The low salt adsorption capacities (SACs) of benchmark carbon materials (usually below 20 mg g–1) are one of the most challenging issues limiting further commercial development of capacitive ...deionization (CDI), an energetically favorable method for sustainable water desalination. Sodium superionic conductor (NASICON)-structured NaTi2(PO4)3 (NTP) materials, especially used in combination with carbon to prepare NTP/C materials, provide emerging options for higher CDI performance but face the problems of poor cycling stability and dissolution of active materials. In this study, we report the development of the yolk–shell nanoarchitecture of NASICON-structured NTP/C materials (denoted as ys-NTP@C) using a metal–organic framework@covalent organic polymer (MOF@COP) as a sacrificial template and space-confined nanoreactor. As expected, ys-NTP@C exhibits good CDI performance, including exemplary SACs with a maximum SAC of 124.72 mg g–1 at 1.8 V in the constant-voltage mode and 202.76 mg g–1 at 100 mA g–1 in the constant-current mode, and good cycling stability without obvious performance degradation or energy consumption increase over 100 cycles. Furthermore, X-ray diffraction used to study CDI cycling clearly exhibits the good structural stability of ys-NTP@C during repeated ion intercalation/deintercalation processes, and the finite element simulation shows why yolk–shell nanostructures exhibit better performance than other materials. This study provides a new synthetic paradigm for preparing yolk–shell structured materials from MOF@COP and highlights the potential use of yolk–shell nanoarchitectures for electrochemical desalination.
In this study, we present microporous carbon (MPC), hollow microporous carbon (HMC) and hierarchically porous carbon (HPC) to demonstrate the importance of strategical designing of nanoarchitectures ...in achieving advanced catalyst (or electrode) materials, especially in the context of oxygen reduction reaction (ORR). Based on the electrochemical impedance spectroscopy and ORR studies, we identify a marked structural effect depending on the porosity. Specifically, mesopores are found to have the most profound influence by significantly improving electrochemical wettability and accessibility. We also identify that macropore contributes to the rate capability of the porous carbons. The results of the rotating ring disk electrode (RRDE) method also demonstrate the advantages of strategically designed double-shelled nanoarchitecture of HPC to increase the overall electron transfer number (
n
) closer to four by offering a higher chance of the double two-electron pathways. Next, selective doping of highly active Fe-N
x
sites on HPC is obtained by increasing the nitrogen content in HPC. As a result, the optimized Fe and N co-doped HPC demonstrate high ORR catalytic activity comparable to the commercial 20 wt% Pt/C in alkaline electrolyte. Our findings, therefore, strongly advocate the importance of a strategic design of advanced catalyst (or electrode) materials, especially in light of both structural and doping effects, from the perspective of nanoarchitectonics.
This study elucidates the role of each class of nanopore by in-depth electrochemical analysis of three types of ZIF-8-derived carbons. Also, engineered co-doping of Fe and N is found essential to selectively form Fe-N
x
sites in the carbon matrix.
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•Effects of CGU structure on ARHCR performance are studied by CFD.•ARHCRs with rotor–stator interactions are far superior to non-interaction ones.•Hemisphere-shaped CGUs show the best ...performance among other common structures.•Effects of diameter, distance, height, and inclination angle are revealed.•This work offers a viable way to design high-performance ARHCRs.
The advanced rotational hydrodynamic cavitation reactors (ARHCRs) that appeared recently have shown obvious advantages compared with conventional devices in various process intensifications. In ARHCRs, the cavitation generation unit (CGU) located on the rotor and stator basically determines their performance. For the first time, the present study investigated the effect of the CGU structure on the performance of a representative ARHCR by utilizing computational fluid dynamics. The amount of generated cavitation and required torque of the axis for various shapes, diameters, interaction distances, heights, and inclination angles of the CGU were analyzed. The results indicate that the interaction-type ARHCR (cavitation is generated by stator-rotor interaction) was far superior to the non-interaction type one. In addition, the hemisphere-shaped CGU demonstrates the best performance compared with that with cone-cylinder, cone, and cylinder shapes. Moreover, by evaluating the effects of various geometrical factors, the hemisphere-shaped CGU with a diameter of 12 mm, an interaction distance of 1 mm, a height of 1 mm, and an inclination angle of 10° achieved the highest performance. The reasons leading to different performance were elaborated in accordance with the flow and pressure field distributions, as well as the generated cavitation patterns. The findings of this work can strongly support the fundamental understanding, design, and application of ARHCRs for process intensifications.
