Facile Molten Salt Method Research Articles

Cascade internal electric field dominated carbon nitride decorated with gold nanoparticles as SERS substrate for thiram assay

The development of valid chemical enhancement strategy with charge transfer (CT) for semiconductors has great scientific significance in surface-enhanced Raman scattering (SERS) technology. Herein, a phosphorus doped crystalline/amorphous polymeric carbon nitride (PCPCN) is fabricated by a facile molten salt method, and is employed as a SERS substrate for the first time. Upon the synergies of phosphatization and molten salt etching, PCPCN owns a cascaded internal electric field (IEF) due to the formation of p-n homojunction (interface-IEF) and crystalline/amorphous homojunction (bulk-IEF). The interface-IEF and bulk-IEF could effectively suppress the recombination of charge carriers and promote electron transfer between PCPCN and target methylene blue (MB), respectively. The strong CT interaction endows PCPCN substrate with superior SERS activity with an enhancement factor (EF) of 5.53 × 105. Au nanoparticles (Au NPs) are subsequently decorated on PCPCN to introduce electromagnetic enhancement for a better SERS response. The Au/PCPCN substrate allows to reliably detect trace crystal violet, as well as the thiram residue on cherry tomato. This work offers an integrated solution to enhance CT efficiency based on collaborative homojunction and internal electric field, and may inspire the design of novel semiconductor-based SERS substrates.

A preparation of niobium diboride (NbB2) via molten salt method: Impact of boron concentration on the structural and electrochemical performance

In this work, niobium diboride (NbB2) nanoparticles were successfully synthesized using a simple and facile molten salt method and examined as electrodes for supercapacitors. The synthesized nanoparticles were characterized using SEM, HRTEM, XRD, XPS, and BET techniques. Also, the electrochemical performance of various NbB2 nanoparticles depending on the various amorphous boron concentrations was systematically investigated using both a neutral (1 M Na2SO4) and a basic (6 M KOH) electrolyte. Electrochemical analysis revealed that the obtained sample denoted as the NbB2–8 exhibited the best electrochemical performance (159.6 F/g at 10 mV/s) in Na2SO4 electrolyte compared to that of the KOH electrolyte (69.6 F/g at 10 mV/s). Such a result can be owing to the size and mobility of ions in the electrolyte. Overall, this work could pave the way for other metal borides’ versatility and potential in energy storage.

A Facile Molten Salt Method for Diverse TiC/C Hybrid as Effective Polysulfide Confinement toward Stable Lithium–Sulfur Batteries

Traditional carbon materials suffer from weak adsorption of lithium polysulfides and excessive consumption of electrolyte. A simple and feasible molten salt method is applied for constructing an active nanocrystalline TiC shell on the surface of porous carbon. The highly active TiC nanoshells endow the core–shell composite with efficient chemical–physical synergistic adsorption, which can effectively confine and convert polysulfides, thereby improving the electrochemical performance of lithium–sulfur batteries. The lithium–sulfur batteries assembled with modified separator deliver a high initial discharge specific capacity of 1396 mAh g−1 at a discharge rate of 0.5 C and a high capacity retention of 747.1 mAh g−1 after 500 cycles, with a high coulombic efficiency of 98% during cycling. Besides, this molten salt method can be applied to modify the porous carbon materials of various composite sulfur cathodes such as graphene, carbon nanotubes, and 3D nonwoven carbon fabrics.

Excellent rate performance enabled by Ni-doping for Co3O4 nanosheet electrodes in supercapacitors

Maintaining a high energy density without sacrificing the intrinsic high power density is the research focus in supercapacitors; however, it is far from satisfactory because of the low capacitance retention under a high current. We report herein a facile molten salt method to deposit nanosheet-structured Co3O4 with Ni in-situ doping on Ni foam. Density functional theory (DFT) calculations indicate that the Ni doping leads to higher conductivity and favorable OH− adsorptions. The optimized Ni-doped Co3O4 (Ni-Co3O4) exhibits an excellent capacitance and rate performance, maintaining 86.12% of the original specific capacitance (3360.0 mF cm−2/2710.3 F g−1) when the current density increases from 2 to 200 mA cm−2. After 10000 cycles at 10 mA cm−2, the capacitance retention is 84.71%. An asymmetric supercapacitor assembled using the electrode and activated carbon paper achieves a high areal energy density of 0.19 mWh cm−2 at a power density of 97.04 mW cm−2, with a capacitance retention of 71.50% after 10000 cycles. The device shows promising comprehensive performances when works under a high current density, which could have great prospects in high-rate energy storages.

