Kinetics Of Methanol Oxidation Research Articles

Potential-dependent photo-electro-catalysis coupling mechanism for methanol oxidation: A case study over Pt/Cu-Nb2O5 nanorod arrays

The sluggish methanol oxidation kinetics has seriously hindered the development of direct methanol fuel cells. Photo-electro-catalysis is expected to accelerate reaction rates, yet suffers from lack of efficient photoelectrocatalysts and more importantly, less understanding on photo-electro-catalysis mechanism. Herein, a unique Cu-Nb2O5 nanorod array with excellent light adsorption and charge transfer ability, on which supports Pt nanoparticles, is constructed for photo-electrocatalytic methanol oxidation reaction (MOR). Systematical investigation discovers a potential-dependent photo-electro-catalysis coupling mechanism, i.e., at lower potential bias where the Fermi level of semiconductor (Ef,s) is beyond the Fermi level of Pt (Ef,Pt), electrons transferring from Pt to semiconductor is switched off, so semiconductor Cu-Nb2O5 alone takes a dominant role for both methanol and water activation; at higher potential bias where Ef,s is below Ef, Pt, electrons flowing from Pt to semiconductor is switched on, so methanol dehydrogenation on Pt surface is allowed energetically. Further investigation on the MOR processes prompts us to propose a MOR pathway that methanol dehydrogenates on Pt surface, with the aid of *OH from the photo-activated water on Cu-Nb2O5 to proceed via formaldehyde, formic acid to carbon dioxide, resulting to a low apparent activation energy and fast kinetics of MOR as compared to its counterpart Pt/Nb2O5. This work not only provides an efficient photoelectrocatalyst for methanol oxidation, but also sheds lights on the underlying photo-electro-catalysis coupling mechanism over semiconductor–metal catalysts.

Laser-Synthesized Co-Doped CuO Electrocatalyst: Unveiling Boosted Methanol Oxidation Kinetics for Enhanced Hydrogen Production Efficiency by In Situ/Operando Raman and Theoretical Analyses.

The present study details the strategic development of Co-doped CuO nanostructures via sophisticated and expedited pulsed laser ablation in liquids (PLAL) technique. Subsequently, these structures are employed as potent electrocatalysts for the anodic methanol oxidation reaction (MOR), offering an alternative to the sluggish oxygen evolution reaction (OER). Electrochemical assessments indicate that the Co-CuO catalyst exhibits exceptional MOR activity, requiring a reduced potential of 1.42V at 10 mAcm-2 compared to that of pure CuO catalyst (1.57V at 10 mAcm-2 ). Impressively, the Co-CuO catalyst achieved a nearly 180mV potential reduction in MOR compared to its OER performance (1.60V at 10 mA cm-2 ). Furthermore, when pairing Co-CuO(+)ǀǀPt/C(-) in methanol electrolysis, the cell voltage required is only 1.51V at 10 mAcm-2 , maintaining remarkable stability over 12h. This represents a substantial voltage reduction of ≈160mV relative to conventional water electrolysis (1.67V at 10 mAcm-2 ). Additionally, both in situ/operando Raman spectroscopy studies and theoretical calculations have confirmed that Co-doping plays a crucial role in enhancing the activity of the Co-CuO catalyst. This research introduces a novel synthetic approach for fabricating high-efficiency electrocatalysts for large-scale hydrogen production while co-synthesizing value-added formic acid.

