Category Archives: ChemSusChem

Mott‐Schottky MXene@WS2 Heterostructure: Structural and Thermodynamic Insights and Application in Ultra Stable Lithium−Sulfur Batteries

Posted on 10 October 2023 by

Separator modification: A MXene@WS₂ Mott-Schottky heterostructure is prepared by simple hydrothermal treatment for separator modification of Li−S battery. Due to the interaction of the built-in electric field and multiple catalytic/adsorption active sites, this catalyst achieves ultra-stable cycle performance.

Abstract

Due to the “shuttle effect” and low conversion kinetics of polysulfides, the cycle stability of lithium sulfur (Li−S) battery is unsatisfactory, which hinders its practical application. The Mott-Schottky heterostructures for Li−S batteries not only provide more catalytic/adsorption active sites, but also facilitate electrons transport by a built-in electric field, which are both beneficial for polysulfides conversion and long-term cycle stability. Here, MXene@WS₂ heterostructure was constructed by in-situ hydrothermal growth for separator modification. In-depth ultraviolet photoelectron spectroscopy and ultraviolet visible diffuse reflectance spectroscopy analysis reveals that there is an energy band difference between MXene and WS₂, confirming the heterostructure nature of MXene@WS₂. DFT calculations indicate that the Mott-Schottky MXene@WS₂ heterostructure can effectively promote electron transfer, improve the multi-step cathodic reaction kinetics, and further enhance polysulfides conversion. The built-in electric field of the heterostructure plays an important role in reducing the energy barrier of polysulfides conversion. Thermodynamic studies reveal the best stability of MXene@WS₂ during polysulfides adsorption. As a result, the Li−S battery with MXene@WS₂ modified separator exhibits high specific capacity (1613.7 mAh g⁻¹ at 0.1 C) and excellent cycling stability (2000 cycles with 0.0286 % decay per cycle at 2 C). Even at a high sulfur loading of 6.3 mg cm⁻², the specific capacity could be retained by 60.0 % after 240 cycles at 0.3 C. This work provides deep structural and thermodynamic insights into MXene@WS₂ heterostructure and its promising prospect of application in high performance Li−S batteries.

Robust and Intimate Interface Enabled by Silicon Carbide as an Additive to Anodes for Lithium Metal Solid‐State Batteries

Posted on 10 October 2023 by

To harness the potential of a lithium anode, silicon carbide is proposed as an additive to mitigate the contact issues at the interface with LLZTO SSE. The Li–SiC composite anode demonstrates an improved wettability owing to the lithiophilic lithium silicate phase formed in situ and utilizes the robustness of SiC to substantially increase the critical current density of the anode–SSE interface.

Abstract

Garnet-type solid-state electrolytes are among the most reassuring candidates for the development of solid-state lithium metal batteries (SSLMB) because of their wide electrochemical stability window and chemical feasibility with lithium. However, issues such as poor physical contact with Li metal tend to limit their practical applications. These problems were addressed using β-SiC as an additive to the Li anode, resulting in improved wettability over Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO) and establishing an improved interfacial contact. At the Li–SiC|LLZTO interface, intimacy was induced by a lithiophilic Li₄SiO₄ phase, whereas robustness was attained through the hard SiC phase. The optimized Li–SiC|LLZTO|Li–SiC symmetric cell displayed a low interfacial impedance of 10 Ω cm² and superior cycling stability at varying current densities up to 5800 h. Moreover, the modified interface could achieve a high critical current density of 4.6 mA cm⁻² at room temperature and cycling stability of 1000 h at 3.5 mA cm⁻². The use of mechanically superior materials such as SiC as additives for the preparation of a composite anode may serve as a new strategy for robust garnet-based SSLMB.

Influence of Residual Water Traces on the Electrochemical Performance of Hydrophobic Ionic Liquids for Magnesium‐Containing Electrolytes

Posted on 10 October 2023 by

This study deals with the fundamental understanding of the effect of trace amounts of water on the electrochemical properties of ionic liquids and their performance toward Mg deposition/dissolution.

