Bifunctional Mechanism Research Articles

Asymmetric Coupled Binuclear-Site Catalysts for Low-Temperature Selective Acetylene Semi-Hydrogenation.

Heterogeneous metal catalysts with bifunctional active sites are widely used in chemical industries. Although their improvement process is typically based on trial-and-error, it is hindered by the lack of model catalysts. Herein, we report an effective vacancy-pair capturing strategy to fabricate 12 heterogeneous binuclear-site catalysts (HBSCs) comprising combinations of transition metals on titania. During the synthesis of these HBSCs, proton-passivation treatment and step-by-step electrostatic anchorage enabled the suppression of single-atom formation and the successive capture of two target metal cations on the titanium-oxygen vacancy-pair site. Additionally, during acetylene hydrogenation at 20 °C, the HBSCs (e.g., Pt1Pd1-TiO2) consistently generated more than two times the ethylene produced by their single-atom counterparts (e.g., Pd1-TiO2). Furthermore, the Pt1Pd1 binuclear sites in Pt1Pd1-TiO2 were demonstrated to catalyze C2H2 hydrogenation via a bifunctional active-site mechanism: initially C2H2 chemisorb on the Pt1 site, then H2 dissociates and migrates from Pd1 to Pt1, and finally hydrogenation occurs at the Pt1-Pd1 interface.

Boosting Alkaline Hydrogen Oxidation Kinetics through Interfacial Environments Induced Surface Migration of Adsorbed Hydroxyl

Constructing bifunctional sites through heterojunction engineering to accelerate water formation has become a pivotal strategy to improve the alkaline hydrogen oxidation reaction (HOR) kinetics, which is mainly focused on the synergistic effect of neighboring sites and the energetics of the surface reaction steps. However, the roles of the surface migration of key intermediates that go beyond the bifunctional mechanism limited to neighboring atoms have usually been ignored. Using the heterostructured Ni3C‐Ni catalyst as a model, we found that the rapid surface migration of OHad species from the positively charged Ni3C to the negatively charged Ni component played a decisive role in facilitating water formation. Such unprecedented surface migration of OHad is induced by the large discrepancy between the local surface charge densities and interfacial environments of the Ni3C and Ni components under operating conditions. Benefiting from this, the resultant Ni3C‐Ni exhibited outstanding mass activity for the alkaline HOR, which was approximately 19‐fold and 21‐fold higher than those of Ni and Ni3C, respectively. These findings not only provide novel insights into the alkaline HOR mechanism of heterostructured catalysts but also open new avenues for developing advanced electrocatalysts for alkaline fuel cells.

Boosting Alkaline Hydrogen Oxidation Kinetics through Interfacial Environments Induced Surface Migration of Adsorbed Hydroxyl.

Constructing bifunctional sites through heterojunction engineering to accelerate water formation has become a pivotal strategy to improve the alkaline hydrogen oxidation reaction (HOR) kinetics, which is mainly focused on the synergistic effect of neighboring sites and the energetics of the surface reaction steps. However, the roles of the surface migration of key intermediates that go beyond the bifunctional mechanism limited to neighboring atoms have usually been ignored. Using the heterostructured Ni3C-Ni catalyst as a model, we found that the rapid surface migration of OHad species from the positively charged Ni3C to the negatively charged Ni component played a decisive role in facilitating water formation. Such unprecedented surface migration of OHad is induced by the large discrepancy between the local surface charge densities and interfacial environments of the Ni3C and Ni components under operating conditions. Benefiting from this, the resultant Ni3C-Ni exhibited outstanding mass activity for the alkaline HOR, which was approximately 19-fold and 21-fold higher than those of Ni and Ni3C, respectively. These findings not only provide novel insights into the alkaline HOR mechanism of heterostructured catalysts but also open new avenues for developing advanced electrocatalysts for alkaline fuel cells.

