2p States Research Articles

Atomic Gap-State Engineering of MoS2 for Alkaline Water and Seawater Splitting.

Transition-metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), have emerged as a generation of nonprecious catalysts for the hydrogen evolution reaction (HER), largely due to their theoretical hydrogen adsorption energy close to that of platinum. However, efforts to activate the basal planes of TMDs have primarily centered around strategies such as introducing numerous atomic vacancies, creating vacancy-heteroatom complexes, or applying significant strain, especially for acidic media. These approaches, while potentially effective, present substantial challenges in practical large-scale deployment. Here, we report a gap-state engineering strategy for the controlled activation of S atom in MoS2 basal planes through metal single-atom doping, effectively tackling both efficiency and stability challenges in alkaline water and seawater splitting. A versatile synthetic methodology allows for the fabrication of a series of single-metal atom-doped MoS2 materials (M1/MoS2), featuring widely tunable densities with each dopant replacing a Mo site. Among these (Mn1, Fe1, Co1, and Ni1), Co1/MoS2 demonstrates outstanding HER performance in both alkaline and seawater alkaline media, with overpotentials at a mere 159 and 164 mV at 100 mA cm-2, and Tafel slopes at 41 and 45 mV dec-1, respectively, which surpasses all reported TMD-based nonprecious materials and benchmark Pt/C catalysts in HER efficiency and stability during seawater splitting, which can be attributed to an optimal gap-state modulation associated with sulfur atoms. Experimental data correlating doping density and dopant identity with HER performance, in conjunction with theoretical calculations, also reveal a descriptor linked to near-Fermi gap state modulation, corroborated by the observed increase in unoccupied S 3p states.

Unraveling the C-C Coupling Mechanism on Dual-Atom Catalysts for CO2/CO Reduction Reaction: The Critical Role of CO Hydrogenation.

The electrochemical reduction reaction (RR) of CO to high value multicarbon products is highly desirable for carbon utilization. Dual transition metal atoms dispersed by N-doped graphene are able to be highly efficient catalysts for this process due to the synergy of the bimetallic sites for C-C coupling. In this work, we screened homonuclear dual-atom catalysts dispersed by N-doped graphene to investigate the potential in CO reduction to C2+ products by employing density functional theory calculations. We have demonstrated that the two adsorbed CO species on bimetallic sites cannot directly couple unless one of the CO molecules is hydrogenated. All the dual metal atom catalysts prefer a similar coupling mechanism, i.e., the asymmetric coupling of *CO on the bridged site and *CHO on the top site, while the Ni2 and Cu2 catalysts exhibit much better performance with moderate adsorption energies and low energy barriers. The enhanced activities are attributed to the decrease of the energy levels of *CO 2p states that weakens the metal-C bonding and thus facilitates the feasible C-C coupling with both low reaction energies and low barriers. These insights have revealed the significant role of the hydrogenation of CO species prior to the coupling step and may provide a theoretical perspective to understand the generation of C2+ products in the CO2/CORR.

Evolution from 3-D to 2-D of a confined hydrogen atom dipole dependent properties when compressed by two parallel planes

Abstract The confinement of an atom by two parallel planes produces changes in the spectra and dipole-dependent electronic properties when evolving from large – 3-D – to narrow – 2-D – inter-plane separation. In this work, the behavior of the dipole electronic properties of a hydrogen atom located half the distance between two impenetrable parallel planes is studied as a function of the inter-plane separation
using the energies and wave functions reported previously by the author [Physica Scripta 99, 065416 (2024)]. The evolution of the line intensities, transition rates, life times, polarizability, and the mean excitation energy are reported as a function of the inter-plane separation. We find that as the inter-plane separation is reduced, all the electronic properties are affected by the shifting of the electronic spectra towards the short wave-length region (EUV) with a boost of the photo-luminosity intensity, reduction of the static polarizability and life-time of the 2s and 2p states, increase of the mean excitation energy, and transition rates for characteristic plane separations. Our numerical results agree, in the limiting cases, to the analytical solutions for a free atom for large inter-plane separations and to those of a 2-D atom for small inter-plane separation, as well as to available experimental data.