Immobilizing ultrafine PtRu alloy nanoparticles onto 3D interconnected MXene-graphene frameworks for highly efficient methanol oxidation

Although direct methanol fuel cell (DMFC) is regarded as a promising power source to establish green energy conversion system, its overall performance is largely limited by the slow methanol oxidation kinetics of current anode catalysts. Herein, we demonstrate a robust and facile bottom-up strategy for the controllable construction of ultrafine PtRu alloy nanoparticles immobilized onto three-dimensional (3D) interconnected Ti3C2Tx MXene-graphene frameworks (PtRu/MXene-G) through a co-assembly process. Interestingly, the utilization of 3D porous MXene-G matrix provides strong interfacial interactions with alloy nanocrystals and promotes the transportation of both reactant and electron during the electrocatalytic process, while the introduction of Ru atoms ameliorates the Pt electronic structure and generates plentiful hydroxyl species for the oxidative removal of CO byproducts. Working together, the resulting PtRu/MXene-G nanoarchitecture with an appropriate Pt/Ru atomic ratio exhibits exceptional methanol oxidation properties in terms of a large electrochemically active surface area of 101.8 m2 g−1, a high mass (specific) activity of 1779.5 mA mg−1 (1.75 mA cm−2), and good long-term stability, all of which are significantly superior to those of conventional Pt/carbon black, Pt/G, Pt/MXene, and Pt/MXene-G catalysts with an identical Pt usage.

Ni and Fe mixed oxide anchored on CNTs, GONRs, and Ti3C2 Mxene as efficient nanocatalysts for direct power generation from methanol electro-oxidation

In the field of heterogeneous catalysis, the selection of appropriate support is an effective strategy due to metal loading reduction and enhancing electron transfer kinetic. In this work, the performance of carbon nanotubes (CNTs), reduced graphene oxide nanoribbons (rGONRs), and titanium carbide nanosheets (Ti3C2 Mxene) as support was investigated on the catalytic performance of NiFe2O4 spinel nanoparticles. The samples were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, BET surface area analysis, field emission scanning, and transmission electron microscopy. The electrochemical properties of samples as fuel cell catalysts were compared using electrochemical techniques. The electrocatalytic activity of samples in methanol oxidation reaction (MOR) was obtained to be: NiFe2O4/Ti3C2> NiFe2O4/rGONRs > NiFe2O4/CNTs > NiFe2O4. The results approve that the Ti3C2 Mxene promotes the catalytic performance of NiFe2O4 and enhances the methanol oxidation kinetics via conductive pathway creation. Therefore, Ti3C2 can lead to great opportunities as an efficient catalyst support for alcohol fuel cells in the future.

The influence of annealing temperature on the electrocatalytic performance of NiCo2O4/rGONRs in the methanol oxidation reaction

Nickel oxide and cobalt oxide have been widely used as adsorbents, gas sensors, catalysts, and electrode materials. In this work, nickel cobaltite nanoparticles were anchored on graphene oxide nanoribbons (NiCo2O4/rGONRs) via a hydrothermal process. The influence of annealing temperature on the crystalline structure and the electrocatalytic performance of nanocomposites was investigated. The electrocatalytic activity of nanocomposites in the methanol oxidation reaction was obtained in the following order: NiCo2O4/rGONR(400)> NiCo2O4/rGONR(600)> NiCo2O4/rGONR(200)> NiCo2O4(400)> NiCo2O4/rGONR(0). The results approved that the increase of annealing temperature up to 400 °C promotes the catalytic performance and subsequently, enhances the methanol oxidation kinetics through changing crystalline structure. The comparison of NiCo2O4(400) nanoparticles with NiCo2O4/rGONR(400) nanocomposite showed that the presence of rGONRs as substrate improves the electrochemical activity and stability of NiCo2O4 nanoparticles. Based on this, NiCo2O4/rGONR(400) nanocomposite has good potential for use as a catalyst in the electrooxidation process of methanol due to its lower onset potential, and charge transfer resistance and greater electrochemical surface area.

