Lower Adsorption Energy Research Articles

Modulating the Local Coordination Environment of M‐Nx Single‐Atom Site for Enhanced Electrocatalytic Oxygen Reduction

AbstractEfficient, durable, and economical oxygen reduction catalysts are key for practical applications such as fuel cells and metal–air batteries. Single atom catalysts (SACs) have attracted sustained and widespread attention owing to their unique electronic properties and exceptional atomic utilization, positioning them as promising electrocatalysts in energy conversion and storage. However, the symmetric charge distribution of the metal site in the symmetric M‐N4 configuration of SACs is not conducive to electron transfer and transport in electrocatalytic reactions, resulting in a low adsorption energy for oxygen reduction reaction (ORR) related species (*OH, *O, and *OOH), which severely limits the intrinsic activity of the electrocatalysts. To overcome this limitation and improve the activity and durability, heteroatom doping can effectively modulate the local coordination environment (LCE) of the metal atom, including the coordinating atoms, coordination shells and coordination number. These modifications have significantly improved the performance of carbon supported SACs with M‐N4 configuration in the ORR. Based on this, a thorough summary of the major progress made in recent years in adjusting the LCE of SACs through doping with heteroatoms is provided and a perspective on the future development is offered here.

MoS[formula omitted] containing (Si, Se, P+Cl) structure doping and (Au and Ag) surface decorating as a sensor of Methanethiol biomarker: A first-principles study

MoS2 monolayer is a highly promising material for gas and biosensors due to its exceptional physical and chemical properties. Recent research suggests that modified MoS2 monolayers demonstrate improved properties compared to unmodified ones. In this study, we employed density functional theory to investigate MoS2 doped and decorated with transition metallic atoms such as Ag and Au, as well as non-metallic atoms like Se, Si, P, and Cl, for the detection of the Methanethiol biomarker. In this regard, the adsorption energy, charge transfer, adsorption distance, I-V, TDOS, PDOS, and sensitivity are calculated for each structure. The results reveal that the adsorption energy and charge transfer of the Methanethiol biomarker on MoS2 modified with Ag, Au, and Si atoms are higher than that of unmodified MoS2. The most significant changes in I-V curves and chemical adsorption occurr in these structures. The highest sensitivity is achieved when the MoS2 monolayer is decorated with Ag atoms, Au decorated, and doped with two Si atoms, respectively. Also, doping with Se, P, and Cl atoms results in the lowest adsorption energy, charge transfer, and sensitivity. This study provides valuable insights into the potential applications of both unmodified and modified MoS2 as Methanethiol biomarker sensor materials.

Research on N, Ne, and P adsorption on boron-germanene nanoribbons for nano sensor applications

The study investigated the adsorption of N, P, and Ne atoms on boron-germanene nanoribbons (BGeNRs) using density functional theory (DFT) and the Vienna Ab initio Simulation Package (VASP). Results indicated that both the pristine and adsorbed configurations exhibited metallic behavior. While the pristine and Ne-adsorbed configurations were nonmagnetic, the N- and P-adsorbed configurations displayed magnetic moments of 1.81 μB and 1.21 μB, respectively. The N-adsorbed configuration had the lowest adsorption energy, whereas the Ne-adsorbed configuration exhibited a positive adsorption energy. Multi-orbital hybridization analysis revealed that hybridization processes predominantly occurred in the conduction band at energy levels corresponding to the σ bond. Charge density difference analysis showed significant charge transfer between the substrate and the adsorbed elements. Additionally, optical properties, including the real and imaginary parts of the dielectric function, absorption coefficient, and electron-hole density, were systematically examined to highlight the variations. The findings underscore the potential application of BGeNR materials in nanosensors.