Investigation of kaonic atom optical potential by the high precision data of kaonic 3He and 4He atoms

Abstract We investigate kaonic atom optical potentials of 3He and 4He phenomenologically based on the latest high precision data of the 2p states of the kaonic atoms in helium (J-PARC E62). We consider a simple phenomenological form for the optical potential proportional to the nuclear density distributions and clarify the meanings and implications of the data by determining the potential parameters by the latest data. We find two sets of potential parameters for each of K− − 3He and K− − 4He that reproduce the data. We then extract the potential parameters consistent with the data of 3He and 4He atoms simultaneously. We report the possible strong isospin dependence of the potential, and the different strength of the data of K− − 3He and K− − 4He in the restrictions on the potential parameters. We mention that the study of the 1s states of the kaonic helium atom is very interesting as a next step. Observing these states could provide valuable information on potential parameters and kaonic nuclear s states because of the mutual influence between the atomic and the nuclear states of kaon with the same orbital angular momentum.

State-Selective Double Photoionization of Atomic Carbon and Neon

Double photoionization (DPI) allows for a sensitive and direct probe of electron correlation, which governs the structure of all matter. For atoms, much of the work in theory and experiment that informs our fullest understanding of this process has been conducted on helium, and efforts continue to explore many-electron targets with the same level of detail to understand the angular distributions of the ejected electrons in full dimensionality. Expanding on previous results, we consider here the double photoionization of two 2p valence electrons of atomic carbon and neon and explore the possible continuum states that are connected by dipole selection rules to the coupling of the outgoing electrons in 3P, 1D, and 1S initial states of the target atoms. Carbon and neon share these possible symmetries for the coupling of their valence electrons. Results are presented for the energy-sharing single differential cross section (SDCS) and triple differential cross section (TDCS), further elucidating the impact of the initial state symmetry in determining the angular distributions that are impacted by the correlation that drives the DPI process.

Tailored pseudopotentials for magnesium surface core level shift calculations

In x-ray photoelectron spectroscopy (XPS), identifying the origin of peaks in the spectrum can be guided by theory calculations. With density functional theory (DFT), using pseudopotentials, one can obtain the difference in photoelectron energy for electrons originating from atoms of different environments, for example surface and bulk atoms, and thus model the surface core level shift (SCLS) energies. The focus in this work is to prepare for calculations of magnesium (Mg) 2p SCLSs in material systems where dispersion interactions play a role, primarily in Mg surface degradation and adsorption of molecules as relevant, for example, in degradable bioimplants. For SCLS DFT calculations in metallic surfaces, the state of the photoelectron must be treated as a core state. In the case of Mg, standard pseudopotentials treat the 2p state as a valence state, not a core state. We therefore need Mg pseudopotentials with the 2p electrons in the core, leaving only two electrons for the valence region (the 3s electron); Two-valence electron pseudopotentials are not common, because DFT calculations of Mg-containing materials usually are better or more easily described using 10 valence electrons. In this work, new two-electron Mg pseudopotentials are therefore created for use in dispersion-inclusive DFT calculations. To our knowledge, no such two-electron Mg pseudopotentials exist, proven to work well with the nonlocal, dispersion-inclusive, exchange-correlation functional vdW-DF-cx or similar functionals. We create a number of two-electron Mg pseudopotentials and their 2p-hole partners, and for four of the most promising we assess their performance in vdW-DF-cx. We provide results for Mg and MgO bulk phases and for the Mg(0001) surface energy, structure, and SCLS, and where possible we compare with results that we obtain by using conventional 10-electron Mg pseudopotentials, all-electron calculations, and with experiments. This work not only reports and tests the specific conditions for creating 2p Mg results, it will also, we believe, be of help in creating other similar pseudopotentials to aid the analysis of XPS spectra in other materials. Published by the American Physical Society 2024

