Activating the Highly Reversible Mo4+/Mo5+ Redox Couple in Amorphous Molybdenum Oxide for High-Performance Supercapacitors

Scheelite Catalysts for Thermal Mineralization of Toluene: A Mechanistic Overview

Toluene, a highly stable aromatic hydrocarbon, is utilized as a benchmark molecule for thermal mineralization by the catalytic community. Mostly, the catalysts used for toluene mineralization either use platinum group metals (PGM) as catalysts or are regulated by a plasma incinerator. Though these catalysts/processes promise better efficiency and lower reaction temperature, they are neither cost-effective nor do they produce thermally stable byproducts. However, most of the metal-oxide catalysts used for toluene degradation are less efficient owing to incomplete mineralization and formation of stable intermediates, which results in higher mineralization temperature. The present work showcases tungsten- and molybdenum-based Scheelites [BaXO4 (X = W, Mo, and Mo0.5W0.5)], which have been utilized for toluene mineralization at ∼200 °C. The intermediates formed during adsorption and thermal reaction are deciphered as a function of temperature using in situ FT-IR studies including their kinetic behavior. These surface intermediates formed over the Scheelite catalysts under an oxidative/inert atmosphere elucidate the toluene mineralization mechanism as a function of temperature/time. The surface active sites for these oxide catalysts for both adsorption and formation of reaction intermediates are deciphered using detailed X-ray photoelectron spectroscopy (XPS) studies. It shows the effective role of the oxidation states of constituent oxides M-O (M = Mo/ W) in the reaction mechanism. Mineralization of toluene in a nonoxidative atmosphere shows a Mars and Van Krevelen (MVK) type of mechanism, suggesting participation of lattice oxygen for the catalytic reaction. To the best of our knowledge, this work represents one of the lowest temperatures achieved for toluene mineralization using oxide catalysts. The identification of reaction intermediates can guide further optimization efforts to minimize the mineralization temperature.

Construction of Multifunctional Conductive Carbon-Based Cathode Additives for Boosting Li6PS5Cl-Based All-Solid-State Lithium Batteries

The electrochemical performance of all-solid-state lithium batteries (ASSLBs) can be prominently enhanced by minimizing the detrimental degradation of solid electrolytes through their undesirable side reactions with the conductive carbon additives (CCAs) inside the composite cathodes. Herein, the well-defined Mo3Ni3N nanosheets embedded onto the N-doped porous carbons (NPCs) substrate are successfully synthesized (Mo-Ni@NPCs) as CCAs inside LiCoO2 for Li6PSC5Cl (LPSCl)-based ASSLBs. This nano-composite not only makes it difficult for hydroxide groups (-OH) to survive on the surface but also allows the in situ surface reconstruction to generate the ultra-stable MoS2-Mo3Ni3N heterostructures after the initial cycling stage. These can effectively prevent the occurrence of OH-induced LPSC decomposition reaction from producing harmful insulating sulfates, as well as simultaneously constructing the highly-efficient electrons/ions dual-migration pathways at the cathode interfaces to facilitate the improvement of both electrons and Li+ ions conductivities in ASSLBs. With this approach, fine-tuned Mo-Ni@NPCs can deliver extremely outstanding performance, including an ultra-high first discharge-specific capacity of 148.61 mAh g-1 (0.1C), a high Coulombic efficiency (94.01%), and a capacity retention rate after 1000 cycles still attain as high as 90.62%. This work provides a brand-new approach of "conversion-protection" strategy to overcome the drawbacks of composite cathodes interfaces instability and further promotes the commercialization of ASSLBs.

La doped-Fe2(MoO4)3 with the synergistic effect between Fe2+/Fe3+ cycling and oxygen vacancies enhances the electrocatalytic synthesizing NH3

