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Capacitive deionization (CDI) is an emerging water desalination technique that holds great potential in solving the global water shortage issue. It is known that, H 2 O 2 formation at the cathode interface causing the performance degradation of activated carbons (ACs) electrode has limited the large-scale implementation of CDI, but up to date there has seldom any effective solution being reported. In this work, we proposed the use of nitrogen-doped carbon spheres (NCSs)-based CDI cathode instead of that made up of activated carbons (ACs). Benefited from the enhanced oxygen reduction ability offering by the abundant active nitrogen dopants, the asymmetrical apparatus assembled by NCSs cathode and ACs anode exhibits an enhanced cycling stability with a retention ratio of 79.6% even after 50 cycles, which surpasses that of symmetrical apparatus (only 18%). This work provides a simple and effective approach to improve the cycling stability of CDI, highlighting the significance of surface nitrogen-doping modification and the importance of interfacial electrochemistry at the nanoscale. [ABSTRACT FROM AUTHOR]

An analysis of sludge (i.e., 63 samples) and biofilm (i.e., 79 samples) sampled from 13 anaerobic membrane bioreactors (AnMBR) was conducted. Predominant microbial community identification and multivariate analysis indicate that these reactors showed different microbial community structure, but these differences had no impact on the overall AnMBR performance. Instead, core microbial genera which occurred in ≥90% of sludge (20 genera) and biofilm (12 genera) samples could potentially account for the AnMBR performance. A further calculation on net growth rate (NGR) of core genera in sludge suggested distribution into two main groups (i.e., I: low relative abundance and NGR, II: high relative abundance or high NGR). Consistent positive correlations between bacterial genera were observed among those that exhibited either high relative abundance or high NGR. The anaerobic microbial consortium in both sludge and biofilm were largely affected by stochastic dispersal and migration processes (i.e., neutral assembly). However, Acinetobacter spp. and Methanobacterium spp. occurred consistently in higher frequency in the biofilm but in lower occurrence frequency in the AnMBR permeate. Findings from this study suggest first, specific core microorganisms exist in the sludge regardless of the operating conditions of the AnMBRs, and second, prevention of biofoulant layer on anaerobic membranes can be devised by minimizing attachment of microbes on surfaces in a non-selective manner. Unlabelled Image • Core genera including 20 in sludge and 12 in biofilm were identified from all reactors. • Among core groups, higher diversity and redundancy in fermenters than methanogens and syntrophs. • Core methanogens and syntrophs had higher net growth rate or relative abundance than most core fermenters. • Consortium in both sludge and biofilm were largely affected by neutral assembly. • Acinetobacter and Methanobacterium in biofilm deviated from neutral assembly. [ABSTRACT FROM AUTHOR]