Next‐generation desalination technologies are needed to meet the increasing demand for clean water. Capacitive deionization (CDI) is a thermodynamically efficient technique to treat non‐potable water ...with relatively low salinity. The salt removal capacity and rate of CDI are highly dependent on the electrode materials, which are preferentially porous to store ions through electrosorption and/or redox reactions. Metal–organic frameworks (MOFs) with “infinite” combinations of transition metals and organic linkers simplify the production of carbonaceous materials often with redox‐active components after pyrolysis. MOFs‐derived materials show great tunability in both compositions and structures but require further refinement to improve CDI performance. This review article summarizes recent progress in derivatives of MOFs and MOF‐like materials used as CDI electrodes, focusing on the structural and compositional material considerations as well as the processing parameters and electrode architectures of the device. Furthermore, the challenges and opportunities associated with this research area are also discussed.
The rational design of precursory metal–organic frameworks (MOFs) is a new approach to improve the non‐Faradaic and Faradaic characteristics of electrode materials and increase the energy efficiency and reduce costs of capacitive deionization (CDI). The key compositional and structural considerations for the pyrolyzed MOF approach and their correlations with CDI performance are comprehensively discussed in this article.
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•Carbon coating and Nb5+ substitution were simultaneously applied to modify Na3V2(PO4)3 composite.•Nb5+ doping could effectively enhance the electron conductivity of the ...materials.•The optimized material exhibits a high specific capacity and good cycling stability.
Featuring favorable ion transfer and high thermal stability, NASICON-structured Na3V2(PO4)3 has been regarded as a promising cathode candidate for sodium-ion batteries. However, this material might be impeded by inferior rate capability owing to its disappointing electron conductivity. To address this issue, a combined technique of carbon coating and Nb5+ doping was carried out for the first time. On one hand, the coated carbon nano-shell could construct an electron-conductive network and buffer the volume stain. On the other hand, the introduction of Nb5+ into the Na3V2(PO4)3 crystal could regulate the relevant crystal parameters and create more vacancies, further facilitating the transfer of sodium ions. As a result, the optimized Nb-doped Na3V2(PO4)3@C material achieved an excellent performance of 81.6 mA h g−1 at 50C and a high-capacity retention ratio of 80.8% even after 1600 cycles. This work not only highlights the significance of carbon coating and Nb5+ doping, but also shows promising opportunities in potential cathode alternatives for sodium-ion batteries.
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•MOFs derived NaTi2(PO4)3/C with controllable surface morphology was synthesized.•NaTi2(PO4)3/C was used as cathode of hybrid capacitive deionization.•The cube/sphere-shaped ...NaTi2(PO4)3/C displayed the best desalination performance.•The relation between surface morphology and desalination performance was studied.
Hybrid capacitive deionization (HCDI), as a major branch of capacitive deionization (CDI), was acknowledged as one of the most promising electrochemical desalination techniques due to its ultrahigh desalination capacity and charge efficiency. Among various HCDI electrode materials, polyanion compounds (NaTi2(PO4)3 (NTP) for instance) have attracted great attention owing to their stable 3D crystal structure and high theoretical capacity. Yet, an important correlation between the surface morphology and desalination performance of the NTP-based composite is still missing, which has become a limitation for the further development of NTP-based HCDI. Herein, we prepared a series of NaTi2(PO4)3/Carbon (NTP/C) composites from metal-organic frameworks with different surface morphologies and subsequently used them as the cathode for HCDI. After systematical study, we found that the surface morphology of the NTP/C has a significant impact on its desalination performance, while the cube/sphere-shaped NTP/C exhibits the highest desalination capacity (74.6 mg g−1) with outstanding long-term stability (only 10 % capacity fading after 35 cycles). The vastly different desalination performance indicates that the surface morphology could greatly affect the “packing density” and charge transfer resistance of the NTP/C, and subsequently influence its desalination performance.
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•Bilayer evaporator composed of MOFs-derived carbon on wood sponge is prepared.•The designed architectures boost the solar-thermal interfacial evaporation performance.•The evaporator ...can extract groundwater from low moisture environment.
