Ethylenediamine modulate bonding interaction of solvation structure for wide-temperature aqueous ammonium-ion capacitor.

Aqueous ammonium-ion capacitors (AAICs) are promising for large-scale energy storage owing to low cost and inherent safety, while their practical applications are suffered from performance under extreme environment. Low ion conductivity and high viscosity, as well as freezing of the electrolyte, are the main issues for the electrochemical performance failure at low temperatures. In this work, the AAICs were assembled with commercial carbon electrodes and antifreeze electrolyte, where the electrolyte with a freezing point lower than -115 °C is developed by using Ethylenediamine (EDA) as an additive with a volume ratio of 50 % to an aqueous solution of 0.5 M NH4Cl. This antifreeze electrolyte displays a superior ionic conductivity of 8.58 mS cm-1 and a weaker viscosity of 8.16 mPa s at low temperatures. Furthermore, the spectroscopic investigations and molecular dynamics (MD) simulations demonstrate that the addition of EDA can break the hydrogen bonds of water molecules and modulate the solvation structure. Therefore, the assembled AAICs with electrolytes of 0.5 M NH4Cl (50 %-EDA) could be operated at wide-temperature conditions steadily, exhibiting excellent capacity, rate performance and good cycling stability. This work provides a simple and effective strategy for wide-temperature energy storage devices.

Biochar-Based Single-Atom Catalyst with Fe-N3O-C Configuration for Efficient Degradation of Organic Dyes by Peroxymonosulfate Activation.

Iron single-atom catalysts (Fe SACs) hold great promise for peroxymonosulfate (PMS) activation and degradation of organic pollutants in wastewater. However, insights into crucial catalytic sites and activation mechanisms of biochar-based Fe SACs for PMS remain a challenge. Herein, cotton stalk-derived biochar-based Fe SACs (Fe SACs-BC) with an asymmetric Fe-N/O-C configuration were prepared, and their PMS activation and acid orange 7 (AO7) degradation mechanisms were investigated. The results showed that the removal efficiency of the Fe SACs-BC catalyst with Fe-N3O-C configuration for AO7 and other five investigated organic dyes reached 95-99% within 15 min. The EPR spectrums, quenching experiments, electrochemical analysis, masking experiments, XPS, and theoretical calculations indicated that degradations of organic dyes were dominated by singlet oxygen, which was generated by direct PMS conversion at the electron-deficient carbon and iron sites in the Fe-N3O-C configuration. The Fe SACs-BC/PMS exhibited high removal efficiency and strong tolerance in different water matrices with a wide pH range, various coexisting anions and interfering substances, showing great potential and applicability for efficient treatment of actual textile wastewaters.

Tailoring B, N-Enriched Carbon Nanosheets via a Gelation-Assisted Strategy for High-Capacity and Fast-Response Capacitive Desalination.

Designing high-performance carbonous electrodes for capacitive deionization with remarkable salt adsorption capacity (SAC) and outstanding salt adsorption rate (SAR) is quite significant yet challenging for brackish water desalination. Herein, a unique gelation-assisted strategy is proposed to tailor two-dimensional B and N-enriched carbon nanosheets (BNCTs) for efficient desalination. During the synthesis process, boric acid and polyvinyl alcohol were cross-linked to form a gelation template for the carbon precursor (polyethyleneimine), which endows BNCTs with ultrathin thickness (∼2 nm) and ultrahigh heteroatoms doping level (14.5 atom % of B and 14.8 atom % of N) after freeze-drying and pyrolysis. The laminar B, N-doped carbon enables an excellent SAC of 42.5 mg g-1 and fast SAR of 4.25 mg g-1 min-1 in 500 mg L-1 NaCl solution, both of which are four times as much as those of activated carbon. Moreover, the density functional theory (DFT) calculation demonstrates that the dual doping of B and N atoms firmly enhances the adsorption capacity of Na+, leading to a prominent chemical SAC for brackish water. This work paves a new way to rationally integrate both conducive surface morphology and systematic effects of B, N doping to construct high-efficiency carbonaceous electrodes for desalination.

Amino acids functionalized vascular-like carbon fibers for efficient capacitive deionization.

Porous carbons have attracted great attention in capacitive deionization (CDI), benefiting from their high surface areas and abundant adsorption sites. However, the sluggish adsorption rate and poor cycling stability of carbons are still concerns, which are caused by the insufficient ion-accessible networks and the side reactions (the co-ion repulsion and oxidative corrosion). Herein, inspired by the blood vessels in organisms, mesoporous hollow carbon fibers (HCF) were successfully synthesized via a template assisted coaxial electrospinning strategy. Subsequently, the surface charge of HCF was modified by various amino acids (arginine (HCF-Arg) and aspartic acid (HCF-Asp)). Combining structure design and surface modulation, these freestanding HCFs present enhanced desalination rate and stability, in which the hierarchal vasculature facilitates electron/ion transport, and the functionalized surface suppresses the side reactions. Impressively, when HCF-Asp and HCF-Arg serve as cathode and anode respectively, the asymmetric CDI device provides an excellent salt adsorption capacity of 45.6 mg g-1, a fast salt adsorption rate of 14.0 mg g-1 min-1 and a superior cycling stability up to 80 cycles. In short, this work evidenced an integrated strategy to exploiting carbon materials with outstanding capacity and stability for high-performance capacitive deionization.

Constructing Active BN Sites in Carbon Nanosheets for High-Capacity and Fast Charging Toward Potassium Ion Storage.

Nitrogen doping is an effective strategy to improve potassium ion storage of carbon electrodes via the creation of adsorption sites. However, various undesired defects are often uncontrollably generated during the doping process, limiting doping effect on capacity enhancement and deteriorating the electric conductivity. Herein, boron element is additionally introduced to construct 3D interconnected B, N co-doped carbon nanosheets to remedy these adverse effects. This work demonstrates that boron incorporation preferentially converts pyrrolic N species into BN sites with lower adsorption energy barrier, further enhancing the capacity of B, N co-doped carbon. Meanwhile, the electric conductivity is modulated via the conjugation effect between the electron-rich N and electron-deficient B, accelerating the charge-transfer kinetics of potassium ions. The optimized samples deliver a high specific capacity, high rate capability, and long-term cyclic stability (532.1 mAh g-1 at 0.05 A g-1 , 162.6 mAh g-1 at 2 A g-1 over 8000 cycles). Furthermore, hybrid capacitors using the B, N co-doped carbon anode deliver a high energy and power density with excellent cycle life. This study demonstrates a promising approach using BN sites for adsorptive capacity and electric conductivity enhancement in carbon materials for electrochemical energy storage applications.