Electrolysis Synthesis of Carbides and Carbon Dioxide Capture in Molten Salts.

The application of carbides in catalysis, batteries, aerospace fields, etc. has been continuously expanded and deepened, which is attributed to the diversified physicochemical properties of carbides via a tune-up of their morphology, composition, and microstructure. The emergence of MAX phases and high entropy carbides with unparalleled application potential undoubtedly further stimulates the research upsurge of carbides. The traditional pyrometallurgical or hydrometallurgical synthesis of carbides inevitably faces the shortcomings of complex process, unacceptable energy consumption, extreme environmental pollution, and beyond. The molten salt electrolysis synthesis method with the superiorities of straightforward route, high efficiency, and environmental friendliness has demonstrated its validity in the synthesis of various carbides, which naturally initiates more research. In particular, the process can achieve CO2 capture while synthesizing carbides based on the excellent CO2 capture capability of some molten salts, which is of great significance for carbon neutralization. In this paper, the synthesis mechanism of carbide by molten salt electrolysis, the process of CO2 capture and carbides conversion, the latest research progress in the synthesis of binary, ternary, multi-component, and composite carbides are reviewed. Finally, the challenges, development perspectives, and research directions of electrolysis synthesis of carbides in molten salts are featured.

Probing and Modulation of the Electric Double Layer at the Insulating Oil-Paper Interface.

Charge accumulation in the insulating oil-paper system determines the operating safety of the converter transformers in high-voltage direct current (HVDC) transmissions. However, it has been a long-standing challenge to reveal the charge distribution of the electric double layer (EDL) at the insulating oil-paper interface and relate it to charge transport. In particular, the EDL and charging mechanisms at the oil-paper interface have not been fully understood. We herein demonstrate that the charge distribution of EDL at the oil-paper interface is probed through Kelvin probe force microscopy (KPFM). The origin charge distribution of EDL without any additives shows that the negative charge gathers on the insulating paper surface, while the positive charge diffuses in the insulating oil, which is derived from the electron affinity difference between insulating oil and insulating paper and acts as an additional obstacle to charge transportation at the oil-paper interface. Interestingly, the additive 3-amino-2,4-triazole (ATA) can tune the charge distribution of EDL by bringing extra hole traps, which significantly decreases the interface barrier and reduces the charge accumulation at the oil-paper interface. As well as increasing charge mobility in oil-paper insulation, ATA also ensures stabilization of operation under polarity inversion conditions by accelerating the dissipation rate of accumulated charge.

Local charge transport at different interfaces in epoxy composites.

Charge transport in insulating composites is fundamental to designing high performance in electrical breakdown strength processes. A fundamental understanding of the charge transport at nanoscale in insulating composites remains elusive. Herein, we fabricate two types of interfaces in epoxy (EP) composites (Al2O3/EP and bubble/EP, respectively). Then the local dynamic charge mobility behavior and charge density are explored usingin situKelvin probe force microscopy. After the external voltage in the horizontal direction is applied, significant differences are demonstrated in the evolution of charge transport for epoxy matrix, filler/bubble, and their interface, respectively. The interface between Al2O3and epoxy is easier to accumulate the negative charges and introduce shallow traps. Lots of positive charges are located around a bubble where deeper traps are present and could prevent charge migration. Thus, this work offers extended experimental support to understanding the mechanism of charge transport in dielectric composites.

Synergetic Effect of Ni2P and MXene Enhances Catalytic Activity in the Hydrogen Evolution Reaction.

Developing highly efficient non-precious electrocatalytic materials for H2 production in an alkaline medium is attractive on the front of green energy production. Herein, we successfully designed an electrocatalyst with superb hydrophilicity, high conductivity, and a kinetically beneficial structure using Ni2P/MXene over a 3D Ni foam (NF) for the alkaline hydrogen evolution reaction (HER) based on the laboratory and computational research works. The designed self-supported and highly effective electrocatalyst achieves a huge boost in the HER activity compared with that of pristine Ni2P nanosheets owing to the distinctive structure and synergy of coupling Ti3C2Tx and Ni2P. More specifically, Ni2P/Ti3C2Tx/NF produces an electric current density of 10 mA·cm-2 under a low overpotential (135 mV) and shows excellent durability under alkaline (1 M KOH) conditions, and the observed performance degradation is negligible. The outstanding HER activity makes the synthetic strategy of Ni2P/Ti3C2Tx/NF a potential approach to be extended to other transition-metal-based electrocatalysts for enhanced catalytic performance.

