Coupling of N-Doped Mesoporous Carbon and N-Ti3 C2 in 2D Sandwiched Heterostructure for Enhanced Oxygen Electroreduction

Unraveling the Ionic Storage Mechanism of Flexible Nitrogen-Doped MXene Films for High-Performance Aqueous Hybrid Supercapacitors

2D MXene nanomaterials have excellent potential for application in novel electrochemical energy storage technologies such as supercapacitors and batteries, but the existing pure MXene is difficult to meet the practical needs. Although the electrochemical properties of modified MXene have been improved, the unclear ion storage mechanism still hinders the development of MXene-based electrode materials. Herein, the study develops flexible self-supported nitrogen-doped Ti3C2 (Py-Ti3C2) films by the highly mobile, high nitrogen content, oxygen-free pyridine-assisted solvothermal method, and then deeply investigates the energy storage mechanism of hybrid supercapacitors in four aqueous electrolytes (H2SO4, Li2SO4, Na2SO4, and MgSO4). The experimental results suggest that the Py-Ti3C2 film electrode exhibits a pseudocapacitance-dominated energy storage mechanism. Particularly, the specific capacity of the Py-Ti3C2 in 1 M H2SO4 (506 F g-1 at 0.1 A g-1) is 4-5 times higher than other electrolytes (≈110 F g-1), which could be attributed to the substantially higher ionic diffusion coefficient of H+ than those of Li+, Na+, Mg2+ with small ionic size, high ionic conductivity, and fast pseudocapacitance response. Theoretical analysis further confirms that Py-Ti3C2 has strengthened conductivity and electrical double-layer capacitance performance. Meanwhile, it has lower free energy for protonation and deprotonation of functional groups, which gives excellent pseudocapacitance performance.

Multilayer Ti3C2-CNTs-Au Loaded with Cyclodextrin-MOF for Enhanced Selective Detection of Rutin

In this work, multi-layer Ti3C2 - carbon nanotubes - gold nanoparticles (Ti3C2-CNTs-Au) and cyclodextrin metal-organic framework - carbon nanotubes (CD-MOF-CNTs) have been prepared by in situ growth method and used to construct the ultra-sensitive rutin electrochemical sensor for the first time. Among them, the large number of metal active sites of Ti3C2, the high electron transfer efficiency of CNTS, and the good catalytic properties of AuNPs significantly enhance the electrochemical properties of the composite carbon nanomaterials. Interestingly, CD-MOF has a unique host-guest recognition and a large number of cavities, molecular gaps, and surface reactive groups, which gives the composite outstanding accumulation properties and selectivity for rutin. Under the optimized conditions, the constructed novel sensor has satisfactory detection performance for rutin in the range of 2 × 10-9 to 8 × 10-7 M with a limit of detection of 6.5 × 10-10 M. In addition, the sensor exhibits amazing anti-interference performance against rutin in some flavonoid compounds and can be used to test natural plant samples (buckwheat, Cymbopogon distans, and flos sophorae immaturus). This work has promising applications in the field of environmental and food analysis, and exploring new directions for the application of Mxene-based composites.

Pt nanoparticles anchored by oxygen vacancies in MXenes for efficient electrocatalytic hydrogen evolution reaction

The improvement of the hydrogen evolution reaction (HER) performance of nanomaterials is associated with the interfacial synergistic interaction and their hydrogen adsorption kinetics. Nevertheless, it is still a challenge to accelerate the proton transfer and optimize the HER kinetics by constructing Pt-supported heterostructures based on the hydrogen spillover phenomenon. Herein, oxygen vacancies on the surface of MXene nanosheets were constructed via a high-temperature annealing method, which was employed to anchor/stabilize Pt nanoparticles and fabricate a Pt/MXene heterostructure. EPR and XPS analyses verified the presence of oxygen vacancies, which could enhance the intrinsic HER activity of the MXene. The HER catalytic performance was investigated by taking into account the surface structure of the MXene affected by the annealing temperature, the concentration of Pt and the number of deposition cycles. Electrochemical results showed that Pt/MXene with higher utilization of Pt was obtained at 900 °C and 0.05 mgPt mL-1. The 0.05-Pt/MXene-900 obtained at deposition of 60 cycles in 0.5 M H2SO4 solution exhibited the optimized HER activity. The overpotential was 22 mV at a current density of 10 mA cm-2 and the Tafel slope was 42.41 mV dec-1. Furthermore, the accelerated HER kinetics was mainly due to the electron trapping ability of the MXene, small particles of Pt, as well as the enhanced charge transfer between the oxygen vacancies of the MXene and Pt. This strategy for constructing Pt-supported heterostructures based on the vacancy anchoring effects provides new ideas for the design of well-defined electrocatalysts toward the HER.