A small amount of sodium difluoro(oxalate)borate additive induces anion-derived interphases for sodium-ion batteries

In sodium-ion batteries, the properties of the electrode-electrolyte interphases (EEIs) layer formed on the electrode surface, dominate the Na+ de-solvation process and Na+ (de)intercalation behavior, thereby influencing the battery performance. Currently, both high-concentration electrolytes and localized high-concentration electrolytes facilitate the formation of anion-derived and inorganic-rich interfacial chemistry, leading to excellent electrochemical performance. However, the expensive lithium salt and/or fluorinated diluent imposes a major concern. Herein, a small amount additive of 0.5 wt% sodium difluoro(oxalate)borate (NaDFOB) with the electron-rich property is introduced into 1 mol L–1 NaClO4/propylene carbonate electrolyte to construct a robust inorganic-rich EEIs via an anion preferential adsorption-decomposition mechanism. Theoretical calculations and experimental results reveal that the DFOB– anion has a lower adsorption energy than the other components, which will be preferentially adsorbed in the inner Helmholtz plane (IHP) with the closer proximity to two electrode surfaces and thus being firstly decomposed to form inorganic-rich interphases, thereby effectively suppressing side reactions. Consequently, both Na-ion half-cells and full-cells using this electrolyte deliver excellent cycling performance. This strategy that regulates the interphase chemistry on the electrode surface through an anion preferential adsorption-decomposition strategy, provides a promising avenue for developing long-term cycling sodium-ion batteries.

Tailoring the Charge Transfer‐Driven Oxidation in van der Waals Ferroelectric NbOI2 Through Hetero‐Interface Engineering

Abstract2D transition metal halide oxides (TMHOs) have attracted much interest due to their intriguing ferroelectrics and excellent nonlinear optics, however, their susceptibility to oxidation makes their basic research and practical application a challenge. Therefore, it is crucial to understand the oxidation mechanism and explore effective strategies for protection. Here, taking van der Waals (vdWs) ferroelectric NbOI2 as an example, oxidation mechanisms and tuning the oxidation behaviors of NbOI2 and its heterostructures by a variety of in situ experiments and first‐principles calculations are discovered. The ambient‐pressure X‐ray photoelectron spectra reveal a self‐limiting oxidation in isolated NbOI2, driven by spontaneously formed iodine vacancies that react with oxygen molecules due to their lower formation and adsorption energies. For the heterostructures with a lower Fermi level (such as WSe2) than transition state VI@NbOI2 (NbOI2 rich in I‐vacancies), the charge transfer from NbOI2 to WSe2 drives the continuous and complete oxidation of NbOI2 flakes. Moreover, the heterostructures with a higher Fermi level (such as graphene) than VI@NbOI2 can weaken the oxidation of NbOI2. By linking the energy band structures to oxidation behavior, the work offers a new oxidation mechanism of 2D air‐sensitive materials and a crucial strategy for improving their chemical stability.

Investigating the impact of acetylenic linkage in C20 fullerene: Utilization in optoelectronic devices and as anode material

This study delves into the diverse characteristics of C80 fulleryne, derived from the incorporation of acetylenic linkages into each chain of the smallest fullerene, C20. Utilizing advanced theoretical computations, we confirm the stability of C80 fulleryne. Notably, its possession of a finite energy gap (0.743 eV) categorizes it as a semiconductor. Further enlightenment into its structural stability, bonding and reactivity stems from an exploration of different energy components, topological descriptors of electron density and chemical reactivity parameters. C80 fulleryne can act as radical scavenger owing to its higher electron affinity (5.5 eV). Spectral analysis revealed the C80 fulleryne’s absorption within the near-infrared region and its intriguing optical transparency with negligible loss in specific regions of the electromagnetic spectrum. Additionally, our investigation scrutinized the viability of C80 fulleryne as an anode material in Lithium-ion batteries. The presence of low adsorption energy (−1.693 eV) and significant amount of Bader charge transfer (0.917 e) between Li-ion and C atoms of C80 fulleryne confirms that Li-ion gets chemisorbed on the C80 fulleryne. Remarkably, this cage acts as a storehouse to host 12 Li ions, precisely one for each of its constituent pentagons within the C80 fulleryne structure, bearing a theoretical capacitance of 335 mAhg−1.