The Thermal Kinetics of Methanol Oxidation on Pt/MWCNT Electrocatalysts in Alkaline Media

The Thermal Kinetics of Methanol Oxidation on Pt/MWCNT Electrocatalysts in Alkaline Media

Kinetics of catalytic oxidation of oxygenated fuels on Pt/ZSM-5 catalyst

To build a set of complete kinetic parameters of oxygenated fuels kinetic model on Pt catalyst, methanol was used as an example to carry out the catalytic oxidation kinetics experiment of oxygenated fuels on Pt/ZSM-5 catalyst. The Power law model and Langmuir–Hinshelwood (L–H) model were established to characterise the catalytic oxidation reaction of methanol. Then the oxidation kinetics of methanol, ethanol, dimethyl ether (DME) and n-butanol on Pt/ZSM-5 was studied under the same experimental conditions. It was found that the reaction orders of fuel molecules (methanol is −0.14) were much less than that of oxygen (1.23) in Power law model. The adsorption constants of fuel molecules were higher than that of oxygen in L–H model. The adsorption characteristics of alcohols on Pt were similar, but the reaction orders of alcohols were not consistent. The adsorption constants and adsorption heat of dimethyl ether were much larger than that of alcohols. The intrinsic reaction rates of four oxygenated fuels on Pt/ZSM-5 were compared at the same input power: r methanol r DME r ethanol r n-butanol. In general, methanol is a suitable oxygenated fuel in the design and development of catalytic micro-combustor.

Heterogeneous Pair Approximation of Methanol Oxidation on TiO2 Reveals Two Reaction Pathways

We propose a novel method to simulate the chemical kinetics of methanol oxidation on the rutile TiO2(110) surface. Such a method must be able to capture the effects of static disorder (site-to-site variations in the rate constants), as well as dynamic correlation (interdependent probabilities of finding reactants next to each other). Combining the intuitions of the mean-field steady state (MFSS) method and the pair approximation (PA), we consider representative pairs of sites in a self-consistent bath of the average pairwise correlation. Preaveraging over the static disorder in one site of each pair makes this half heterogeneous pair approximation (HHPA) efficient enough to simulate systems of several species and calibrate rate constants. According to the simulated kinetics, a static disorder in the hole transfer steps suffices to reproduce the stretched exponentials in the observed kinetics. The dominant hole scavengers are found to be temperature-dependent: the methoxy anion at 80 K and the methanol molecule at 180 K. Moreover, two distinct subpopulations of 5-coordinate titanium (Ti5c) sites emerge, a high-activity group and a low-activity group, even though no such division exists in the rate constants. Since the division is quite insensitive to the details of static disorder, the emergence of the two groups might play a significant role in a variety of photocatalytic processes on TiO2.

Enhanced methanol oxidation on PtNi nanoparticles supported on silane-modified reduced graphene oxide

Developing low cost, highly efficient, and long-term stability electrocatalysts are critical for direct oxidation methanol fuel cell. Despite huge efforts, designing low-cost electrocatalysts with high activity and long-term durability remains a significant technical challenge. Here, we prepared a new kind of platinum-nickel catalyst supported on silane-modified graphene oxide (NH2-rGO) by a two-step method at room temperature. Powder X-ray diffraction, UV–vis spectroscopy, Raman, FTIR spectroscopy and X-ray photoelectron spectroscopy results confirm that GO was successfully modified with 3-aminopropyltriethoxysilane (APTES), which helps to uniformly disperse PtNi nanoparticles. Cyclic voltammetry, chronoamperometry, CO-stripping and rotating disk electrode (RDE) results imply that PtNi/NH2-rGO catalyst has significantly higher catalytic activity, enhance the CO toxicity resistance, higher stability and much faster kinetics of methanol oxidation than commercial Pt/C under alkaline conditions.

Engineering intermetallic-metal oxide interface with low platinum loading for efficient methanol electrooxidation

