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[Display omitted] • The activated biochar (AB) and V 2 AlC-OH x MAX phase were used for Cr(VI) removal. • The asymmetric AB//V 2 AlC-OHx possesses both EDLC and pseudocapacitive behaviors. • The SEC of AB//V 2 AlC-OH x of 47.2 mg g−1 with removal efficiency of 99 % was observed. • The conversion of 60% Cr(VI) into Cr(III) during CDI processes enhances the removal efficiency. • Excellent cyclic performance for at least 20 adsorption–desorption cycles. The development of high-value-added biomass-derived carbonaceous as electrode material from agricultural wastes has received considerable attention. In this study, the activated biochar (AB) derived from the badam tree leaves (BTL) and functionalized 2D metal-carbide materials, V 2 AlC-OH x , have been successfully synthesized by alkaline treatment and microwave-assisted hydrothermal method, respectively, and then used as the asymmetric electrode materials for capacitive deionization application to remove Cr(VI) ions from aqueous solutions. The large specific surface area and the interconnected meso- and macro-porous channels of AB provide active sites and short ion diffusion paths to accelerate ion transport and electrosorption. In addition, the highly crystalline 2D architecture of V 2 AlC-OH x offers suitable lattice fringes for electron transfer. The conversion of Cr(VI) into Cr(III) on the surface of V 2 AlC-OH x , followed by the capture of Cr(III) onto the AB cathode has triggered the enhanced removal of Cr(VI). The AB//V 2 AlC-OH x asymmetric CDI device exhibits superior deionization performance for Cr(VI) removal with a specific electrosorption capacity of 47.2 mg g−1 and removal efficiency of 99 %. Excellent cyclic performance for at least 20 adsorption–desorption cycles is also observed, indicating the excellent durability of the fabricated materials. These results demonstrate that AB and V 2 AlC-OH x are promising CDI electrodes for the removal of metal ions and other hazardous pollutants from industrial effluents. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mesoporous NCS were synthesized by controlled self-assembly method. • NCS enriched with nitrogen-doped active sites and interconnected framework. • NCS-900 exhibited an ultra-high electrosorption capacity of 149.35 mg/g for NO 3 – at 1.2 V. • A novel stirring CDI was used to accelerate the ion mass transfer rate. Nitrate contamination in the water environment has become an increasingly serious problem. Capacitive deionization (CDI), an emerging electrochemical water treatment technique, possesses a promising potential for efficient nitrate removal. Herein, we prepared nitrogen-doped carbon spheres (NCS) by controlled self-assembly using nano-SiO 2 as a sacrificial template and constructed a novel stirring CDI (SCDI) using NCS as nitrate capture electrodes. The interconnected framework and controllable mesoporous structure of NCS-900 enhance the transfer and diffusion of nitrate ions. In addition, the defects caused by the nitrogen-doped increase the active sites of NCS-900, resulting in outstanding specific capacitive properties. SCDI system promotes mass transfer and allows them to be more uniformly distributed in solution. As a consequence, the concentration of ions near the electrode is elevated, which enhances the removal capacity and reaction rate of the process. Importantly, the SCDI system using NCS-900 as the electrode achieved an ultrahigh nitrate electrosorption capacity of 149.35 mg/g with a rapid removal rate of 7.46 mg/g/min at 1.2 V condition in 5 mM NaNO 3 solution, which was much higher than that of reported nitrate capture electrodes. The superior nitrate removal performance can be ascribed to the synergy between the novel electrode material NCS with high adsorption capacity and the reaction device SCDI with improved system dynamics. In addition, the stability and selectivity of nitrate electrosorption were maintained well in the comprehensive conditions and actual sewage. This work opens a new path for efficient nitrate removal by CDI technology. [ABSTRACT FROM AUTHOR]

• MCDI was probed for wastewater reuse in pilot-scale using ion selective electrodes. • The coated electrodes showed better performance attributing to its low resistivity. • NO 3 − was selectively removed attributing to its high permselectivity through AEM. • Faster flow rate and lower potential enhanced NO 3 − selectivity in single-pass mode. • The flat coated layer kept organic substances from accumulating on the surface. This study investigated membrane capacitive deionization (MCDI) at a pilot-scale using ion-selective polymer-coated carbon electrodes for wastewater reuse. Several issues have been addressed to verify the suitability of MCDI for wastewater reclamation: electrosorption performance, removal efficiency and selectivity of ions present in wastewater, optimization of operating conditions, and performance degradation in long-term caused by the accumulation of organic contaminants. The coated electrodes had better adsorption capacities and charge efficiencies than the conventional MCDI system, which was attributed to their low electrical resistance induced by the thin coated layer. The pilot-scale MCDI test cell involved 50 pairs of anion- and cation-selective electrodes and achieved good removal efficiency of ions from the wastewater effluent, particularly for problematic charged impurities, such as nitrate (NO 3 −) (up to 91.08% of NO 3 − was removed). Increasing the flow rate and reducing the applied potential were shown to be efficient for achieving better water quality by enhancing the NO 3 − selectivity. Last, the 15 d operation showed good reproducibility in electrosorption and regeneration for the coated electrodes, despite the fact that high concentrations of organics were contained in the wastewater feed solution (12.4 mg/L of dissolved organic carbon). [ABSTRACT FROM AUTHOR]