Abstract

A trace amount of water is typically unavoidable as an impurity in ionic liquids, which is a huge challenge for their application in Mg-ion batteries. Here, we employed molecular sieves of different pore diameters (3, 4, and 5 Å), to effectively remove the trace amounts of water from 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPip-TFSI) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI). Notably, after sieving (water content <1 mg ⋅ L⁻¹), new anodic peaks arise that are attributed to the formation of different anion-cation structures induced by minimizing the influence of hydrogen bonds. Furthermore, electrochemical impedance spectroscopy (EIS) reveals that the electrolyte resistance decreases by ∼10 % for MPPip-TFSI and by ∼28 % for BMP-TFSI after sieving. The electrochemical Mg deposition/dissolution is investigated in MPPip-TFSI/tetraglyme (1 : 1)+100 mM Mg(TFSI)₂+10 mM Mg(BH₄)₂ using Ag/AgCl and Mg reference electrodes. The presence of a trace amount of water leads to a considerable shift of 0.9 V vs. Mg^2+/Mg in the overpotential of Mg deposition. In contrast, drying of MPPip-TFSI enhances the reversibility of Mg deposition/dissolution and suppresses the passivation of the Mg electrode.

Hydrothermal Fabrication of Carbon‐Supported Oxide‐Derived Copper Heterostructures: A Robust Catalyst System for Enhanced Electro‐Reduction of CO2 to C2H4

Posted on 10 October 2023 by

From CO₂ to C₂H₄ : Cu _x O/C heterostructures prepared by a facile method with optimised Cu/C ratio and morphological/structural properties efficiently drive direct CO₂ electrochemical conversion to C₂H₄ at relevant current densities.

Abstract

Anthropogenic CO₂ can be converted to alternative fuels and value-added products by electrocatalytic routes. Copper-based catalysts are found to be the star materials for obtaining longer-chain carbon compounds beyond 2e⁻ products. Herein, we report a facile hydrothermal fabrication of a highly robust electrocatalyst: in-situ grown heterostructures of plate-like CuO−Cu₂O on carbon black. Simultaneous synthesis of copper-carbon catalysts with varied amounts of copper was conducted to determine the optimum blend. It is observed that the optimum ratio and structure have aided in achieving the state of art faradaic efficiency for ethylene >45 % at −1.6 V vs. RHE at industrially relevant high current densities over 160 to 200 mA ⋅ cm⁻². It is understood that the in-situ modification of CuO to Cu₂O during the electrolysis is the driving force for the highly selective conversion of CO₂ to ethylene through the *CO intermediates at the onset potentials followed by C−C coupling. The excellent distribution of Cu-based platelets on the carbon structure enables rapid electron transfer and enhanced catalytic efficiency. It is inferred that choosing the right composition of the catalyst by tuning the catalyst layer over the gas diffusion electrode can substantially affect the product selectivity and promote reaching the potential industrial scale.

Co‐Doping of Al3+ and Ti4+ and Electrochemical Properties of LiNiO2 Cathode Materials for Lithium‐Ion Batteries

Posted on 10 October 2023 by

Co-doping modification of LiNiO₂ : The replacement of Ni atoms with Al³⁺ and Ti⁴⁺ ions respectively can improve the charge/discharge cycling performance of LiNiO₂ cathode materials, and their co-doping can more efficiently suppress the Ni²⁺/Li⁺ cation mixing, irreversible phase transition of H2 and H3. Thus, the electrochemical performances exhibit significant synergistic effects.

Abstract

LiNiO₂ cathode material for lithium-ion batteries has the advantages of high specific capacity, abundant resources, and low cost, but it suffers from difficulties in preparation, structural instability, and serious capacity decay. In this work, highly pure and layered structural LiNi_0.95Al _a Ti_0.05-a O₂ (a=0, 0.025, 0.05) cathode materials were synthesized by a simply sol-gel method. The cation mixing of Ni²⁺ and Li⁺, structural deterioration, irreversible conversion between H2 and H3 phases and unstable surface and CEI (Cathode-electrolyte interface) film can be effectively suppressed by co-doping with Al³⁺ and Ti⁴⁺. A preferred LiNi_0.95Al_0.025Ti_0.025O₂ sample provides a discharge specific capacity of 223 mAh g⁻¹ at 0.1 C and 148.32 mAh g⁻¹ at 5 C, a capacity retention of 72.7 % after 300 cycles at 1 C and a Li⁺ diffusion coefficient of about 2.0×10⁻⁹ cm² s⁻¹.