Tuning the Electronic Structure of the CoP/Ni2P Nanostructure by Nitrogen Doping for an Efficient Hydrogen Evolution Reaction in Alkaline Media.

As one of the most sustainable, efficient, and cleanest ways for hydrogen production, electrochemical water splitting relies heavily on cost-efficient and stable electrocatalysts. Herein, a self-supported and nitrogen-doped hybrid CoP/Ni2P was synthesized through a simple two-step hydrothermal process followed by low-temperature phosphorization and nitridation (N-CoP/Ni2P@NF). Both experimental and density functional theory calculation results suggest that nitrogen doping can tune the electrical structure of the CoP/Ni2P heterostructure and thus optimize the free energy of adsorbed H on the surface of N-CoP/Ni2P@NF and accelerate the electronic transport activity. The prepared N-CoP/Ni2P@NF exhibits excellent electrocatalytic hydrogen evolution reaction (HER) performance, which merely requires an overpotential of -46 mV at -10 mA cm-2 and shows a negligible decay after a long durability test for 72 h in alkaline (1.0 M KOH) media. Consequently, this work supplies a novel strategy with great potential for designing transition metal phosphate-based catalysts with high HER performance.

Nitrogen-Doped MoS2/Ti3C2TX Heterostructures as Ultra-Efficient Alkaline HER Electrocatalysts.

Molybdenum disulfide (MoS2) is intrinsically inert for the hydrogen evolution reaction (HER) in alkaline media due to its electronic structures. Herein, we tune the electronic structures of MoS2 by a combined strategy of post-N doping coupled with the synergistic effect of Ti3C2TX. The as-prepared N-doped MoS2/Ti3C2TX heterostructures show remarkable alkaline HER activity with an overpotential of 225 mV at 140 mA cm-2, which ranks the N-doped MoS2/Ti3C2TX heterostructures among the best MoS2/MXene-based electrocatalysts reported for alkaline HER. The first-principles calculations indicate that the N doping can enhance the activation of nearby S sites of MoS2/Ti3C2TX and thus promote the HER process. This strategy provides a promising way to develop high-efficiency MoS2/MXene heterostructure catalysts for alkaline HER.

Oxygen-Bridged Cobalt-Chromium Atomic Pair in MOF-Derived Cobalt Phosphide Networks as Efficient Active Sites Enabling Synergistic Electrocatalytic Water Splitting in Alkaline Media.

Electrochemical water splitting offers a most promising pathway for "green hydrogen" generation. Even so, it remains a struggle to improve the electrocatalytic performance of non-noble metal catalysts, especially bifunctional electrocatalysts. Herein, aiming to accelerate the hydrogen and oxygen evolution reactions, an oxygen-bridged cobalt-chromium (Co-O-Cr) dual-sites catalyst anchored on cobalt phosphide synthesized through MOF-mediation are proposed. By utilizing the filling characteristics of 3d orbitals and modulated local electronic structure of the catalytic active site, the well-designed catalyst requires only an external voltage of 1.53 V to deliver the current density of 20 mA cm-2 during the process of water splitting apart from the superb HER and OER activity with a low overpotential of 87 and 203 mV at a current density of 10 mA cm-2 , respectively. Moreover, density functional theory (DFT) calculations are utilized to unravel mechanistic investigations, including the accelerated adsorption and dissociation process of H2 O on the Co-O-Cr moiety surface, the down-shifted d-band center, a lowered energy barrier for the OER and so on. This work offers a design direction for optimizing catalytic activity toward energy conversion.

Self-healing of electrical damage in insulating robust epoxy containing dynamic fluorine-substituted carbamate bonds for green dielectrics.