[Display omitted] • Supercapacitor has excellent electrochemical behavior, can be used as advanced energy storage device. • Numerous eco-efficient regulation strategies are proposed to manufacture coal-derived porous carbon. • Coal-derived porous carbon electrode exhibit superior energy/power density and remarkable rate property. • Coal-derived porous carbon achieve clean and high value-added utilization of coal resources. Large-scale consumption of renewable energy (RE) is the driving force underpinning the sustainable development of the world. However, the intermittence and randomness of its working mode leads to low energy density and high dispersion. The collaborative model of "power generation coupled with energy storage" is the main way to achieve a safe and stable supply of RE. Supercapacitor have both high energy density of secondary batteries and large power density of conventional capacitors, making up for the shortcomings of two energy storage devices, which can be used as advanced energy storage devices for RE. Electrode materials determine the comprehensive performance of supercapacitor. Porous carbon in carbonaceous materials presents rich pore structure, stable physicochemical characteristics, low price and easy industrial promotion, which is the goal pursued of human science. Coal is high in reserve and carbon content, and low cost. Preparation of functional nano carbon electrode materials from coal is expected to solve the problem of low investment and large scale manufacture. The review focus on the latest research of coal-derived porous carbon, with special attention to synthesis methods, regulation strategies, and structural optimization. The efficient application of coal-derived porous carbon for supercapacitor is discussed and further research challenges are proposed. [ABSTRACT FROM AUTHOR]

• A quadruple-functional-salt strategy is firstly proposed for the synthesis of N/P -doped carbons. • The carbonization mechanism of the carbons is revealed by in-situ thermal analysis. • Carbon electrodes show high performance in half-cell/pouch-cell K-ion capacitors. • In-situ Raman/XRD and DFT calculations give insights into the energy storage mechanisms. Heteroatom-doped porous carbons are regarded as promising electrodes for K-ion capacitors. However, current synthetic methods suffer from problems of low efficiency and use unsustainable precursors, and this has restricted wide application of these materials. Moreover, the mechanisms of energy-storage by heteroatom-doped porous carbon electrodes in K-ion capacitors are not well understood. In this work, we prepare porous carbons having honeycomb-like hierarchical structures and doped with P/N heteroatoms by using a low-cost fish scale and K 3 PO 4 as precursor and auxiliary, respectively. K 3 PO 4 and its derivatives not only serve as collagen-hydrolysis reagents during the pre-treatment process, but also act as dopants, templates, and activators during the subsequent carbonization process. Deionized water is the only solvent required in the whole synthesis process. The as-prepared carbons were used as electrodes in K-ion capacitors and their energy-storage mechanisms studied by detailed in-situ characterization methods and DFT calculations. The optimized carbon anode and cathode were used to assemble a pouch K-ion capacitor, which showed high energy density (184.6 Wh kg−1), high power density (4.8 kW kg−1), and long lifetime (retaining 90% of the initial capacity after 10,000 cycles). [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel bimetallic ZAMC-13 porous carbon electrode was firstly reported. • The electrode showed a remarkable phosphate electrosorption capacity of 539.85 mg/g. • The desorption efficiency was maintained at 90.59% after 20 consecutive cycles. • Heteroatom doping boosted electrochemical activities and oxygen vacancies. • Synergetic effects of electric field, active sites, and vacancy sites were achieved. Elimination of phosphate is essential to control eutrophication and improve water quality. Nevertheless, the removal capacity of dephosphorization agents in conventional methods is far from satisfactory. Herein, we proposed an electro-assisted adsorption method and fabricated a novel bimetallic Zr-Al metal organic framework (MOF) derived hierarchically porous carbon (ZAMC-13) electrode for efficient phosphate electrosorption. The results of systematic experimental indicated that the synergistic contribution of Zr and Al can boost the electrochemical activities and oxygen vacancies, thus resulting in an increased reaction rate and removal capacity. The ZAMC-13 electrode, as expected, demonstrated a remarkable phosphate electrosorption capacity of 539.85 mg/g at 1 V, with an exceptional regeneration performance of 90.59% after 20 consecutive cycles using a reverse voltage. The electrosorption behavior was