In Situ Unraveling Surface Reconstruction of Ni‐CoP Nanowire for Excellent Alkaline Water Electrolysis

The surface reconstruction behavior of transition metal phosphides precursors is considered as an important method to prepare efficient oxygen evolution catalysts, but there are still significant challenges in guiding catalyst design at the atomic scale. Here, the CoP nanowire with excellent water splitting performance and stability is used as a catalytic model to study the reconstruction process. Obvious double redox signals and valence evolution behavior of the Co site are observed, corresponding to Co2+/Co3+ and Co3+/Co4+ caused by auto‐oxidation process. Importantly, the in situ Raman spectrum exhibits the vibration signal of Co–OH in the non‐Faradaic potential interval for oxygen evolution reaction, which is considered the initial step in reconstruction process. Density functional theory and ab initio molecular dynamics are used to elucidate this process at the atomic scale: First, OH− exhibits a lower adsorption energy barrier and proton desorption energy barrier at the configuration surface, which proposes the formation of a single oxygen (–O) group. Under a higher –O group coverage, the Co–P bond is destroyed along with the POx groups. Subsequently, lower P vacancy formation energy confirm that the Ni‐CoP configuration can fast transform into a highly active phase. Based on the optimized reconstruction behavior and rate‐limiting barrier, the Ni‐CoP nanowire exhibit an excellent overpotential of 1.59 V at 10 mA cm−2 for overall water splitting, which demonstrates low degradation (2.62%) during the 100 mA cm−2 for 100 h. This work provide systematic insights into the atomic‐level reconstruction mechanism of transition metal phosphides, which benefit further design of water splitting catalysts.

Enhanced corrosion resistance of NbTaMoW medium entropy alloy coatings in simulated PEMFC environments: Experimental and computational insights

An anti-corrosive and conductive NbTaMoW medium entropy alloy (MEA) coating was deposited on 304 stainless steel using a dual-cathode glow discharge technology. This MEA coating exhibits a single body-centered cubic phase with about 10 nm grains, and forms a passivation film with significantly enhanced corrosion resistance at any given HF concentration. The lower adsorption energy of Nb atoms for oxygen atoms leads to the enrichment of Nb oxides in the passivation film, which is beneficial for hindering the rapid diffusion of F− ions. These findings underscore the potential of NbTaMoW MEA coatings to improve the durability and efficiency of PEMFCs.

Effective synthesis and characterization of citric acid cross-linking of modified ferrous metal-organic framework and chitosan nanocomposite sponge for Th(IV) elimination: Adsorption isotherms, kinetic analysis, and optimization by Box-Behnken design

This research presents a novel nanocomposite of ferrous metal-organic framework (Fe(II)-MOF) that has been encapsulated with chitosan matrix, leading to the development of a new adsorbent referred to as NH2-Fe(II)-MOF@CSC composite sponge. This composite sponge has shown effectiveness in removing radioactive thorium (IV) contamination from water sources. The adsorbent underwent characterization using techniques including FTIR, PXRD, BET analysis, and SEM. The adsorbent has a high surface area of 1360.8 m2/g. The most effective conditions for adsorbing Th(IV) were found to be a pH of 5, using 0.02 g of adsorbent dose per 25 mL, and maintaining a contact time of 100 min. The composite sponge demonstrated an impressive maximum adsorption capacity of 618.8 mg/g for Th(IV). The adsorption process was fitted to Langmuir isothermally and kinetically fitted to pseudo-second-order. Nonetheless, the relatively low adsorption energy of 6.22 kJ/mol suggests that the main adsorption mechanism is physisorption, which is marked by weaker van der Waals forces. This discovery could have implications for the material's potential for easy regeneration. In the analysis of the influence of temperature on the adsorption of Th(IV), it was discovered that the adsorption process is endothermic because the positive ΔHo value was 24.48 kJ.mol−1. Furthermore, a positive ΔSo value of 87.46 J.mol−1 K−1 suggests the existence of disorder at the solid-solution interface. Conversely, a temperature rise resulted in a higher negatively charged ΔGo, indicating that the adsorption process is spontaneous. The research also examined the mechanism of interaction, such as π-π interaction, hydrogen bonding, pore filling, and electrostatic interaction. It was noted that the adsorbent can be efficiently used for a maximum of six cycles, demonstrating its economic viability. The adsorption outcomes were optimized using the Box Behnken design (BBD).

