Janus MXene nanosheets with a strain-induced reversible magnetic state transition for storing information without electricity.

The application of strain induces a transition in the ground-state magnetic configuration of Janus TiVC MXene from A-AFM to FM. A new system and method of solid-state disk information storage without electricity is developed based on the as-discovered reversible magnetic state transition in TiVC, which can achieve efficient storage of information in extremely harsh conditions.

Engineering dual-crystal configurations in perovskite oxides boosts electrocatalysis of lithium-oxygen batteries.

Sculpting crystal configurations can vastly affect the charge and orbital states of electrocatalysts, fundamentally determining the catalytic activity of lithium-oxygen (Li-O2) batteries. However, the crucial role of crystal configurations in determining the electronic states has usually been neglected and needs to be further examined. Herein, we introduce orthorhombic and trigonal system into 0.5La0.6Sr0.4MnO3-0.5LaMn0.6Co0.4O3 (LSMCO) by selectively incorporating Sr and Co cations into the LaMnO3 framework during the sol-gel process, which is used to explore the relationship among crystal structure, electronic states and catalytic performance. Based on both experimental and theoretical calculations, the dual-crystal configurations induce strong lattice distortion, which promotes MnO6 octahedra vibration and shortened MnO bonds. Furthermore, the suppressed Jahn-Teller distortion weakens the orbital arrangement and accelerates the charge delocalization, leading to the conversion of Mn3+ to Mn4+ and optimized electronic states. Ultimately, this resulted in optimized Mn 3d and O 2p orbital hybridization and activated lattice oxygen function, leading to a significant improvement in electrocatalytic activity. The LSMCO catalyzed Li-O2 battery achieves enhanced discharge capacity of 14498.7 mAh/g and cycling stability of 258 cycles. This work highlights the significance of inner structure and presents a feasible strategy for engineering crystal configurations to boost electrocatalysis of Li-O2 batteries.

Scalable fabrication of ultra-fine lithiophilic nanoparticles encapsulated in soft buffered hosts for long-life anode-free Li2S-based cells.

Minimizing the amount of metallic lithium (Li) to zero excess to achieve an anode-free configuration can help achieve safer, higher energy density, and more economical Li metal batteries. Nevertheless, removal of excess Li creates challenges for long-term cycling performance in Li metal batteries due to the lithiophobic copper foils as anodic current collectors. Here, we improve the long-term cycling performance of anode-free Li metal batteries by modifying the anode-free configuration. Specifically, a lithiophilic Au nanoparticle-anchored reduced graphene oxide (Au/rGO) film is used as an anodic modifier to reduce the Li nucleation overpotential and inhibit dendrite growth by forming a lithiophilic LixAu alloy and solid solution, which is convincingly evidenced by density functional theory calculations and experimentally. Meanwhile, the flexible rGO film can also act as a buffer layer to endure the volume expansion during repeated Li plating/stripping processes. In addition, the Au/rGO film promotes a homogeneous distribution of the electric field over the entire anodic surface, thus ensuring a uniform deposition of Li during the electrodeposition process, which is convincingly evidenced by finite element simulations. As expected, the Li||Au/rGO-Li half-cell shows a highly stable long-term cycling performance for at least 500 cycles at 0.5 mA cm-2 and 0.5 mA h cm-2. A Li2S-based anode-free full cell allows achieving a stable operation life of up to 200 cycles with a capacity retention of 63.3%. This work provides a simple and scalable fabrication method to achieve anode-free Li2S-based cells with high anodic interface stability and a long lifetime.

Nonflammable Polyfluorides-Anchored Quasi-Solid Electrolytes for Ultra-Safe Anode-Free Lithium Pouch Cells without Thermal Runaway.