Cementite with substitutional Nb atoms based on first-principles calculations

Abstract Cementite is the strengthening phase in pearlite, and its mechanical properties determine the strength of the pearlite. A crystal model of niobium-substituted Fe3C was constructed. The stability, charge density, and elastic constants of the model were calculated, and the effects of niobium (Nb) substitution on the properties of Fe3C were discussed. FeNb8d 2 C is the most stable Nb-substituted structure. The reaction energy of FeNb8d 2 C is −0.796 eV, with a magnetic moment of 0.07 μB/f.u. At the Fermi level, the DOS of FeNb8d 2 C is 4.24, displaying metallic properties. Nb substitution enhances the symmetry of the DOS in Fe3C. The covalent bonding in FeNb8d 2 C, predominantly consisting of σ and π bonds, is formed by the hybridization of Nb 3 d states and C 2p states. FeNb8d 2 C is mechanical stability. It exhibits the strongest resistance to linear compression along the [100] direction and the highest shear deformation resistance along the (010) plane. Nb substitution increases the toughness of Fe3C, enhances isotropy on the (010) plane, and improves the resistance to linear compression along the [010] direction.

Highly Durable Barium Iridates for Oxygen Evolution Electrocatalysis Via Atomic Ordering of Nb5+/Ta5+(d 0) and Suppression of Lattice Oxygen Participation

Proton exchange membrane water electrolyzers (PEMWEs) play a pivotal role in the journey towards a sustainable hydrogen society [1]. Despite offering remarkable current density and exceptional hydrogen purity (99.99%), the highly acidic nature of sulfonated fluoropolymer membranes hinders material selection for anode catalysts to facilitate the oxygen evolution reaction (OER) [2]. Therefore, iridium-based electrocatalysts are regarded as indispensable choices owing to their strong resistance to corrosion under acidic environments based on Pourbaix diagram [3]. However, despite their remarkable stability and performance in acid, two main unsolved issues remained in iridium-based electrocatalysts. The first is the scarcity of iridium, which hampers the widespread adoption of PEMWEs. Iridium accounts for 25 % of the total cost of membrane electrode assemblies (MEA), making the reduction of iridium content an urgent necessity. The other unsolved issue is the suppression lattice oxygen evolution reaction (LOER) [4]. While LOER offers an opportunity to overcome the theoretical OER overpotential, such lattice oxygen participation also induces oxygen gas evolution from [IrO6] crystals and consequently lattice collapse. Hence, there is a pressing need for alternative catalysts with lower iridium content but limited LOER to achieve comparable activity and stability to commercial IrO2.In this study, using hexagonal 9R-perovskite BaIrO3 as starting materials, we systematically demonstrate the d orbital contribution to structural durability according to lattice oxygen participation, especially d 0 states of Nb5+ and Ta5+. The choice of BaIrO3 as a reference catalyst was governed by its structural robustness from face-sharing connectivity between [IrO6] clusters, which is more difficult to disassemble compared to IrO2 with edge-, and corner-sharing configurations [5]. Two notable features were observed when transition-metals (Mn, Co, Ni, In, Nb, and Ta) were doped into BaIrO3; i) phase transformation occurs from 9R- to 6H- or 12R-type polymorphs and 2) dopants occupy specific sites in a very ordered manner (Figure 1a). We directly observed such ordering natures by atomic-column resolved scanning transmission electron microscopy (STEM). When Nb5+ and Ta5+ added, 12R-Ba4NbIr3O12 and Ba4TaIr3O12 were formed with Nb and Ta cations located in bridging sites between face-sharing [Ir3O12] trimers.Density functional theory (DFT) calculations were conducted to study the electronic structure of Ba4NbIr3O12 (Figure 1b). The electron configuration of Nb5+ consists of fully filled 4p 6 and empty 4d 0 states, thereby Nb 4d orbitals contribute to the upper electronic band above +2 eV. Consequently, in contrast to the large overlap between O 2p states (black arrow) with Ir 5d states in [IrO6], O 2p states (red arrow) of [NbO6] beneath the Fermi level are significantly suppressed. These findings indicate that [NbO6] serves as an OER inactive site and prevents structural disassembly by limiting lattice oxygen participation. We also carried out time-of-flight SIMS to quantitatively compare lattice oxygen contribution between pristine BaIrO3 and Ba4NbIr3O12 during OER using anodic cycling samples in 1 M HClO18 4. As depicted in Figure 1b, substantially lower amount of O18 was detected in Ba4NbIr3O12 than in BaIrO3, which directly demonstrated the significant suppression of LOER.The catalytic longevity of IrO2, BaIrO3, and Ba4NbIr3O12 was evaluated by cyclic voltammetry (CV) and chronoamperometry (CA) tests (see Figure 1c). The relative catalytic behavior was compared in terms of preserving OER activities by normalizing with initial current densities. Both CV and CA results provide straightforward evidence, validating that Ba4NbIr3O12 is prominent among the three catalysts. As a result, we have developed promising electrocatalysts with both low iridium content and higher durability, which stem from the synergism of chemical ordering of d0 cations to suppress lattice oxygen participation and robust face-sharing trimers in the structures. Our research proposes the proper management of chemical ordering in oxides offers a straightforward yet effective approach for developing electrocatalysts with significantly enhanced longevity.

