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Constructing multiple nanosized heterogeneous structures with an in situ optimized coordination environment for dispersing and stabilizing noble metal single atoms (SAs) is a highly effective strategy for high-efficiency utilization of SAs and improving the electrocatalytic performances of the oxygen evolution reaction (OER). Herein, a multi-crystalline-amorphous heterogeneous composite (CoP2@CN–Ir(200)) composed of crystalline CoP2, amorphous CoOx and amorphous N-doped carbon was constructed for in situ loading of Ir SAs by cyclic voltammetry (CV) electrodeposition in an ionic liquid. By precisely controlling the electrodeposition cycles, the loading matrix of Ir SAs was simultaneously reconstructed and optimized. Some of the crystalline CoP2 is transformed into amorphous CoOx with activated high-valence Co; a coordination environment toward oxygenated species is built with more lattice oxygen and stronger adsorption ability of oxygen; the abundant heterointerfaces and the enhancement of the oxidation state disperse and stabilize Ir atoms in the form of OER-favorable high-valence Ir3+/Ir4+ by covalent Ir–O bonds (including Ir–O–Co bonds). As a result, abundant active sites with high intrinsic activity are exposed, and an accelerated charge transfer rate can be achieved, endowing CoP2@CN–Ir(200) with an outstanding electrocatalytic activity. Ultralow overpotentials of 189 and 300 mV at 10 and 100 mA cm−2, respectively, are achieved with a small Tafel slope of 36.9 mV dec−1, surpassing most reported remarkable Ir-related catalysts. [ABSTRACT FROM AUTHOR]

The surface and interface chemistry are critical for controlling the properties of two‐dimensional transition metal carbides and nitrides (MXenes). Numerous efforts have been devoted to the functionalization of MXenes with small inorganic ligands; however, few etching methods have been reported on the direct bonding of organic groups to MXene surfaces. In this work, we demonstrated an efficient and rapid strategy for the direct synthesis of 2D Ti3C2Tx MXene nanosheets with organic terminal groups in an organic Lewis acid (trifluoromethanesulfonic acid) solvent, without introducing additional intercalations. The dissolution of aluminum and the subsequent in situ introduction of trifluoromethanesulfonic acid resulted in the extraction of Ti3C2Tx MXene (T=CF3SO3−) (denoted as CF3SO3H−Ti3C2Tx) flakes with sizes reaching 15 μm and high productivity (over 70 %) of monolayers or few layers. More importantly, the large CF3SO3H−Ti3C2Tx MXene nanosheets had high colloidal stability, making them promising as efficient electrocatalysts for the hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Stainless-steel pickling sludge (SSPS) and blast-furnace gravity dust (BFGD) are solid wastes and hazardous materials produced during iron- and steel-making processes and are important secondary metallurgical resources. The comprehensive use of these two materials shows important environmental significance and economic value. Herein, the elemental content, phase composition, and microstructure of SSPS and BFGD samples were then analyzed. Then, a high-temperature process for SSPS, BFGD, and their mixtures (mass ratio of 1:1) in air and N2 was analyzed by thermogravimetry and differential scanning calorimetry, and the high-temperature calcination products were identified and analyzed using X-ray diffraction. In air, the mixture of SSPS and BFGD can generate SFCA after roasting at 1200 °C. In N2, the carbon in the BFGD reduced the CaSO4 in SSPS to CaS. Based on the high-temperature phase-transformation behavior of the SSPS and BFGD mixture under aerobic and anaerobic conditions, a novel process flow of mixture pelletizing‒sintering agglomeration–blast furnace smelting was proposed for the synergistic treatment of SSPS and BFGD. This process is expected to provide innovation for stainless steel production enterprises to realize the closed circuit recycling of solid waste without leaving the factory. [ABSTRACT FROM AUTHOR]