Promoting Bifunctional Oxygen Catalyst Activity of Double-Perovskite-Type Cubic Nanocrystallites for Aqueous and Quasi-Solid-State Rechargeable Zinc-Air Batteries

Transition metal oxide materials are promising oxygen catalysts that are alternatives to expensive and precious metal-containing catalysts. Integration of transition metal oxides with high activity for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an important pathway for good bifunctionality. In contrast to the conventional physical mixing and hybridization strategies, perovskite-type oxide provides an ideal structure for the integration of the transition metal element atoms on an atomic scale. Herein, B-site ordered double-perovskite-type La1.6Sr0.4MnCoO6 nanocrystallites with ultra-small cubic (20–50 nm) morphology and high specific surface areas (25 m2 g−1) were proposed. Rational designs were integrated to promote the ORR-OER catalysis, e.g., introducing oxygen vacancies via A-site cation substitution, further increasing surface oxygen vacancies via integration of a small amount of Pt/C and nanosizing of the material via a facile molten-salt method. The batteries with the La1.6Sr0.4MnCoO6 nanocrystallites and an aqueous alkaline electrolyte demonstrate decent discharge−charge voltage gaps of 0.75 and 1.10 V at 1 and 30 mA cm−2, respectively, and good cycling stability of 250 h (1500 cycles). A coin-type battery with a gel−polymer electrolyte also presents a good performance.

Design and structure optimization of coal-based hierarchical porous carbon by molten salt method for high-performance supercapacitors

Porous carbon is considered as one of the most ideal materials for supercapacitors due to its low cost, large specific area and high electrical conductivity. Here, we report a facile molten salt method to design and optimize the structure of porous carbon using coal as the precursor, and NaCl/ZnCl2 as the pore-forming agent and a strong polar solvent at high temperature. Through adjusting NaCl content in NaCl/ZnCl2 and the calcination temperature, the effects of preparation conditions on the morphologies and electrochemical properties of porous carbon are systematically explored. As a result, C-0.05N-700 exhibits a large specific surface area of 2548 m2 g−1, high yield of 42.9 wt% and specific capacitance of 344.3 F g−1 at 0.25 A g−1. The assembled symmetric supercapacitor displays a high energy density of 8.1 Wh kg−1 in 6 M KOH and 32 Wh kg−1 in 1 M Na2SO4, respectively. This work provides a referential strategy for the controllable preparation of hierarchical porous carbon with large specific surface area, and reveals the influence law of the preparation conditions on the properties of coal-based porous carbon nanomaterials, and the preparation route is cost-effective. Meanwhile, it can offer a new thought for the effective utilization of coal.

Trojan strategy assisted phase-pure Fe-NiCo2S4 for industrial anion-exchange membrane water electrolyzer

Precise doping into phase-pure structure is very challenging for industrial electrocatalysts keeping high activity and stability. Herein, a facile molten salt method is adopted to synthesize Fe-NiCo2S4 @NIF with a pure phase structure using NiFe foam (NIF) as substrate, achieving controllable Fe doping assisted by inner Fe element in NIF through trojan strategy. Physical characterizations and density functional theory (DFT) calculations reveal that Fe doping not only maintains mechanical strength but also optimizes the electronic structure and reduces *OOH adsorption energy barrier. Consequently, Fe-NiCo2S4 @NIF only needs a low overpotential of 325 mV to reach the industrial current density of 1000 mA cm−2 and run stably for 1000 h for oxygen evolution reaction (OER). The anion exchange membrane (AEM) water electrolyzer (Fe-NiCo2S4 @NIF//(Pt/C)) reaches the current density of 1000 mA cm−2 at a cell voltage of 1.83 V, which operates at the average energy efficiency of 72% for 100 h.

In-situ scalable fast fabrication of Cu-Cu2+1O nanorods for highly efficient electrocatalytic reduction into ammonia under neutral medium

The development of a highly efficient and durable electrocatalyst for nitrate reduction reaction (NO3RR) wastewater valorization to ammonia (NH3) is a promising strategy. However, it is challenging to design scalable low-cost electrocatalysts with high activity, high selectivity, and long-term stability by a facile and simple method. Herein, we construct this scalable Cu-based nanoarray with muti-oxidation states grown directly on nickel foam (NF) substrate (Cu2+1O@Cu/NF) using a facile molten salt method combined in-situ electrochemical reduction. The as-prepared Cu2+1O@Cu/NF nanoarrays reveal a high NH3 yield of 20.14 mg h−1 cm−2 at −0.95 V vs. a reversible hydrogen electrode (vs. RHE), Faradaic efficiency of 99.38% at −0.55 V vs. RHE in the neutral potassium phosphate (PBS) buffer solution with 50 mM NaNO3, which is ascribed to its electron redistribution with abundant oxygen vacancies and favorable charge/mass transfer.