The electrocatalytic nitrogen reduction reaction (NRR) is a crucial process in addressing energy shortages and environmental concerns by synthesizing the NH3. However, the difficulty of N2 activation and fewer NRR active sites limit the application of NRR. Therefore, the NRR performance can be improved by rapid electron transport paths to participate in multi-electron reactions and N2 activation. Doping with transition metal element is a viable strategy to provide electrons and electronic channels in the NRR. This study focuses on the synthesis of Fe2(MoO4)3 (FeMo) and x%La-doped FeMo (x = 3, 5, 7, and 10) using the hydrothermal method. La-doping creates electron transport channels Fe2+-O2--Fe3+ and oxygen vacancies, achieving an equal molar ratio of Fe2+/Fe3+. This strategy enables the super-exchange in Fe2+-O2--Fe3+, and then enhances electron transport speed for a rapid hydrogenation reaction. Therefore, the synergistic effect of Fe2+/Fe3+ cycling and oxygen vacancies improves the NRR performance. Notably, 5%La-FeMo demonstrates the superior NRR performance (NH3 yield rate: 29.6 μg h-1 mgcat-1, Faradaic efficiency: 5.8%) at -0.8 V (vs. RHE). This work analyzes the influence of the catalyst electronic environment on the NRR performance based on the effect on different valence states of ions on electron transport.

Surface Reconstruction on Metal Nitride during Photo-oxidation

The efficient conversion and storage of solar energy for chemical fuel production presents a challenge in sustainable energy technologies. Metal nitrides (MNs) possess unique structures that make them multi-functional catalysts for water splitting. However, the thermodynamic instability of MNs often results in the formation of surface oxide layers and ambiguous reaction mechanisms. Herein, we present on the photo-induced reconstruction of a Mo-rich@Co-rich bi-layer on ternary cobalt-molybdenum nitride (Co3 Mo3 N) surfaces, resulting in improved effectiveness for solar water splitting. During a photo-oxidation process, the uniform initial surface oxide layer is reconstructed into an amorphous Co-rich oxide surface layer and a subsurface Mo-N layer. The Co-rich outer layer provides active sites for photocatalytic oxygen evolution reaction (POER), while the Mo-rich sublayer promotes charge transfer and enhances the oxidation resistance of Co3 Mo3 N. Additionally, the surface reconstruction yields a shortened Co-Mo bond length, weakening the adsorption of hydrogen and resulting in improved performance for both photocatalytic hydrogen evolution reaction (PHER) and POER. This work provides insight into the surface structure-to-activity relationships of MNs in solar energy conversion, and is expected to have significant implications for the design of metal nitride-based catalysts in sustainable energy technologies.

A dual-photoelectrode fuel cell-driven self-powered aptasensor based on the 1D/2D In2S3/MoS2@Fe-CNTs heterojunction for the ultrasensitive detection of Staphylococcus aureus

A novel dual-electrode photo-fuel cell (PFC)-driven self-powered aptasensor was manufactured for the sensitive and selective detection of Staphylococcus aureus (S. aureus) using the one-dimensional (1D)/2D Schottky heterojunction comprising bimetallic indium/molybdenum sulfide nanosheets and iron-doped carbon nanotube (Fe-CNT) (denoted as In₂S₃/MoS₂@Fe-CNTs) as the photocathode. Given the generation of a robust interface at In₂S₃/MoS₂ and Fe-CNTs, the charge separation and transfer ability of photoexcited electron-hole pairs were enforced, thus improving the output voltage of the assembled PFC. In addition, the numerous active sites of the 1D/2D In₂S₃/MoS₂@Fe-CNTs Schottky heterojunction enabled the immobilization of large amounts of aptamer. Accordingly, the proposed PFC-driven self-powered aptasensor exhibited a wide linear range in 10-1 × 10⁷ CFU mL^-1 with a detection limit of 1.2 CFU mL^-1 toward S. aureus. High selectivity, excellent reproducibility, good stability, and acceptable regenerability, as well as great potential practicality, were also achieved for the detection of S. aureus using the developed PFC-driven self-powered aptasensor. This work not only provides a new photoactive material based on a robust 1D/2D Schottky heterojunction, but also constructs a novel PFC-based self-powered aptasensing strategy based on dual-photoelectrodes and with satisfactory performance for the detection of foodborne pathogens in diverse environments.