Constructing a distinctive electrochemical interface with low platinum content to boost the sluggish methanol electrooxidation kinetics is critical for commercializing the direct methanol fuel cells. Herein, we have synthesized highly active electrocatalysts with unique intermetallic-metal oxide interfaces through a facile pyrolysis method. Physical characterizations demonstrate that the obtained PtFe(1:2)@a-FeOx/NC-C catalyst with low platinum content of 7.2 wt% possesses an interfacial structure composed of face-centered tetragonal (L10) PtFe intermetallic nanoparticles accompanied with amorphous iron oxide. Electrochemical measurements show that the synthesized PtFe(1:2)@a-FeOx/NC-C catalyst not only exhibits excellent methanol electrooxidation activities with a mass activity of 1.48 A mg-1Pt and a specific activity of 2.34 mA cm-2Pt in acid medium, but also possesses better CO-tolerant performance and faster methanol oxidation kinetics compared with commercial Pt/C. The improved electrochemical performances may ascribe to the modified electronic structure by alloying platinum with iron and the special PtFe@a-FeOx interface, which render strong synergistic interactions between bimetallic PtFe nanoparticles and amorphous iron oxide. Consequently, the presented strategy offers new prospects into the construction of low-cost electrocatalysts with unique electrochemical interface for enhancing catalytic performances.

Photodriven Charge Accumulation and Carrier Dynamics in a Water-Soluble Carbon Nitride Photocatalyst.

Charge accumulation in photoactive molecules and materials holds great promise in solar energy conversion as it allows for decoupling solar‐driven charging from (dark) redox reactions. In this contribution, light‐driven charge accumulation was investigated for a recently reported novel water‐soluble carbon nitride [K,Na‐poly(heptazine imide); K,Na‐PHI] photocatalyst, which exhibits excellent activity and stability in highly selective photocatalytic oxidation of alcohols and concurrent reduction of dioxygen to H2O2 under quasi‐homogeneous conditions. An excellent charge storage ability of the K,Na‐PHI material was demonstrated, showing an optimal density of accumulated electrons (32.2 μmol of electrons per gram) in the presence of 10 vol % MeOH as a sacrificial electron donor. The long‐lived electrons accumulated under anaerobic conditions as K,Na‐PHI.− radical ions were utilized in interfacial electron transfer to O2 or methyl viologen in a subsequent dark reaction. Ultrafast time‐resolved spectroscopy was employed to reveal the kinetics of charge‐carrier recombination and methanol oxidation. Geminate recombination of electrons and holes within approximately 100 ps was followed by trap‐assisted recombination. The presence of methanol as a sacrificial electron donor accelerated the decay of the transient absorption signal when a static sample was used. This behavior was ascribed to the faster charge recombination in the presence of the radical anions generated after hole extraction. The work suggests that photodriven electron storage in the water‐soluble carbon nitride is enabled by localized trap states, and highlights the importance of the effective electron donor for creating long‐lived photo‐generated carbon nitride radicals.

Boosting cell performance and fuel utilization efficiency in a solar assisted methanol microfluidic fuel cell

Solar generated hydrogen from an optimized P25 thin film of 3.2 mg/cm2 with 0.25% of platinum as co-catalyst improves the peak power output of a methanol microfluidic fuel cell operated with a methanol to water ratio of 1:1 almost ninefold, from 22 mW/cm2 to 213 mW/cm2. Different methanol to water ratios in the fuel tank generate similar amounts of hydrogen, but the cell performance has large variations due to the different oxidation kinetics of hydrogen and methanol in the fuel breathing anode, resulting in a mixed-potential anodic performance. The trade-off between power output and fuel utilization diminishes in this system. The methanol utilization efficiency at peak power operation increases from 50% (for 0.2 V) to 78% (for 0.5 V) for methanol to water ratio of 1:1. The result indicates that in-situ generation of hydrogen by solar light can be applied to both portable and large-scale stationary fuel cells.

Microkinetic Modeling of the Oxygen Evolution Reaction (OER) on Hydrous Iridium Oxide during Dynamic Operation

