Jesus Palma

Optimizing the energy efficiency of capacitive deionization reactors working under real-world conditions.

Capacitive deionization (CDI) is a rapidly emerging desalination technology that promises to deliver clean water while storing energy in the electrical double layer (EDL) near a charged surface in a capacitive format. Whereas most research in this subject area has been devoted to using CDI for removing salts, little attention has been paid to the energy storage aspect of the technology. However, it is energy storage that would allow this technology to compete with other desalination processes if this energy could be stored and reused efficiently. This requires that the operational aspects of CDI be optimized with respect to energy used both during the removal of ions as well as during the regeneration cycle. This translates into the fact that currents applied during deionization (charging the EDL) will be different from those used in regeneration (discharge). This paper provides a mechanistic analysis of CDI in terms of energy consumption and energy efficiencies during the charging and discharging of the system under several scenarios. In a previous study, we proposed an operational buffer mode in which an effective separation of deionization and regeneration steps would allow one to better define the energy balance of this CDI process. This paper reports on using this concept, for optimizing energy efficiency, as well as to improve upon the electro-adsorption of ions and system lifetime. Results obtained indicate that real-world operational modes of running CDI systems promote the development of new and unexpected behavior not previously found, mainly associated with the inhomogeneous distribution of ions across the structure of the electrodes.

Nanostructured porous wires of iron cobaltite: novel positive electrode for high-performance hybrid energy storage devices

The demand for more efficient energy storage systems stimulates research efforts to seek and develop new energy materials with promising properties. In this regard, binary metal oxides have attracted great attention due to their better electrochemical performance as compared to their single oxide analogues. Herein, nanostructured porous wires of FeCo2O4 were grown on nickel foam via a facile hydrothermal route and employed as binder/additive-free electrodes to investigate the electrochemical behavior of FeCo2O4 as electrode materials for supercapacitors. The FeCo2O4 sample exhibits a high specific capacitance of 407 F g−1 at a scan rate of 10 mV s−1 in the initial cycling. After cycling for 2000 cycles, electro-activation of the material results in subsequent increase in capacitance up to 610 F g−1, showing promising characteristics of this material for energy storage. The performance of the prepared FeCo2O4 sample is found to be much better than that of the corresponding single oxides. Furthermore, porous nanostructured FeCo2O4//AC asymmetric supercapacitors were assembled and could achieve a high energy density of 23 W h kg−1 and a maximum power density of 3780 W kg−1.

Surface modification of metal oxide nanocrystals for improved supercapacitors

TiO2 (anatase) nanocrystals were prepared and their surface was modified by sol–gel deposition of vanadium oxide species. The resulting surface-modified TiO2 combines the good properties of both materials and new, synergistic properties arise, resulting in an increased electrical conductivity, voltage window, specific capacitance, and cycling stability.

Role of textural properties and surface functionalities of selected carbons on the electrochemical behaviour of ionic liquid based-supercapacitors

In the present study, five different activated carbons are used as active electrode materials in Ionic Liquid based-Supercapacitors (IL-SCs). Selection of carbons was made according to their different textural and surface properties and includes microporous, microporous–mesoporous and mesoporous carbons with specific surface areas (SDFT) ranging from 1400 to 2200 m2 g−1 and pore lengths (Lo) ranging from 0.7 to 2.8 nm. These carbons are used to build IL-SCs using the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) as the electrolyte. IL-SCs are electrochemically characterized by electrochemical impedance spectroscopy (EIS) and by galvanostatic charge/discharge (C/D) methods at 25 °C and at 60 °C. The effect of increasing the temperature and the voltage window on electrochemical performance is analysed. The performance of IL-SCs in terms of specific capacitance (Cs) and specific energy (Ereal) strongly increased with temperature and with maximum voltage (Vmax) reaching values as high as 245 F g−1 and 58 Wh kg−1 at 60 °C and 3.5 V. The influence of both textural properties and surface chemistry of the carbons on the performance of IL-SCs is analysed in detail.

New Operational Modes to Increase Energy Efficiency in Capacitive Deionization Systems

In order for capacitive deionization (CDI) as a water treatment technology to achieve commercial success, substantial improvements in the operational aspects of the system should be improved in order to efficiently recover the energy stored during the deionization step. In the present work, to increase the energy efficiency of the adsorption-desorption processes, we propose a new operational procedure that utilizes a concentrated brine stream as a washing solution during regeneration. Using this approach, we demonstrate that by replacing the electrolyte during regeneration for a solution with higher conductivity, it is possible to substantially increase round-trip energy efficiency. This procedure was experimentally verified in a flow cell reactor using a pair of carbon electrodes (10(2) cm geometric area) and NaCl solutions having concentrations between 50 and 350 mmol·L(-1). According to experimental data, this new operational mode allows for a better utilization of the three-dimensional structure of the porous material. This increases the energetic efficiency of the global CDI process to above 80% when deionization/regeneration currents ratio are optimized for brackish water treatment.