Laser Promoting Oxygen Vacancies Generation in Alloy via Mo for HMF Electrochemical Oxidation

It is well known that nickel-based catalysts have high electrocatalytic activity for the 5-hydroxymethylfurfural oxidation reaction (HMFOR), and NiOOH is the main active component. However, the price of nickel and the catalyst's lifetime still need to be solved. In this work, NiOOH containing oxygen vacancies is formed on the surface of Ni alloy by UV laser (1J85-laser). X-ray absorption fine structure (XAFS) analyses indicate an interaction between Mo and Ni, which affects the coordination environment of Ni with oxygen. The chemical valence of Ni is between 0 and 2, indicating the generation of oxygen vacancies. Density functional theory (DFT) suggests that Mo can increase the defect energy and form more oxygen vacancies. In situ Raman electrochemical spectroscopy shows that Mo can promote the formation of NiOOH, thus enhancing the HMFOR activity. The 1J85-laser electrode shows a longer electrocatalytic lifetime than Ni-laser. After 15 cycles, the conversion of HMF is 95.92%.

Carbon-encapsulated Co2P/P-modified NiMoO4 hierarchical heterojunction as superior pH-universal electrocatalyst for hydrogen production

The development of hydrogen evolution reaction (HER) technology that operates stably in a wide potential of hydrogen (pH) range of electrolytes is particular important for large-scale hydrogen production. However, the rational design of low-cost and pH-universal electrocatalyst with high catalytic performance remains a huge challenge. Herein, Co₂P nanoparticles strongly coupled with P-modified NiMoO₄ nanorods are directly grown on nickel foam (NF) substrates through carbon layer encapsulation (denoted as C-Co₂P@P-NiMoO₄/NF) by hydrothermal, deposition, and phosphating processes. This novel kind of hierarchical heterojunction has abundant heterogeneous interfaces, strong electronic interactions, and optimized reaction kinetics, representing the highly-active pH-universal electrodes for HER. Remarkably, the C-Co₂P@P-NiMoO₄/NF catalyst shows excellent HER properties in acidic and basic electrolytes, where the overpotentials of 105 mV and 107 mV are applied to drive the current density of 100 mA cm^-2. In addition, a low overpotential of 177 mV at 100 mA cm^-2 along with high stability is realized in 1 M phosphate buffer solution (PBS), which is close to the state-of-the-art non-precious metal electrocatalysts. Our work not only provides a class of robust pH-universal electrocatalyst but also offers a novel way for the rational design of other heterogeneous materials bythe interface regulation strategy.

An Amorphous Anode for Proton Battery

Developing advanced electrode materials is crucial for improving the electrochemical performances of proton batteries. Currently, the anodes are primarily crystalline materials which suffer from inferior cyclic stability and high electrode potential. Herein, we propose amorphous electrode materials for proton batteries by using a general ion-exchange protocol to introduce multivalent metal cations for activating the host material. Taking Al3+ as an example, theoretical and experimental analysis demonstrates electrostatic interaction between metal cations and lattice oxygen, which is the primary barrier for direct introduction of the multivalent cations, is effectively weakened through ion exchange between Al3+ and pre-intercalated K+. The as-prepared Al-MoOx anode therefore delivered a remarkable capacity and outstanding cycling stability that outperforms most of the state-of-the-art counterparts. The assembled full cell also achieved a high voltage of 1.37 V. This work opens up new opportunities for developing high-performance electrodes of proton batteries by introducing amorphous materials.

An Amorphous-Crystalline Nanosheet Arrays Structure for Ultrahigh Electrochemical Performance Supercapattery

Hybrid supercapacitors (HSCs), also called supercapattery, which can substitute for low power density batteries have attracted extensive interest. However, when HSCs comes to commercial applications, there is still space for improvement in energy density. It seems that designing of electrode with high capacity is an effective measure. Herein, amorphous-crystalline MoO₃ -Ni₃ S₂ /NF-0.5 nanosheet arrays are developed as battery-type electrodes. Specifically, the sheet-like structure of crystalline Ni₃ S₂ can achieve rich structural nanocrystallization, improving the redox reaction efficiency. Meanwhile, the disordered structure and irregular surface of the amorphous MoO₃ are conducive to maximize the contact between the electrode and electrolyte, slowing down the volume change caused by the continuous charge-discharge process. As a result, it displays an ultrahigh areal specific capacity of 8.52 C cm^-2 at 5 mA cm^-2 , and superior lifespan up to 7500 cycles with 90.0% retention. Further, when assembled into HSCs, the specific capacity reaches 1.47 C cm^-2 , corresponding to an energy density of 4.18 mWh cm^-2 at a power density of 0.34 mW cm^-2 . Totally, the design of the unique structure displays a valuable measure for rational development of high energy density hybrid energy storage devices that are not limited to supercapacitors.