In an energy system which is based on intermittent renewable sources, efficient energy storage and conversion technologies are needed. Proton exchange membrane (PEM) electrolysis is a promising technology for the storage of electrical energy in the form of hydrogen. In PEM electrolyzers, the oxygen evolution reaction (OER) is seen as the bottleneck due to its high overpotential. To enhance the overall performance, highly active but stable OER catalysts are essential. Oxidized iridium shows good activity for the OER and is more stable compared to other materials such as ruthenium oxide[1]. It has been shown that electrochemically grown hydrous iridium oxide is particularly favorable[2]. A better understanding of the changes of its complex surface structure and chemistry during dynamic operations is crucial for practical applications and for obtaining deep insights in factors that affect its activity and stability.In the present work we investigate the surface states of hydrous iridium during the OER. For this purpose, we implement a dynamic physical model to simulate the formation of different types of intermediate states. A complete set of microkinetic equations is derived, solved and validated with cyclovoltammetric data (see figure 1). By solving the surface species balances dynamically, the phenomena that are observable in cyclovoltammetric, chronoamperometric and impedance spectroscopic experiments can be interpreted quantitatively[3].Applying this method onto hydrous iridium oxide we are able to study the degree of oxidation of the iridium atoms at the surface at various electrode potentials. In a wide potential region from 0.4 V vs RHE up to the OER potential range, the simulation predicts the amount of adsorbed -OH, -O, -OOH and -OO species, which determine the overall oxidation state of the iridium. The characteristic peaks and shoulders in the cyclovoltammogram are assigned to the single reaction steps. By comparing different mechanisms, a deep understanding of the predominant reaction pathway is gained. Furthermore, the quantification of microkinetic rate constants allows us to define rate determining reaction steps during the dynamic operation. With this study we confirm that the mechanism in figure 1, in which two parallel reaction pathways are present, can describe the experimental cyclovoltammogram quantitatively.[1] S. Cherevko et al., Oxygen and hydrogen evolution reactions on Ru, RuO 2 , Ir, and IrO 2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stability, Catalysis Today 262 (2016) 170–180[2] S. Cherevko et al., Oxygen evolution activity and stability of iridium in acidic media. Part 2. –Electrochemically grown hydrous iridium oxide, Journal of Electroanalytical Chemistry 774 (2016) 102–110[3] U. Krewer et al., Impedance spectroscopic analysis of the electrochemical methanol oxidation kinetics, Journal of Electroanalytical Chemistry, 589 (2006) 148–159 Figure 1

Sustainable and selective formic acid production from photoelectrochemical methanol reforming at near-neutral pH using nanoporous nickel-iron oxyhydroxide-borate as the electrocatalyst

Industrial production of formic acid requires a highly energy-intensive process involving carbonylation of methanol with fossil fuel-based CO to methyl formate and subsequent hydrolysis of methyl formate to formic acid. In this study, we present a sustainable and selective production of formic acid from methanol-reforming using electro-synthesized nanoporous nickel-iron oxyhydroxide-borate thin film (nanoFe:Ni-Bi) as the electrocatalyst at near-neutral pH. We found that the incorporation of a suitable amount of iron not only facilitated the formation of active Ni3+ species but also improved the kinetics of methanol oxidation with active Ni3+ species, resulting in the significant enhancement in the formate production. Notably, nanoFe:Ni-Bi with optimal Fe content exhibited a turnover frequency (TOF) of 152.71 ± 9.95 h−1 with Faradic efficiency for formate production (FEformate) of 66.3 ± 1.7%, whereas nanoporous nickel oxyhydroxide-borate only showed a TOF of 56.65 ± 12.68 h−1 with FEformate of 30.5 ± 5.6%. In addition, a highly efficient and selective photoelectrochemical methanol-reforming system using nanoFe:Ni-Bi modified BiVO4 photoanode was established. In contrast to the negligible activity of the pristine BiVO4 photoanode, nanoFe:Ni-Bi modified BiVO4 photoanode exhibited formate production rate of 5.7 ± 1.0 μmole cm−2h−1 with a FEformate of 94.6 ± 12.3% at an applied potential of 0.55 V vs. RHE under light illumination. This study provides a sustainable and less-energy intensive alternative route for the production of formic acid.