further revealed using kinetic and isotherm models. Besides, the phosphate electrosorption mechanisms, which were primarily dominated by ligand exchange, electrostatic attraction, oxygen vacancies consumption, and electric field, were elucidated. Furthermore, the energy consumption and operating cost for electro-assisted phosphate removal are as low as 0.0108 kWh/kg P and 0.020 $/m3, respectively. This work demonstrates a deep understanding and promotes a new level of electro-assisted phosphate adsorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fungal hypha activated carbon pad (FhACPad) is a promising electrode for desalination. • FhACPad is a freestanding electrode readily prepared from the fungus suspension for CDI. • The continuous and porous structure of FhACPad facilitates both electron and ion transfer. • FhACPad with hierarchical pores exhibits a high desalination capacity of 35.6 mg NaCl /g. Capacitive deionization (CDI) is an emerging technology for water desalination, especially low-salinity water. Freestanding porous carbon-based electrodes with rapid electron transfer rate and effective ion diffusion features are desired to achieve high desalination performance. Here, a porous carbon pad derived from the fungal hyphae of Aspergillus niger was prepared as a precursor of the electrode. After carbonization and activation, the intertwined and hierarchical porous structure of the fungal hypha pad was well-preserved, producing a freestanding fungal hypha activated carbon pad (FhACPad) electrode for MCDI. The interconnected carbon fibers and open pore structure of the FhACPad yielded an electrode with high electrical conductivity and rapid ion transport properties. The novel FhACPad exhibited a gravimetric salt adsorption capacity of 35.6 ± 2.3 mg NaCl /g with an average desalination rate of 1.2 mg NaCl /g electrode /min from a 585 mg/L NaCl aqueous solution at a cell voltage of 1.2 V and a flow rate of 1 mL/min. As a result, the FhACPad outperformed conventional powdered activated carbon (PAC) electrodes and the most recently reported porous carbon electrodes under similar desalination conditions. This work also provides insights into the structure-performance relationships of CDI electrodes and shows a great potential of fungal biomass-derived porous carbon electrodes for high-performance MCDI applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developed a carbonized MIP-202/MXene (CMM) for selective electrosorption of U(VI). • MXene provides pseudocapacitance/intercalation effect and conductive base. • Two composite structures were observed during preparation of CMMs. • The CMM electrode exhibited excellent adsorption capacity and selectivity for U(Ⅵ). As the key element in the nuclear industry, uranium (U) has been widely concerned for its stable acquisition and efficient recycling. Capacitive deionization (CDI), which known as a seawater desalination technology, has shown great potential for uranium-adsorption. However, the poor selectivity restricts the application of CDI in uranium extraction. In this work, a carbonized MIP-202/MXene (CMM) composite was developed for highly efficient selective electrosorption of U(VI) from multi-ionic water. The uniformly decorated MIP-202 can prevent MXene from aggregation and provide rich pore structures, large specific surface area and additional nitrogen source for the efficient electrosorption of U(VI). With the addition of MXene nanosheets, a conductive network was introduced into the CMM and improved mechanical robustness of material to facilitate rapid charge transfer at the interface. As a result, the CMM electrode exhibited a maximum adsorption capacity of 582.46 mg g−1 calculated from Langmuir model and a removal ratio of 89.1% at 1.2 V in UO 2 2+ solution. The selectivity adsorption of CMM for UO 2 2+ can reach 92.3% when treated with multi-ionic solution. Besides, there is an interesting fact that the decreased ratio of added MXene can got a higher adsorption capacity, which may cause by the two composite structures formed when the mixing ratio changed. Overall, the excellent conductivity, high adsorption capacity and selectivity make CMM a promising electrode in CDI for efficient extraction of uranium from water. [ABSTRACT FROM AUTHOR]

[Display omitted] • A porous structured carbon electrode reactor was designed for wastewater treatment. • Mass and electron transfer were significantly enhanced. • Radical and nonradical oxidation jointly contributed to the degradation of MNZ. • With reactive species confined inside the electrodes, organics were vastly removed. • This technology remained a high efficacy in complicated water matrixes. The co-activation of persulfate (PS) using electricity and carbon is a novel method used in sulfate radical-based advanced oxidation processes. However, the full utilisation of the synergistic effects between diverse reactions on both electrodes to achieve high PS activation and efficient removal of contaminants remains challenging. In this study, we designed porous graphite to serve as two electrodes and a continuous-flow reactor; this system resulted in internal PS activation and the degradation of organics within a specified "confined space". With the enhancement of mass and electron transfer in the reactor, the model contaminant metronidazole (MNZ) was successfully degraded with a removal efficiency of 94.79%. The