Physicochemical properties of La0.5Ba0.5Co1-xFexO3-δ (0 ≤ x ≤ 1) as positrode for proton ceramic electrochemical cells

We report on essential properties of materials in the series La0.5Ba0.5Co1-xFexO3-δ as positrodes for proton ceramic electrochemical cells (PCECs). The unit cell and thermochemical expansion coefficient (TCEC) of these cubic perovskites decrease with iron content x, the TCEC of La0.5Ba0.5FeO3-δ going as low as 11·10-6 1/K. The materials behave as LaMO3 perovskites with small band gaps and Ba acting as acceptors compensated by electron holes and oxygen vacancies. The electrical properties are dominated by p-type conduction with high large polaron mobilities for the Co-rich compositions at low temperatures, shifting towards small polaron mobilities with increasing Fe content. X-ray absorption spectroscopy (XAS) shows that Co is in a high spin state and takes on the main part of the cation oxidation state changes, and that hole states are in orbitals overlapping with the O 2p states, confirming the large polaronic behaviour, while holes on Fe are more localised at the cation. Hydration is more pronounced in inert atmospheres, as hydration of oxygen vacancies is easier than hydrogenation and increases with Fe content, in line with the commonly accepted finding that delocalization of holes disfavours protonation. Fe-rich compositions benefit from lower TCEC and higher hydration and hence expected proton permeability, at the cost of lower electronic conductivity. The surfaces are hydrophobic irrespective of Fe content, suggesting weak chemisorption of the underlaying water layer, possibly giving relatively many available surface sites for oxygen adsorption, but limited surface proton conductance – both of importance to positrodes for operando PCECs.

Electrochemical Reactions of LiCoO2-Li3BO3 Composite Electrode Constructed on Li6.6La3Zr1.6Ta0.4O12 solid Electrolyte Sheet Studied By in Situ Hard X-Ray Photoelectron Spectroscopy (HAXPES)

