Methanol Oxidation Process Research Articles

Enhanced Electrocatalytic Performance of the FePt/PPy-C Composite toward Methanol Oxidation.

A novel FePt/PPy-C composite nanomaterial has been designed and investigated as a methanol oxidation reaction (MOR) electrocatalyst. The FePt nanoparticles with an average diameter of about 3 nm have been prepared by the co-reduction method and then loaded onto the PPy-C composite support. The electrocatalytic performance is affected by the composition of the FePt nanoparticles. The experimental results indicated that the Fe1.5Pt1/PPy-C catalyst exhibited excellent catalytic activity and stability for MOR, with mass activity and specific activity of 1.76 A mgPt-1 and 2.71 mA cm-2, respectively, which are 5.18 and 4.60 times higher than that of the commercial Pt/C catalyst. Density functional theory (DFT) has been employed to simulate the electrical structures of catalyst supports, and the mechanism of the methanol oxidation process has been further analyzed. The heterojunctions of the PPy-C interface could accelerate the electron migration from the electrocatalytic center to the electrodes. The possibility of methanol oxidation has been improved effectively, which can be confirmed by the d-band center and CO adsorption energy on FePt nanoparticles in the DFT calculation results.

Samarium-doped vanadium pentoxide nanorods anchored reduced graphene oxide nanocomposite as a bi-functional electrode material for supercapacitor and direct methanol oxidation fuel cell applications

In this work, we demonstrate a novel, facile synthesis of reduced graphene oxide nanosheets decorated samarium-doped vanadium pentoxide (RGO/Sm:V2O5) nanocomposite material and explore its application toward supercapacitor and direct methanol oxidation process. As-fabricated material and electrode were well-characterized to evaluate its surface morphology and functionalities. Results indicate a maximum capacitance value of 544 F/g for RGO/Sm:V2O5 modified electrode than the 2% Sm:V2O5 (346 F/g) and V2O5 (133 F/g) modified electrodes. In addition, an excellent Rct value (3.2 Ω) was achieved for the RGO-loaded Sm:V2O5 electrode than the 2% Sm:V2O5 electrode (4.7Ω). The RGO/Sm:V2O5 electrode also shows higher cyclic efficiency (98 %) at the 1000th cycle than the non-RGO loaded Sm:V2O5 electrodes. Furthermore, the fabricated electrodes were also examined for the direct methanol oxidation performances, and the results indicate a higher current density value of 181 mA/cm2 for RGO/Sm:V2O5 electrode than 2% Sm:V2O5 electrode (139 mA/cm2). The excellent electrochemical performance of the RGO/Sm: V2O5 electrode is mainly due to the presence of RGO nanosheet in the synthesized nanocomposite material. Therefore, as-prepared material can be applied as an excellent alternative electrode material for energy storage and conversion systems.

CuNi2O4/MWCNTs nanocatalyst for methanol and ethanol electro-oxidation

The widespread use of cheap and efficient catalysts in energy storage and production in electrochemical processes led our research team to the synthesis and evaluation of CuNi2O4/MWCNTs nanocatalyst for alcohol oxidation. Nanocatalyst was characterized in terms of structure and morphology by X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDAX). The ability of CuNi2O4/MWCNTs was evaluated with cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analyses in the oxidation process of methanol and ethanol alcohols in alkaline media. The optimal concentration of methanol and ethanol for CuNi2O4/MWCNTs and CuNi2O4 was obtained to investigate the methanol oxidation reaction and ethanol oxidation reaction processes. The mechanism of these processes was also evaluated in detail. The stability of both nanocatalysts was investigated by performing several consecutive CVs and in 3600 s by chronoamperometric analysis. The results showed the good stability of this catalyst. The synergistic effect of placing CuNi2O4 on the surface of carbon nanotubes improved the oxidation process of methanol and ethanol. In general, the proposed catalyst can be an efficient, stable, and cheap option and at the same time very stable for use in alcohol fuel cells.

Research development of anti-CO poisoning in electrocatalytic methanol oxidation processes: a review

This review examines research advancements in anti-CO poisoning during the electrocatalytic methanol oxidation reaction (MOR).