Hybrid capacitive deionization (HCDI), normally consisting of a faradaic electrode, typically inorganic intercalation compounds, and an electric double layer carbon electrode, is an efficient and high performance alternative to the conventional capacitive deionization. In this work, for the first time we introduced a redox-active polyimide, poly[N,N′-(ethane-1,2-diyl)-1,4,5,8-naphthalenetetracarboxiimide] (PNDIE) as a novel electrode material of HCDI. In 1 M NaCl solution, PNDIE exhibits a capacitor-like fast rate performance and a high specific capacity of 89.9 mAh g−1 at 0.2 A g−1 (corresponding to 359.6 F g−1 at 0.9 V voltage), which outperforms those of most reported carbonaceous and faradaic electrode materials for desalination application. When used as cathode of HCDI with activated carbon anode, PNDIE shows a high sodium uptake capacity of 54.2 mg g−1 and excellent electrochemical stability under open-air environment. Moreover, the parasitic side reaction of PNDIE cathode with dissolved oxygen in HCDI was detailedly studied, which should also cause some capacity loss in HCDI with faradaic electrode but was seldom reported in the previous work. The strategy in this work should provide a new insight in exploring novel redox-active and stable HCDI polymer electrode instead of conventional inorganic intercalation compounds for highly efficient and stable desalination application. Unlabelled Image • Redox-active polyimide, PNDIE is introduced in hybrid capacitive deionization. • PNDIE exhibits an excellent desalination performance and stability as the cathode. • The parasitic side reaction of PNDIE with dissolved oxygen is studied in details. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDHs) have shown remarkable potentials in supercapacitors for their highly-redox capacitance. However, the poor contact with substrate, slow charge transfer and ion diffusion, and low electrical conductivity limit their capacitor performance. In this work, a flexible free-standing supercapacitor was designed, with in-situ grown hollow-structured NiCo layered double hydroxide (H–NiCo LDH) as the active material based on a partial Ni ion substitution of Co ion in ZIF-67, and flexible carbon material as the substrate. Systematical investigation has been conducted in terms of nanostructures of the active material NiCo LDH (hollow or laminar structure) and flexible carbon substrates (acidified carbon cloth or acidified carbon fibers). A hollow-structured NiCo LDH@acidified carbon cloth (H–NiCo LDH@ACC) sample showed a promising capacity of 1377 mC/cm2 (3060 mF/cm2) at 1 mA/cm2, a low charge transfer resistance of 0.15 Ω, a capacity retention of 70% and a coulombic efficiency retention of 99% upon 10,000 cycles at 80 mA/cm2. PDMS-sealed solid-state H–NiCo LDH@ACC//AC devices were fabricated with an energy density of 0.0708 mWh/cm2 at a power density of 0.7 mW/cm2, with no obvious capacity decrease upon bending angles from 0° to 180°. SEM, EDS, XPS, and XRD analyses indicated the H–NiCo LDH has been in-situ grown on flexible carbon substrates. Hollow-structured LDH accelerated charge transfer and ion diffusion compared with a laminar-structured LDH. Acidified carbon cloth (ACC) showed better electrical conductivity compared with the biomass-derived acidified carbon fibers. Thus, a H–NiCo LDH@ACC is proposed as a promising candidate of a flexible supercapacitor. Image 1 • Hollow-structured NiCo layered double hydroxide (LDH) was in-situ grown on flexible carbon substrate for supercapacitor. • Hollow-structured LDH accelerated charge transfer and ion diffusion compared with a laminar-structured LDH. • Acidified carbon cloth showed better electrical conductivity compared with the acidified carbon fibers as substrate. [ABSTRACT FROM AUTHOR]

Currently, hybrid capacitive deionization (HCDI) with faradaic material cathode and active carbon (AC) anode has attracted much attention due to its very excellent desalination performance even in highly-concentrated saline water. However, the carbon oxidation reaction occurring at a potential of 0.7–0.9 V in a CDI system still exists at the carbon anode in a HCDI system, which causes the performance degradation during long-term operation. Introducing costly ion exchange membranes has been reported to solve this issue. In this work, we report a more simple and cost-saving approach to improve the desalination performance of membrane-free HCDI cell by using nickel hexacyanoferrate/reduced graphene oxide (NiHCF/rGO) cathode which possesses high theoretic capacity and low Na+ intercalation/extraction potential at a low voltage operation (0.6 V). A high desalination capacity of 22.8 mg g−1 is achieved for this membrane-free HCDI cell, higher than those for the conventional AC//AC CDI cell. More importantly, the AC//NiHCF/rGO cell shows a stable cycling performance with a capacity retention of 78% at 0.6 V over 100 desalination-regeneration cycles, significantly improved compared with that at 1.2 V. The strategy should provide a helpful guidance for practical CDI operation. Unlabelled Image • Nickel hexacyanoferrate/reduced graphene oxide (NiHCF/rGO) electrode is prepared. • Hybrid capacitive deionization (HCDI) consists of NiHCF/rGO cathode with AC anode. • Low voltage operation is used to suppress the oxidation reaction on AC anode. • HCDI exhibits both high desalination capacity and stable cycling performance. [ABSTRACT FROM AUTHOR]