Singlet oxygen generation in light-assisted peroxymonosulfate activation by carbon nitride: Role of elevated crystallinity

Carbon nitride (CN) is an emerging 2D non-metal semiconductor material that could be used in photocatalysis and advanced oxidation processes (AOPs) for pollutants degradation. The radical-induced degradation by CN in photocatalysis or photo-assisted AOPs was widely reported in previous studies. Nevertheless, how the non-radical degradation by CN materials could be achieved under irradiation is neither well understood nor controlled. In this work, crystalline carbon nitride (CCN) was synthesized via a facile molten-salt method, and used to activate peroxymonosulfate (PMS) under visible light (>420 nm) to selectively and efficiently degrade tetracycline (TC). Compared to the traditional polymeric carbon nitride (PCN), CCN was found to be a superior PMS activator with the assistance of visible light, which was ascribed to the increased crystallinity of CN tri-s-triazine units and the increased number of catalytic sites, thereby optimizing the photoelectric properties. The activation performance could be further improved by copper loading, with TC degradation rate nearly six times more than that of PCN. EPR trapping and quenching tests showed that singlet oxygen (1O2) was the dominant reactive oxygen species in the CCN/PMS/visible light system, attributing to the increased graphitic N sites and formation of electron-deficient C in C–N bonding between neighboring tri-s-triazine units upon crystallinity elevation in CCN. In contrast to the conventional radical-based photocatalysis and AOP processes, the visible light-assisted non-radical AOP degradation was highlighted for the selectivity and the remarkable resistance to the impacts of background inorganic anions or natural organic matter (up to 10 mg/L) in the actual water matrix. This work revealed the 1O2 generation mechanism by CN-based materials under the joint assistance of visible light illumination and crystallinity elevation, and its excellent removal performance demonstrates the great potential of CCN-based materials in the practical wastewater treatment.

Semi-coke-based amorphous porous carbon synthesized by a molten salt assisted method for superior lithium storage

Amorphous porous carbon with a network structure composed of nanosheets was prepared from semi-coke by a facile molten salt method.

Densely populated tiny RuO2 crystallites supported by hierarchically porous carbon for full acidic water splitting.

The exploitation of highly active bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acidic media has been a subject receiving immense interest. However, the existing catalysts usually suffer from low catalytic efficiency and poor corrosion resistance under acidic conditions. Herein, we report a facile molten salt method to fabricate ruthenium dioxide nanoparticles supported by hierarchically porous carbon (RuO2/PC) as a bifunctional electrocatalyst for full water splitting under strong acidic conditions. The formation of a densely populated nanocrystalline RuO2/carbon heterostructure helps expose catalytic sites, accelerates the mass transfer rate, and further enhances the acid resistance of RuO2 nanoparticles. The as-synthesized RuO2/PC consequently exhibits superior catalytic performance for the OER with an overpotential of 181 mV upon 10 mA cm-2 compared to that of the commercial RuO2 (343 mV) and a comparable performance to Pt/C for the HER (47.5 mV upon 10 mA cm-2) in 0.5 M H2SO4. The RuO2/PC shows promising stability with little degradation over ∼24 h. Impressively, the water electrolyzer based on RuO2/PC shows an overpotential of 326 mV at 10 mA cm-2, much lower than that of the electrolyzer based on the combination of Pt/C and RuO2 (400 mV), indicating its great potential towards practical application.

The acidic OER activation-decay process of highly active Ir–Ni mixed oxide modified by capping agent for both particle fining and Ir–OH formation

Developing highly active catalyst for oxygen evolution reaction (OER) with low noble metal loading is crucial for the application of proton exchange membrane (PEM) water electrolysis. Ir-transition metal (TM) binary catalyst with chemical leaching was reported to perform excellent activity with TM leaching. However, most of the studies on the activation-decay focused on the final status, and the variation process remains unclear. With cysteamine·HCl, a modified facile molten salt method was applied to prepared highly active Ir–Ni mixed oxide (c-xNiIrMO), which perform 5.5 times higher mass activity than commercial IrO2. The variation of active surface area, intrinsic activity, conductivity of prepared catalyst layer during the activation process are studied to unveil the key factors for the activity enhancement. With further stability test, c-xNiIrMO with Ni content lower than 67% performs decrease intrinsic activity and improved kinetic performance in the first hundred cycles. After obtaining a stable Ir0.95Ni0.05Ox structure, further cycling results in typical activity decay with dissolution of Ir.

