Mo Clusters Research Articles

A computational study of the role of cobalt in thiophene adsorption on small Mo and MoCo clusters as site models for the HDS process

Non periodic density functional theory calculations are used to investigate the role of cobalt atoms in the adsorption of thiophene on small Mo and MoCo clusters. Metallic aggregates play the role of those active sites found in the true catalysts. Two interaction modes between thiophene and metallic sites are considered, namely, the S-mode, in which the organosulfur molecule interacts through the S atom, and the R-mode, in which the interaction takes place through the thiophene ring. A large number of sites, in which thiophene effectively adsorbs, was found, both in the monometallic case and in the bimetallic one. Considerably larger adsorption energies were found when thiophene interacts via the R-mode than when adsorption occurs through the S-mode. The activation of C-S bonds is also more important for R-mode cases than for S-mode ones. Further analysis made on some selected systems and based on density of states and molecular orbital overlap population-projected density of states reveals that thiophene and metallic clusters interact in an energy range around −6.0 eV with respect to the Fermi energy. Bands observed at energies below −6.0 eV correspond to thiophene states that become shifted with respect to the values obtained for isolated thiophene depending on the strength of the interaction. Bands above -6.0 eV describe how C and S atoms interact with Co and Mo ones, providing both bonding and antibonding patterns that helps to understand the overall interaction. Most important is the finding that cobalt atoms seem to play no relevant role during the adsorption of thiophene on metallic sites. Thus, present results obtained using non periodic GGA density functional theory seem to point to cobalt taking part in another step of the overall HDS process, hydrogen adsorption or hydrogen attack to C-S bonds, for instance.

Two-dimensional Mo3-TiS2 monolayer hosting high moisture resistance and abundant surface-chemisorbed oxygen for effective detection of SF6 decomposition gases: Atomic-scale study

Monitoring the SF6 decomposition gas (DPA) by gas sensors can be used to predict the operating status of power equipment, and the sensitivity performance of gas sensors is deeply influenced by the humidity resistance and surface oxygen adsorption performance of their sensing materials. The present research aims to explore a high‐valence transition‐metal ion doped transition metal dichalcogenide (TMD) monolayer that hosts high moisture resistance and abundant surface-chemisorbed oxygen suitable for detecting DPA. Using first-principles methods, the adsorption behavior of three representative types of gases (HF, SO2, and CO2) in DPA, H2O, and O2 on Mo3-TiS2 monolayer are considered. Our results show that SO2 and CO2 molecules are adsorbed above the Mo3 cluster through chemical adsorption, while HF molecule is physically adsorbed. The desorption times for SO2 and CO2 on Mo3-TiS2 adsorbent are 9.89 s at 348 K and 34.96 s at 398 K, respectively. Introducing dopant Mo3 resulted in better anti-humidity performance of TiS2, as the force of Mo3-TiS2 monolayer towards H2O molecule is weakened compared to the intrinsic adsorption system. Additionally, Mo3-TiS2 monolayer exhibits an exceptionally high affinity for O2 molecule, leading to the rupture of chemical bond in O2, and the chemisorbed oxygen ions are acquired through the charge transfer between Mo3 cluster and O2 molecule. The computational findings in this article offer theoretical backing for advancing the development of gas sensors utilizing Mo3-TiS2 and its utilization in the realm of DPA detection.

Possibility and stabilizing effect of Mo clusters in the Ni-based single-crystal superalloy

Nickel-based single-crystal superalloys are crucial materials for the preparation of aero-engine turbine blades. Many solute elements are added to superalloys for strengthening. However, the relationship between the clustering behavior of solute atoms and the properties of nickel-based single-crystal superalloys is still unclear. Herein, we conduct first-principles calculations on γ phases with Mo−Mo and Mo−Mo−Ru clusters to reveal the possibility and stabilizing mechanism of solute clusters. Introducing Mo lowers the total energy, binding energy, and formation energy of the γ phase due to the replacement of weak Ni−Ni interaction with strong Mo−Ni bonding. Note that the γ phase containing the Mo−Mo cluster is more stable than that containing a Mo single atom, possibly owing to a wide affecting range. The Ru atom added to the γ phase can further boost system stability, and it tends to form a Mo−Mo−Ru cluster. The stabilizing impact of the Mo−Mo−Ru cluster is demonstrated to be the replacement of weak Ni−Mo interaction by the strong Ru−Mo interaction, which may be derived from the enhanced d-orbital hybridization.