Soil-water extraction based on interfacial solar-thermal technology is a promising strategy to provide affordable freshwater in remote and poor inland areas. A double-layer solar evaporator is prepared on a wood sponge with a one-step brush-printing coating of zeolitic imidazolate framework-8 (ZIF-8)-derived nanostructured carbon. In this typical architecture, the ZIF-8-derived carbon coating inherits the original porous, dodecahedral framework, thus forming a chapped, rough morphology that synergistically promotes photothermal conversion. Wood sponges manufactured from raw wood offer privileged water-extraction advantages, including an abundance of super hydrophilic channels that ensure efficient bulk-water pumping and steam release. The double-layer solar evaporator shows high sunlight absorbance (∼97.8 %), low thermal conductivity (0.12 W m−1 K−1), stronger capillary force, and rapid water transport (30 cm min−1). Consequently, apparent pure water-evaporation and soil water-extraction rates reach 1.42 and 0.57 kg m-2h−1 under a one-sun light intensity, respectively. Therefore, the ZIF-8-based wood sponge can efficiently achieve interfacial evaporation and soil water extraction, providing a novel pathway for obtaining clean drinking water in arid inland areas.
Capacitive deionization (CDI) is an effective desalination technique offering an appropriate route to obtain clean water. In order to obtain excellent CDI performance, a rationally designed structure ...of electrode materials has been an urgent need for CDI application. In this work, a novel graphene sponge (GS) was proposed as CDI electrode for the first time. The GS was fabricated via directly freeze-drying graphene oxide solution followed by annealing in nitrogen atmosphere. The morphology, structure and electrochemical performance of GS were characterized by scanning electron microscopy, Raman spectroscopy, nitrogen adsorption-desorption, X-ray photoelectron spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The electrosorption performance of GS in NaCl solution was studied and compared with pristine graphene (PG). The results show that due to the unique 3D interconnected porous structure, large accessible surface area and low charge transfer resistance, GS electrode exhibits an ultrahigh electrosorption capacity of 14.9 mg g(-1) when the initial NaCl concentration is ~500 mg L(-1), which is about 3.2 times of that of PG (4.64 mg g(-1)), and to our knowledge, it should be the highest value reported for graphene electrodes in similar experimental conditions by now. These results indicate that GS should be a promising candidate for CDI electrode.
To improve the long-term stability of capacitive deionization (CDI), one effective strategy is to introduce ion-exchange membranes into CDI (called as MCDI) owing to their ability to separate ...electrodes from oxidants. However, detailed explorations on the electrode corrosion in MCDI are seldom reported up to now. In this work, we studied in details the cathode oxidation in an anion-exchange membrane CDI (AEM-CDI) by employing activated carbon (AC) anode and different cathodes, AC and carbon sphere (CS). The results show that the anodes display a slight change during long cycling due to the isolation effect of AEM. However, the electrosorption capacity of AC cathode is slowly reduced, while CS cathode exhibits an improved electrosorption ability during the long-term operation. By analyzing the structure, morphology and element variations of original and cycled cathodes, it is found that both of specific surface area (SSA) and zero charge potential (Epzc) of AC cathode are reduced, while CS cathode exhibits an enhanced SSA and Epzc, indicating that the desalination performance of AEM-CDI cell, even with cathode materials with low Epzc value and SAA, can be enhanced via effectively utilizing cathode oxidization.
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•Cathode oxidation in anion-exchange membrane capacitive deionization was studied.•Structure and element variations of original and cycled cathodes were investigated.•The desalination performance of the system was enhanced due to cathode oxidation.
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•Nitrogen-doped carbon nanotubes are synthesized by thermal conversion of polypyrrole nanotubes.•Nitrogen-doped carbon nanotubes are applied membrane capacitive deionization electrode ...materials for the first time.•Nitrogen-doped carbon nanotubes exhibit a maximum desalination capacity of 17.18 mg g−1.
The exploration of new family of nitrogen-doped carbon materials with superior performance is of significant interests in capacitive deionization (CDI) or membrane CDI (MCDI) field. In this work, nitrogen-doped carbon nanotubes (nit-CNTs) were synthesized by thermal conversion of polypyrrole nanotubes in nitrogen atmosphere. Thanks to their interconnected nanotube structure providing more accessible space for ion accommodation, shortened ion diffusion pathway for fast ion adsorption/desorption, and optimized nitrogen doping species for improved electrical conductivity and increased sodium ion adsorption, the nit-CNTs exhibit a maximum desalination capacity of 17.18 mg g−1 and a good cycling stability with little capacity fading after 20 cycles, highlighting their practicality for water desalination. This work not only showcases a new case of nitrogen-doped carbon materials for MCDI application, but also highlights the significance of one-dimensional hollow nanotubes and nitrogen doping chemistry.
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