Morphology and size effect of ceria on methanol oxidation in non-thermal plasma

The morphology effect and size effect of Ceria (CeO2) on methanol oxidation in non-thermal plasma (NTP) system were investigated. CeO2-Rod and CeO2-Cube with individual three sizes were synthesized and presented strong morphology-dependent and size-dependent activity, namely, CeO2-rod catalyst exhibited superior performance than CeO2-Cube, while each of them showed improved catalytic activity as the size reduced. Various characteristic methods showed that CeO2-Rod in smaller size possesses more surface adsorbed oxygen species than CeO2-Cube. Further experiments confirmed that the dependence of catalytic activity on CeO2 morphologies and CeO2 sizes was derived from their ozone utilization. To further investigate the difference of surface reaction pathways between the catalysts, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments were conducted and the results showed that the methanol adsorption behavior and oxidation process on catalyst surface differ in CeO2 morphologies.

Palladium supported on NiFe layered double hydroxide as an effective electrocatalyst for methanol electro-oxidation

Pt and Pd have an excellent catalytic capacity for methanol oxidation and have the highest discharge efficiency among direct methanol fuel cell anode materials. However, the catalyst produces carbon monoxide and other intermediates (*COad) during the methanol oxidation process, causing Pt/Pd active site poisoning. In this work, Pd was introduced into the layered double hydroxide (NiFe-LDH) by hydrothermal method, and CO-poisoning was successfully inhibited. NiFe-LDH has a larger Pd-loaded surface and provides a more efficient platform for the formation of *OH, which can effectively promote the oxidation of *COad (2 *OHad+*COad→CO2 +H2O) and improve the activity of Pd. The Pd/Ni4Fe6-LDH shows excellent OER activity (overpotential is 268 mV @ 20 mA cm−2) and MOR activity (mass activity is 2665.3 mA mg−1Pd). The Ni4Fe6-LDH synergetic Pd opens the door for reducing the CO-poison and enhancing the MOR durability for the long-use life of DMFCs.

CeO2-NiO-rGO as a nano-electrocatalyst for methanol electro-oxidation

This study provides the methanol oxidation capability of two nanocatalysts, CeO2-NiO (CN) and CeO2-NiO-rGO (CNR), synthesized by a cost-effective hydrothermal method. The synergistic effect of compositing CeO2-NiO with reduced graphene oxide was evaluated. These synergic effect makes a good electrochemical active surface area and suitable electrical conductivity for catalyst. In addition, rGO with good electrical conductivity revealed considerable improvement in the methanol oxidation reaction performance of the catalyst. The cyclic stability measurements of CeO2-NiO-rGO showed a high retention ability of 96% in 500 consecutive cyclic voltammetry cycles, while the stability of CeO2-NiO in the same number of cycles is about 93%. The complementary methanol oxidation process results indicated an oxidation current density up to 49.5 and 68.5 mA cm−2 for CN and CNR at a scan rate of 20 mV s−1, respectively. The proposed catalyst can be considered as an attractive, stable, and inexpensive candidate in the field of methanol oxidation to use in methanol fuel cells.