Full-Space Electric Field in Mo-Decorated Zn2In2S5 Polarization Photocatalyst for Oriented Charge Flow and Efficient Hydrogen Production.

Integration of photocatalytic hydrogen (H2) evolution with oxidative organic synthesis presents a highly attractive strategy for the simultaneous production of clean H2 fuel and high-value chemicals. However, the sluggish dynamics of photogenerated charge carriers across the photocatalysts result in low photoconversion efficiency, hindering the wide applications of such a technology. Herein, this work overcomes this limitation by inducing the full-space electric field via charge polarization engineering on a Mo cluster-decorated Zn2In2S5 (Mo-Zn2In2S5) photocatalyst. Specifically, this full-space electric field arises from a cascade of the bulk electric field (BEF) and local surface electric field (LSEF), triggering the oriented migration of photogenerated electrons from [Zn-S] regions to [In-S] regions and eventually to Mo cluster sites, ensuring efficient separation of bulk and surface charge carriers. Moreover, the surface Mo clusters induce a tip enhancement effect to optimize charge transfer behavior by augmenting electrons and proton concentration around the active sites on the basal plane of Zn2In2S5. Notably, the optimized Mo1.5-Zn2In2S5 catalyst achieves exceptional H2 and benzaldehyde production rates of 34.35 and 45.31mmol gcat -1 h-1, respectively, outperforming pristine ZnIn2S4 by 3.83- and 4.15-fold. These findings mark a significant stride in steering charge flow for enhanced photocatalytic performance.

Theoretical insights into Mo cluster modified Fe5C2 catalysts for electrocatalytic nitrogen reduction

The pursuit of green ammonia synthesis via electrocatalytic nitrogen reduction (NRR) faces challenges in developing high-performance, selective electrocatalysts. Inspired by the nitrogenase Fe-Mo cofactor, this study explores the catalytic efficiency of Mo clusters anchored on Fe5C2 for NRR. We investigate structural stability, N2 adsorption, and Gibbs free energy, revealing that Mon clusters on Fe5C2 demonstrate robust NRR selectivity and notable catalytic activity. Each of the three cluster structures demonstrated superior adsorption capacity in the "side-on" configuration. Among the studied cluster configurations, the Mo5-Fe5C2 shows the lowest limiting potential (-0.24 V), and the Mo4-Fe5C2 exhibits heightened selectivity for NRR, minimizing interference from the hydrogen evolution reaction (HER). This enhanced performance is attributed to the unique structure and interactive dynamics of Mon-Fe5C2 and the electron orbital interactions facilitating direct nitrogen charge transfer. Our findings underscore the potential of Mo cluster-modified Fe5C2 as a pioneering catalyst for electrocatalytic nitrogen reduction.

The Role of Mo Single Atoms and Clusters in Enhancing Pt Catalyst for Benzene Hydrogenation: Distinguishing Between Benzene Spillover and Electronic Effect

The Role of Mo Single Atoms and Clusters in Enhancing Pt Catalyst for Benzene Hydrogenation: Distinguishing Between Benzene Spillover and Electronic Effect

Prolonged exhumation and preservation of the Yuku molybdenum ore field, East Qinling, China: Constraints from medium- to low-temperature thermochronology

