Facile Assembly of Co-Ni Layered Double Hydroxide Nanoflakes on Carbon Nitride Coated N-doped Graphene Hollow Spheres with High Electrochemical Capacitive Performance

High buffering capacity cobalt-doped nickel hydroxide electrode as redox mediator for flexible hydrogen evolution by two-step water electrolysis

Two-step water electrolysis has been proposed to tackle the ticklish H2/O2 mixture problems in conventional alkaline water electrolysis recently. However, low buffering capacity of pure nickel hydroxide electrode as redox mediator limited practical application of two-step water electrolysis system. A high-capacity redox mediator (RM) is urgently needed to permit consecutive operation of two-step cycles and high-efficiency hydrogen evolution. Consequently, a high mass-loading cobalt-doped nickel hydroxide/active carbon cloth (NiCo-LDH/ACC) RM is synthesized via a facile electrochemical method. The proper Co doping can apparently enhance the conductivity and simultaneously remain the high-capacity of the electrode. Density functional theory results further confirms more negative values in redox potential of NiCo-LDH/ACC than Ni(OH)2/ACC on account of the charge redistribution induced by Co doping, which can prevent the parasitic O2 evolution on RM electrode during decoupled H2 evolution step. As a result, the NiCo-LDH/ACC combined the superiorities of high-capacity Ni(OH)2/ACC and high-conductivity Co(OH)2/ACC, and the NiCo-LDH/ACC with 4:1 ratio of Ni to Co presented a large specific capacitance of 33.52F/cm2 for reversible charge-discharge and high buffering capacity with two-step H2/O2 evolution duration of 1740 s at 10 mA/cm2. The necessary input voltage (2.00 V) of the whole water electrolysis was broken into two smaller ones, 1.41 and 0.38 V, for H2 and O2 production, respectively. NiCo-LDH/ACC provided a favorable electrode material for the practical application of two-step water electrolysis system.

Stability-Enhanced α-Ni(OH)2 Pillared by Metaborate Anions for Pseudocapacitors

α-Ni(OH)₂ is an ideal candidate material for a supercapacitor except for its low conductivity and poor stability. In this work, BO₂^--intercalated α-Ni_xCo_(1-x)(OH)₂ is synthesized by a hydrothermal method at a low cost. The Co dopant can decrease the charge-transfer resistance and enhance the cyclic stability. The special unsaturated electronic state of BO₂^- enhances the bonding with metal ions and attracts water molecules. Thus, the BO₂^- ions support the hydroxide layers as pillars and create efficient paths for proton transportation, optimizing the utilization of α-Ni(OH)₂. The three-dimensional (3D) flowerlike morphology supplies an enormous number of active sites, and r-GO is added to improve the conductivity. As a result, the modified α-Ni(OH)₂ exhibits the specific capacitance of 2179, 1592, and 1423 F·g^-1 at 1, 20, and 40 A·g^-1, respectively, showing improved rate performance. Matching with the commercial activated carbon (AC) as an anode, the asymmetric capacitor delivers an energy density of 40.66 W·h·kg^-1 when its power density is 187.06 W·kg^-1. Meanwhile, it retains 81.5% capacitance of the initial cycle at 5 A·g^-1 after 3000 cycles. With conductivity enhanced and structure stabilized, the modified α-Ni(OH)₂ confronts broader fields of application.

Intrinsic Oxidase-like Nanoenzyme Co4S3/Co(OH)2 Hybrid Nanotubes with Broad-Spectrum Antibacterial Activity

Improving the antibacterial activity of nanomaterials and avoiding the use of H₂O₂ are vital for biosecurity and public health. In this work, novel Co₄S₃/Co(OH)₂ hybrid nanotubes (HNTs) for the first time were successfully synthesized through the control of Na₂S treatment of Co(CO₃)_0.35Cl_0.20(OH)_1.10 precursor. On the basis of Kirkendall effect, acicular precursor was vulcanized to form Co₄S₃/Co(OH)₂ HNTs that possess great properties including favorable storage ability and ideal stability. By tailoring the composition and structure, Co₄S₃/Co(OH)₂ HNTs were found to have profound oxidase-like catalytic activities. When pH = 3 precursor was treated with 900 mg of Na₂S, Co₄S₃/Co(OH)₂ HNTs exhibit superior performance. Owing to the outstanding oxidase-like activity, Co₄S₃/Co(OH)₂ HNTs can eliminate Escherichia coli, Pseudomonas aeruginosa, Staphylococcus sciuri, and Bacillus without the help of H₂O₂. It turned out that the sterilization ability came from the superoxide anion radical generated by Co₄S₃/Co(OH)₂ HNTs. With Co₄S₃/Co(OH)₂ HNTs, the intracellular reactive oxygen species level can be enhanced and the toxicity of H₂O₂ can be absolutely avoided. Overall, the synthesis of antibacterial nanomaterials is unparalleled and the results of this work would facilitate the utilization in medical science, new energy, and environmental catalysis.

Preparation of Porous Activated Carbons for High Performance Supercapacitors from Taixi Anthracite by Multi-Stage Activation

Coal-based porous materials for supercapacitors were successfully prepared using Taixi anthracite (TXA) by multi-stage activation. The characterization and electrochemical tests of activated carbons (ACs) prepared in different stages demonstrated that the AC from the third-stage activation (AC_III) shows good porous structures and excellent electrochemical performances. AC_III exhibited a fine specific capacitance of 199 F g⁻¹ at a current density of 1 A g⁻¹ in the three-electrode system, with 6 mol L⁻¹ KOH as the electrolyte. The specific capacitance of AC_III remained 190 F g⁻¹ even despite increasing the current density to 5 A g⁻¹, indicating a good rate of electrochemical performance. Moreover, its specific capacitance remained at 98.1% of the initial value after 5000 galvanostatic charge-discharge (GCD) cycle tests at a current density of 1 A g⁻¹, suggesting that the AC_III has excellent cycle performance as electrode materials for supercapacitors. This study provides a promising approach for fabricating high performance electrode materials from high-rank coals, which could facilitate efficient and clean utilization of high-rank coals.