Electrocatalytic performance of CeO2-decorated rGO as an anode electrocatalyst for the methanol oxidation reaction

CeO2 nanoparticles are well known for their stability and reactivity in different catalytic applications. However, there have been only a few reports on the applications of CeO2 nanoparticles in methanol electro-oxidation. In this work, the synthesis of CeO2/reduced graphene oxide (rGO) hybrid nanomaterial by the hydrothermal method as anode material for methanol oxidation is reported. The nanoparticles are characterized by X-ray diffraction microscopy, Raman spectroscopy, and scanning and transmission electron microscopy. The electrochemical properties of the catalysts are evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. CeO2/rGO shows higher activity toward methanol oxidation than CeO2 because of the specific surface area of rGO and its electrical conductivity. Furthermore, from impedance analysis the charge transfer resistance of CeO2/rGO is 312 Ω, which is three times lower than that of CeO2 (913 Ω), indicating rGO increases methanol oxidation kinetics.

Advancement toward Polymer Electrolyte Membrane Fuel Cells at Elevated Temperatures.

Elevation of operational temperatures of polymer electrolyte membrane fuel cells (PEMFCs) has been demonstrated with phosphoric acid-doped polybenzimidazole (PA/PBI) membranes. The technical perspective of the technology is simplified construction and operation with possible integration with, e.g., methanol reformers. Toward this target, significant efforts have been made to develop acid-base polymer membranes, inorganic proton conductors, and organic-inorganic composite materials. This report is devoted to updating the recent progress of the development particularly of acid-doped PBI, phosphate-based solid inorganic proton conductors, and their composite electrolytes. Long-term stability of PBI membranes has been well documented, however, at typical temperatures of 160°C. Inorganic proton-conducting materials, e.g., alkali metal dihydrogen phosphates, heteropolyacids, tetravalent metal pyrophosphates, and phosphosilicates, exhibit significant proton conductivity at temperatures of up to 300°C but have so far found limited applications in the form of thin films. Composite membranes of PBI and phosphates, particularly in situ formed phosphosilicates in the polymer matrix, showed exceptionally stable conductivity at temperatures well above 200°C. Fuel cell tests at up to 260°C are reported operational with good tolerance of up to 16% CO in hydrogen, fast kinetics for direct methanol oxidation, and feasibility of nonprecious metal catalysts. The prospect and future exploration of new proton conductors based on phosphate immobilization and fuel cell technologies at temperatures above 200°C are discussed.

Significantly enhanced performance of direct methanol fuel cells at elevated temperatures

The performance of direct methanol fuel cells (DMFCs) is constrained by the sluggish kinetics of methanol oxidation reaction. Increasing the temperature can effectively increase the methanol oxidation kinetics, offering new opportunities to achieve high performance. Here we studied the performance of DMFCs based on the newly developed silica impregnated phosphoric acid doped polybenzimidazole (PA/PBI/SiO2) composite membrane. The composite membrane shows a proton conductivity of 2.9–4.1 × 10−2 S cm−1 at temperatures between 200 and 250 °C and is stable at high temperatures. The cells using the composite membrane successfully delivered a peak power density of 136 mW cm−2 and 237 mW cm−2 at 260 °C using the Pt/C and PtRu/C as the anode catalysts, respectively. The cells with the PA/PBI/SiO2 composite membrane show a much higher power output than that with conventional PA/PBI membranes. Most importantly, the results demonstrate that there exists a distinct transition temperature around 205 °C for the performance of DMFCs. Above this transition temperature, the increase in power density with temperature is 208 mWcm−2/100 °C, which is more than 4 times higher than 50 mWcm−2/100 °C obtained at temperatures below 205 °C. The presence of such transition temperature for DMFCs is most likely due to the significantly enhanced kinetics of the methanol oxidation reaction at elevated temperatures. Operation at elevated temperatures, i.e., above 205 °C, is most effective to significantly enhance the power performance of DMFCs.