Molybdenum (Mo) is an important globally strategic metal and mostly occurs as molybdenite (MoS2) in diverse Mo deposits. The Yuku ore field includes multiple porphyry-skarn Mo deposits and forms a significant world-class Mo cluster in the Qinling molybdenum belt, central China. Previous studies on the ore field were largely related to its genesis, and did not highlight the post-mineralization modifications that are important to formulate prospecting strategies. The exhumation and preservation processes of the ore field through multiple tectonic events also remain poorly understood. Here, we conducted multi-method apatite U-Pb, fission-track and (U-Th)/He and zircon (U-Th)/He medium- to low-temperature thermochronology and related thermal history modelling on granitoids from the ore-hosting Shibaogou and Yuku plutons in the Yuku ore field, and integrated published studies to unravel the post-mineralization exhumation and preservation of Mo deposits. The newly determined apatite U-Pb (158.3–104.9 Ma), zircon (U-Th)/He (158.2–115.0 Ma), apatite fission-track (90.8–63.1 Ma), and apatite (U-Th)/He (67.8–35.3 Ma) ages in this study document multiple cooling pulses during post-magma emplacement. The low-temperature thermochronological ages of 158.2–35.3 Ma also record the post-mineralization cooling and exhumation history. The thermal history modelling indicates an Early Cretaceous (132–125 Ma) rapid cooling pulse, two enhanced (or accelerated) cooling pulses at ca. 125–59 Ma and post-10 Ma, together with a slow cooling or reheating pulse at ca. 59–10 Ma in the Yuku ore field. The Early Cretaceous rapid cooling is related to the coeval collisional tectonics of the East Qinling Orogen. The enhanced cooling at ca. 125–59 Ma is triggered by the post-collisional assembly of the North China and Yangtze Blocks, the subduction of Paleo-Pacific Plate, and the sinistral strike-slip motion of the nearby Tan-Lu Fault Zone. The slow cooling during ca. 59–10 Ma and the post-10 Ma enhanced cooling are correlated with the extensional tectonics derived by the subduction of Pacific Plate and the far-field effects from India-Eurasia collision. The Yuku area underwent lower exhumation in comparison to the nearby Shibaoguo and Huangbeiling areas in the Yuku ore field, which thus is helpful to the preservation of Mo deposits. The un-exhumated areas within 1.0 km at the inner and outer contact zones between the Yuku pluton and its wall rocks are postulated to be favorable sites for Mo prospecting. In addition, the un-exhumated areas surrounding other Late Mesozoic plutons in the Luanchuan region are also suggested to have high potential for Mo exploration.

A comprehensive exploration of structural and electronic properties of molybdenum clusters

Molybdenum clusters, characterized by their unique structure and intriguing catalytic properties, have gained significant attention in recent years. In several existing studies, density functional theory (DFT) methods have been used to find the lowest energy Mo clusters and explore their electronic and magnetic structure. In all cases, with the exception of a single recent study, where a genetic algorithm was employed, initial geometries of the clusters, prior to geometry optimization, were chosen using heuristic approaches based on symmetry considerations and known structures. DFT calculations were performed using different types of pseudopotentials, from soft to hard, and different types of basis sets. However, no comprehensive study has yet been carried out in which a DFT method with the best control on its precision would be complemented by a reliable global minimum search method to find the lowest energy Mo clusters. In this work, we employ a combination of a plane wave-based DFT method and ab initio random structure searching technique to find the lowest energy clusters of up to 10 Mo atoms. In each case, the search has been performed for clusters with different spin multiplicities, which enabled us to explore their magnetic structure. The results are compared for both hard and soft pseudopotentials stressing the importance of treating more electrons explicitly, in agreement with some of the previous studies. For most of the low-energy magnetic structures found, we investigate the distribution of their spin densities, and for all low energy clusters, we confirm their stability by calculating their vibrational structure. For a few smallest clusters, the results of multiconfigurational quantum chemistry calculations are also discussed. Finally, free energies of the Mo clusters, within the quasi-harmonic approximation, are also calculated and discussed.