The relationship between the high-frequency performance of supercapacitors and the type of doped nitrogen in the carbon electrode

Nitrogen doping has been widely used to improve the performance of carbon electrodes in supercapacitors, particularly in terms of their high-frequency response. However, the charge storage and electrolyte ion response mechanisms of different nitrogen dopants at high frequencies are still unclear. In this study, melamine foam carbons with different configurations of surface-doped N were formed by gradient carbonization, and the effects of the configurations on the high-frequency response behavior of the supercapacitors were analyzed. Using a combination of experiments and first-principle calculations, we found that pyrrolic N, characterized by a higher adsorption energy, increases the charge storage capacity of the electrode at high frequencies. On the other hand, graphitic N, with a lower adsorption energy, increases the speed of ion response. We propose the use of adsorption energy as a practical descriptor for electrode/electrolyte design in high-frequency applications, offering a more universal approach for improving the performance of N-doped carbon materials in supercapacitors

Designing water resistant high entropy oxide materials

The ubiquitous presence of moisture usually shows adverse effects on industrial catalysis. Herein, a concept of engineering entropy to design water-resistant oxide catalysts is proposed. The C3H6 oxidation by spinel ACr2O4 (A=Ni, Mg, Cu, Zn, Co) catalysts is selected as a model. Through DFT calculation, the adsorption energy of C3H6, the dissociation energy of molecular H2O on the oxide surface, and the formation energy of oxygen vacancy all suggest better performance induced by higher configurational entropy. Indeed, (Ni0.2Mg0.2Cu0.2Zn0.2Co0.2)Cr2O4 experimentally show excellent water resistance (>100 h) in C3H6 oxidation, while in sharp contrast binary oxides (e.g., NiCr2O4, CoCr2O4) are deactivated in 20 h. H2O-TPD, in-situ Raman, and in-situ FTIR all confirm the low H2O adsorption energy and strong hydrothermal stability of high entropy oxide, which is attributed to their lower Gibbs free energy. This work may inspire the rational design of water-resistant catalysts.

Differentiated adsorption of acetaminophen and diclofenac via alkyl chain-modified quaternized SBA-15: Insights from molecular simulation

The increasing presence of pharmaceuticals and personal care products (PPCPs) in aquatic systems pose significant environmental concerns. This study addresses this issue by synthesizing quaternized mesoporous SBA-15 (QSBA) with varied alkyl chain lengths of C1QSBA, C8QSBA, and C18QSBA. QSBA utilizes dual mechanisms: hydrophobic interactions via the alkyl chain and electrostatic attraction/ion exchange via the ammonium group. Diclofenac (DCF) and acetaminophen (ACT) were selected as target PPCPs due to their contrasting dissociation properties and hydrophobicity, which are the main characteristics of PPCPs. The adsorption of DCF and ACT revealed that longer alkyl chains enhanced the adsorption capacity of ACT through hydrophobic interactions, whereas dissociated DCF (DCF–) adsorption was superior owing to its high hydrophobicity (log Kow = 4.5) and electrostatic attraction. pH levels between 6 and 8 resulted in a high affinity for DCF–. Notably, among the three alkyl chains, only C18QSBA exhibited the most effective adsorption for DCF–. These PPCPs adsorption trends were confirmed through molecular simulations of adsorption under conditions in which competing ions coexisted. The molecular simulations show that while DCF– has lower adsorption energy than Cl−, OH−, and H3O+ ions in QSBA, enhancing its adsorption under various pH conditions. Conversely, ACT exhibits a higher adsorption energy, which reduces its adsorption efficiency. This suggests the potential application of QSBA with long alkyl chains in the treatment of highly hydrophobic and negatively charged PPCPs. Furthermore, this study emphasizes the importance of simulating adsorption under competing ion conditions.