Thin Layer Sonoelectrochemistry: Electrocatalysis in Oxygen Reduction Reaction (ORR) and Methanol Electrolysis

In electrochemical energy systems such as fuel cells, important reactions include the oxygen reduction reaction (ORR) and methanol oxidation. Even with platinum catalysts, oxygen reduction kinetics in water at acidic pH are slow. In H₂ proton exchange membrane fuel cells (PEM FCs), ORR is the rate determining kinetic process. In direct reformation fuel cells run on methanol with an oxygen or air cathode, methanol oxidation kinetics are rate limiting. Limitations include slow electron transfer processes coupled to generation of oxidation by-products that adsorb to the electrode and lead to passivation. Sonoelectrochemistry in thin layers of electrolyte enhances electrochemical rates without visible cavitation using low power oscillators [1]. Here, thin layer sonoelectrochemistry coupled with cyclic voltammetry is used to evaluate impacts of sonication in a thin layer on the electrochemical response of oxygen and methanol . For voltammetry at platinum electrodes for saturated oxygen in acidic aqueous electrolyte, the rate of the ORR is enhanced several orders of magnitude as shown by fit of the cyclic voltammetric data. For stoichiometric (50:50) methanol in water with acid electrolyte, oxidation and reduction currents at platinum electrodes are increased almost ten fold as shown in cyclic voltammetric responses. Sonication may increase the rates of electron transfer and remove deposited partial oxidation products. Improved kinetics of oxygen reduction and methanol electrolysis may provide a means to improved electrochemical energy technologies, including hydrogen and direct reformation fuel cells. The energy needed to drive the oscillator represents a low parasitic loss on fuel cell performance. Reference [1] Johna Leddy, Chester G. Duda, Jacob Lyon, and William J. Leddy III, "Thin Layer Sonoelectrochemistry and Sonoelectrochemistry Devices and Methods," published 28 May 2015 as US Patent Application 20150147594 A1.

Octahedral gold-silver nanoframes with rich crystalline defects for efficient methanol oxidation manifesting a CO-promoting effect

Three-dimensional bimetallic nanoframes with high spatial diffusivity and surface heterogeneity possess remarkable catalytic activities owing to their highly exposed active surfaces and tunable electronic structure. Here we report a general one-pot strategy to prepare ultrathin octahedral Au3Ag nanoframes, with the formation mechanism explicitly elucidated through well-monitored temporal nanostructure evolution. Rich crystalline defects lead to lowered atomic coordination and varied electronic states of the metal atoms as evidenced by extensive structural characterizations. When used for electrocatalytic methanol oxidation, the Au3Ag nanoframes demonstrate superior performance with a high specific activity of 3.38 mA cm−2, 3.9 times that of the commercial Pt/C. More intriguingly, the kinetics of methanol oxidation on the Au3Ag nanoframes is counter-intuitively promoted by carbon monoxide. The enhancement is ascribed to the altered reaction pathway and enhanced OH− co-adsorption on the defect-rich surfaces, which can be well understood from the d-band model and comprehensive density functional theory simulations.

Synthesis of 3D Flower-Like Ni0.6Zn0.4O Microspheres for Electrocatalytic Oxidation of Methanol

The 3D flower-like Ni0.6Zn0.4O microspheres were prepared by calcination treatment of Ni–Zn LDHs (layered double hydroxides) that were obtained through a hydrothermal method. The yielded Ni0.6Zn0.4O microspheres were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). The results showed that the calcinated microspheres of Ni0.6Zn0.4O still well maintained the flower-like architecture of Ni–Zn LDHs. The surface area, total pore volume, and average pore diameter of the Ni0.6Zn0.4O microspheres were obtained with the values of 36.106 m2 g−1, 0.111 cm3 g−1, and 5.676 nm, respectively. As modified anode active materials, the Ni0.6Zn0.4O microspheres exhibited excellent electrocatalytic performance and fast electrochemical kinetics for methanol oxidation in strong alkaline electrolyte where the high surface area of flower-like Ni0.6Zn0.4O microspheres provides the high contact probability between catalysts and reactants. The presence of Zn also improves the electron transfer within catalysts inside. Also, the Ni0.6Zn0.4O modified electrode maintained good electrocatalytic performance during the term of 36,000 s.