Microscopic growth mechanism and edge states of monolayer 1T′-MoTe2

Transition metal ditellurides (TMTDs) have versatile physical properties, including non-trivial topology, Weyl semimetal states and unique spin texture. Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications. Here, we demonstrate the epitaxial growth of 1T′-MoTe2 on Au (111) and graphitized silicon carbide (Gr/SiC) by molecular beam epitaxy (MBE). We investigate the morphology of the grown 1T′-MoTe2 at the atomic level by scanning tunnelling microscopy (STM) and reveal the corresponding microscopic growth mechanism. It is found that the unique ordered Te structures preferentially deposited on Au (111) regulate the growth of monolayer single crystal 1T′-MoTe2, while the Mo clusters were preferentially deposited on the Gr/SiC substrate, which impedes the ordered growth of monolayer MoTe2. We confirm that the size of single crystal 1T′-MoTe2 grown on Au (111) is nearly two orders of magnitude larger than that on Gr/SiC. By scanning tunnelling spectroscopy (STS), we observe that the STS spectrum of the monolayer 1T′-MoTe2 nano-island at the edge is different from that at the interior, which exhibits enhanced conductivity.

Operando Spectroscopy Observation of Mo Clusters-Ti3 C2 TX Catalyst/Support Interface's Dynamic Evolution in Hydrogen Evolution Reaction.

The interaction between catalyst and support plays an important role in electrocatalytic hydrogen evolution (HER), which may explain the improvement in performance by phase transition or structural remodeling. However, the intrinsic behavior of these catalysts (dynamic evolution of the interface under bias, structural/morphological transformation, stability) has not been clearly monitored, while the operando technology does well in capturing the dynamic changes in the reaction process in real time to determine the actual active site. In this paper, nitrogen-doped molybdenumatom-clusters on Ti3 C2 TX (MoACs /N-Ti3 C2 TX ) is used as a model catalyst to reveal the dynamic evolution of MoAcs on Ti3 C2 TX during the HER process. Operando X-ray absorption structure (XAS) theoretical calculation and in situ Raman spectroscopy showed that the Mo cluster structure evolves to a 6-coordinated monatomic Mo structure under working conditions, exposing more active sites and thus improving the catalytic performance. It shows excellent HER performance comparable to that of commercial Pt/C, including an overpotential of 60mV at 10mA cm-2 , a small Tafel slope (56mV dec-1 ), and high activity and durability. This study provides a unique perspective for investigating the evolution of species, interfacial migration mechanisms, and sources of activity-enhancing compounds in the process of electroreduction.

Sequential electrocatalysis by single molybdenum atoms/clusters doped on carbon nanotubes for removing organic contaminants from wastewater

Oxygen reduction reaction (ORR) can realize the goal of in-situ H2O2 generation. A suitable catalyst ensures a proper binding strength between the electrocatalyst and the intermediate (i.e., *OOH), thereby avoiding the 4-electron ORR process and H2O production. Herein, we demonstrate that single molybdenum (Mo) atoms/clusters doped on carbon nanotubes can effectively alter the ORR pathway to generate H2O2; meanwhile, the established sequential ORR system for H2O2 production can tandemly remove ibuprofen (IBU) and other organic contaminants from water and wastewater. The results reveal that single atomic Mo clusters preferentially acted as the active sites that are merely required to overcome 0.11 eV downhill to form *OOH. Surprisingly, this tandemly constructed ORR with in-situ generated H2O2 performed better than the in-vitro H2O2 system. These findings offer a promising solution to reduce the costs related to the production and transportation of H2O2 for various applications, including the oxidation and removal of emerging organic contaminants from water and wastewater.

Mixed Ion/Electron Conductive Li3N-Mo Interphase Enabling Stable and Ultrahigh-Rate Lithium Metal Anodes.