Nitrogen- and fluorine-doped bimetallic carbide as active and stable oxygen reduction reaction electrocatalyst

Nitrogen- and fluorine-doped bimetallic carbide composites with graphite matrix (abbreviated as C19Cr7Mo24/NG and C19Cr7Mo24/FG) are synthesized through carbonization at 1300 °C. The C19Cr7Mo24/NG displays an initial half-wave potential (E1/2) of 0.873 V and suffers merely 3 mV decrease in E1/2 within 60,000 CV cycles for oxygen reduction reaction (ORR) in alkaline media. A H2/O2 fuel cell testing system using the C19Cr7Mo24/NG as cathode maintains 95.9% of the initial peak power density (1.08 W cm-2) within 60,000 cycles. The C19Cr7Mo24/FG shows higher ORR activity than the C19Cr7Mo24/NG. The positive and negative charge centers caused by the N or F dopants are the critical reasons to their high activities. While F and bimetallic carbide more favor electron transfer respectively than the N and monometallic carbide. Their excellent stabilities originate from interactions among atoms due to electron transfer and the intrinsic chemical inertness of graphite and bimetallic carbides.

Wet chemical synthesis of rhodium nanoparticles anchored on cobalt/nitrogen-doped carbon nanofibers for high-performance alkaline and acidic hydrogen evolution

Constructing high-activity electrocatalysts towards hydrogen evolution reaction (HER) is an essential way to achieve efficient, green and sustainable energy from water electrolysis. In this work, rhodium (Rh) nanoparticles anchored on cobalt (Co)/nitrogen (N)-doped carbon nanofibers (NCNFs) catalyst is prepared by the electrospinning-pyrolysis-reduction method. The synergy effect between Co-NCNFs and Rh nanoparticles contributes to the superior HER activity and favorable durability. The optimized 0.15Co-NCNFs-5Rh sample exhibits ultralow overpotentials of 13 and 18 mV to reach 10 mA cm-2 in an alkaline and acidic electrolyte, surpassing many Rh-based or Co-based electrocatalysts reported in the literature. Additionally, the Co-NCNFs-Rh sample shows a better HER activity than benchmark Pt/C catalyst in an alkaline medium at all current densities and in an acidic condition at higher current densities, offering its promising practical applications. Thus, this work provides an efficient methodology to construct high-performance HER electrocatalysts.

Ternary alloy (FeCoNi) nanoparticles supported on hollow porous carbon with defects for enhanced oxygen evolution reaction

Low-cost non-noble metal nanoparticles are promising electrocatalysts that can catalyze oxygen evolution reaction (OER). Various factors such as poor activity and stability hinder the practical applications of these materials. The electroactivity and durability of the electrocatalysts can be improved by optimizing the morphology and composition of the materials. Herein, we report the successful synthesis of hollow porous carbon (HPC) catalysts loaded with ternary alloy (FeCoNi) nanoparticles (HPC-FeCoNi) for efficient OER. HPC is firstly synthesized by a facile carbon deposition method using the hierarchical porous zeolite ZSM-5 as the hard template. Numerous defects are generated on the carbon shell during the removal of zeolite template. Subsequently, FeCoNi alloy nanoparticles are supported on HPC by a sequence of impregnation and H₂ reduction processes. The synergistic effect between carbon defects and FeCoNi alloy nanoparticles endows the catalyst with an excellent OER performance (low overpotential of 219 mV; Tafel slope of 60.1 mV dec^-1) in a solution of KOH (1 M). A stable potential is maintained during the continuous operation over 72 h. The designed HPC-FeCoNi presents a platform for the development of electrocatalysts that can be potentially applied for industrial OER.

Defect-Enriched Hollow Porous Carbon Nanocages Enable Highly Efficient Chlorine Evolution Reaction

Metal-free carbon-based catalysts are crucial for the electrocatalytic chlorine evolution reaction (CER) to reduce the usage of noble metals and industrial cost. However, the corresponding catalytic activity of high overpotential and low durability hinders their wide application. Here, a hollow porous carbon (HPC) nanocage with a controlled oxygen electronic state around designed carbon defects for CER activity is reported. Alkali etching can bring defects in zeolite with a hollow structure. In a hard template strategy, the type of carbon defects is directly related to etching degree of the zeolite template. More importantly, the oxygen atoms can be "borrowed" from the zeolite framework by the defective carbon. The electron density around unsaturated O atoms can be decreased on the minor defects in carbon compared with that on large defects which is favorable for the adsorption of Cl^- . Consequently, the as-synthesized HPC nanocages with minor defects show excellent electrocatalytic performance for CER with a low overpotential of 94 mV at current density of 10 mA cm^-2 with good stability, which is superior to the commercial precious metal catalyst of dimensionally stable anode (DSA), and the best in the reported carbon materials. The designed carbon materials provide an option for metal-free industrial catalysts with significant CER activities.