates between acidic and basic reservoirs under sunlight to treat acidic wastewater sustainably. We present a strategy that harvests energy from an ionic ...gradient associated with acidic solution neutralization and water photo-oxidation under UV light. In contrast to neutralization batteries, these photo-assisted acid-base machines operate with an interconnected battery ensemble comprising (A) a photo-assisted acid battery composed of photo-anode (TiO2) for water photo-oxidation and a selective self-assembled cathode consisting of poly(3,4-ethylenedioxythiophene) and phosphomolybdic acid for proton insertion; (B) a proton-alkali ion battery composed of the self-assembled electrode for proton deinsertion and a cathode made of copper hexacyanoferrate for potassium ion electro-insertion, which can be used as portable or stationary power source; (C) an alkali ion-air battery composed of the polycyanometalate for potassium ion deinsertion and a platinum cathode for the oxygen reduction reaction (ORR). This ensemble avoids reverse water splitting reactions and dismisses the need for external electrical power sources, which increases machine efficiency. Experiments demonstrate that acidic solution neutralization from pH = 1.3 to pH = 6.0 can harvest 102.6 kJ per mol of electro-inserted proton: this process converts energy from sunlight and from ionic gradient into electrical work. Therefore, the strategy presented here may contribute to environmental preservation and sustainable growth.
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•Novel electrochemical system that can harvest energy from neutralization reactions.•The battery ensemble avoids the use of an external electrical source.•This acid-base machine can harvest >100 kJ per mol of electroinserted ions.•This machine can be used for the treatment of acid wastewater, for example.
Abstract The Nobel Prize in Chemistry 2019 recognized the importance of Li-ion batteries and the revolution they allowed to happen during the past three decades. They are part of a broader class of ...electrochemical energy storage devices, which are employed where electrical energy is needed on demand and so, the electrochemical energy is converted into electrical energy as required by the application. This opens a variety of possibilities on the utilization of energy storage devices, beyond the well-known mobile applications, assisting on the decarbonization of energy production and distribution. In this series of reviews in two parts, two main types of energy storage devices will be explored: electrochemical capacitors (part I) and rechargeable batteries (part II). More specifically, we will discuss about the materials used in each type of device, their main role in the energy storage process, their advantages and drawbacks and, especially, strategies to improve their performance. In the present part, electrochemical capacitors will be addressed. Their fundamental difference to batteries is explained considering the process at the electrode/electrolyte surface and the impact in performance. Materials used in electrochemical capacitors, including double layer capacitors and pseudocapacitive materials will be reviewed, highlighting the importance of electrolytes. As an important part of these strategies, synthetic routes for the production of nanoparticles will also be approached (part I).
This study proposes a thermodynamic machine that operates between acid and basic reservoirs in four stages. Two of these stages are buffered isothermal steps. The other two stages constitute an open ...system and allow the passage of acid and base. The machine consists of a neutralization pseudocapacitor that, after a full cycle, carries out work generated from partial change in entropy associated with a change in the hydrogen potential after the neutralization process. Thermodynamic formalism is presented under reversible stages. This presentation enables determination of the maximum efficiency, related to the difference between the hydrogen potential of the acid reservoir and of the resulting solution after neutralization in the machine. Hence, the hydrogen potential scale can be defined as a function of the efficiency of the reversible acid–base machine regardless of the electrochemical cell composition. Electroactive thin films formed from phosphomolybdic acid and poly(3,4-ethylenedioxythiophene) have been investigated as proof of concept in electrolytic solutions at several pH values; their efficiency was close to the efficiency predicted by the thermodynamic approach. Therefore, this model allows one to estimate the maximum energy harvesting of neutralization pseudocapacitors and financial return for the treatment of acid wastewater, contributing to sustainable growth.
Abstract Candida spp. is considered an important cause of healthcare-associated infections worldwide. Currently, the emergence and spread of resistant Candida isolates are being increasingly ...reported, making the development of new agents urgently needed. In this study, we showed the in vitro anti-Candida activity of seven synthetic 3-alkylpyridine alkaloid analogs. Among them, alkaloid 1 presented a potent antifungal effect, which was independent of its capacity of binding with the fungal membrane ergosterol or cell wall. Analog 1 showed fungistatic and fungicidal effects against C. albicans (MIC 7.8 μg/mL and MFC 62.5 μg/mL), C. glabrata, C. krusei (MIC and MFC 31.2 μg/mL), and C. tropicalis (MIC 31.2 μg/mL and MFC 125 μg/mL). The time kill-curve study showed that compound 1 has a potent fungicidal effect in vitro, eliminating C. albicans cells. Furthermore, an in vitro synergistic effect with ketoconazole was observed for compound 1. This compound also eliminated the yeast-to-hypha transition. However, it showed high cytotoxicity against mammalian cells. Taken together, these findings support the use of compound 1 as a prototype to develop new anti-Candida agents, but molecular modifications should be done to minimize the high cytotoxicity obtained.
Abstract In the second part of the review on electrochemical energy storage, the devolvement of batteries is explored. First, fundamental aspects of battery operation will be given, then, different ...materials and chemistry of rechargeable batteries will be explored, including each component of the cell. In negative electrodes, metallic, intercalation and transformation materials will be addressed. Examples are Li or Na metal batteries, graphite and other carbonaceous materials (such as graphene) for intercalation of metal-ions and transition metal oxides and silicon for transformation. In the positive electrode section, materials for intercalation and transformation will be reviewed. The state-of-the-art on intercalation as lithium cobalt oxide and nickel containing oxides will be approached for intercalation materials, whereas sulfur and metal-air will also be explored for transformation. Alongside, the role of electrolyte will be discussed concerning performance and safety, with examples for the next generation devices. Finally, a general future perspective will address both electrochemical capacitors and batteries.
Sodium vanadium fluorophosphate (NVPF) has shown promising properties as a positive electrode in sodium-ion batteries mainly due to its high operating voltage; however, it has significant electronic ...and kinetic limitations that must be addressed. In this study, we investigated how a simple and straightforward mechanochemical treatment can be a valuable alternative to overcome these limitations. NVPF electrodes before and after (NVPF-bm) mechanochemical treatment were compared. For NVPF-bm, the contribution from the sodiation/desodiation of Na
1
+
increased from 23 to 40% as Na
2
+
decreased from 38 to 48% of the total produced capacity at ∼0.5 C (70 mA g
−1
); additionally, the discharge capacities were 30% greater than those of NVPF at 0.8 C (100 mA g
−1
); nevertheless, after 150 cycles, NVPF-bm presented a coulombic efficiency of 96.2% and a capacity retention of 82.6%. The calculated diffusion coefficients for NVPF-bm were 22 × 10
−10
and 1.0 × 10
−10
cm
2
s
−1
, compared to 6.5 × 10
−11
and 2.5 × 10
−11
cm
2
s
−1
for NVPF for the sodiation and desodiation processes, respectively. Furthermore, for the charge and discharge processes, NVPF-bm presented a charge transfer resistance three times smaller and diffusion lengths of 2.1 and 0.3 μm, respectively, compared to 8.0 and 13 μm, respectively, for NVPF. These results demonstrate the kinetic enhancements of the electrode as a direct consequence of the mechanochemical treatment. Therefore, this approach impacts not only the synthesis and morphology but also the inherent electrochemical storage capacity of the NVPF.
We employed a solvent-free mechanochemical post-treatment on a fluorophosphate electrode for sodium-ion batteries. Electrochemical analysis showed enhanced kinetic properties and improved ionic mobility while maintaining crystal structure.
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