Lithium (Li) metal is a promising anode for high-energy-density batteries; however, its practical viability is hampered by the unstable metal Li-electrolyte interface and Li dendrite growth. Herein, a mixed ion/electron conductive Li3N-Mo protective interphase with high mechanical stability is designed and demonstrated to stabilize the Li-electrolyte interface for a dendrite-free and ultrahigh-current-density metallic Li anode. The Li3N-Mo interphase is simultaneously formed and homogeneously distributed on the Li metal surface by the surface reaction between molten Li and MoN nanosheets powder. The highly ion-conductive Li3N and abundant Li3N/Mo grain boundaries facilitate fast Li-ion diffusion, while the electrochemically inert metal Mo cluster in the mosaic structure of Li3N-Mo inhibits the long-range crystallinity and regulates the Li-ion flux, further promoting the rate capability of the Li anode. The Li3N-Mo/Li electrode has a stable Li-electrolyte interface as manifested by a low Li overpotential of 12 mV and outstanding plating/stripping cyclability for over 3200 h at 1 mA cm-2. Moreover, the Li3N-Mo/Li anode inhibits Li dendrite formation and exhibits a long cycling life of 840 h even at 30 mA cm-2. The full cell assembled with LiFePO4 cathode exhibits stable cycling performance with 87.9% capacity retention for 200 cycles at 1C (1C = 170 mA g-1) as well as high rate capability of 83.7 mAh g-1 at 3C. The concept of constructing a mixed ion/electron conductive interphase to stabilize the Li-electrolyte interface for high-rate and dendrite-free Li metal anodes offers a viable strategy to develop high-performance Li-metal batteries.

Mo Cluster Support on C2 N as a Highly-efficient Catalyst for Electrocatalytic Nitrogen Reduction Reaction.

The conversion of nitrogen to ammonia by electrocatalysis under mild conditions is a valuable research direction, which has been a sustainable alternative to the traditional Haber-Bosch method. However, the conversion remains a huge challenge in chemistry at this time. In this work, the density functional theory (DFT) is used to study the electrocatalytic nitrogen reduction reaction (NRR) performance of Mo12 clusters on C2 N monolayer (Mo12 -C2 N). It is found that the diversity of active sites of the Mo12 cluster provides favorable reaction paths for intermediates, which reduces reaction barrier of NRR. Mo12 -C2 N shows excellent NRR performances with limiting potentials of -0.26 V vs. reversible hydrogen electrode (RHE).

Enhanced NH3 Sensing Performance of Mo Cluster-MoS2 Nanocomposite Thin Films via the Sulfurization of Mo6 Cluster Iodides Precursor.

The high-performance defect-rich MoS2 dominated by sulfur vacancies as well as Mo-rich environments have been extensively studied in many fields, such as nitrogen reduction reactions, hydrogen evolution reactions, as well as sensing devices for NH3, which are attributed to the under-coordinated Mo atoms playing a significant role as catalytic sites in the defect area. In this study, the Mo cluster-MoS2 composite was creatively synthesized through a one-step sulfurization process via H2/H2S gas flow. The Mo6 cluster iodides (MIs) coated on the fluorine-doped tin oxide (FTO) glass substrate via the electrophoretic deposition method (i.e., MI@FTO) were used as a precursor to form a thin-film nanocomposite. Investigations into the structure, reaction mechanism, and NH3 gas sensing performance were carried out in detail. The results indicated that during the gas flowing, the decomposed Mo6 cluster iodides played the role of template and precursor, forming complicated Mo cluster compounds and eventually producing MoS2. These Mo cluster-MoS2 thin-film nanocomposites were fabricated and applied as gas sensors for the first time. It turns out that after the sulfurization process, the response of MI@FTO for NH3 gas increased three times while showing conversion from p-type to n-type semiconductor, which enhances their possibilities for future device applications.