Promoting role of Europium on Multi-Walled Carbon Nanotube (MWCNT) supported Platinum catalyst for Ethanol Electro-Oxidation in Direct Alcohol Fuel Cell (DAFC)

Implementing rare earth metals with platinum for Ethanol Oxidation Reactions (EOR) has received significant interest in the promising DEFC. Incorporation of europium, a rare earth metal, influences the electron density of the Pt, and the resulting catalytic activity is reinforced. Herein, different molar ratios of binary PtEu electrocatalysts supported over MWCNT were synthesized using the borohydride reduction method. The purpose of the investigation was to determine how the atomic structure, composition, and activity of the electrocatalyst correlate to the EOR. Structure, bulk composition, morphology, and bonding of the electrocatalyst were investigated through X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray (EDX), Fourier Transform Infrared spectroscopy (FTIR), and RAMAN spectroscopy. Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), chronoamperometry (CA), and Electrochemical Impedance Spectroscopy (EIS) techniques were employed to probe the electro-oxidation kinetics on the electrocatalyst's surface. During the EOR circumstances, the PtEu electrocatalysts showed a captivating composition-structure-activity relationship, consistent with the findings. Notably, all the physical and electrochemical analyses demonstrate that the bimetallic composition of the 84:16 electrocatalyst has shown higher EOR activity through a bifunctional mechanism. The results provide novel insights into the ethanol oxidation process over bimetallic alloy electrocatalysts, which is crucial for designing robust and efficient electrocatalysts for DEFC.

Molybdenum triggers the bifunctional mechanism of oxygen evolution reaction of Fe34-xNi25Co25MoxB8P8 amorphous alloy with boosted catalytic activity

High-valence metals (such as, Mo, W, Zr and Nb) have recently been reported that promote oxygen evolution reaction (OER) activity of the 3d-transition metal electrocatalysts. These high-valence metals play a key role on surface self-reconstruction process and stabilizing the low-valence active sites. However, further understand their effect on the OER mechanism is challenging, especially in amorphous electrocatalysts with complicated structure. Here, we integrate high-valence Mo with 3d metals (Fe, Co and Ni), fabricating Fe34-xCo25Ni25MoxP8B8 amorphous electrocatalysts by the melt-spinning method. We employ in-situ Raman spectroscopy to characterize the species evolution during OER, and find that the higher OER performance is originated from a bifunctional mechanism involves two catalytic sites (NiOOH and FeOOH) enabled by high-valence Mo dissolution. Benefit from this, the Fe34-xCo25Ni25MoxP8B8 with Mo show higher OER performance compared with Fe34-xCo25Ni25MoxP8B8 without Mo. For 3d-metal OER electrocatalyst, this study provides a new understanding on the effect of high-valence metals.

Novel Insight into the Synergistic Mechanism for Pd and Rh Promoting the Hydro-Defluorination of 4-Fluorophenol over Bimetallic Rh-Pd/C Catalysts.

This study explores the synergistic effect between the Rh and Pd of bimetallic Rh-Pd/C catalysts for the catalytic hydro-defluorination (HDF) of 4-fluorophenol (4-FP). It was found that 4-FP could not be efficiently hydro-defluorinated over 6% Pd/C and 6% Rh/C due to the inherent properties of Pd and Rh species in the dissociation of H2 and the activation of C-F bonds. Compared with 6% Pd/C and 6% Rh/C, bimetallic Rh-Pd/C catalysts, especially 1% Rh-5% Pd/C, exhibited much higher catalytic activity in the HDF of 4-FP, suggesting that the synergistic effect between the Rh and Pd of the catalyst was much more positive. Catalyst characterizations (BET, XRD, TEM, and XPS) were introduced to clarify the mechanism for the synergistic effect between the Rh and Pd of the catalyst in the HDF reaction and revealed that it was mainly attributed to the bifunctional mechanism: Pd species were favorable for the dissociation of H2, and Rh species were beneficial to the activation of C-F bonds in the HDF reaction. Meanwhile, the interaction between Rh and Pd species enabled Rh and Pd to exhibit a more positive synergistic effect, which promoted the migration of atomic H* from Pd to Rh species and thus enhanced the HDF of 4-FP. Furthermore, 1% Rh-5% Pd/C prepared using 20-40 equiv NaBH4 exhibited the best performance in the catalytic HDF of 4-FP. Catalysis characterizations suggested that appropriate Rh3+/Rh0 and Pd2+/Pd0 ratios were beneficial to the dissociation of H2 and the activation of C-F bonds, which caused the more positive synergistic effect between the Rh and Pd of Rh-Pd/C in the HDF reaction. This work offers a valuable strategy for enhancing the performance of catalytic HDF catalysts via promoting synergistic effects.

