Aminotriazine derived N-doped mesoporous carbon with a tunable nitrogen content and their improved oxygen reduction reaction performance.

The electrocatalytic activity of carbon materials is highly dependent on the controlled modulation of their composition and porosity. Herein, mesoporous N-doped carbon with different amounts of nitrogen was synthesized through a unique strategy of using a high nitrogen containing CN precursor, 3-amino 1,2,4 triazine (3-ATZ) which is generally used for the preparation of carbon nitrides, integrated with the combination of a templating method and high temperature treatment. The nitrogen content and the graphitisation of the prepared materials were finely tuned with the simple adjustment of the carbonisation temperature (800-1100 °C). The optimised sample as an electrocatalyst for oxygen reduction reaction (ORR) exhibited an onset potential of 0.87 V vs. RHE with a current density of 5.1 mA cm-2 and a high kinetic current density (Jk) of 33.1 mA cm-2 at 0.55 V vs. RHE. The characterisation results of the prepared materials indicated that pyridinic and graphitic nitrogen in the carbon framework promoted ORR activity with improved four-electron selectivity and excellent methanol tolerance and stability. DFT calculations demonstrated that the structural and planar defects in the N-doped carbon regulated the surface electronic properties of the electrocatalyst, leading to a reduction in the energy barrier for the ORR activity. This strategy has the potential to unlock a platform for designing a series of catalysts for electrochemical applications.

Tuning Phase Transition and Thermochromic Properties of Vanadium Dioxide Thin Films via Cobalt Doping.

Vanadium dioxide (VO2) featuring a distinct thermally triggered phase transition is regarded as the most attractive thermochromic material for smart window applications. However, the high transition temperature (∼67 °C) and moderate luminous transmittance (<50%) of the pristine VO2 circumvent room temperature applications. In this work, epitaxial cobalt-doped VO2 thin films were fabricated to tailor the electric and optical properties on a c-plane sapphire substrate. At the highest doping concentration of 10%, the transition temperature of VO2 is reduced to 44 °C, accompanied by a high luminous transmittance of 79% for single-element Co-doped VO2. The roles of cobalt doping and detailed band variation are fully explained experimentally and by modeling (DFT calculation), respectively. Furthermore, the dramatically increased carrier concentration in cobalt-doped VO2 underscores the promising future of cobalt-doped VO2 unveiled by temperature-dependent Hall effect measurement.

Ordered Mesoporous Boron Carbon Nitrides with Tunable Mesopore Nanoarchitectonics for Energy Storage and CO2 Adsorption Properties.

Porous boron carbon nitride (BCN) is one of the exciting systems with unique electrochemical and adsorption properties. However, the synthesis of low-cost and porous BCN with tunable porosity is challenging, limiting its full potential in a variety of applications. Herein, the preparation of well-defined mesoporous boron carbon nitride (MBCN) with high specific surface area, tunable pores, and nitrogen contents is demonstrated through a simple integration of chemical polymerization of readily available sucrose and borane ammonia complex (BAC) through the nano-hard-templating approach. The bimodal pores are introduced in MBCN by controlling the self-organization of BAC and sucrose molecules within the nanochannels of the template. It is found that the optimized sample shows a high specific capacitance (296 F g-1 at 0.5 A g-1 ), large specific capacity for sodium-ion battery (349 mAg h-1 at 50 mAh g-1 ), and excellent CO2 adsorption capacity (27.14 mmol g-1 at 30 bar). Density functional theory calculations demonstrate that different adsorption sites (BC, BN, CN, and CC) and the large specific surface area strongly support the high adsorption capacity. This finding offers an innovative breakthrough in the design and development of MBCN nanostructures for energy storage and carbon capture applications.

Design of P-Doped Mesoporous Carbon Nitrides as High-Performance Anode Materials for Li-Ion Battery.

Herein, we demonstrate a simple and unique strategy for the preparation of P-doped into the substructure of mesoporous carbon nitride materials (P-MCN-1) with ordered porous structures as a high-energy and high-power Li-ion battery (LIB) anode. The P-MCN-1 as an anode in LIB delivers a high reversible discharge capacity of 963 mAh g-1 even after 1000 cycles at a current density of 1 A g-1, which is much higher than that of other counterparts comprising s-triazine (C3H3N3, g-C3N4), pristine MCN-1, and B-containing MCN-1 (B-MCN-1) subunits or carbon allotropes like CNT and graphene (rGO) materials. The P-MCN-1 electrode also exhibits exceptional rate capability even at high current densities of 5, 10, and 20 A g-1 delivering 685, 539, and 274 mAh g-1, respectively, after 2500 cycles. The high electrical conductivity and Li-ion diffusivity (D), estimated from electrochemical impedance spectra (EIS), very well support the extraordinary electrochemical performance of the P-MCN-1. Higher formation energy, lower bandgap value, and high Li-ion adsorption ability predicted by first principle calculations of P-MCN-1 are in good agreement with experimentally observed high lithium storage, stable cycle life, high power capability, and minimal irreversible capacity (IRC) loss. To the best of our knowledge, it is an entirely new material with the combination of ordered mesostructures with P codoping in carbon nitride substructure which offers superior performance for LIB, and hence we believe that this work will create new momentum for the design and development of clean energy storage devices.