Three-dimensional carbon nanofiber networks encapsulated in cobalt–molybdenum metal clusters on nitrogen-doped carbon as ultra-efficient electrocatalysts for hydrogen evolution reactions

Efficient and cost-effective catalysts have been developed for the production of hydrogen via water electrolysis. In this study, we develop a strategy for the fabrication of carbon nanofiber catalysts loaded with CoMo clusters covered by a nitrogen-doped carbon network (CoMo/CN@CNFs/MEL). The surface of two-dimensional carbon fibers was coated with a nitrogen-doped carbon network via melamine pyrolysis, thereby forming three-dimensional (3D) networks. These 3D network catalysts exhibited excellent catalytic performance in the hydrogen evolution reaction with 1 M KOH, requiring an overpotential of only 148 mV to reach a current density of 10 mA cm−2 owing to synergistic effects resulting from their structure and composition. The catalytic performance of the CoMo/CN@CNFs/MEL catalysts was comparable to that of commercial Pt/C at high current densities owing to their unique structural features, including restricted Co–Mo clusters, porous nitrogen-doped carbon frameworks, continuous conducting carbon nanofibers, and carbon nitride networks. This work provides a promising approach to transition metal-based catalysts with improved stability and atom utilization efficiency.

Low‐Coordinated Mo Clusters for High‐Efficiency Electrocatalytic Hydrogen Peroxide Production

AbstractElectrocatalytic oxygen reduction reaction (ORR) to generate hydrogen peroxide (H2O2) via a 2e− pathway offers a green alternative to the energy‐extensive anthraquinone process; however, the challenge lies in the development of low cost and effective 2e− ORR catalysts. In this work, a highly selective and stable Mo clusters supported by nitrogen‐doped carbon polyhedrons catalyst for direct H2O2 electrosynthesis are first designed, which shows a high H2O2 selectivity (>77%) in the applied potential range varying from 0.2 to 0.65 V vs RHE, and an excellent mass activity of 29.0 A gcat.−1 (at 0.65 V) with negligible activity decay over 10 000 cycles in an alkaline medium. Moreover, the catalyst displays a yield rate of 136.2 ± 1.5 ppm cm−2 h−1 at −20 mA cm−2 in a continuous flow cell with neutral electrolyte. Taken together, the obtained performance metrics are comparable to the best‐reported ORR results. Density‐functional theory analyses reveal that Mo clusters can donor electrons to activate O2 molecules and strengthen the *OOH binding on Mo sites as well, thus inducing a high H2O2 selectivity. The present work provides a unique insight into the atomic introduction of metal clusters‐based materials for 2e− ORR to H2O2 powered by renewable energy.

Influence of carbon on hydrogen retention in molybdenum for nuclear material application: A first-principles investigation

• Systematic DFT simulations for the effect of carbon on the H retention in Mo. • Impurity carbon cannot trap H atoms in perfect Mo. • Impurity carbon has little effect on the H vacancy capturing in Mo. • Mo-carbon layer prevents the H diffusion and permeation in Mo. Mo has been applied to nuclear material, in which H and carbon impurities are unavoidable. In view of this, we have studied the effect of carbon on the H retention in Mo using first-principles simulations. In perfect Mo, there is always repulsion between H and carbon, and impurity carbon cannot capture H atoms. With the appearance of vacancy in Mo, vacancy and carbon-vacancy cluster trap seven and six H atoms, respectively. This means that impurity carbon has little effect on the H vacancy capturing. Finally, we explore the H diffusion by considering the presence of one Mo-carbon layer in Mo. Away from the Mo-carbon layer, H jumps along the optimal route with a diffusion barrier of 0.12 eV. As H moves close and passes through the Mo-carbon layer, the H diffusion barrier is increased to 0.73 eV. Therefore, the repulsive interaction between H and carbon can increase the H energy barrier in the vicinity of the Mo-carbon layer, which prevent the H diffusion and permeation in Mo. The current results can explain the promoting mechanism of bubble formation due to impurity carbon implantation and help us design future Mo-based nuclear material.