Catalytic Synergy between Lewis Acidic Alumina and Pt in Hydrodechlorination for Plastic Chemical Recycling.

Pyrolysis-based plastic chemical recycling has gained significant industrial attention due to its advantage of eliminating complex plastic sorting processes. However, plastic pyrolysis oil contains various components that require stringent removal before subsequent processes. In particular, Cl compounds originating from the decomposition of poly(vinyl chloride) can cause serious corrosion of reactors and catalyst deactivation in downstream processes. While extensive research has been conducted on the removal of other heteroatoms (S, N, and O) from organic compounds via hydrotreating, studies on the removal of Cl have been scarce. In this study, hydrodechlorination over Pt catalysts on various supports is comprehensively investigated using 1,2-dichloroethane as a model reactant. Our results demonstrate that Pt on γ-Al2O3 can exhibit exceptionally high catalytic activity compared to those on other supports due to a distinct bifunctional mechanism. Rigorous studies reveal that the Lewis acidic pentacoordinated Al sites of γ-Al2O3 activate C-Cl bonds, whereas Pt activates H2 and provides spillover H to remove Cl as HCl. The bifunctional mechanism enables the minimized use of precious Pt (<0.1 wt %) to achieve high activity. Pt/γ-Al2O3 also allows for efficient Cl removal (96.8%) with high stability in treating waste plastic pyrolysis oil containing 7500 ppm of Cl.

Behaviour of Pt10-xRux/C catalysts towards the hydrogen oxidation reaction in acidic medium in the presence of adsorbed CO

Pt10-xRux/C materials are synthesised using a classical polyol method and comprehensively characterised by thermogravimetric analysis, inductively coupled plasma – optical emission spectroscopy, electron transmission microscopy and x-ray diffraction. In N2-saturated electrolyte, the PtRu/C catalysts display lower onset potentials for adsorbed CO (COads) removal than the pure Pt/C one. Although the surface coverages of Pt by Ru are high, the PtRu/C catalysts display higher activity than the Pt/C one towards the hydrogen oxidation reaction (HOR), but the same mechanism occurs on all the catalysts. However, when the surface of the catalysts is saturated by COads, the HOR starts at a lower potential on Pt/C than on PtRu/C; Pt/C displays higher activity toward the HOR in the presence of COads between 0.40 and 0.55 V vs RHE. On Pt/C, a small part of COads desorbs into CO2 from 0.40 V through an Eley-Rideal mechanism, freeing very active Pt sites for the HOR. For potentials higher than 0.55 V vs RHE, the PtRu/C catalysts display higher activity for COads removal through the bifunctional mechanism. Ru atoms also block the most active Pt sites for the COads removal and the HOR.

Synergistic effect of amino and hydroxyl bifunctional modified h-BN on interfacial thermal conductivity in polydimethylsiloxane matrix: Simulations and experiments

As a widely used thermal conductive matrix material, the interface problem between polydimethylsiloxane (PDMS) and thermal conductive fillers needs to be solved urgently. The interfacial heat transfer mechanism between PDMS and hexagonal boron nitride (h-BN) modified by different groups was studied by combining density functional theory (DFT) simulation and molecular dynamics (MD) simulation. The bi-functionalization of h-BN was achieved by the environmentally friendly 6-aminocaproic acid (ACA) additive-assisted water ball milling process. The h-BN/PDMS composite thermal interface materials were prepared using a simple rolling method. The thermal conductivity of the obtained sample reached 1.256 W m−1 K−1 at a filler loading of 15 wt%. The proposed bifunctional synergistic heat transfer mechanism is expected to provide theoretical guidance for the preparation of high thermal conductivity and insulating PDMS used in electronic communications.

