Mo-Doped Mesoporous RuO2 Spheres as High-Performance Acidic Oxygen Evolution Reaction Electrocatalyst.

The development of highly active and acid-stable electrocatalysts for oxygen evolution reaction (OER) is of great significance for water electrolysis technology. Herein, a highly efficient molybdenum-doped mesoporous ruthenium dioxide sphere (Mo-RuO2 ) catalyst is fabricated by a facile impregnation and post-calcination method using mesoporous carbon spheres to template the mesostructure. The optimal Mo0.15 -RuO2 catalyst with Mo doping amount of 15 mol.% exhibits a significantly low overpotential of 147 mV at 10 mA cm-2 , a small Tafel slope of 38 mV decade-1 , and enhanced electrochemical stability in acidic electrolyte, far superior to the commercial RuO2 catalyst. The experimental results and theoretical analysis reveal that the remarkable electrocatalytic performance can be attributed to the large surface area of the mesoporous spherical structure, the structural robustness of the interconnected mesoporous framework, and the change in the electronic structure of Ru active sites induced by Mo doping. These excellent advantages make Mo-doped mesoporous RuO2 spheres a promising catalyst for highly efficient electrocatalytic OER in acidic media.

Molybdenum-Doped Cobalt-Free Cathode Realizing the Electrochemical Stability by Enhanced Covalent Bonding.

The doping strategy effectively enhances the capacity and cycling stability of cobalt-free nickel-rich cathodes. Understanding the intrinsic contributions of dopants is of great importance to optimize the performances of cathodes. This study investigates the correlation between the structure modification and their performances of Mo-doped LiNi0.8Mn0.2O2 (NM82) cathode. The role of doped Mo's valence state has been proved functional in both lattice structural modification and electronic state adjustment. Although the high-valence of Mo at the cathode surface inevitably reduces Ni valence for electronic neutrality and thus causes ion mixing, the original Mo valence will influence its diffusion depth. Structural analyses reveal Mo doping leads to a mixed layer on the surface, where high-valence Mo forms a slender cation mixing layer, enhancing structural stability and Li-ion transport. In addition, it is found that the high-valence dopant of Mo6+ ions partially occupies the unfilled 4d orbitals, which may strengthen the Mo─O bond through increased covalency and therefore reduce the oxygen mobility. This results in an impressive capacity retention (90.0% after 200 cycles) for Mo-NM82 cathodes with a high Mo valence state. These findings underscore the valence effect of doping on layered oxide cathode performance, offering guidance for next-generation cathode development.

Boosting the Electrical Transfer by Molybdenum Doping for Robust and Flexible NiSe-Based Supercapacitor.

NiSe is a promising electrode material for enhancing the energy density of supercapacitors, but it faces challenges such as sensitivity to electrolyte anions, limited specific capacity, and unstable cycling. This study employs a strategy of metal atom doping to address these issues. Through a hydrothermal reaction, Mo-doped NiSe demonstrates significant improvement in electrochemical performance, exhibiting high capacity (799.90 C g-1), splendid rate performance, and excellent cyclic stability (90% capacity retention). The introduction of Mo induces charge redistribution in NiSe, leading to a reduction in the band gap. Theoretical calculation reveals that Mo doping can effectively enhance the electrical conductivity and the adsorption energy of NiSe. A flexible printed hybrid Mo-doped NiSe-based supercapacitor is fabricated, demonstrating superior electrochemical performance (367.04 mF cm-2) and the ability to power timers, LEDs, and toy fans. This research not only deepens the understanding of the electrochemical properties of metal-doped NiSe but also highlights its application potential in high-performance supercapacitors.

Mo-Incorporated Magnetite Fe3 O4 Featuring Cationic Vacancies Enabling Fast Lithium Intercalation for Batteries.