LiCoO2 is one of the commercially used cathode materials in lithium-ion batteries due to its relatively high cycle performance and theoretical capacity density of 274 mAh g-1. However, the practical capacity density is limited to ~140 mAh g-1 under the operation below 4.2 V vs. Li+/Li because the high-voltage charging often results in rapid capacity fading.[ 1 ] The degradation mechanism under high-voltage charging has been studied from the structural and electronic aspects using various techniques, such as x-ray diffraction (XRD)[ 2 ] and x-ray photoelectron spectroscopy (XPS).[ 3 ] During the high-voltage charging up to 4.7 V, LiCoO2 transforms from the H3 phase to the H1-3 and then to the O1 phase.[ 1 ] While only the oxidation of Co3+ to Co4+ occurs as a result of the electron extraction from Co 3d (t2g) states during charging up to 4.2 V, the oxidation of O2- to O- also occurs as a result of the electron extraction from O 2p states due to the hybridization of t2g and O 2p orbitals.[ 3 ] These structural changes and oxygen redox are considered as an origin of rapid capacity fading under the high-voltage operation. Although understanding of the high-voltage degradation mechanism may lead to the development of high potential positive electrode materials, change of chemical and electronic structure of LiCoO2 under high-voltage operation yet to be fully clarified.In the present study, we developed a laboratory-based operando hard x-ray photoelectron spectroscopy (HAXPES) system equipped with a Cr-Kα source (5414.9 eV) and bias application apparatus, that enables us HAXPES measurements of all-solid-state cells during charge/discharge cycles, and applied it to investigate the electrochemical reactions of a LiCoO2-Li3BO3 composite electrode layer constructed on a Li6.6La3Zr1.6Ta0.4O12 solid electrolyte sheet.The galvanostatic charge/discharge potential profiles exhibited plateaus corresponding to the delithiation from the H1 and H3-LiCoO2 at around 3.9 and 4.6 V during the charging, respectively. In the subsequent discharging, the cell voltage rapidly dropped from 4.7 V to around 4.2 V without the plateau region at around 4.6 V. In addition to the absence of 4.6 V plateau, the capacity density of 3.9 V plateau in the discharging process was substantially smaller than that of the charging process, confirming the irreversibility caused by high-voltage operation. In the Co 2p3/2 region of the pristine cell, a main peak and a broad satellite peak characteristic to LiCoO2 were observed.[ 4 ] The main peak was deconvoluted into two peaks originated from Co3+ ions of the LiCoO2 and final state effect[ 4,5 ] at around 780 eV and 780.6 eV, respectively. After the charging up to 4.2 V, the main peak was asymmetrically broadened to a higher binding energy because of appearance of Co4+ peak at around 781 eV. After the subsequent discharging, the full width half maximum (FWHM) of Co4+ peak decreased while of Co3+ ions remained unchanged, confirming the reversible redox reaction of Co3+/4+ ions under the operation below 4.2 V. In the O 1s region of the pristine cell, two peaks corresponding to O2- in LiCoO2 lattice and Li2CO3 adsor After the charging up to 4.7 V, however, a new peak corresponding to peroxo-like oxygen dimer ((O2)n- , (n<2))[ 6 ] appeared simultaneously with the disappearance of lattice O2-, as well as the appearance of Co4+ peak as is the case of 4.2 V operation, suggesting the oxidation of lattice O2-. After the subsequent discharging, the FWHM of Co4+ peak and peak intensity of lattice O2- did not fully revert to those of pristine cell, suggesting the irreversible redox reaction to retain Co4+ and (O2)n- species. Further details on the spectral features LiCoO2-Li3BO3 composite electrode under high-voltage operation measured by operando HAXPES system will be discussed.

Validation of quantum espresso software in estimating the optical parameters of CaAlSiN3 crystal

This communication presents a theoretical analysis of certain optical properties of the CaAlSiN3 (CASN) crystal through first principles calculation. For the first time, this work validates the optical properties of the crystal performed using Quantum ESPRESSO (Acronym for opEn-Source Package for Research in Electronic Structure, Simulation, and Optimization) Plane Wave Self Consistent Field (PWscf). The calculated optical joint density of states show that the absorption begins at 4.8 eV and exhibits two sharp peaks and one broad peak at 48 nm, 64 nm, and 170 nm. The absorption range is in good agreement with our experimental observations. The dielectric function shows electric polarization between the 2p state of nitrogen and 3d state of calcium. The crystal’s static refractive index is 1.87 with a maximum value of 6.4 in the visible region, which is optimal for optical devices. The absorption coefficient confirms experimentally comparable optical states with no notable anisotropy.