Dual-type atomic Ru promoted bifunctional catalytic process realizing ultralow overpotential for Li-O2 batteries

Developing well-defined catalysts to ameliorate overpotential and cycling capability is imperative for high-performance Li-O2 batteries. However, conventional catalysts face fundamental challenges that ORR and OER with different rate-determining steps are catalyzed by the same active center, inevitably weakening the selectivity and activity. Herein, we report a cross-scale catalyst with ultrafine RuPt nanoparticles and surrounding RuPt pairs on porous carbon (RuPt NPs@RuPt-N-C). The planted Ru single atoms within Pt nanoparticles and carbon matrix contribute to a fresh bifunctional catalytic mechanism for enhancing ORR/OER catalytic kinetics. As a proof-of-concept application in Li-O2 batteries, this catalyst realizes extremely low overpotentials of only 0.43 V and superior cyclic stability of 209 cycles at 200 mA g−1. Experimental and computational results disclose that for Pt NPs@Pt-N-C without Ru functionalization, only Pt-N-C works as ORR/OER active centers. By contrast, for RuPt NPs@RuPt-N-C, due to downshifted d-band center and enhanced charge transfer with LiO2 intermediate, the Pt nanocrystals are fully activated by Ru atoms, making RuPt nanocrystals as preferable ORR kinetics promoter for the formation of easily-decomposed nanoflower Li2O2. Moreover, adjacent RuPt pairs with weakened O2 affinity can work as major OER center, contributing to accelerating the following Li2O2 decomposition. This work expands the frontier of cross-scale electrocatalysts with tailored bifunctional catalysis properties for other electrocatalytic fields.

Rational one-step synthesis of porous PtAg nanowires for methanol oxidation with a CO-poisoning tolerance: An experimental and theoretical study

Binary Pt-based porous nanowires (PNWs) are highly promising for electrochemical applications owing to their high surface areas, abundant active sites, and immense durability against aggregation, but their simple template-free synthesis for methanol oxidation reaction (MOR) is rarely reported. Herein, we provide a simple and template-free method for the one-step fabrication of PtAgx PNWs via autocatalytic and oriented attachment growth mechanism in an autoclave. This drives the formation of ultra-long PtAg PNWs (∼1.5 µm length and 20 nm width) with agglutinated pores (2–10 nm), high Ag content (22–34 at%), and upshifted d-band center. These merits endowed the MOR mass activity of PtAg PNWs (2.22 mA/µgPt) by 2.26 and 2.81 times than those of Pt PNWs and commercial Pt/C catalyst, respectively, based on equivalent Pt mass besides a superior stability and CO-poisoning tolerance. The MOR activity of PtAg PNWs outperformed previously reported PtAg nanostructures. Density functional theory (DFT) simulations confirmed the bifunctional MOR mechanism with a lower energy barrier for dissociative adsorption of methanol molecules (0.49 eV) and CO oxidation on PtAg PNWs than that on Pt PNWs. This study may allow the formation of Pt-based PNWs alloys with various metals for MOR.

Bifunctional mechanism of oxygen evolution reaction and oxygen reduction reaction induced by surface reconstruction in Perovskite electrocatalysts

Elucidation of the relationship among crystal structure, material compositions, and electrocatalytic performance is beneficial to the design of electrocatalysts with high activity. Specially, for bifunctional electrocatalysts, there is a lack of the unified understanding of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) mechanisms. Based on the first-principles calculations, LaCoO3 surface reconstructions with different OH coverage under OER/ORR condition are determined. Thereby, the different reaction pathways for OER and ORR with the cooperation of Co and O sites are revealed, under which Co and lattice O sites are activated dynamically, and an overpotential of 0.35 V for the OER and 0.44 V for the ORR are obtained. Furthermore, the octahedra lattice distortion-related bifunctional mechanism (DRBM) is proposed from electron structure analysis, and the bifunctional activity of different B-site doped LaCoO3 (LaCoMO3) are studied. Based on this mechanism, we find that OER, ORR, and their bifunctional activity of LaCoMO3 all exhibit a volcano trend as a function of the O-B-O bond angle formed by Co and lattice oxygen. Consequently, we predict that Mn, Cr, Fe, and Ti doped LaCoO3 electrocatalysts exhibit remarkable bifunctional activity, which is corroborated by the reported experimental results.