flow-through design remarkably outperformed the flow-by design, which reflected the stronger restrain of side reactions, larger electrochemical active surface area, higher active-site exposure, lower charge-transfer resistance, and higher diffusion coefficient of porous graphite electrodes. Kinetic experiments, radical scavenging experiments, and electron paramagnetic resonance tests carried out in split cells demonstrated that direct electron transfer, ∙OH oxidation, and non-radical oxidation with active PS* and 1O 2 collectively contributed to the degradation of MNZ in the anode; SO 4 −∙ oxidation played the most significant role in the cathodic cell. Finally, the broad applicability of the reactor was confirmed by the treatment of diverse water matrixes and wastewater containing various persistent organic contaminants, showing great potential for practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crude glycerol from biodiesel was used to obtain a new sustainable activated carbon. • The polyglycerol activated carbon electrodes successfully desalinate brackish water. • Operation within the potential stability window ensured the long-term stability. • Asymmetric configurations (CDI) and MCDI improved the charging efficiency. • The best stable desalination performance was achieved using the membrane CDI at 1.6 V. Capacitive deionization (CDI) is a promising electrochemical technology for water desalination that can contribute to reducing water scarcity. At the same time, appropriate routes for the disposal or reuse of liquid wastes are also a major current concern. Based on the water-waste nexus concept, this work demonstrates that crude glycerol from biodiesel plants can be successfully used to obtain a new sustainable activated carbon. After polymerization, the crude glycerol was carbonized and activated to obtain polyglycerol activated carbon (PGAC), which was employed as an electrode for CDI desalination of brackish water. Evaluation was made of the electrode performance and stability over cycles of electrosorption/desorption, using different cell configurations (symmetric, asymmetric, and membrane CDI) and cell voltages (E cell). It was observed that maintaining the potential of zero charge of the negative and positive electrodes outside their working domains during the cycles enabled minimization of that part of the applied potential deviated to co-ion repulsion, consequently improving the salt adsorption capacity (SAC) and charge efficiency (Q E). Furthermore, maintaining the potential of the positive electrode below the oxidation potential by controlling the applied E cell could ensure electrode stability. The best desalination performance using the PGAC electrode was achieved using the membrane CDI configuration (at 1.6 V), resulting in stable SAC (∼ 27.1 mg g−1) and Q E (∼100%) over 50 cycles. The low cost and high SAC and Q E values suggested that the PGAC electrode could be considered a potential candidate for use in CDI desalination. [ABSTRACT FROM AUTHOR]

• CNTs were organized on Ni foam by a facile and mild (room temperature) method. • CNTs provided strong chemical bond to increase bridging between NiCoO 2 and Ni foam. • Hierarchical NiCoO 2 @CNTs@NF binder-free integrated electrode was fabricated. • The self-assembled CNTs layer boosts the performance and stability of supercapacitor. • Low contact resistance and fast ion diffusion are responsible for excellent capacitance. Supercapacitors possess an essential application in storing intermittent energy and powering electric vehicles or wearable electronics. It should be a promising approach by combining carbon nanomaterials with metal oxides to promote energy density and maintain high power density and durable stability. Herein, carbon nanotubes (CNTs) were firstly organized on the surface of nickel foam (NF) by a facile and mild (room temperature) metal-induced self-assembly process. Afterward, NiCoO 2 nanosheets are bonded by CNTs films via hydrothermal method, and then the integrated NiCoO 2 @CNTs@NF electrodes were successfully fabricated. The kinds of self-supporting electrodes have some advantages of hierarchical three-dimensional (3D) network structure, strong binding force between NiCoO 2 nanosheets and Ni foam substrate, excellent conductivity tunnel for ions and electrons transport, and abundant active sites for ions adsorption and fast faradic redox reaction. Accordingly, the NiCoO 2 @CNTs@NF integrated electrode present the superior capacitive properties and stabilities because of outstanding synergistic effect between CNTs as electric double-layer capacitance (EDLC) materials and NiCoO 2 nanosheets as Faradic pseudocapacitance materials. Asymmetric supercapacitors (ASCs) were also fabricated based on NiCoO 2 @CNTs@NF electrodes and active carbon supported on Ni foam electrodes. The ASCs show prominent performances of a high special capacitance (151 F g−1 at 5 mA cm−2), an outstanding rate capability (83.8% when current densities changed from 5 to 50 mA cm−2), durable stability (above 90% after 5000 cycles), and a high energy density (56.0 Wh kg−1). Such three ASCs devices connected in series can light up four blue light-emitting diodes (LEDs) that operates at a minimum voltage of 2 V. The presented work provides an efficient approach to design an outstanding electrode by combining active materials with a metal substrate. [ABSTRACT FROM AUTHOR]