Transition metal oxides (TMOs) as high-capacity electrodes have several drawbacks owing to their inherent poor electronic conductivity and structural instability during the multi-electron conversion reaction process. In this study, the authors use an intrinsic high-valent cation substitution approach to stabilize cation-deficient magnetite (Fe3 O4 ) and overcome the abovementioned issues. Herein, 5 at% of Mo4+ -ions are incorporated into the spinel structure to substitute octahedral Fe3+ -ions, featuring ≈1.7 at% cationic vacancies in the octahedral sites. This defective Fe2.93 ▫0.017 Mo0.053 O4 electrode shows significant improvements in the mitigation of capacity fade and the promotion of rate performance as compared to the pristine Fe3 O4 . Furthermore, physical-electrochemical analyses and theoretical calculations are performed to investigate the underlying mechanisms. In Fe2.93 ▫0.017 Mo0.053 O4 , the cationic vacancies provide active sites for storing Li+ and vacancy-mediated Li+ migration paths with lower energy barriers. The enlarged lattice and improved electronic conductivity induced by larger doped-Mo4+ yield this defective oxide capable of fast lithium intercalation. This is confirmed by a combined characterization including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT) and density functional theory (DFT) calculation. This study provides a valuable strategy of vacancy-mediated reaction to intrinsically modulate the defective structure in TMOs for high-performance lithium-ion batteries.

Tuning electronic structure of hedgehog-like nickel cobaltite via molybdenum-doping for enhanced electrocatalytic oxygen evolution catalysis.

As a typical spinel oxide, nickel cobaltite (NiCo2O4) is considered to be a promising and reliable oxygen evolution reaction (OER) catalyst due to its abundant oxidation states and the synergistic effect of multiple metal species. However, the electrocatalytic OER performance of NiCo2O4 has always been limited by the low specific surface area and poor intrinsic conductivity of spinels. Herein, the hedgehog-like molybdenum-doped NiCo2O4 (Mo-NiCo2O4) catalyst was prepared as an efficient OER electrocatalyst via a facile hydrothermal method followed with high-temperature annealing. The Mo-NiCo2O4-0.075 with Mo doping concentration of âˆ¼ 1.95 wt% exhibits excellent OER performance with a low overpotential of 265 mV at a current density of 10 mA·cm-2and a Tafel slope of 126.63 mV·dec-1, as well as excellent cyclingstability.The results demonstrated that the hedgehog-like structure provides Mo-NiCo2O4 with the high surface area and mesopores that enhance electrolyte diffusion and optimal active site exposure. The in-situ Raman spectra and density functional theory calculations show that the Mo cations doping improve the intrinsic conductivity of the NiCo2O4 while modulating the chemisorption of intermediates. Meanwhile, the energy barriers of *OH and O* formation decrease significantly after Mo doping, effectively facilitating water dissociation and optimizing the reaction kinetics.

A High-Performance and Durable Direct-Ammonia Symmetrical Solid Oxide Fuel Cell with Nano La0.6Sr0.4Fe0.7Ni0.2Mo0.1O3-δ-Decorated Doped Ceria Electrode.

Solid oxide fuel cells (SOFCs) offer a significant advantage over other fuel cells in terms of flexibility in the choice of fuel. Ammonia stands out as an excellent fuel choice for SOFCs due to its easy transportation and storage, carbon-free nature and mature synthesis technology. For direct-ammonia SOFCs (DA-SOFCs), the development of anode catalysts that have efficient catalytic activity for both NH3 decomposition and H2 oxidation reactions is of great significance. Herein, we develop a Mo-doped La0.6Sr0.4Fe0.8Ni0.2O3-δ (La0.6Sr0.4Fe0.7Ni0.2Mo0.1O3-δ, LSFNM) material, and explore its potential as a symmetrical electrode for DA-SOFCs. After reduction, the main cubic perovskite phase of LSFNM remained unchanged, but some FeNi3 alloy nanoparticles and a small amount of SrLaFeO4 oxide phase were generated. Such reduced LSFNM exhibits excellent catalytic activity for ammonia decomposition due to the presence of FeNi3 alloy nanoparticles, ensuring that it can be used as an anode for DA-SOFCs. In addition, LSFNM shows high oxygen reduction reactivity, indicating that it can also be a cathode for DA-SOFCs. Consequently, a direct-ammonia symmetrical SOFC (DA-SSOFC) with the LSFNM-infiltrated doped ceria (LSFNM-SDCi) electrode delivers a superior peak power density (PPD) of 487 mW cm-2 at 800 °C when NH3 fuel is utilised. More importantly, because Mo doping greatly enhances the reduction stability of the material, the DA-SSOFC with the LSFN-MSDCi electrode exhibits strong operational stability without significant degradation for over 400 h at 700 °C.