Sol-gel auto-combustion synthesis of bimetallic Pt-Co/Al2O3 catalysts for hydrogen production via acetic acid steam reforming

Green hydrogen production from renewable biomass via bio-oil catalytic steam reforming was a prospective technology. In order to accelerate the development of high-performance and long-term catalyst, we selected acetic acid as a typical bio-oil model compound to carry out the studies of steam reforming. Excellent bimetallic Pt-Co/Al2O3 catalysts were prepared using a sol-gel auto-combustion method. The effects of the molar ratio of ethylene glycol: citric acid: metal ions (EG/CA/M) on the catalyst structure and subsequent reforming performance were systematically investigated. It was found that the catalyst’s textural properties, reducibility, basic sites, and the dispersion of active metal could be carefully tuned by the EG/CA/M ratio. The catalyst prepared under EG/CA/M ratio of 6:3:1 performed the best reactivity in acetic acid steam reforming, showing a 97.6% acetic acid conversion and a 96.6% H2 yield at the reaction conditions of 650 °C, steam to carbon molar ratio of 5, and space velocity of 6957 h–1. Furthermore, a bifunctional reaction mechanism of acetic acid catalytic steam reforming was proposed by in-situ diffuse reflective infrared Fourier transform spectroscopy analysis coupled with density functional theory calculations.

Synergistic catalysis of Ru0-Ru3+ in MOF supported ultrafine Ru nanoparticles catalyst promotes ethyl levulinate to γ-valerolactone

Synthesis of bifunctional catalysts is very important for the hydrogenation of biomass to advanced biofuels, but its efficient regulation is difficult. In this work, a tunable bifunctional Ru/LaQS catalyst with Lewis acid and metal hydrogenation sites was prepared by stable MOFs (LaQS) supported ultrafine Ru nanoparticles (NPs). When the optimal Ru2/LaQS catalyst catalyzed bio-based ethyl levulinate (EL) to γ-valerolactone (GVL), the EL conversion and GVL selectivity reached 99.9% under mild conditions of 100 °C. The excellent catalytic performance is mainly attributed to the synergistic effect of Ru0-Ru3+ on ultrafine Ru NPs with only 1.60 nm generated by metal-support interaction, which is proved by experimental characterization and theoretical calculation. Moreover, the electron density of hydrogenation active site Ru0 and the content of acidic site Ru3+ can be modulated by Ru loading. Among them, the activation of H2 was promoted by the high electron density of Ru0 generated through metal-support electronic interactions. The enhanced medium-strong acidic site Ru3+ not only improved the activation of EL, but also promoted the intramolecular dealcoholization of the intermediate to GVL. The synergistic catalytic mechanism of Ru0-Ru3+ on ultrafine Ru NPs was speculated. The excellent stability was mainly attributed to the metal-support interaction stabilizing the ultrafine Ru NPs, which prevents the agglomeration and loss of Ru NPs during cycling. This work provides an in-depth understanding of the bifunctional catalytic mechanism, which is of guiding significance for the design and preparation of MOFs-based catalysts for biomass hydrogenation.