Theoretical analysis of argon 2p states' density ratios for nanosecond plasma optical emission spectroscopy

A theoretical analysis of excited argon state densities responsible for optical emission spectra of atmospheric pressure argon plasma is presented for its use in plasma diagnostics. Nanosecond pulsed barrier discharges are simulated using spatially one- and two-dimensional fluid-Poisson models using the reaction kinetics model presented by Stankov et al. [1], which considers all ten argon 2p states (Paschen notation) separately. The very first (single) discharge and repetitive discharges with frequencies from 5 kHz to 100 kHz are considered. A semi-automated procedure is utilized to find appropriate 2p states for electric field determination using an intensity ratio method, which is based on a time-dependent collisional-radiative model. The fluid simulations in combination with the semi-automated procedure are used to quantify the sensitivity of selected 2p-state ratios to given preionization of the gas. A highly sensitive time-correlated single photon counting experiment shows clearly that the selected ratio is sensitive to the electric field variation in the streamer head, yet additional calibration is needed for absolute values determination. Different approaches for effective lifetime determination are tested and applied also to measured data. The influence of radial and axial 2p state density integration on the intensity ratio method is discussed. The above mentioned models and procedures result in a flexible theory-based methodology applicable for development of new diagnostic techniques.

Cross-luminescence in BaF[formula omitted] crystals doped with M[formula omitted] and RE[formula omitted] ions: Hybrid density functional theory study

Radiation resistant inorganic materials emitting cross-luminescence are one of the most prospective candidates for new generation ultrafast detectors for medical tomography. Radiative transitions leading to cross-luminescence occur between valence and core states, and therefore calculations of the electronic structure of doped materials can explain ultrafast transitions and predict new cross-luminescent materials. In current work we demonstrate results of ab initio calculations of undoped and doped BaF2 by means of hybrid density functional theory. As a result of the work, the density of states (DOS) for nominally pure BaF2 and a whole series of BaF2 doped with various trivalent ions were obtained. The positions of the core energy levels of dopant ions lying between the Ba(5p) zone and the F(2s) zone, as well local geometries and formation energies were calculated. Our calculations show that the 5p states of impurity ions can be located below the 5p zone of barium by several eV. This opens up opportunities for transitions from the core 5p Ba zone to impurity 5p states, which might be involved in experimentally observed appearance of an ultrafast component in doped BaF2.

Achieving complete solid-solution reaction in layered cathodes with reversible oxygen redox for high-stable sodium-ion batteries

P2-type layered Mn-based oxides are promising cathode materials for sodium-ion batteries (SIBs), but it is still challenging to achieve both high capacity and stability because of complex phase transitions and irreversible oxygen release at high voltage. To address these challenges, an optimal P2-type Na0.67Mn0.8Cu0.15Ti0.05O2 (NMCT) cathode with a complete solid-solution reaction and reversible oxygen redox reaction over a wide voltage range was developed. The introduction of the Na–O–Ti configuration leads to fewer delocalized electrons on oxygen and thus enhances oxygen redox activity, while the high energetic overlap between O 2p and Cu 3d states and the increased Mn–O hybridization strengthen the rigidity of oxygen framework to achieve reversible and stable oxygen redox reaction. In addition, the reinforced TM–O interaction, combined with the ameliorated Mn3+ Jahn-Teller distortion and disrupted Na+/vacancy ordering, synergistically eliminate the undesired P2–OP4 phase transition and lead to a complete solid-solution reaction, which greatly facilitates Na+ transport kinetics and stabilizes structural integrity. As a consequence, improved rate performance and cycling stability are achieved for NMCT. Our present study provides a promising avenue for simultaneously utilizing the reversible oxygen redox activity and maintaining the structural integrity to accomplish the capacity-stability trade-off of Mn-based oxide cathodes for constructing practical SIBs.