(Electro)catalytic oxidation of sulfide and recovery of elemental sulfur from sulfide-laden streams.

MnxOy coated over TiO2 nanotube array substrate was doped with Mo and polyaniline (PANI) and applied for electrochemical desulfurization of concentrated sulfide (HS-) solutions at basic pH, typical of biogas scrubbing solutions and industrial wastewater. Mo and PANI co-dopants significantly enhanced the anode activity towards sulfide oxidation and ensured its complete stability even in highly corrosive sulfide solutions (e.g., 200 mM HS-). This was due to the increased electrochemically active surface area, improved coating conductivity and reduced charge transfer resistance. The (electro)catalytic oxidation of HS- demonstrated robust performance with very limited impact of different operational parameters (e.g., dissolved oxygen, anode potential, HS- concentration). Due to the formation of elemental sulfur (S0) layer at the anode surface at basic pH, longer term anode usage requires its periodic removal. Chemical dissolution of S0 with toluene allows its rapid removal without affecting the anode activity, and easy recrystallization and recovery of pure sulfur.

Changes to Material Phase and Morphology Due to High-Level Molybdenum Doping of ZnO Nanorods: Influence on Luminescence and Defects.

The influence of Mo on the electronic states and crystalline structure, as well as morphology, phase composition, luminescence, and defects in ZnO rods grown as free-standing nanoparticles, was studied using a variety of experimental techniques. Mo has almost no influence on the luminescence of the grown ZnO particles, whereas shallow donors are strongly affected in ZnO rods. Annealing in air causes exciton and defect-related bands to drop upon Mo doping level. The increase of the Mo doping level from 20 to 30% leads to the creation of dominating molybdates. This leads to a concomitant drop in the number of formed ZnO nanorods.

Rational Design of Molybdenum-Doped Cobalt Nitride Nanowire Arrays for Robust Overall Water Splitting.

Rational design of efficient electrocatalysts is highly imperative but still a challenge for overall water splitting. Herein, we construct self-supported Co3 N nanowire arrays with different Mo doping contents by hydrothermal and nitridation processes that serve as robust electrocatalysts for overall water splitting. The optimal Co3 N-Mo0.2 /Ni foam (NF) electrode delivers a low overpotential of 97 mV at a current density of 50 mA cm-2 as well as a highly stable hydrogen evolution reaction (HER). Density functional theory (DFT) calculations prove that Mo doping can effectively modulate the electronic structure and surface adsorption energies of H2 O and hydrogen intermediates on Co3 N, leading to improved reaction kinetics with high catalytic activity. Further modification with FeOOH species on the surface of Co3 N-Mo0.2 /NF improves the oxygen evolution reaction (OER) performance benefiting from the synergistic effect of dual Co-Fe catalytic centers. As a result, the Co3 N-Mo0.2 @FeOOH/NF catalysts display outstanding OER catalytic performance with a low overpotential of 250 mV at 50 1 mA cm-2 . The constructed Co3 N-Mo0.2 /NF||Co3 N-Mo0.2 @FeOOH/NF water electrolyzer exhibits a small voltage of 1.48 V to achieve a high current density of 50 mA cm-2 at 80 °C, which is superior to most of the reported electrocatalysts. This work provides a new approach to developing robust electrode materials for electrocatalytic water splitting.

Modified sol-gel process for synthesis of molybdenum oxide-doped titanium dioxide.