Co3O4 Supported on β‐Mo2C with Different Interfaces for Electrocatalytic Oxygen Evolution Reaction

Posted on 10 October 2023 by

At the interface: The detailed analysis of the interface between Co₃O₄ and different β-Mo₂C supports is reported for electrocatalytic oxygen evolution reaction (OER). The compact interface enhanced the conductivity of the material and also regulated the interfacial electron redistribution of atoms (Mo, Co). The synergistic effect between Mo₂C and Co₃O₄ effectively improved the OER performance.

Abstract

Interface engineering is an effective strategy for improving the activity of catalysts in electrocatalytic oxygen evolution reaction (OER). Herein, Co₃O₄ supported on β-Mo₂C with different interfaces were investigated for electrocatalytic OER. The morphological diversity of β-Mo₂C supports allowed different Co₃O₄-Mo₂C interactions. Various techniques characterized the composition and microstructure of the interface in the composites. Due to the strong interaction between Co₃O₄ nanoparticles and β-Mo₂C nanobelts with opposing surface potentials, compact interface was observed between Co₃O₄ active species and β-Mo₂C nanobelt support. The compact interface enhanced the conductivity of the material and also regulated the interfacial electron redistribution of Mo and Co atoms, promoting the charge transfer process during OER. In addition, the surface loading of Co₃O₄ can effectively improve the hydrophilicity of the surface. β-Mo₂C has the capability in dissociating H₂O molecules. Thus, an example has been carefully demonstrated for interface engineering in electrocatalytic OER.

Redox Targeting‐based Neutral Aqueous Flow Battery with High Energy Density and Low Cost

Posted on 10 October 2023 by

A neutral aqueous single-molecule redox-targeting (SMRT)-based Prussian blue (PB)−Fe/S flow battery was demonstrated. Especially, the energy density of a battery based on [Fe(CN)₆]^3−/4−-containing catholyte is increased to 92.8 Wh L⁻¹. Moreover, the PB−Fe/S flow battery exhibits outstanding performance with long cycle life over 7000 cycles (4500 h), and the chemical cost of the PB−Fe/S full cell is as low as 19.26 $ kWh⁻¹.

Abstract

Neutral aqueous flow batteries with common traits of the redox flow batteries, such as the independence of energy and power, scalability and operational flexibility, and additional merits of outstanding safety and low corrosivity show great promise for storing massive electrical energy from solar and wind energy. Particularly, the ferricyanide/ferrocyanide ([Fe(CN)₆]^3−/4−) couple has been intensively employed as redox mediator to store energy in the catholyte ascribed to its abundance, low corrosivity, remarkable redox reversibility and stability. However, the low energy density arising from poor solubility of [Fe(CN)₆]^3−/4− restricts their commercial applications for energy storage systems. In this study, the practical energy density of a [Fe(CN)₆]^3−/4−-based catholyte is significantly boosted from 10.5 to 92.8 Wh L⁻¹ by combining the counter-ion effect and the single-molecule redox-targeting (SMRT) reactions between [Fe(CN)₆]^3−/4− and Prussian blue (Fe₄[Fe(CN)₆]₃, PB)/Prussian white (PW). Paired with concentrated K₂S anolyte, we demonstrate a neutral aqueous SMRT-based PB−Fe/S flow battery with ultra-long lifespan over 7000 cycles (4500 h) and ultra-low chemical cost of electrolytes in the cell as 19.26 $ kWh⁻¹. Remarkably, under the influences of SMRT reactions in the presence of PB granules in the catholyte, the capacity after 7000 cycles of the PB−Fe/S flow battery is 181.8 % of the initial capacity without PB.

Paraformaldehyde as C1 Synthon: Electrochemical Three‐Component Synthesis of Tetrahydroimidazo[1,5‐a]quinoxalin‐4(5H)‐ones in Aqueous Ethanol

Posted on 10 October 2023 by

Glue! A green and practical one-pot method for the electrochemical three-component synthesis of tetrahydroimidazo[1,5-a]quinoxalin-4(5H)-ones using cheap and environmentally benign paraformaldehyde as a C1 synthon, was developed. In this strategy, EtOH played dual roles (eco-friendly solvent and waste-free pre-catalyst) and the in situ generated ethoxide promoted triple sequential deprotonations.