Selective electrosorption of heavy metal ions from wastewater with S-doped hierarchical porous carbon derived from waste Camellia oleifera shell

Capacitive deionization (CDI) has garnered significant attention in desalination and the removal of heavy metal ions. The quest for cost-effective and high-performance electrode materials is crucial to advance CDI applications. Herein, we report a sulfur-doped hierarchical porous carbon (SPC) derived from waste camellia oleifera shells via a sustainable hydrothermal carbonization process followed by KOH/ammonium salt activation. The optimized SPC-0.2 exhibits exceptional characteristics, featuring a high specific surface area of 1875 m2 g−1 and substantial sulfur doping at 8.65 %, leading to enhanced specific capacitance (161.3 F g−1) in a 1 M NaCl solution. Under optimal operating conditions (1.2 V, 10 mL min−1, 500 mg L−1 NaCl), the SPC-0.2 electrode achieves a notable desalination capacity of 26.64 mg g−1. In particular, the electrode can selectively remove >99 % of Cr3+ and Cu2+ ions (each 10 mg L−1) in a 100 mg L−1 NaCl solution. This high selectivity is attributed to the formation of sulfides via low adsorption energies between the doped sulfur atoms and the targeted heavy metal ions. Furthermore, the SPC-0.2 electrode demonstrates robust reusability and high efficiency in the actual water body. Collectively, our findings underscore the significant potential of the synthesized SPC as an electrode material for CDI, particularly in the selective capacitive removal of heavy metal ions from wastewater. This work not only contributes to the circular economy by using waste biomass, but also offers a viable solution for environmental remediation.

Assessment of Warionia saharea Essential Oil as a Green Corrosion Inhibitor for Mild Steel in HCl: Experimental and Computational Studies

The objective of this research work is the study of the inhibitory effect of Warionia saharea essential oil (WSEO) on the corrosion of mild steel (MS) in molar HCl solution, employing both experimental and theoretical methods. This inhibitory effect (IE) has been evaluated by using a combination of weight loss measurements (LW) and various electrochemical methods, such as open circuit potential (OCP), potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) experiments. The LW results indicated that IE increased with inhibitor concentration, reaching 83.34% at 3.00 g/L. The PDP analysis suggested that WSEO functions as a mixed inhibitor, while in the EIS results the Rct values increased with inhibitor concentration to reach 165.8 Ω cm2 at 2.00 g/L, suggesting a defensive film formation by WSEO molecules over the metallic surface. The thermodynamic study demonstrated that the WSEO molecules adsorption on the MS surface followed a Langmuir isotherm, involving mixed physical and chemical (physicochemical) adsorption on the MS surface. Theoretical methods, including density functional theory (DFT) and molecular dynamics (MD) simulations, were employed to elucidate the inhibition mechanisms of the three main components of WSEO. The quantum chemical analysis, using density functional theory (DFT) and molecular dynamics (MD) simulations, showed a low ΔEgap value of 6.30 eV and a low adsorption energy (Eads) value on an Fe (110) substrate of −258 Kcal/mol for (E)-Nerolidol, indicating the significant contribution of this molecule to the overall corrosion inhibition effect of WSEO. The scanning electron microscope (SEM) analysis verified the presence of a protective film formed by the inhibitor on the MS surface. This study highlights the potential of WSEO as a sustainable and green corrosion inhibitor in acidic environments.

Integration of vanadium diphosphide with 2D cobalt phosphide architected as an extensible redox active positrode for alkaline supercapacitor

Metal phosphides in the form of rationally constructed two-dimensional (2D) nanosheets hold significant promise as versatile materials for energy storage applications. This study introduces a novel hybrid supercapacitor electrode, composed of a binder-free vanadium phosphide integrated cobalt phosphide (VP@CP) on a nickel foam substrate. The fabrication process involves the hydrothermal growth of Co2(OH)2BDC (BDC- 1,4-benzenedicarboxylate) nanosheets on a Ni-foam substrate (CMF-Ni), followed by the deposition of VO2 on CMF nanosheets (VO@CMF-Ni) using chronoamperometry and phosphorization of the VO@CMF-Ni to yield VP@CP-Ni nanosheets. Particularly, the density functional theory (DFT) results show that the VP2 integrated Co2P sample provides metallic behavior and low adsorption energy of OH− ions, resulting in improved electrochemical redox process. These bimetallic phosphides exhibit outstanding properties, including enhanced pathways for rapid ion transport and storage, increased electronic conductivity, and expanded electroactive regions facilitating the faradaic charge storage process. Due to the presence of vanadium and cobalt coupled sites, the fabricated VP@CP-Ni electrode was able to attain a maximum areal capacity (CAR) of 971 mA h cm−2 at 6 mA cm−2. Additionally, the fabricated hybrid device (HDC) exhibits an impressive specific energy (SE) of 30.9 Wh kg−1 at a specific power (SP) of 1344 W kg−1, and excellent cyclic durability. These remarkable results stimulate the exploration of such possible 2D VP@CP-Ni nanosheets with promising charge storage electrode capabilities to develop a future era of energy storage devices.