Methanol Fueled Low Temperature Solid Oxide Fuel Cell with Pt-SDC Anodes

A low-temperature solid oxide fuel cell (LT-SOFC) is a next-generation energy conversion device and has advantages of high energy efficiency, fast start up and shut down and eco-friendliness. In addition, since it has the advantage of being able to use various fuels such as hydrogen, alcohol, and methane gas, research is being actively conducted in recent years. However, LT-SOFC using hydrogen as a fuel has difficulties in storing and transporting fuel, making it difficult to apply as a portable device. On the other hand, methanol fuel is an attractive alternative fuel because it is easier to transport and store than hydrogen fuel and has a high volumetric energy density. However, when methanol is applied to LT-SOFC, there is a disadvantage in performance due to the complicated oxidation process and CO poisoning. Complex methanol oxidation reaction (MOR) and CO poisoning reduce the performance and durability of fuel cells. Therefore, it is important to use a catalyst that can prevent CO poisoning and improve the oxidation reaction of methanol. Pt is an effective catalyst for methanol decomposition and is one of the materials widely used in direct methanol fuel cell (DMFC). However, there is a problem in that it is vulnerable to CO generated during the methanol oxidation process. It is known that CO is adsorbed on the Pt surface, blocks the active site, and reduces catalytic activity. Therefore, alloying Pt with samaria-doped ceria (SDC) with high oxygen storage capacity (OSC) and good OH generation capacity can be effective to reduce CO poisoning and coking.In this study, we prepared the cells with Pt-SDC cermet anodes with the Pt volume percent of 69 (Pt 0.69), 83 (Pt 0.83), 92 (Pt 0.92), and 95 (Pt 0.95) volume% by varying Pt and SDC powers in the co-sputtering process. In the electrochemical impedance spectroscopy (EIS), ohmic resistance was similar between all samples; on the other hand, activation resistance was measured to be 24.0, 19.5, 31.8, 30.8, and 53.0 Ω∙cm2 at Pt 0.69, Pt 0.83, Pt 0.92, Pt 0.95, and Pt 1 samples, respectively, confirming the lowest activation resistance at Pt 0.83. We speculate that the MOR is improved by the increase of triple phase boundary (TPB) sites and the facilitation of bifunctional CO oxidation mechanisms with higher content of SDC up to 17 mol% (Pt 0.83). However, in the anode with excessive SDC content (31 mol%, Pt 0.69), the Pt is oxidized to form PtO2, lowering the catalytic activity.

Dual Matrix Influence on Ni(II) Rich Hybrid Catalyst for Electrochemical Methanol Oxidation Reaction

AbstractThe influence of two different surface matrices, that is, zeolite‐Y and multi‐walled carbon nanotubes (MWCNTs), on the electrocatalytic ability of Ni(OH)2 combined with MnO2 has been studied. The Ni and Mn loaded in different ratio exhibited different current density with respect to the change in the nature of support. The MnO2−Ni(OH)2 catalyst decorated like a fish in a net‐stock at the interface of the zeolite‐Y and the MWCNT with high Ni(II) content provided the highest current density of 3.8 Amg−1 and 3.6 Amg−1 with platinum and graphitic rod as counter electrode, respectively. The study revealed that both the concentration of the Ni(II) as well as the nature of the support influenced the electrochemical behaviour of MnO2−Ni(OH)2. The electrochemical surface area as well as the durability of the catalyst having two different supports showed higher values in comparison to those in single matrix. The plot of current density vs. square root of scan rate showed diffusion control methanol oxidation process. The results predicted that the MnO2−Ni(OH)2 catalyst containing both zeolite‐Y and MWCNT surface indicated that under the highly basic condition it can withstand for long period without significant loss in current density during the methanol oxidation reaction process.

Thermal kinetics study on the conversion of β-MoO3 to α-MoO3; A molybdenite concentrate derivative as a catalyst

Herein, thermal decomposition kinetics of molybdic acid (MA) obtained from the leaching of molybdenite concentrate are extensively studied as a precursor for the preparation of molybdenum trioxide (MoO3). The thermal kinetics equation of the reaction suggests that the precursor (MA, H2MoO4.H2O) is converted to β-MoO3 and then to α-MoO3 due to the heating process, giving rise to a transformation temperature of 260-320°C, the average activation energy of about 26.53 ± 0.02 kJ/mol, and a pre-exponential factor of 107 1/min for the transformation of β-MoO3 to α-MoO3. Moreover, differential scanning calorimetry reveals that the volume diffusion mechanism controls the crystallization reaction, leading to the decomposition of MA. Our results indicate that Johnson-Mehl-Avrami (JMA) kinetics with nucleation and three-dimensional growth mechanism can model the experimental data with acceptable accuracy. The catalytic attributes of the stable β-MoO3/α-MoO3 compound provided an efficiency of over 89 % for the oxidation process of methanol to formaldehyde.