Theoretical insight into the reaction mechanism of ammonia dehydrogenation on iron-based clusters

Ammonia (NH3) molecule decomposition is a promising approach for H2 production with COx-free. Density functional theory (DFT) calculations are employed to investigate the NH3 molecule stepwise dehydrogenation on Fe6M (M = Fe, Mo, Ni, and Co) clusters. The stability of these clusters has been investigated, and the result shows that the stability of Fe-based clusters is enhanced with doping of other metals. The catalytic activity of metal clusters for ammonia decomposition is systematically investigated by analyzing the adsorption property and reaction barriers. NH3 prefers to bind to the atop metal atom through the N end, which is agreement with the electrostatic potential analysis. Moreover, the adsorption energies of NH3 are related to the d-band center of Fe-based clusters. The reaction energy barriers show that the last dehydrogenation step (NH* + * ⇌ N* + H*) is the rate-determining step for most investigated clusters. The overall dehydrogenation process is exothermic reaction, and by comparing the rate-determining step, the Fe6Mo(l) and the Fe6Ni(l) clusters can efficiently promote the NH3 dissociation reaction.

Synergistic modulation of local environment for electrochemical nitrate reduction via asymmetric vacancies and adjacent ion clusters

Electrochemical conversion of nitrate to ammonia is widely considered a “two birds with one stone” approach to alleviate the nitrate pollution in water and simultaneously to generate the valuable green NH3 fuels. However, it remains challenging due to the lack of efficient electrocatalysts for practical utilization. Herein, we investigate the synergistic effect between asymmetric Cu-Ov-W sites (Ov represents oxygen vacancy) and adjacent Mo clusters in tuning the local electronic environment around active sites of catalysts for substantially enhanced nitrate reduction. The dynamic balance between the adsorption and desorption of O in NO3- caused by asymmetric Ov and the promoted protonation process due to Mo clusters are responsible for boosting the entire process. Such synergistic effect modulates the local electronic environment for binding the reaction intermediates and dramatically facilitates the intermediate formation in rate-determining steps (*NO→*NOH and *NOH→*N), leading to the high NH3 Faradaic efficiency and yield rate of 94.60% and 5.84 mg h−1 mgcat.−1 at − 0.7 V vs. RHE, respectively.

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li2+xMo1-xO3 Solid Solutions.

A broad range of cationic nonstoichiometry has been demonstrated for the Li-rich layered rock-salt-type oxide Li2MoO3, which has generally been considered as a phase with a well-defined chemical composition. Li2+xMo1-xO3 (-0.037 ≤ x ≤ 0.124) solid solutions were synthesized via hydrogen reduction of Li2MoO4 in the temperature range of 650-1100 °C, with x decreasing with the increase of the reduction temperature. The solid solutions adopt a monoclinically distorted O3-type layered average structure and demonstrate a robust local ordering of the Li cations and Mo3 triangular clusters within the mixed Li/Mo cationic layers. The local structure was scrutinized in detail by electron diffraction and aberration-corrected scanning transmission electron microcopy (STEM), resulting in an ordering model comprising a uniform distribution of the Mo3 clusters compatible with local electroneutrality and chemical composition. The geometry of the triangular clusters with their oxygen environment (Mo3O13 groups) has been directly visualized using differential phase contrast STEM imaging. The established local structure was used as input for density functional theory (DFT)-based calculations; they support the proposed atomic arrangement and provide a plausible explanation for the staircase galvanostatic charge profiles upon electrochemical Li+ extraction from Li2+xMo1-xO3 in Li cells. According to DFT, all electrochemical capacity in Li2+xMo1-xO3 solely originates from the cationic Mo redox process, which proceeds via oxidation of the Mo3 triangular clusters into bent Mo3 chains where the electronic capacity of the clusters depends on the initial chemical composition and Mo oxidation state defining the width of the first charge low-voltage plateau. Further oxidation at the high-voltage plateau proceeds through decomposition of the Mo3 chains into Mo2 dimers and further into individual Mo6+ cations.