Power systems and electrical grids are critical for the development of renewable energy. Electrical treeing is one of the major factors that lead to electrical damage in insulating dielectrics and decline in the reliability of power equipment and ultimately results in catastrophic failure. Here, we demonstrate that bulk epoxy damaged by electrical treeing is able to efficiently heal repeatedly to recover its original robust performance. The classical dilemma between the insulating properties and electrical-damage healability is overcome by dynamic fluorinated carbamate bonds. Moreover, the dynamic bond enables the epoxy to have admirable degradability, which is demonstrated to be used as an attractive green degradable insulation coating. When used as a matrix for fiber-reinforced composites, the reclaimed glass fibers after decomposing the epoxy maintained their original morphology and functionality. This design provides a novel approach for developing smart and green dielectrics to enhance the reliability, sustainability and lifespan of power equipment and electronics.

Interfacial Insight of Charge Transport in BaTiO3/Epoxy Composites.

Space charge accumulation greatly influences the dielectric performance of epoxy composites under high voltage. It has been reported that nano-fillers can suppress the charge accumulation in the bulk of insulation materials. However, it is still unclear how the nano-fillers influence the charge distribution at the interface between the filler and polymeric matrix. In this work, the dielectric properties and the local dynamic charge mobility behavior at the interface of barium titanate/epoxy resin (BTO/EP) composites were investigated from both bulk and local perspectives based on the macroscopic test techniques and in-situ Kelvin probe force microscopy (KPFM) methods. Charge injection and dissipation behavior exhibited significant discrepancies at different interfaces. The interface between BTO and epoxy is easy to accumulates a negative charge, and nanoscale BTO (n-BTO) particles introduces deeper traps than microscale BTO (m-BTO) to inhibit charge migration. Under the same bias condition, the carriers are more likely to accumulate near the n-BTO than the m-BTO particles. The charge dissipation rate at the interface region in m-BTO/EP is about one order of magnitude higher than that of n-BTO/EP. This work offers experimental support for understanding the mechanism of charge transport in dielectric composites.

Recent Advances in Inorganic Electrochromic Materials from Synthesis to Applications: Critical Review on Functional Chemistry and Structure Engineering.

For the assembly of electrochromic devices (ECDs) with generally multilayer structures, supportive components usually are needed to be incorporated with EC materials. Herein, we reviewed several impressive methods to design and fabricate ECDs with high performance and versatility based on recent frontier research. The first part of the review is centered on the desirability and strengthening mechanism of nanostructured inorganic EC materials. The second part illustrates the recent advances in transparent conductors. We then summarize the demands and means to modify the formation of electrolytes for practicable ECDs. Moreover, efforts to increase the compatibility with the EC layer and ion capacity are delineated. At the end, the application prospects of inorganic ECDs are further explored, which offers a guideline for the industrialization process of ECDs.

A novel recycling approach for efficient extraction of titanium from high-titanium-bearing blast furnace slag.

The recycling of high-titanium-bearing blast furnace slag (TiO2 > 23 wt.%) is an urgent problem that has attracted global research attention. To achieve high-efficiency, low-consumption, clean, and high value-added recycling utilization, a new process is proposed herein, which entails reacting a CH4-H2-N2 gas mixture with the titanium-bearing blast furnace slag to initially produce Ti(C, N, O) at a low temperature, whereafter the product is purified and chlorinated. The effects of Fe2O3, urea, and sawdust on the reduction and carbonitriding characteristics are also investigated. The results indicate that the Fe2O3 additive can promote the formation of Ti(C, N, O), while urea and sawdust are instrumental for enhancing gas diffusion in solid powders. The proposed novel recycling process was assessed and it evinced many advantages and great feasibility.

Induction of Co2P Growth on a MXene (Ti3C2Tx)-Modified Self-Supporting Electrode for Efficient Overall Water Splitting.

It still is a challenge to create a superior and easily coupled bifunctional electrocatalyst for water splitting impelled by a low voltage. In this work, the controlled growth of Co2P NAs on the surface of a MXene (Ti3C2Tx)-modified self-supporting electrode is demonstrated as a competent and reliable bifunctional electrocatalyst for efficient water splitting. The heterointerface in Co2P@Ti3C2Tx with an optimized adsorption free energy of H*, H2O, and better conductivity can give enhanced HER (hydrogen evolution reaction) activity, with a low overpotential (42 mV) at 10 mA cm-2. Additionally, the OER (oxygen evolution reaction) activity has also been similarly strengthened by the synergy of Co2P and MXene with an overpotential of 267 mV to arrive at 10 mA cm-2. Furthermore, the excellent bifunctional electrode (Co2P@Ti3C2Tx∥Co2P@Ti3C2Tx) exhibits efficient engineering water-splitting performance (1.46 V@10 mA cm-2) in alkaline solution. This simple design can propose a promising approach to exploit precious-metal-free catalysts for energy conversion.

