MXene, an emerging 2D material, has aroused great concern in the field of supercapacitors owing to its charming properties. However, the relatively low specific capacitance of pristine MXene is unsatisfactory, which is caused by the restacking issue of MXene nanosheets. In this paper, a facile and cost-effective electrostatic self-assembly followed by hydrothermal method was adopted to prepare NiCo 2 S 4 decorated multilayer MXene nanosheets (MXene/NiCo 2 S 4 ). The introduced NiCo 2 S 4 effectively alleviates the self-restacking of MXene nanosheet and facilitates ion accessibility. Hence, the as-prepared MXene/NiCo 2 S 4 electrode displays a maximum specific capacitance of 1211.1 F g −1 at 1 A g −1 , surpassing the NiCo 2 S 4 electrode (938.4 F g −1 at 1 A g −1 ) and pure MXene electrode (84.2 F g −1 at 1 A g −1 ). The assembled asymmetrical supercapacitor utilizing hybrid MXene/NiCo 2 S 4 and RGO delivers a high energy density of 38.7 Wh kg −1 and high power density of 6137 W kg −1 . This work can provide a reliable reference for the synthesis of hybrid MXene/sulfide electrodes with ideal electrochemical performance.
Chao Wang,Wei Liu,Mingzheng Liao,Jiahong Weng,Jian Shen,Ying Chen,Yanping Du
Catalyst sintering caused by high temperature operating conditions during ethanol steam reforming (ESR) is a common issue for traditional catalysts with low Tammann temperature metals. In recent years, high entropy oxides have been popular in thermal catalysis due to their special thermodynamics and kinetics characteristics, which is expected to be a suitable approach for enhancing catalyst stability. This paper first reports the application of HEO in ESR and the characterization. The results exhibited a nano structure (CoCrFeNiAl)3O4 HEO with a spinel-phase and was successfully synthesized by a polyol hydrothermal precipitation-calcination method. An abundance of oxygen vacancies were formed, and were further enriched in a hydrogen atmosphere as the M–O bond opened. Interestingly, its self-reorganization featured the rendered the metals spilling out of the HEO bulk phase as active species for hydrogen production during ESR, whereas the isolated metal cation randomly dissolved into the parent metal oxide cell again after the reaction instead of agglomerating over the catalyst surface. This gave the (CoCrFeNiAl)3O4 a large number of dispersed active sites, as well as a high thermal stability. In addition, 81% of the hydrogen yield as well as 85% of H2 selectivity were achieved at 600 °C. This research might offer possibilities for the development of thermal catalytic hydrogen production under high temperature conditions such as steam reforming.
Fundamental knowledge about the production and oxidation chemistry of polycyclic aromatic hydrocarbons (PAHs) is essential for developing predictive soot models. In contrast to the significant progress in understanding the formation/growth kinetics of PAHs, the detailed oxidation kinetics of PAHs remains to be fully established. This study investigates the oxidation kinetics of indene, the simplest PAH, as a foundational step for examining larger PAHs. Experiments were conducted in a flow reactor at temperatures from 850 to 1350 K, under a pressure of 0.04 atm and an equivalence ratio of 0.5. Characteristic products were quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry, including large resonance-stabilized PAH radicals with 3–4 aromatic rings. Results indicate that even under highly oxidative conditions, the mass growth pathways of indene remain competitive, leading to the production of various large PAHs. This phenomenon is unique to indene oxidation and has not been observed in other bicyclic aromatics. A detailed kinetic model was developed to interpret these findings, revealing that PAH formation is predominantly driven by the indenyl radical. This study further calculates the rate coefficients for the dominant mass growth pathway of indenyl, specifically its self-recombination reaction, to enhance predictions of indenyl and bi-indene. Notably, while spiran and bridging mechanisms are comparably important in cyclopentadienyl mass growth, the spiran mechanism is favored for indenyl, suggesting that the addition of a benzenoid ring significantly alters the reactivity of cyclopenta-like radicals. Comparative analysis with indene pyrolysis experiments reveals that under oxidative conditions, the indenyl radical preferentially decomposes into smaller species, e.g., cyclopentadienyl or cyclopentadiene, thereby enhancing the yields of PAHs that depend on C 5 species as precursors. In the early reaction stage (<1220 K), oxidation reactions promote indenyl formation, thus increasing the proportion of mass growth products. However, at higher temperatures (>1220 K), enhanced oxidation reactions of indenyl lead to its decomposition, outcompeting mass growth reactions and sharply reducing the proportion of mass growth products.
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