Hydrocracking of non‐edible vegetable oil and waste cooking oils for the production of light hydrocarbon fuels: A review

AbstractThe high demand for biofuels by surfacing economies with environmental issues has resulted in a more in‐depth search for new biofuel feedstocks. Non‐edible oils have become the centre of investigation as biofuel feedstocks since they do not compete with food sources. This review evaluates hydrocracking as a biofuel production method and further elucidates different feedstocks, the effects of hydrocracking catalysts, and operating parameters to obtain optimum yields and selectivity of desired products. The bifunctional catalyst mechanism is also explained. The hydrocracking technique is found to be more advantageous than other biofuel production techniques such as transesterification and pyrolysis due to its ability to produce valuable products of better quality and with higher yields. Coke formation is one of the challenges faced by hydrocracking despite that it can be reduced by high hydrogen pressure; this will increase the cost of the entire process.

The Effect of SnO&lt;sub&gt;2&lt;/sub&gt; and Rh on Pt Nanowire Catalysts for Ethanol Oxidation

In this study, we synthesized Pt-Rh nanowires (NWs) through chemical reduction of metallic precursors using formic acid at room temperature, excluding the use of surfactants, templates, or stabilizing agents. These NWs were supported on two substrates: carbon (Vulcan XC-72R) and carbon modified with tin oxide (SnO&lt;sub&gt;2&lt;/sub&gt;) via the sol-gel method (10 wt.% SnO&lt;sub&gt;2&lt;/sub&gt;). We explored the electroactivity of Pt/SnO&lt;sub&gt;2&lt;/sub&gt;/C, Pt-Rh/C, Pt-Rh/SnO&lt;sub&gt;2(commercial)&lt;/sub&gt;/C (commercial SnO&lt;sub&gt;2&lt;/sub&gt;), and Pt-Rh/SnO&lt;sub&gt;2&lt;/sub&gt;/C NWs toward electrochemical oxidation of ethanol in acidic media using various techniques, including CO-stripping, cyclic voltammetry, derivative voltammetry, chronoamperometry, and steady-state polarization curves. Physical characterization involved X-ray diffraction and transmission electron microscopy. The synthesized NWs exhibit higher ethanol oxidation activity than the commercial Pt/C (Johnson Matthey™) catalyst. Rh atoms are hypothesized to enhance complete ethanol oxidation, while the NW morphology improves ethanol adsorption at the catalyst surface for subsequent oxidation. Additionally, the choice of support material plays a significant role in influencing the catalytic activity. The superior catalytic activity of Pt-Rh/SnO&lt;sub&gt;2&lt;/sub&gt;/C NWs may be attributed to the facile dissociation of the C-C bond, low CO adsorption (electronic effect due to Rh presence), and the bifunctional mechanism facilitated by the oxophilic nature of the SnO&lt;sub&gt;2&lt;/sub&gt; support.

Optimizing Nickel Orbital Occupancy via Co‐Modulation of Core and Shell Structures to Accelerate Alkaline Hydrogen Electro‐Oxidation Reaction

AbstractNickel‐based catalysts are recognized as a promising alternative to platinum‐based catalysts for the alkaline hydrogen oxidation reaction (HOR) yet suffer from poor stability and relatively low activity. Herein, a nitrogen ligand‐assisted approach is reported to encapsulate nickel‐copper nanoparticles within few carbon layers, and by modulating the core and shell components/structure, the charge distribution in the nanostructures can be finely regulated. The optimized Ni93Cu7@NC catalyst exhibits outstanding HOR activity with an intrinsic activity of 61.0 µA cm−2 and excellent stability, which is among the most advanced Ni‐based HOR catalysts. Notably, an alkaline exchange membrane fuel cell utilizing this catalyst achieves a peak power density of 381 mW cm−2 and maintains stability at 100 mA cm−2 for over 24 h. Experimental and theoretical investigations unveil that the electron re‐distribution at the interface of NiCu core and nitrogen‐doped carbon reduces the electron occupancy in Ni 4s‐H 1s bonding orbitals and Ni 3dz2/yz‐O 2p antibonding orbitals, leading to a weakened hydrogen binding energy and enhance hydroxide binding energy. Consequently, the limiting energy for the HOR is reduced following a bifunctional mechanism on the Ni93Cu7@NC. This work provides a core‐shell co‐modulation strategy to accurately regulate the electronic structure of transition metals to design robust catalysts.