Facile synthesis of NiCoMnO4 nanoparticles as novel electrode materials for high-performance asymmetric energy storage devices

In attempt to reduce the amount of toxic Co in cobalt oxides, NiCoMnO4 nanoparticles were synthesized via a facile hydrothermal route and their electrochemical properties have been investigated as a novel electrode material for supercapacitors. Samples have been characterized using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), and X-ray photoelectron spectroscopy (XPS). N2 adsorption/desorption measurements demonstrated a high specific surface area of 175 m2 g−1. The morphology of the samples has been probed with scanning (SEM) and transmission (TEM) electron microscopy. The electrochemical properties of the NiCoMnO4 nanoparticles have been evaluated as electrode materials for energy storage application by means of various electrochemical techniques including cyclic voltammetry, galvanostatic charge–discharge measurements, and electrochemical impedance spectroscopy. According to the obtained results, the NiCoMnO4 electrodes showed significant improved capacitive performance in comparison with pure oxides (e.g. NiO, Co3O4, and Mn3O4). The NiCoMnO4 electrodes with a high mass loading of ∼10 mg cm−2 exhibited a high specific capacitance of 510 F g−1 at 1 A g−1, and a desirable rate capability (retaining 285 F g−1 at 10 A g−1). Finally, asymmetric devices based on NiCoMnO4 nanoparticles as positive electrodes and reduced graphene oxide nanosheets as negative electrodes were assembled, showing a remarkable performance including high energy (20 W h kg−1), and stunning power density (37.5 kW kg−1).

Functional porous carbon nanospheres from sustainable precursors for high performance supercapacitors

Functional porous carbon nanospheres with tunable textural properties and nitrogen functionalities were synthesized from a cheap and sustainable phenolic carbon precursor (tannic acid) and nitrogen precursor (urea) using a facile one-step salt-templating method. The diverse functional carbons were obtained by calcination of mixtures of different molar ratios of urea to tannic acid (0 : 1, 5 : 1, 9 : 1, 13 : 1 and 17 : 1) with a eutectic salt (NaCl/ZnCl2) that was used as the porogen. The physico-chemical characterization of the obtained microporous carbons demonstrated that the textural properties, morphology, surface functionalities, and conductivity were strongly influenced by the molar ratio of urea to tannic acid. The nitrogen content in the carbons increased with the molar ratio of urea, reaching a maximum of 8.83% N at the highest molar ratio while the specific surface area (SBET) of the microporous carbons varied from 890 m2 g−1 to 1570 m2 g−1 depending on the synthesis conditions. The electrochemical performance of the carbon nanospheres in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14FSI) was also significantly influenced by the synthesis conditions due to the combined effect of textural properties, morphology, nitrogen functionalities and electrical conductivity. Supercapacitors based on the functional porous carbon synthesized with a molar ratio of urea to tannic acid of 9 : 1 exhibited the best performance, with a specific capacitance as high as 110 F g−1 and a real energy density of 33 W h kg−1, when charged–discharged at 3.5 V in PYR14FSI.

An Innovative Concept of Membrane-Free Redox Flow Battery by Using Two Immiscible Redox Electrolytes

Abstract Flexible and scalable energy storage solutions are necessary for mitigating fluctuations of renewable energy sources. The main advantage of redox flow batteries is their ability to decouple power and energy. However, they present some limitations including poor performance, short‐lifetimes, and expensive ion‐selective membranes as well as high price, toxicity, and scarcity of vanadium compounds. We report a membrane‐free battery that relies on the immiscibility of redox electrolytes and where vanadium is replaced by organic molecules. We show that the biphasic system formed by one acidic solution and one ionic liquid, both containing quinoyl species, behaves as a reversible battery without any membrane. This proof‐of‐concept of a membrane‐free battery has an open circuit voltage of 1.4 V with a high theoretical energy density of 22.5 Wh L−1, and is able to deliver 90 % of its theoretical capacity while showing excellent long‐term performance (coulombic efficiency of 100 % and energy efficiency of 70 %).

Interconnected metal oxide CNT fibre hybrid networks for current collector-free asymmetric capacitive deionization

Capacitive deionization (CDI), a water desalination technology based on the electro-deposition of salt ions in porous electrodes, is considered a simple, non-energy intensive method to produce clean water. This work introduces a new current collector-free CDI architecture based on electrodes consisting of a porous metal oxide (MOx) network interpenetrated into porous fibres of carbon nanotubes (CNTf). The full CDI device, comprising a stack of γ-Al2O3/CNTf and SiO2/CNTf anodes and cathodes, respectively, has a large salt adsorption capacity of 6.5 mg g−1 from brackish water (2.0 gNaCl L−1) and very high efficiency of 86%, which translates into a low energy consumption per gram of salt removed (∼0.26 W h g−1). This is an 80% improvement compared with reference devices based on activated carbon electrodes and titanium foil current collectors. The remarkable efficiency obtained is due to the morphology of the electrodes, in which the CNT fibres act simultaneously as a current collector, active material and support for the metal oxide. Such architecture leads to high capacitance while minimizing internal resistance, as confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. The fact that full electrodes can be made continuously, as demonstrated on 4 km of CNTf, makes the fabrication process more attractive.

On the challenge of developing wastewater treatment processes: capacitive deionization

AbstractDue to the increasing worldwide water scarcity associated with the climate change there is the need to increase the injection of wastewater into the overall water cycle. As a consequence wastewater treatment is within the largest energy use sector in many developed countries. In recent years, capacitive deionization (CDI), which is based on the principle of electrosorption of ions on charged high surface area electrodes, the same as charging and discharging an electrochemical double-layer capacitor, has been reported to be a promising technology which is an alternative to other classical water treatment methods such as reverse osmosis (RO) and evaporation processes. We see that this technology is gaining increased scientific interest since 2006. However, not too many publications indicate the feasibility of the kWh/m3 consumption in CDI systems for brackish water treatment (500–30,000 ppm). The common assumption proposes that the main problem may be the ions adsorption capability of the electrode ...