A modified sol-gel method was developed for the synthesis of pure and transition-metal-doped titanium dioxide. The process involves the hydrolysis of titanium tetraisopropoxide, which was used as a catalyst precursor, and molybdenum chloride, which was used as a doping agent. The shape and size of the final product were characterized by scanning electron microscopy, and the catalyst activity for the photocatalytic degradation of methylene blue in aqueous solutions was tested. The results indicate significant improvements in both the morphology and performance of the catalyst synthesized by the proposed method when compared to those obtained via the conventional approach using the same materials and quantities.•The main highlights of the proposed method are as follows.•Utilization of a double-jacketed cooling system to control and prevent temperature fluctuations during hydrolysis.•Ultrasonication during the reaction minimizes particle agglomeration during nanoparticle formation.•The use of two different alcohols and separation into two mixtures were experimentally demonstrated to delay gel formation, and hence, morphologically homogeneous catalyst nanoparticles were achieved.

Influence of molybdenum doping on the structural, optical and electronic properties of WO3 for improved solar water splitting.

Doping WO3 with foreign atoms is a very efficient strategy to modify the structural, optical and electronic properties which could influence its photoelectrochemical (PEC) water splitting activity. In this study, we report a simple and efficient single-step strategy for the fabrication of molybdenum (Mo)-doped WO3 thin films. The characterization results show that doping Mo into WO3 leads to a significant change in the morphology without changing its crystal structure. Elemental mapping and EDS analysis revealed that Mo was homogeneously doped into the crystal lattice of WO3 in the at.% range of 0-10.31. The incorporation of Mo into WO3 reduced the band-gap of WO3 and increased its light absorption ability. Notably, X-ray photoelectron spectroscopic valence band-edge analysis confirmed that substitution of Mo into WO3 led to a downward shift in the conduction band minimum without any significant change in the valence band maximum with respect to Fermi level. The fabricated Mo-doped WO3 electrodes exhibited a higher photocurrent compared to undoped WO3 samples under simulated 1.5AM sunlight without the addition of a water oxidation catalyst. The procedure proposed herein provides a simple and systematic approach for the fabrication of band-gap-tailored WO3 photoanodes by Mo doping for efficient PEC water splitting.

Molybdenum-Doped PdPt@Pt Core-Shell Octahedra Supported by Ionic Block Copolymer-Functionalized Graphene as a Highly Active and Durable Oxygen Reduction Electrocatalyst.

Development of highly active and durable electrocatalysts that can effectively electrocatalyze oxygen reduction reactions (ORR) still remains one important challenge for high-performance electrochemical conversion and storage applications such as fuel cells and metal-air batteries. Herein, we propose the combination of molybdenum-doped PdPt@Pt core-shell octahedra and the pyrene-functionalized poly(dimethylaminoethyl methacrylate)-b-poly[(ethylene glycol) methyl ether methacrylate] ionic block copolymer-functionalized reduced graphene oxide (Mo-PdPt@Pt/IG) to effectively augment the interfacial cohesion of both components using a tunable ex situ mixing strategy. The rationally designed Mo-PdPt@Pt core-shell octahedra have unique compositional benefits, including segregation of Mo atoms on the vertexes and edges of the octahedron and 2-3 shell layers of Pt atoms on a PdPt alloy core, which can provide highly active sites to the catalyst for ORR along with enhanced electrochemical stability. In addition, the ionic block copolymer functionalized graphene can facilitate intermolecular charge transfer and good stability of metal NPs, which arises from the ionic block copolymer interfacial layer. When the beneficial features of the Mo-PdPt@Pt and IG are combined, the Mo-PdPt@Pt/IG exhibits substantially enhanced activity and durability for ORR relative to those of commercial Pt/C. Notably, the Mo-PdPt@Pt/IG shows mass activity 31-fold higher than that of Pt/C and substantially maintains high activities after 10 000 cycles of intensive durability testing. The current study highlights the crucial strategies in designing the highly active and durable Pt-based octahedra and effective combination with functional graphene supports toward the synergetic effects on ORR.