Molten salt electrodeposition of crystalline silicon (Si) films from silicon dioxide (SiO2) in molten calcium chloride (CaCl2)-calcium oxide (CaO) has been systematically investigated. The dissolution-electrodeposition mechanism was studied by cyclic voltammetry (CV), in situ X-ray diffraction (XRD), and in situ Raman spectroscopy. The results show that different silicate ions, including SiO32−, SiO44−, would be generated in molten salt and could be influenced by the molar ratios of additive SiO2 and CaO, as well as the electrolytic parameters. In particular, with the increase of electrodeposition time, SiO44− increased as the dominated silicate ions in molten salt. Furthermore, different current densities, time and substrates would also have vital influences on the electrodeposition process and the electrodeposited Si products. Si products with tunable morphology have been deposited on different substrates by adjusting the electrodeposition conditions. The deposited crystalline Si films exhibit homogeneous epitaxial structures, in particular, the epitaxial Si film grown on the 110-oriented Si wafer possesses uniform inverted pyramid structure. The ohmic resistivity test and microstructure analysis results show that the electrodeposited epitaxial crystalline Si films have the similar properties and characteristics as their single crystal Si wafer substrates. In general, the investigation of the dissolution-electrodeposition mechanism and its epitaxial growth behavior helps the progress of this one-step CaO-assisted dissolution-electrodeposition process for the production of epitaxial Si films. [ABSTRACT FROM AUTHOR]

Carbide-derived carbon (CDC) as an unconventional porous carbon material has been widely used for various applications. In this work, Ti3AlC2-derived porous carbon (Ti3AlC2-CDC) was electrochemically synthesized at 900°C and 3.0 V in molten CaCl2-NaCl. The obtained Ti3AlC2-CDC with abundant slit-like mesopores showed a high specific surface area of 425 m2/g. The variation of the morphology from the Ti3AlC2 precursor to Ti3AlC2-CDC was investigated, with the Ti3AlC2-CDC demonstrating a typical loose layered morphology and amorphous carbon structure. The intermediate products were also systematically analyzed to investigate the molten salt electrochemical etching process. It was found that Ti3AlC2 can be oxidized by residual O2− in the molten salt to form tiny Al2O3 particles on the anodic Ti3AlC2 surface during the etching process, then Ti3AlC2-CDC can be obtained by successively removing these Al2O3, Al, and Ti from the Ti3AlC2 precursor. [ABSTRACT FROM AUTHOR]

Ti3AlC2 is electrochemically synthesized from titanium‐rich slag/Al2O3/C mixtures in molten salts. The intermediate products are systematically analyzed to investigate the formation process of Ti3AlC2. The results show that the synthesis process typically involves an electrodeoxidation process and in situ carburization/combination process. In addition, most of the undesired metallic oxides contained in the titanium‐rich slag are removed effectively during the electrolysis process, and the removal mechanism of these undesired metallic oxides is further discussed. The influences of different molten salts (including molten CaCl2 and CaCl2–NaCl) and temperatures (range of 800–1000 °C) on the final products are also studied. The results show that these electrosynthesis conditions influence the morphology and phase composition of the products. The synthesized Ti3AlC2 particles possess an irregular plate‐like morphology. It is suggested that the molten salt electrochemical synthesis technology is a promising process to produce Ti3AlC2 and/or other MAX phases from multicomponent complex ores. [ABSTRACT FROM AUTHOR]

Two-dimensional Ti 3 C 2 T x MXene materials, with metal-like conductivities and versatile terminals, have been considered to be promising surface modification materials for Zn-metal-based aqueous batteries (ZABs). However, the oxygen-rich and hybridized terminations caused by conventional methods limit their advantages in inhibiting zinc dendrite growth and reducing corrosion-related side reactions. Herein, -O-depleted, -Cl-terminated Ti 3 C 2 T x was precisely fabricated by the molten salt electrochemical etching of Ti 3 AlC 2 , and controlled in situ terminal replacement from -Cl to unitary -S or -Se was achieved. The as-prepared -O-depleted and unitary-terminal Ti 3 C 2 T x as Zn anode coatings provided excellent hydrophobicity and enriched zinc-ionophilic sites, facilitating Zn 2+ horizontal transport for homogeneous deposition and effectively suppressing water-induced side reactions. The as-assembled Ti 3 C 2 S x @Zn symmetric cell achieved a cycle life of up to 4200 h at a current density and areal capacity of 2 mA cm -2 and 1 mAh cm -2 , respectively, with an impressive cumulative capacity of up to 7.25 Ah cm -2 at 5 mA cm -2 //2 mAh cm -2 . These findings provide an effective electrochemical strategy for tailoring -O-depleted and unitary Ti 3 C 2 T x surface terminals and advancing the understanding of the role of specific Ti 3 C 2 T x surface chemistry in regulating the plating/stripping behaviors of metal ions., (© 2024 Wiley-VCH GmbH.)