The safe operation of rechargeable batteries is crucial because of numerous instances of fire and explosion mishaps. However, battery chemistry involving metallic lithium (Li) as the anode is prone to thermal runaway in flammable organic electrolytes under abusive conditions. Herein, an in situ encapsulation strategy is proposed to construct nonflammable quasi-solid electrolytes through the radical polymerization of a hexafluorobutyl acrylate (HFBA) monomer and a pentaerythritol tetraacrylate (PETEA) crosslinker. The quasi-solid system eliminates the inherent flammability of ether electrolytes with zero self-extinguishing time owing to the gas-phase radical capturing ability of HFBA. Additionally, the graphitized carbon layer generated during the decomposition of PETEA at high temperatures obstructs the heat and oxygen required for combustion. When coupled with Au-modified reduced graphene oxide anodic current collectors and lithium sulfide cathodes, the assembled anode-free Li-metal cell based on the quasi-solid electrolyte exhibits no signs of cell expansion or gas generation during cycling, and thermal runaway is eliminated under multiple mechanical, electrical, and thermal abuse scenarios and even rigorous strikes. This nonflammable quasi-solid configuration with gas- and condensed-phase flame-retardant mechanisms can drive a technological leap in anode-free Li-metal pouch cells and secure the practical applications necessary to power this society in a safe manner.

Manipulating hydrogen and coordination bond chemistry for reversible zinc metal anodes.

Aqueous zinc ion hybrid capacitors (ZHCs) are promising as electrochemical energy storage devices due to their safety and cost-effectiveness. However, the practical application of aqueous ZHCs is impeded by zinc dendrite growth and side reactions induced by H2O during long-term cycling. Herein, an organic small molecule, dimethyl sulfoxide (DMSO), is elaborately introduced into 2 M ZnSO4 electrolyte to simultaneously overcome these challenges. As convincingly evidenced by experimental and theoretical results, the DMSO reconstructs the Zn[(H2O)6]2+ structure and original hydrogen bond networks at the molecular level. By forming coordination bonds with Zn2+ and hydrogen bonds with H2O due to the stronger electron donating ability of oxygen in molecule, DMSO establishes a Zn2+ solvation shell structure that inhibits H2O decomposition and dendrite growth. As a proof of concept, the implementation of this hybrid electrolyte in a Zn||Cu asymmetrical cell results in a high Coulombic efficiency (CE) of over 99.8% for 568 cycles at a current density of 2 mA cm-2. Furthermore, the full cells using this hybrid electrolyte coupled with activated carbon (AC) cathode can operate for over 30,000 cycles. These results suggest that reconstructing the solvation structure and hydrogen bond networks guide the design of electrolytes for the development of high-performance aqueous ZHCs.

N, F-enriched inorganic/organic composite interphases to stabilize lithium metal anodes for long-life anode-free cells.

The practical application of lithium metal batteries is considered to be one of the most promising successors for lithium-ion batteries due to their ability to meet the high-energy storage demands of modern society. However, their application is still hindered by the unstable solid electrolyte interphase (SEI) and uncontrollable dendrite growth. In this study, we propose a robust composite SEI (C-SEI) that consists of a fluorine doped boron nitride (F-BN) inner layer and an organic polyvinyl alcohol (PVA) outer layer. Both theoretical calculations and experimental results demonstrate that the F-BN inner layer induces the formation of favourable components (LiF and Li3N) at the interface, promoting rapid ionic transport and inhibiting electrolyte decomposition. The PVA outer layer acts as a flexible buffer in the C-SEI, ensuring the structural integrity of the inorganic inner layer during lithium plating and stripping. The C-SEI modified lithium anode shows a dendrite-free performance and stable cycle over 1200 h, with an ultralow overpotential (15 mV) at 1 mA cm-2 in this study. This novel approach also enhances the stability of capacity retention rate by 62.3% after 100 cycles even in anode-free full cells (C-SEI@Cu||LFP). Our findings suggest a feasible strategy for addressing the instability inherent in SEI, showing great prospects for the practical application of lithium metal batteries.

First-Principles Study of the Ferromagnetic Properties of Cr2CO2 and Cr2NO2 MXenes.

Massive attention has been paid to MXenes due to their intriguing properties and potential diverse applications. Extensive studies using first-principles calculations on the electronic structures of MXenes Cr2CO2 and Cr2NO2 were performed in this paper. Based on the accurate Heyd-Scuseria-Ernzerhof (HSE) calculations, Cr2CO2 is clarified to be a ferromagnetic semiconductor; meanwhile, Cr2NO2 is a half-metallic material, which is consistent with previous results. In particular, by analyzing the contribution of the orbitals to the band structures and density of states, the basic mechanism of ferromagnetism was analyzed in detail. Our theoretical work might promote the spintronics study and application of Cr-contained MXenes.