Molten-salt-mediated synthesis of Na+ doped Bi4TaO8Cl nanosheets with exposed {001} facets for enhanced photocatalytic degradation

Regulating the exposed surfaces of semiconductors is believed to be a versatile strategy to boost their photoactivity. Herein, the Na+ doped Bi4TaO8Cl (BTOC) nanosheets with the exposed {001} active faces were synthesized via a facile molten salt method. The size of BTOC nanosheets could be readily tuned by controlling the feeding content of the molten salts (NaCl and KCl). Benefited from the cooperative effect of the Na+ doping and the exposed active {001} facets, the optimal BTOC-24 nanosheets exhibited high photoactivity. Under 5 W white LED light irradiation, the degradation rates of BTOC-24 nanosheets for ofloxacin (OFL) and Rhodamine B (RhB) were 84.1% and 97.3%, which were drastically enhanced by 2 and 6-folds than that of bulk BTOC, respectively. The mechanism for the improved photoactivity was also investigated. This work demonstrates the synergetic effect of engineering the thickness and exposed crystal face towards the enhanced photoactivity of 2D BTOC, which also shows significant implications for designing other 2D semiconductor nanosheet with efficient environmental remediation performance.

Molten Salts Assisted Interfacial Engineering for Efficient and Low‐Cost Full‐Inorganic Antimony Sulfide Solar Cells

AbstractAntimony sulfide (Sb2S3) is emerging as a promising light harvesting material owing to its brilliant photoelectric property. However, the performance of Sb2S3‐based solar cells is partly limited by serious back contact interface recombination and hole transportation resistance. High‐efficiency Sb2S3 devices typically use Spiro‐OMeTAD and/or Au as back contact materials, but their stability and cost are a concern. In this sense, a surface modification scheme by lithium‐doping is first introduced for Sb2S3 via a facile molten salt method. The ions in the molten state have high mobility and activity, enabling doping reactions to complete within a short time. The lithium‐doped Sb2S3 thin film has a smooth and well‐bonded surface, preferred (hk1) orientations, and an upshifted valence band maximum (VBM), which favors the hole extraction. Finally, a device using carbon as an electrode, which is more than a dozen times cheaper than gold, raises the short‐circuit current density (JSC) from 12.35 to 14.40 mA cm−2, and the power conversion efficiency (PCE) from 4.47% to 6.16%. This is among the highest PCE reported for full‐inorganic Sb2S3 solar cells, which demonstrates a facile interface modification technique via molten alkali salt to improve the performance of Sb2S3 solar cells.

In-situ electrochemical conversion of Na5V12O32@graphene for enhanced cycle stability in aqueous zinc ion batteries

HypothesisNa5V12O32 (NVO) is a potential cathode for aqueous zinc ion batteries (AZIBs). However, it suffers severe capacity decay due to the dissolution of the active material. The structural design may be an effective solution to the problem. ExperimentsHerein, we construct a typical two-dimensional hierarchical structure of Na5V12O32@graphene (NVO@G) via a facile molten salt method. FindingsThe capacity fading problem is solved by the in-situ conversion of NVO@G to a more stable hierarchical system during cycling. The in-situ formed zinc pyrovanadate (Zn3V2O7(OH)2·2H2O, ZVO) nanosheets on the surface of graphene exhibits excellent zinc-ion storage stability. The presence of graphene induces the growth of NVO nanobelts to construct the typical two-dimensional hierarchical structure. Additionally, the in-situ conversion makes the formed ZVO nanosheets contact with graphene better. Benefitting from the hierarchical nanostructure and in-situ phase conversion, the NVO@G electrode shows excellent long-term stability (96.4% retention after 340 cycles at 0.3 A g−1, 85.7% retention after 4400 cycles at 5 A g−1) and high zinc ion storage capacity (220 mAh g−1 at 0.3 A g−1), which is superior to those of most electrode materials previously reported.