The surface and interface chemistry are critical for controlling the properties of two-dimensional transition metal carbides and nitrides (MXenes). Numerous efforts have been devoted to the functionalization of MXenes with small inorganic ligands; however, few etching methods have been reported on the direct bonding of organic groups to MXene surfaces. In this work, we demonstrated an efficient and rapid strategy for the direct synthesis of 2D Ti 3 C 2 T x MXene nanosheets with organic terminal groups in an organic Lewis acid (trifluoromethanesulfonic acid) solvent, without introducing additional intercalations. The dissolution of aluminum and the subsequent in situ introduction of trifluoromethanesulfonic acid resulted in the extraction of Ti 3 C 2 T x MXene (T=CF 3 SO 3 - ) (denoted as CF 3 SO 3 H-Ti 3 C 2 T x ) flakes with sizes reaching 15 μm and high productivity (over 70 %) of monolayers or few layers. More importantly, the large CF 3 SO 3 H-Ti 3 C 2 T x MXene nanosheets had high colloidal stability, making them promising as efficient electrocatalysts for the hydrogen evolution reaction., (© 2024 Wiley-VCH GmbH.)

Single-atom catalysts (SACs) with maximized metal atom utilization and intriguing properties are of utmost importance for energy conversion and catalysis science. However, the lack of a straightforward and scalable synthesis strategy of SACs on diverse support materials remains the bottleneck for their large-scale industrial applications. Herein, we report a general approach to directly transform bulk metals into single atoms through the precise control of the electrodissolution-electrodeposition kinetics in ionic liquids and demonstrate the successful applicability of up to twenty different monometallic SACs and one multimetallic SAC with five distinct elements. As a case study, the atomically dispersed Pt was electrodeposited onto Ni 3 N/Ni-Co-graphene oxide heterostructures in varied scales (up to 5 cm × 5 cm) as bifunctional catalysts with the electronic metal-support interaction, which exhibits low overpotentials at 10 mA cm -2 for hydrogen evolution reaction (HER, 30 mV) and oxygen evolution reaction (OER, 263 mV) with a relatively low Pt loading (0.98 wt%). This work provides a simple and practical route for large-scale synthesis of various SACs with favorable catalytic properties on diversified supports using alternative ionic liquids and inspires the methodology on precise synthesis of multimetallic single-atom materials with tunable compositions., Competing Interests: Competing interests statement:The authors declare no competing interest.

Sustainable and low-carbon-emission silicon production is currently one of the main focuses for the metallurgical and materials science communities. Electrochemistry, considered a promising strategy, has been explored to produce silicon due to prominent advantages: (a) high electricity utilization efficiency; (b) low-cost silica as a raw material; and (c) tunable morphologies and structures, including films, nanowires, and nanotubes. This review begins with a summary of early research on the extraction of silicon by electrochemistry. Emphasis has been placed on the electro-deoxidation and dissolution-electrodeposition of silica in chloride molten salts since the 21st century, including the basic reaction mechanisms, the fabrication of photoactive Si films for solar cells, the design and production of nano-Si and various silicon components for energy conversion, as well as storage applications. Besides, the feasibility of silicon electrodeposition in room-temperature ionic liquids and its unique opportunities are evaluated. On this basis, the challenges and future research directions for silicon electrochemical production strategies are proposed and discussed, which are essential to achieve large-scale sustainable production of silicon by electrochemistry., (Copyright © 2023 Feng Tian et al.)

The two-dimensional MAX phases with compositional diversity are promising functional materials for electrochemical energy storage. Herein, we report the facile preparation of the Cr 2 GeC MAX phase from oxides/C precursors by the molten salt electrolysis method at a moderate temperature of 700°C. The electrosynthesis mechanism has been systematically investigated, and the results show that the synthesis of the Cr 2 GeC MAX phase involves electro-separation and in situ alloying processes. The as-prepared Cr 2 GeC MAX phase with a typical layered structure shows the uniform morphology of nanoparticles. As a proof of concept, Cr 2 GeC nanoparticles are investigated as anode materials for lithium-ion batteries, which deliver a good capacity of 177.4 mAh g -1 at 0.2 C and excellent cycling performance. The lithium-storage mechanism of the Cr 2 GeC MAX phase has been discussed based on density functional theory (DFT) calculations. This study may provide important support and complement to the tailored electrosynthesis of MAX phases toward high-performance energy storage applications., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Pang, Tian, Xiong, Li, Zhang, Chen, Wang, Li, Wang, Yu, Xu, Lu and Zou.)