Rational strategy for boosting productivity of salicylamide from urea and phenol over metal oxides via modulation their acidic-basic characters

The industrial viability of green synthesis of salicylamide from urea and phenol is obstructed by the low salicylamide productivity using metal oxides as the catalysts. Here, a series of single- and mixed-oxides having different metal compositions (Zn, Mg, Fe, Al) with varied acidic-basic characters were prepared to catalyze all the identified comprising paths of reaction between urea and phenol. Based on in situ FTIR characterization, a bi-functional mechanism that urea and phenol were separately activated on the acidic and basic centers to collaboratively promote the synthesis of salicylamide, was disclosed. Nevertheless, the surface active sites would be blocked due to the strong absorption of urea when catalysts exhibited extra acidity. Additionally, the secondary reactions would aggravate sharply over too basic samples. Thanks to its well-balanced acidity/basicity, Zn-Al mixed oxide provided the best catalytic performance. Herein, we offer a rational approach to develop metal oxides for the effective manufacture of salicylamide.

In-situ sodium chloride template synthesis of γ-WO3 hollow cubes for high-sensing and dual-selective hydrazine/dibutylamine detection at different temperatures

The fabrication of a chemiresistive sensor with dual-selectivity to highly toxic and explosive N2H4/dibutylamine (DBA) remains challenging due to no report. To this aim, we synthesized uniform (NH4)0.33WO3 cuboid precursors through optimized solvothermal reaction and in-situ formed NaCl template. Subsequently, the precursors were calcined in air to transform into γ-WO3 hollow cubes (WO3-HC) assembled from near-spherical nanoparticles, and the effect of calcination temperature on microstructures and gas-sensing properties was investigated. Among, WO3-HC-5 obtained by calcining precursor at 500 °C has broad pore channels, large specific surface area and abundant oxygen vacancy defects. Under the catalytic synergy of surface W6+ Lewis acid with dangling bonds, WO3-HC-5 sensor realizes the bifunctional monitoring of N2H4 and DBA. It presents large response value (S = 606.6) to 100 ppm N2H4 at 50 °C and a good response (S = 76.7) to the same concentration of DBA at 217 °C, and has fast response rate, low practical detection limit, satisfactory stability and humidity resistance. WO3-HC-5 represents the first metal oxide-based sensor with dual-selectivity towards aforementioned harmful gases at different operating temperatures. Moreover, the bifunctional mechanism has been characterized and analyzed in detail.

Molybdenum–Based Electrocatalysts for Direct Alcohol Fuel Cells: A Critical Review

&lt;p&gt;Direct alcohol fuel cells (DAFCs) have gained much attention as promising energy conversion devices due to their ability to utilize alcohol as a fuel source. In this regard, Molybdenum-based electrocatalysts (Mo-ECs) have emerged as a substitution for expensive Pt and Ru–based co-catalyst electrode materials in DAFCs, owing to their unique electrochemical properties useful for alcohol oxidation. The catalytic activity of Mo-ECs displays an increase in alcohol oxidation current density by several folds to 1000–2000 mA mg&lt;sub&gt;Pt&lt;/sub&gt;&lt;sup&gt;−1&lt;/sup&gt;, compared to commercial Pt and PtRu catalysts of 10–100 mA mg&lt;sub&gt;Pt&lt;/sub&gt;&lt;sup&gt;−1&lt;/sup&gt;. In addition, the methanol oxidation peak and onset potential have been significantly reduced by 100–200 mV and 0.5–0.6 V, respectively. The performance of Mo-ECs in both acidic and alkaline media has shown the potential to significantly reduce the Pt loading. This review aims to provide a comprehensive overview of the bifunctional mechanism involved in the oxidation of alcohols and factors affecting the electrocatalytic oxidation of alcohol, such as synthesis method, structural properties, and catalytic support materials. Furthermore, the challenges and prospects of Mo-ECs for DAFCs anode materials are discussed. This in-depth review serves as valuable insight toward enhancing the performance and efficiency of DAFC by employing Mo-ECs.&lt;/p&gt;