N8− Polynitrogen Stabilized on Nitrogen-Doped Carbon Nanotubes as an Efficient Electrocatalyst for Oxygen Reduction Reaction

Ambient-Pressure Recoverable Polynitrogen Solids Assembled by Pentazolate Rings with High Energy Density

Crystal structure predictions and first-principles calculations were used to predict three polynitrogen solids (aP8-N, aP12-N, and oP24-N) that possess competitive enthalpies as compared to the synthesized open-chain N₈ phase at pressures in the range of 0-60 GPa. aP8-N, aP12-N, and oP24-N contain edge-shared, N₂-linked, and N-bridged pentazolate rings and form molecular N₈, molecular N₁₂, and quasi-one-dimensional N_∞ ribbons, respectively. The calculations of formation enthalpies show that the three polynitrogen solids can be synthesized by compressing cyclo-N₅ salts in hydrogen-saturated environments. Molecular simulations suggest that the three polynitrogen solids have the ability of quench recoverability under ambient conditions once being synthesized at high pressure. With estimated energy densities in the range of 5.6-6.5 kJ/g, these three polynitrogen phases show notable promise for applications as high-energy-density materials.

Cu2O nanoparticles anchored on 3D bifunctional CNTs/copper foam cathode for electrocatalytic degradation of sulfamethoxazole over a broad pH range

In this paper, nanoscale Cu₂O particles was successfully anchored at defect sites of carbon nanotubes (CNTs), which doped on three-dimensional copper foam (CF) electrode (Cu₂O@CNTs/CF). The compound as cathode was synthesized via dip-coating and rapid electrodeposition followed by annealing procedure, and conducted in heterogeneous electro-Fenton (EF) system. The Cu₂O@CNTs/CF composites electrode enabled activate O₂ to generate H₂O₂ in situ and further Cu⁰/Cu₂O synergistic catalysis to produce reactive oxygen species for a broad pH-range via the heterogeneous EF process. Cu⁰ on the surface of CF also contributed to the reduction of Cu²⁺ to Cu⁺, thereby enhancing the stability of the electrode. The effects of critical parameters such as precursor-ligand dosage, the initial pH value, initial pollutant concentration and current density on the degradation of the antibiotic sulfamethoxazole (SMX) were investigated. The as-obtained electrode performed both effective catalytic activity and good reusability. Almost 100% removal rate was reached within 75 min over a broad pH range (3 to 11) during the heterogeneous EF process, with the current density of 12 mA cm^-2 and the removal efficiency of SMX decreased by only 9.0% after 8 recycle runs. Furthermore, quenching experiments indicated that hydroxyl radicals (·OH) were main species responsible for the SMX oxidation. In addition, the possible degradation pathways of SMX were proposed, which were based on nine identified intermediates. The comprehensive work is elucidated to accelerate the development of the in-situ production of H₂O₂ during the heterogeneous EF system and provide new insights to achieve high-efficiency degradation of pollutants via copper-based catalytic materials.

Accelerating the Oxygen Reduction Reaction and Oxygen Evolution Reaction Activities of N and P Co-Doped Porous Activated Carbon for Li-O2 Batteries

Rechargeable lithium–oxygen (Li-O2) batteries represent state-of-the-art electrochemical energy storage devices that provide high energy densities. However, their commercialization is challenging owing to their low charging/discharging efficiencies, short battery lives, high overpotentials, and high cathode manufacturing costs. In this study, we prepared a metal-free, N,P co-doped, porous activated carbon (N,P-PAC) electrode via KOH activation and P doping for application as a Li-O2 battery cathode. When used in a rechargeable Li-O2 battery, the N,P-PAC cathode showed a high specific discharge capacity (3724 mA h g−1 at 100 mA g−1), an excellent cycling stability (25 cycles with a limit capacity of 1000 mA h g−1), and a low charge/discharge voltage gap (1.22 V at 1000 mA h g−1). The N,P-PAC electrode showed a low overpotential (EOER-ORR) of 1.54 V. The excellent electrochemical performance of the N,P-PAC electrode can mainly be attributed to its large active area and oxygen-containing functional groups generated via KOH activation and P-doping processes. Therefore, the N,P-PAC prepared in this study was found to be a promising eco-friendly and sustainable metal-free cathode material for Li-O2 batteries.