Circular dichroism in multiphoton ionization of resonantly excited helium ions near channel closing

The circular dichroism (CD) of photoelectrons generated by near-infrared (NIR) laser pulses using multiphoton ionization of excited He+ ions in the 3p(m= +1) state is investigated. The ions were prepared by circularly polarized extreme ultraviolet (XUV) pulses. For circularly polarized NIR pulses co- and counter-rotating relative to the polarization of the XUV pulse, a complex variation of the CD is observed as a result of intensity- and polarization-dependent Freeman resonances, with and without additional dichroic AC-Stark shifts. The experimental results are compared with numerical solutions of the time-dependent Schrödinger equation to identify and interpret the pronounced variation of the experimentally observed CD.

Al-N3 Bridge Site Enabling Interlayer Charge Transfer Boosts the Direct Photosynthesis of Hydrogen Peroxide from Water and Air.

Manipulating the electronic environment of the reactive center to lower the energy barrier of the rate-determining water oxidation step for boosting the direct generation of H2O2 from water, air, and sunlight is fascinating yet remains a grand challenge. Driven by a first-principles screening across a series of metal single atoms in carbon nitride, we report a class of an Al-N3 bridge site enabling interlayer charge transfer in carbon nitride nanotubes (CNNT-Al) for the highly efficient photosynthesis of H2O2 directly from water, oxygen, and sunlight. We demonstrate that the interlayered Al-N3 bridge site in CNNT-Al is able to activate the neighboring surface N atom for promoting the rate-determining step of the two-electron water oxidation to H2O2. It is also able to act as a bridge for enhancing the vertical interlaminar charge transfer due to the hybridization between the 3s and 3p states of the interstitial Al atom and the conduction band of two adjacent carbon nitride layers. Collectively, these factors lead to a highest photocatalytic mass activity of 1410.2 μmol g-1 h-1 (with a photocatalyst concentration of 1 g L-1) for direct photosynthesis of H2O2 out of all CN-based photocatalysts and a 7-fold higher solar-to-chemical conversion efficiency (0.73%) compared to that of the natural photosynthesis of typical plants (∼0.1%). Most importantly, the CNNT-Al-based flow reactor can steadily produce H2O2 for 200 h and be directly used for the on-site degradation of organic dye in water. The CNNT-Al-based flow reactor can also kill a 10 times higher concentration of bacteria in deionized water than that in natural water with 100% efficiency, which makes our design economically appealing for practical water treatment.

Harnessing the Unconventional Cubic Phase in 2D LaNiO3 Perovskite for Highly Efficient Urea Oxidation

AbstractPhase engineering is a critical strategy in electrocatalysis, as it allows for the modulation of electronic, geometric, and chemical properties to directly influence the catalytic performance. Despite its potential, phase engineering remains particularly challenging in thermodynamically stable perovskites, especially in a 2D structure constraint. Herein, we report phase engineering in 2D LaNiO3 perovskite using the strongly non‐equilibrium microwave shock method. This approach enables the synthesis of conventional hexagonal and unconventional trigonal and cubic phases in LaNiO3 by inducing selective phase transitions at designed temperatures, followed by rapid quenching to allow precise phase control while preserving the 2D porous structure. These phase transitions induce structural distortions in the [LaO]+ layers and the hybridization between Ni 3d and O 2p states, modifying local charge distribution and enhancing electron transport during the six‐electron urea oxidation process (UOR). The cubic LaNiO3 offers optimal electron transport and active site accessibility due to its high structural symmetry and open interlayer spacing, resulting in a low onset potential of 1.27 V and a Tafel slope of 33.1 mV dec−1 for UOR, outperforming most current catalysts. Our strategy features high designability in phase engineering, enabling various electrocatalysts to harness the power of unconventional phases.