Crystalline Carbon Nitride Supported Copper Single Atoms for Photocatalytic CO2 Reduction with Nearly 100% CO Selectivity.

Single metal atom photocatalysts have received widespread attention due to the rational use of metal resources and maximum atom utilization efficiency. In particular, N-rich amorphous g-C3N4 is always used as a support to anchor single metal atoms. However, the enhancement of photocatalytic activity of g-C3N4 by introducing a single atom is limited due to the bulk morphology and the excess defects of amorphous g-C3N4. Here, we report crystalline g-C3N4 nanorod supported copper single atoms by molten salts and the reflux method. The prepared single Cu atoms/crystalline g-C3N4 photocatalyst (Cu-CCN) shows highly selective and efficient photocatalytic reduction of CO2 under the absence of any cocatalyst or sacrificial agent. The introduction of single Cu atoms can be used as the CO2 adsorption site, thus increasing the adsorption capacity of Cu-CCN samples to CO2. Theoretical calculation results show that reducing CO2 to CH4 on Cu-CCN samples is an entropy-increasing process, whereas reducing CO2 to CO is an entropy-decreasing process. As a result, the Cu-CCN samples exhibited enhanced photocatalytic CO2 reduction with nearly 100% selective photocatalytic CO2 to CO conversion. The mechanism of photocatalytic CO2 reduction over Cu-CCN samples was proposed based on in situ Fourier transform infrared spectra, X-ray absorption spectroscopy, and density functional theory calculation. This work provides an in-depth understanding of the design of photocatalysts for enhancing active sites of the reactants.

Synergistic effects of heteroatom-decorated MXene catalysts for CO reduction reactions.

In this study, using the density functional theory calculations, we present a strategy to improve the activity and selectivity of electrocatalytic CO reduction reactions (CORRs) towards CH4 production occurring on single transition metal (TM) atoms embedded in a defective MXene Mo2-xTiC2Oy with one oxygen vacancy. Owing to the unique geometric and electronic structures, the exposed TM-Mo-Mo triangle can serve as an active site, and the surrounding oxygen atoms can break the scaling relationships between the CORR intermediates via the steric hindrance. The synergistic effects result in an excellent catalytic performance for CORRs. Based on the extensive investigation of series of candidates, W-decorated MXene was identified as the most promising CORR electrocatalyst, with a high selective activity towards the CH4 production and strong suppression of competing hydrogen evolution reactions (HERs). The adsorption free energy of *COH [ΔGads (*COH)] is proposed as a descriptor to establish a relationship with the catalytic activity. Our rational design principles and rapid screening methods may shed light on the development of other highly efficient CORR electrocatalysts, as well as the other electrochemical systems.

Mg-Doping improves the performance of Ru-based electrocatalysts for the acidic oxygen evolution reaction.

Magnesium doped ultra-fine RuO2 nanoparticles are prepared by a one-step annealing of Ru-exchanged Mg-MOF-74. Mg-RuO2 exhibits excellent oxygen evolution reaction performance with a low overpotential of 228 mV at 10 mA cm-2. The excellent performance is attributed to the altered electronic structure and the optimized surface atomic arrangement.

Highly Selective Electrochemical Reduction of CO2 to Alcohols on an FeP Nanoarray.

Electrochemical reduction of CO2 into various chemicals and fuels provides an attractive pathway for environmental and energy sustainability. It is now shown that a FeP nanoarray on Ti mesh (FeP NA/TM) acts as an efficient 3D catalyst electrode for the CO2 reduction reaction to convert CO2 into alcohols with high selectivity. In 0.5 m KHCO3 , such FeP NA/TM is capable of achieving a high Faradaic efficiency (FE CH 3 OH ) up to 80.2 %, with a total FE CH 3 OH + C 2 H 5 OH of 94.3 % at -0.20 V vs. reversible hydrogen electrode. Density functional theory calculations reveal that the FeP(211) surface significantly promotes the adsorption and reduction of CO2 toward CH3 OH owing to the synergistic effect of two adjacent Fe atoms, and the potential-determining step is the hydrogenation process of *CO.

Theoretical Investigation on the Single Transition-Metal Atom-Decorated Defective MoS2 for Electrocatalytic Ammonia Synthesis.