Co-Doped Ni3N Nanosheets with Electron Redistribution as Bifunctional Electrocatalysts for Efficient Water Splitting.

Preparation of high-activity and earth-abundant bifunctional catalysts for efficient electrochemical water splitting are crucial and challenging. Herein, Co-doped Ni3N nanosheets loaded on nickel foam (Co-Ni3N) were synthesized. The as-prepared Co-Ni3N exhibits excellent catalytic activity toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline media. Density functional theory (DFT) calculation reveals that Co-Ni3N with redistribution of electrons not only can facilitate the HER kinetics but also can regulate intermediates adsorption energies for OER. Specifically, the Co-Ni3N exhibits high efficiency and stable catalytic activity, with an overpotential of only 30 and 270 mV at a current density of 10 mA cm-2 for the HER and OER in 1 M KOH, respectively. This work provides strong evidence to the merit of Co doping to improve the innate electrochemical performance in bifunctional catalysts, which might have a common impact in many similar metal-metal nitride electrocatalysts.

Mathematical modeling of the reaction of metal oxides with methane.

Methane reduction has attracted substantial interest in recent years because an abundant amount of natural gas has been found and methane possesses a strong reduction ability. However, due to the complexity of the reaction, the reductive-kinetics model has not been developed very well. This work reported a new mathematical model for methane reduction. The model is in a form of explicit functions incorporating many parameters to increase its precision. Particularly, it considers the comparison of methane cracking rate and reaction rate. Both the gas diffusion in the product layer and chemical reaction controlled-kinetics formulae were deduced by considering three kinds of shapes (spherical, cylindrical and lamellar) of particles. Also, by employing two parameters (shape coefficient S c and equivalent diameter d 0), the formulae for the same reduction mechanism could be unified to one formula, which was easier to use. The simulation of the model also considers both isothermal and non-isothermal processes of methane reduction. Furthermore, it can describe the reduction of oxides of varied-valence metals. The kinetics of reduction of metal oxides by methane agrees with the results obtained in the practical system.

Reduction of perovskite-geikielite by methane-hydrogen gas mixture: Thermodynamic analysis and experimental results.

The present study investigated the reduction and carbonization behavior of perovskite-geikielite by using CH4-H2 gas mixture, which aimed to recycle the titanium resource in titanium-bearing blast furnace slag. Thermodynamic phase equilibrium analysis in the CaTiO3-CH4-H2, MgTiO3-CH4-H2 and CaTiO3-MgTiO3-CH4-H2 systems was performed by FactSage. The analysis indicated that CaTiO3 could be ultimately reduced and carbonized to TiCxOy by CH4-H2 gas mixture at temperature above 1300 °C, while the temperature for reduction of MgTiO3 was above 1200 °C. MgTiO3 is found to be reduced prior to CaTiO3 in the CaTiO3-MgTiO3-CH4-H2 systems. The reduction experiments of perovskite-geikielite were carried out in a temperature range of 1300 °C to 1450 °C in a flowing CH4-H2 atmosphere. Experimental results showed that perovskite-geikielite could be reduced completely to TiCxOy at 1400 °C and above after 8 h reduction, while geikielite was reduced prior to perovskite. The reduction and carbonization extent of samples increased with increasing time and temperature when in a low temperature range (below 1400 °C). However, a much higher temperature (above 1400 °C) would hinder further carbonization of TiCxOy for the production of deposited carbon. Addition of iron oxides to sample strongly facilitated the reduction reaction, and even promoted the reduction of titanium to be completed at only 1300 °C after 8 h reduction. The gas-solid reaction provided a low temperature method to reduce and carbonize perovskite and geikielite, and thus it provided a possible way to use titanium-bearing blast furnace slag.