Abstract

A green and practical method for the electrochemical synthesis of tetrahydroimidazo[1,5-a]quinoxalin-4(5H)-ones through the three-component reaction of quinoxalin-2(1H)-ones, N-arylglycines and paraformaldehyde was reported. In this strategy, EtOH played dual roles (eco-friendly solvent and waste-free pre-catalyst) and the in situ generated ethoxide promoted triple sequential deprotonations.

Face‐Dependent Reconstruction of Bi‐Oxyiodides toward Selective Growth of (BiO)2CO3 Edge Side to Maximize CO2 Conversion Efficiency

Posted on 10 October 2023 by nTaewaen Lim, nJunhyeok Seon

Chemical reconstruction of orthorhombic Bi₅O₇I to well-aligned array of (BiO)₂CO₃ nanosheets, selectively exposing the CO₃ ²⁻ moiety at the edge side was demonstrated. This significantly improved the catalytic efficiency for CO₂-to-formate conversion to 100 % Faradaic efficiency in a low overpotential region.

Abstract

Chemical reconstruction of bismuth oxyiodides using bicarbonates is tried to selectively grow (BiO)₂CO₃ edge side. Orthorhombic o-Bi₅O₇I undergoes a total reconstruction process by its phase transformation into tetragonal (BiO)₂CO₃ (BOC-o) to form a well-aligned nanosheet array with maximally exposing CO₃ ²⁻ moiety at the edge side. The post-reconstruction BOC-o catalyst achieved 100 % Faradaic efficiency at −0.86 V vs. RHE for CO₂-to-formate conversion. However, another conservative reconstruction of tetragonal t-BiOI into tetragonal (BiO)₂CO₃ (BOC-t) exposed majorly a less reactive [BiO]⁺ layer. At low overpotential regions, the catalytic cycle of BOC-o begins with the initial conversion of the CO₃ ²⁻ moiety into formate at the [−OBi−(CO₃)−BiO−] site, but at high overpotential regions, the [BiO]⁺ layer undergoes reduction to metallic Bi and multi-catalytic species proceed with CO₂ reduction. Otherwise, the deactivation of Bi⁺ site by an organic molecule switched on another catalysis of proton reduction, preventing CO₂ reduction.

Integration of Cobalt Phthalocyanine, Acetylene Black and Cu2O Nanocubes for Efficient Electroreduction of CO2 to C2H4

Posted on 10 October 2023 by

A tandem catalyst, Cu₂O NCs-C-Copc, consisting of acetylene black, cobalt phthalocyanine (Copc) and Cu₂O nanocubes was developed for efficient converting of CO₂ to C₂H₄. We propose the Cu₂O NCs-C-Copc mechanism suppressing side reactions and simultaneously enriching CO. Here, we report faradaic efficiencies of C₂H₄ formation of up to 58.42 % at −1.1 V vs. RHE in 0.1 M KHCO₃ and 70.31 % at −0.76 V vs. RHE in 1.0 M KOH.

Abstract

Suppressing side reactions and simultaneously enriching key intermediates during CO₂ reduction reaction (CO₂RR) has been a challenge. Here, we propose a tandem catalyst (Cu₂O NCs-C-Copc) consisting of acetylene black, cobalt phthalocyanine (Copc) and cuprous oxide nanocubes (Cu₂O NCs) for efficient CO₂-to-ethylene conversion. Density-functional theory (DFT) calculation combined with experimental verification demonstrated that Copc can provide abundant CO to nearby copper sites while acetylene black successfully reduces the formation energies of key intermediates, leading to enhanced C₂H₄ selectivity. X-ray photoelectron spectroscopy (XPS) and potentiostatic tests indicated that the catalytic stability of Cu₂O NCs-C-Copc was significantly enhanced compared with Cu₂O NCs. Finally, the industrial application prospect of the catalyst was evaluated using gas diffusion electrolyzers. The of Cu₂O NCs-C-Copc can reach to 58.4 % at −1.1 V vs. RHE in 0.1 M KHCO₃ and 70.3 % at −0.76 V vs. RHE in 1.0 M KOH. This study sheds new light on the design and development of highly efficient CO₂RR tandem catalytic systems.