Enhanced photocatalytic H2 production of graphitic carbon nitride via implantation of lithium and potassium ions

Photocatalytic water splitting technology using sunlight to produce hydrogen is considered to be an effective method to solve the energy crisis. Graphitic carbon nitride (g-C3N4) as an attractive two-dimensional semiconductor with visible-light response, has been widely applied in water splitting. However, poor light absorption and fast carrier recombination limit the potential application. Herein, the novel g-C3N4 (MCN) embedded by lithium and potassium ions were prepared by the facile molten salt method. Detailed characterizations have proved that the presence of Li+ and K+ could improve the crystallinity and decrease the band gap of g-C3N4, thus effectively promoting carrier separation and expanding light absorption. Theoretical calculation results also have shown that the appearance of Li+ and K+ could significantly reduce the over potential of hydrogen evolution. The MCN exhibits a higher photocatalytic hydrogen evolution rate (239.41 μmol/h), which is 18.2 times than pure g-C3N4 (13.1 μmol/h). This work provides a new idea for the design and preparation of novel 2D photocatalysts.

α-MoB2 Nanosheets for Hydrogen Evolution in Alkaline and Acidic Media

α-MoB2 is recognized as the most efficient molybdenum boride for electrocatalytic hydrogen evolution reaction (HER). However, the convenient synthesis of single phase α-MoB2 is still challenging, and its HER activity in alkaline electrolytes remains unclear. Herein, we report the first successful synthesis of the α-MoB2 nanosheets by a simple and facile molten salt method through the MoCl5 and NaBH4 reaction at 850 °C. The α-MoB2 nanosheets exhibit a remarkable HER performance in alkaline electrolytes, delivering a low overpotential of 124 mV at a current density of 10 mA/cm2. In acidic electrolytes, an improved performance was found in comparison to that of the bulk and nano α-MoB2 with an overpotential as low as 141 mV at 10 mA/cm2. Such HER performance arises from the nanosheet structure that allows more active planes to be exposed. In addition, the α-MoB2 nanosheets possess an outstanding stability in both acidic and alkaline media, showing negligible current density drop even after 3000 cycles and more than 24 h of potentiostatic operation.

Facile fabrication of 3D flower-like V2Al1-CT as an anode for lithium-ion batteries

Herein, the 3D flower-like V 2 Al 1- x CT z with an estimated petaloid nanosheet thickness of 10–20 nm were firstly obtained by etching the submicro-sized V 2 AlC precursors, which were synthesized at 1000 °C holding for 5 h in (Na,K)Cl melt by a facile molten salt method, in 40 wt% HF at room temperature. The synthesis mechanism of V 2 AlC is possibly related to the disproportionation reaction of V-ions on carbon surface in molten salts to form V 2 C, followed by the intercalation of Al into V 2 C. Subsequently, the 3D flower-like V 2 Al 1- x CT z was applied as an anode in lithium-ion batteries, releasing ~215.2 mA h g −1 in the continuous 500 cycles at 0.5 A g −1 , which exhibits the superiority in the reversible capacity in contrast with some reported micro-sized layered V 2 CT z MXenes. Such excellent electrochemical characteristics of V 2 Al 1- x CT z could be mainly ascribed to its unique submicro-sized flower-like morphology with high specific surface areas and abundant electrochemical sites for accommodating the reversible insertion/extraction of Li-ions. • 3D flower-like V 2 Al 1- x CT z was firstly obtained by etching the submicro-sized V 2 AlC precursors. • Thickness of the nanosheets on V 2 Al 1- x CT z with a lot of defects was estimated as 10–20 nm. • The V 2 Al 1- x CT z exhibits desirable electrochemical performances as an anode in LIBs. • It may be extended to the synthesis of MXenes with diverse morphologies as anodes for LIBs.

Synthesis and electrochemical performances of cathode material Fe0.5Co0.5S2 for thermal batteries by a facile molten salt method

Synthesis and electrochemical performances of cathode material Fe0.5Co0.5S2 for thermal batteries by a facile molten salt method

Structurally Disordered RuO2 Nanosheets with Rich Oxygen Vacancies for Enhanced Nitrate Electroreduction to Ammonia

AbstractElectrochemical reduction of nitrate pollutants to ammonia has emerged as an attractive alternative for ammonia synthesis. Currently, many strategies have been developed for enhancing nitrate reduction to ammonia (NRA) efficiency, but the influence of the degree of structural disorder is still unexplored. Here, carbon‐supported RuO2 nanosheets with adjustable crystallinity are synthesized by a facile molten salt method. The as‐synthesized amorphous RuO2 displays high ammonia Faradaic efficiency (97.46 %) and selectivity (96.42 %), greatly outperforming the crystalline counterparts. The disordered structure with abundant oxygen vacancies is revealed to modulate the d‐band center and hydrogen affinity, thus lowering the energy of the potential‐determining step (NH2*→NH3*).