Using density functional theory calculations, we explored the potential of defective MoS2 sheets decorated with a series of single transition-metal (TM) atoms as electrocatalysts for the N2 reduction reaction (NRR). The computed reaction free-energy profiles reveal that the introduction of embedded single TM atoms significantly reduces the difficulty to break the N≡N triple bond and thus facilitates the activation of inert nitrogen. Onset potential close to -0.6 V could be achieved by anchoring various TMs, such as Sc, Ti, Cu, Hf, Pt, and Zr, and the formation of the second ammonia molecule limits the overall process. The Ti-decorated nanosheet possesses the lowest free-energy change of -0.63 eV for the potential determining step. To better predict the catalysis performance, we introduced a descriptor, φ, which is the product of the number of valence electron and electronegativity of the decorated TM. It shows a good linear relationship between the d-band center and binding energy of nitrogen, except for those metals with less than half-filled d-band. Although the metals in Group IIIB and IVB have strong adsorption interactions with N atoms, the Gibbs free-energy changes for desorption of the second ammonia are unexpectedly low. The selectivity of these systems toward nitrogen reduction reaction (NRR) is also significantly improved. Therefore, those defective MoS2 decorated with Sc, Ti, Zr, and Hf are suggested as promising electrocatalysts for NRR, for their both high efficiency and selectivity.

Ceria-reduced graphene oxide nanocomposite as an efficient electrocatalyst towards artificial N2 conversion to NH3 under ambient conditions.

For over a century, NH3 synthesis via the Haber-Bosch process has brought huge energy costs and high CO2 emission. The electrochemical N2 reduction reaction is an environmentally-benign alternative, which can be driven by renewable energy. In this work, CeO2 nanoparticle-reduced graphene oxide nanocomposites (CeO2-rGO) behave as an efficient non-noble-metal N2 reduction reaction electrocatalyst with excellent selectivity. In 0.1 M Na2SO4, CeO2-rGO achieves a high faradaic efficiency of 4.78% and a large NH3 yield of 16.98 µg h-1 mgcat.-1 at -0.7 V vs. reversible hydrogen electrode. The catalytic mechanism was explored using density functional theory calculations.

Electrocatalytic N2-to-NH3 conversion with high faradaic efficiency enabled using a Bi nanosheet array.

Electrocatalytic N2 reduction represents a promising alternative to the conventional Haber-Bosch process for ambient N2-to-NH3 fixation, but it is severely challenged by competitive hydrogen evolution, which limits the current efficiency for NH3 formation. In this work, a nanosheet array of metallic Bi, an environmentally benign elemental substance previously predicted theoretically to have low hydrogen-evolving activity, is proposed as a superior catalyst for N2 reduction electrocatalysis. Electrochemical tests show that the Bi nanosheet array on Cu foil as a stable 3D catalyst electrode achieves a high faradaic efficiency of 10.26% with an NH3 yield rate of 6.89 × 10-11 mol s-1 cm-2 at -0.50 V vs. the reversible hydrogen electrode in 0.1 M HCl, rivalling the performances of most reported noble-metal-free catalysts operating in acids. Density functional theory calculations suggest that Bi effectively activates the N[triple bond, length as m-dash]N bond and the alternating mechanism is energetically favourable.

Electrocatalytic Hydrogenation of N2 to NH3 by MnO: Experimental and Theoretical Investigations.

NH3 is a valuable chemical with a wide range of applications, but the conventional Haber-Bosch process for industrial-scale NH3 production is highly energy-intensive with serious greenhouse gas emission. Electrochemical reduction offers an environmentally benign and sustainable route to convert N2 to NH3 at ambient conditions, but its efficiency depends greatly on identifying earth-abundant catalysts with high activity for the N2 reduction reaction. Here, it is reported that MnO particles act as a highly active catalyst for electrocatalytic hydrogenation of N2 to NH3 with excellent selectivity. In 0.1 m Na2SO4, this catalyst achieves a high Faradaic efficiency up to 8.02% and a NH3 yield of 1.11 × 10-10 mol s-1 cm-2 at -0.39 V versus reversible hydrogen electrode, with great electrochemical and structural stability. On the basis of density functional theory calculations, MnO (200) surface has a smaller adsorption energy toward N than that of H with the *N2 → *N2H transformation being the potential-determining step in the nitrogen reduction reaction.