Low oxygen adsorption energy barrier architectures to facilitate microenvironmental photocatalytic disinfection in Wei River

Photocatalytic disinfection is an eco-friendly strategy that uses solar energy to purify bacteria-contaminated water. However, improvements in photocatalysts tend to focus on thermodynamics while neglecting kinetic interactions that involve oxygen. Here, we propose the MOF-on-MOF heterojunction NR-HKUST-1@Cu/ZIF-8 (NH@CZ) for kinetic photocatalytic disinfection; the heterojunction reduced bacterial load by nearly 8-log within 20 min. The NH@CZ structure exhibits a high specific surface area with Cu2O8 and CuN4 sites that provide substantial oxygen storage capacity and binding sites. In vitro experiments demonstrated the effective delivery of oxygen to photocatalytic reactions via NH@CZ, leading to enhanced superoxide radical (·O2-) generation. Experimental analysis and theoretical calculations confirm that the formation of heterojunctions in NH@CZ provides an efficient pathway for oxygen reduction by reducing the energy barrier associated with oxygen adsorption. Mechanistic studies show that reactive oxygen species (ROS) disrupt bacterial cell membranes, resulting in the release of cellular contents (e.g., potassium ions and macromolecular proteins) and subsequent cell death. Furthermore, the oxygen-carrying NH@CZ killed all microorganisms in Wei River water samples within 45 min. The MOF-on-MOF heterojunction offers a promising pathway to enhance ROS generation and provides valuable insights into advances in water disinfection technology.

Improved electrochemical performance of Ag-modified Bi0.7Sr0.3FeO3 cathodes by electroless plating for intermediate-temperature solid oxide fuel cells

The Bi0.7Sr0.3FeO3-δ (BSFO)-Ag composite cathode is prepared by modifying BSFO with in-situ chemical plating of Ag. The plated Ag effectively reduces the polarization resistance (Rp) of BSFO. At the Ag loading of 20 wt.%, the optimized Rp of BSFO at 650oC in air condition is 0.35 Ω cm2, which is only 18.6% of that of BSFO cathode (1.88 Ω cm2). The electrochemical performance improvement is primarily attributed to the low oxygen adsorption energy (Eads) domain at the interfaces of BSFO-Ag, as indicated by the first-principles calculations (Eads, -0.81eV). Thus, the addition of Ag changes the cathodic reaction rate control step from the molecular oxygen on the cathode surface adsorption and diffusion to charge transfer on the cathode. The maximum power density (Pmax) of the prepared single cell at 650oC is 450.98 mW cm-2 using H2 (∼3 vol.% H2O) as fuels. The open-circuit voltage (OCV) does not decay significantly (around 0.66 V) after 50 h at the current density of 400 mA cm-2, showing good long-term stability.

Superlight Ambient Temperature Reversible Hydrogen Storage Media Based on Alkali and Alkali Earth Metal-Functionalized 2D Square-Octagon BCN Monolayer.

Energy has always been the engine of human beings; however, because of the environmental pollution caused by traditional fossil fuels, the development of more sustainable energy resources is urgently needed. The hydrogen storage medium is essential for its realization. Here, we introduce a hydrogen storage material, a two-dimensional (2D) square-octagon BCN (SO-BCN) monolayer, composed of lightweight elements (B, C, and N) and strategically functionalized with alkali and alkali earth metal atoms (Li, Na, Mg, and K). Notably, Li@SO-BCN and Mg@SO-BCN exhibit exceptional reversible hydrogen storage capabilities, surpassing the DOE standard of 5.5 wt %, with gravimetric capacities of 7.129 wt % and an impressive value of 11.656 wt %, alongside low adsorption energies of -0.21 eV/H2 and -0.268 eV/H2 at room temperature, respectively. Our investigation, which combines analysis of the atomic structure, electronic structure, and hydrogen process, reveals distinct mechanisms at play: Li activates the substrate, creating additional adsorption sites on the SO-BCN monolayer. Compared with Li, the functionalization of Mg atoms not only activates SO-BCN via charge transfer but also allows Mg2+ to act as a potent attractor for H2 molecule adsorption. This work provides both promising candidates for future hydrogen storage media based on 2D monolayers and a design paradigm for next-generation hydrogen storage materials, emphasizing the synergy of electron-donating species, substrate activation, and hierarchical porous structures.