Bifunctional Effects of MoO3/S-ZrO2 and Mo2C/S-ZrO2 Catalysts in Transesterification of Groundnut Oil

Successful doping via impregnation and carburization under CH4/H2 atmosphere were respectively employed to achieve the formation of MoO3/S-ZrO2 and Mo2C/S-ZrO2 catalysts. The synthesis of both materials was confirmed as illustrated by the binding energies associated with XPS spectra of C1s, Mo 3p and Mo 3d states. In addition to compatible BET surface areas of 120 and 97m2g-1, both catalysts were found to exhibit appreciable densities of surface Mo species as revealed by the N2-adsorption data. These species enhanced catalytic activity and prompted the catalyst to exhibit bifunctional properties during transesterification of groundnut oil. When compared with the support system (i.e. S-ZrO2), the overall catalytic performance at 60oC, 0.5g of catalyst and 1:6 (oil: methanol) followed the trend S-ZrO2 &lt; MoO3/S-ZrO2 &lt; Mo2C/S-ZrO2. Another appreciable result is the conformity of the derived biodiesel with international specifications approved by ASTM for B100 and other fuel grades of methyl esters.

Unraveling the Anionic Redox Chemistry in Aqueous Zinc‐MnO2 Batteries

AbstractActivating anionic redox reaction (ARR) has attracted a great interest in Li/Na‐ion batteries owing to the fascinating extra‐capacity at high operating voltages. However, ARR has rarely been reported in aqueous zinc‐ion batteries (AZIBs) and its possibility in the popular MnO2‐based cathodes has not been explored. Herein, the novel manganese deficient MnO2 micro‐nano spheres with interlayer “Ca2+‐pillars” (CaMnO‐140) are prepared via a low‐temperature (140 °C) hydrothermal method, where the Mn vacancies can trigger ARR by creating non‐bonding O 2p states, the pre‐intercalated Ca2+ can reinforce the layered structure and suppress the lattice oxygen release by forming Ca−O configurations. The tailored CaMnO‐140 cathode demonstrates an unprecedentedly high rate capability (485.4 mAh g−1 at 0.1 A g−1 with 154.5 mAh g−1 at 10 A g−1) and a marvelous long‐term cycling durability (90.6 % capacity retention over 5000 cycles) in AZIBs. The reversible oxygen redox chemistry accompanied by CF3SO3− (from the electrolyte) uptake/release, and the manganese redox accompanied by H+/Zn2+ co‐insertion/extraction, are elucidated by advanced synchrotron characterizations and theoretical computations. Finally, pouch‐type CaMnO‐140//Zn batteries manifest bright application prospects with high energy, long life, wide‐temperature adaptability, and high operating safety. This study provides new perspectives for developing high‐energy cathodes for AZIBs by initiating anionic redox chemistry.

Unraveling the Anionic Redox Chemistry in Aqueous Zinc-MnO2 Batteries.

Activating anionic redox reaction (ARR) has attracted a great interest in Li/Na-ion batteries owing to the fascinating extra-capacity at high operating voltages. However, ARR has rarely been reported in aqueous zinc-ion batteries (AZIBs) and its possibility in the popular MnO2-based cathodes has not been explored. Herein, the novel manganese deficient MnO2 micro-nano spheres with interlayer "Ca2+-pillars" (CaMnO-140) are prepared via a low-temperature (140 °C) hydrothermal method, where the Mn vacancies can trigger ARR by creating non-bonding O 2p states, the pre-intercalated Ca2+ can reinforce the layered structure and suppress the lattice oxygen release by forming Ca-O configurations. The tailored CaMnO-140 cathode demonstrates an unprecedentedly high rate capability (485.4 mAh g-1 at 0.1 A g-1 with 154.5 mAh g-1 at 10 A g-1) and a marvelous long-term cycling durability (90.6 % capacity retention over 5000 cycles) in AZIBs. The reversible oxygen redox chemistry accompanied by CF3SO3 - (from the electrolyte) uptake/release, and the manganese redox accompanied by H+/Zn2+ co-insertion/extraction, are elucidated by advanced synchrotron characterizations and theoretical computations. Finally, pouch-type CaMnO-140//Zn batteries manifest bright application prospects with high energy, long life, wide-temperature adaptability, and high operating safety. This study provides new perspectives for developing high-energy cathodes for AZIBs by initiating anionic redox chemistry.