Cr2O3 Nanoparticle-Reduced Graphene Oxide Hybrid: A Highly Active Electrocatalyst for N2 Reduction at Ambient Conditions.

Electrochemical reduction is an eco-friendly alternative for energy-saving artificial N2 fixation. The development of this process requires efficient N2 reduction reaction (NRR) electrocatalysts to overcome the challenge with N2 activation. We show that a Cr2O3 nanoparticle-reduced graphene oxide hybrid (Cr2O3-rGO) is as an outstanding catalyst for electrochemical N2-to-NH3 conversion under ambient conditions. In 0.1 M HCl, Cr2O3-rGO achieves a high NH3 yield of 33.3 µg h-1 mg-1cat. at -0.7 V vs RHE and a high Faradaic efficiency of 7.33% at -0.6 V vs RHE, with excellent selectivity for NH3 synthesis and stability. Density functional theory calculations were executed to gain further insight into the mechanisms.

High-Performance N2-to-NH3 Conversion Electrocatalyzed by Mo2C Nanorod.

The synthesis of NH3 is mainly dominated by the traditional energy-consuming Haber-Bosch process with a mass of CO2 emission. Electrochemical conversion of N2 to NH3 emerges as a carbon-free process for the sustainable artificial N2 reduction reaction (NRR), but requires an efficient and stable electrocatalyst. Here, we report that the Mo2C nanorod serves as an excellent NRR electrocatalyst for artificial N2 fixation to NH3 with strong durability and acceptable selectivity under ambient conditions. Such a catalyst shows a high Faradaic efficiency of 8.13% and NH3 yield of 95.1 µg h-1 mg-1 cat at -0.3 V in 0.1 M HCl, surpassing the majority of reported electrochemical conversion NRR catalysts. Density functional theory calculation was carried out to gain further insight into the catalytic mechanism involved.

3-Fold-Periodic Size-Dependence in Electronic Properties of Monolayer-TMDC Nanotriangles.

Stable nanotriangles of monolayer transitional metal dichalcogenides (referred herein as MS2 mNTs) grown via ordinary deposition conditions, where M = Mo or W, exhibit a peculiar 3-fold periodic size-dependence in electronic and chemical properties. For " k" being the number of M atoms per edge, mNTs are (a) intrinsic-semiconducting when k = 3 i + 1, such as k = 7, 10, 13, 16; (b) metallic-like with no bandgap when k = 3 i; (c) n+ semiconducting when k = 3 i - 1. Besides changes in electronic properties, the catalytic properties for hydrogen evolution reaction also switch from active for k = 3 i and 3 i - 1 to inactive for k = 3 i + 1. The peculiar periodic size-dependence roots from the chemistry of edge-reconstruction and the consequential evolution of band structure. Further, such chemistry and thereby the size-dependence can be manipulated by adding or depleting the atomic concentration of sulfur atoms along the mNT edges.

Efficient Hydrogen Evolution Electrocatalysis at Alkaline pH by Interface Engineering of Ni2P-CeO2.

It is of significant importance to develop effective non-noble-metal catalysts for hydrogen evolution electrocatalysis under basic conditions. In this study, we demonstrate the facile construction of a Ni2P-CeO2 interface based on the central point that low-temperature phosphidation of the NiO-CeO2 precursor only converts NiO into Ni2P selectively. The resulting Ni2P-CeO2 nanosheet array on Ti mesh behaves as a durable catalyst for alkaline hydrogen evolution reaction (HER) electrocatalysis, and it can reach 20 mA cm-2 at an overpotential of 84 mV in 1.0 M KOH, outperforming all reported Ni phosphide HER catalysts. Density functional theory calculations reveal that the Ni2P-CeO2 interface can promote water dissociation and optimize hydrogen adsorption free energy.

Creating high quality Ca:TiO2-B (CaTi5O11) and TiO2-B epitaxial thin films by pulsed laser deposition.

We demonstrate, in great detail, a completely waterless synthesis route to produce highly crystalline epitaxial thin films of TiO2-B and its more stable variant CaTi5O11, using pulsed laser deposition (PLD).