PVP-assisted synthesis of NiSnO3 firmly anchored on graphene as a high-performance lithium battery: A combination of theoretical and experimental study.

Tiny NiSnO3 nanoparticles with the assistance of polyvinylpyrrolidone (PVP) are prepared to uniformly and stably "bond" on the surface of graphene to form a stable NiSnO3/RGO-PVP structure. At the same time, the excellent performance of lithium-ion batteries (LIBs) with the use of NiSnO3/RGO-PVP structure is verified through a dual combination of experiment and theory. The resulting NiSnO3/RGO-PVP structure enhanced the performance of LIBs with high cycling stability and better rate capability; even after undergoing rate performance tests at different high current densities, the NiSnO3/RGO-PVP electrode can still reach a capacity of 624 mA h g-1 at 200 mA g-1 after 400 cycles. The superior electrochemical performance of NiSnO3/RGO-PVP nanocomposites can be attributed to the synergistic effects between tiny NiSnO3 nanoparticles synthesized with the assistance of PVP and RGO, which can be verified through first-principles calculations based on DFT. The charge transfer between NiSnO3 and RGO through an electron density difference indicates a strong interaction between the two. Meanwhile, the low adsorption energies (-3.914, -0.77, and -0.65eV), low diffusion barriers (0.025, 0.49, and 0.141eV), and high diffusion coefficients (1.79 × 10-3, 5.38 × 10-11, and 2.97 × 10-5cm2s-1) of lithium ions at three different positions indicate the excellent rate performance of the NiSnO3/RGO-PVP heterostructure, which is consistent with experimental results. This work analyzes the excellent electrochemical performance of NiSnO3/RGO-PVP from the experimental results and supports the reliability of the experimental results through theoretical calculations.

Oxygen vacancy–rich K-Mn3O4@CeO2 catalyst for efficient oxidation degradation of formaldehyde at near room temperature

Synthesis of catalysts with high catalytic degradation activity for formaldehyde (HCHO) at room temperature is highly desirable for indoor air quality control. Herein, a novel K-Mn3O4@CeO2 catalyst with excellent catalytic oxidation activity toward HCHO at near room temperature was reported. In particular, the K addition in K-Mn3O4@CeO2 considerably enhanced the oxidation activity, and importantly, 99.3 % conversion of 10 mL of a 40 mg/L HCHO solution at 30 °C for 14 h was achieved, with simultaneous strong cycling stability. Moreover, the addition of K species considerably influenced the chemical valence state of Mn from +4 (ε-MnO2) to +8/3 (Mn3O4) on the surface of CeO2, which obviously changed the tunnel structure and the number of oxygen vacancies. One part of K species is uniformly dispersed on K-Mn3O4@CeO2, and the other part exists in the tunnel structure of Mn3O4@CeO2, which is mainly used to balance the negative charge of the tunnel and prevent collapse of the structure, providing enough active sites for the catalytic oxidation of HCHO. We observed a phase transition from tunneled KMnO2 to Mn3O4 to tunneled MnO2 with the decreasing K+ content, in which K-Mn3O4@CeO2 exhibited higher HCHO oxidation activity. In addition, K-Mn3O4@CeO2 exhibited lower oxygen vacancy formation and HCHO adsorption energies in aqueous solution based on density functional theory calculations. This is because the K species provide more active oxygen species and richer oxygen vacancies on the surface of K-Mn3O4@CeO2, promote the mobility of lattice oxygen and the room-temperature reduction properties of oxygen species, and enhance the ability of the catalyst to replenish the consumed oxygen species. Finally, a possible HCHO catalytic oxidation pathway on the surface of K-Mn3O4@CeO2 catalyst is proposed.