Silver catalysts for the partial oxidation of alcohols

The review analyzes state of the art in the partial oxidation of alcohols to carbonyl compounds over Ag catalysts, including the partial oxidation of methanol to formaldehyde, oxidation of ethylene glycol to glyoxal, and oxidation of ethanol to acetaldehyde. For the methanol oxidation process, conditions for implementing the BASF and ICI technologies are considered and the entire chain of transformations from natural gas to formaldehyde is estimated in terms of exergy. When considering modern kinetic studies for the partial oxidation of alcohols on silver, some recent publication are analyzed, particularly those devoted to the application of a ring-shaped reactor to suppress the homogeneous steps of formaldehyde decomposition, the development of a new approach to simulation of the process taking into account different reactivity of the catalyst, and the creation of a simulator to calculate the methanol oxidation process using a neural network with a genetic algorithm. Main steps in the development of a technology for the partial oxidation of ethylene glycol to glyoxal on Ag catalysts are briefly described. The author analyzes modern experimental and theoretical works devoted to the formation mechanisms of oxygencontaining active sites on the silver surface and their involvement in the conversion of alcohols to carbonyl compounds, as well as the new Ag-containing catalytic compositions.

ZnO-MWCNT @ Fe3O4 as a novel catalyst for methanol and ethanol oxidation

Zinc oxide is considered a practical substance in various fields of science, but the low electrical conductivity of zinc oxide seems to be one of the main reasons for its limited use in alcohol oxidation for application in fuel cells. In this study, the ZnO, ZnO-MWCNT, and ZnO-MWCNT@Fe3O4 catalysts were synthesized by hydrothermal method, and their structures and morphologies were characterized by XRD, SEM, EDX, TEM, and BET. To evaluate the electrochemical performance of catalysts, their electro-catalytic ability was investigated in methanol and ethanol oxidation processes. The results showed that the addition of Fe3O4-decorated multi-wall carbon nanotubes to the structure of zinc oxide created the active oxidation sites and increased the conductivity and specific area in the catalyst. The synergistic effects of placement of the catalyst components to each other increased the methanol and ethanol oxidation ability of ZnO-MWCNT@Fe3O4, and the excellent stability of 91% was obtained during 500 cycles in the MOR process. The proposed catalyst introduces ZnO-based materials as a catalyst that has promising potential applications in alcohol oxidation.

A remarkable three-component RuO2-MnCo2O4/rGO nanocatalyst towards methanol electrooxidation

A three-part nano-catalyst including ruthenium oxide, manganese cobalt oxide, and reduced graphene oxide nanosheet in form of RuO2-MnCo2O4/rGO is synthesized by one-step hydrothermal synthesis. The material is placed on a glassy carbon electrode (GCE) for electrochemical studies. The ability of these nano-catalysts in the oxidation process of methanol in an alkaline medium for usage in direct methanol fuel cells (DMFC) was examined with electrochemical tests of cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The effect of the addition of rGO to the nanocatalyst structure in the methanol oxidation reaction (MOR) process was investigated. We introduced the RuO2-MnCo2O4/rGO as a nanocatalyst with excellent cyclic stability of 97% after 5000 cycles in the MOR process. Besides, the study of the Tafel plots and the effect of temperature and scan rate in the MOR process showed that RuO2-MnCo2O4/rGO nanocatalyst has better electrochemical properties than MnCo2O4 and RuO2-MnCo2O4. This high electrocatalytic activity could be related to the synergistic effect of placement of metal oxides of ruthenium, manganese, and cobalt near each other and putting them on rGO, which enhances conductivity and surface area and improve electron transfer. The decrease in the resistance against charge transfer and the increment in the anodic current density illustrated that the reaction rate is enhanced at higher temperature. Thus RuO2-MnCo2O4/rGO shows robust stability and superior performance for MOR.

Sequential electrodeposition of Cu\u2013Pt bimetallic nanocatalysts on boron-doped diamond electrodes for the simple and rapid detection of methanol

In this work, a novel electrochemical sensor for methanol determination was established by developing a bimetallic catalyst with superiority to a monometallic catalyst. A Cu–Pt nanocatalyst was proposed and easily synthesized by sequential electrodeposition onto a boron-doped diamond (BDD) electrode. The successful deposition of this nanocatalyst was then verified by scanning electron microscopy and energy dispersive spectroscopy. The electrodeposition technique and sequence of metal deposition significantly affected the surface morphology and electrocatalytic properties of the Cu–Pt nanocatalyst. The presence of Cu atoms reduced the adsorption of other species on the Pt surface, consequently enhancing the long-term stability and poisoning tolerance of Pt nanocatalysts during the methanol oxidation process. This advanced sensor was also integrated with sequential injection analysis to achieve automated and high-throughput analysis. This combination can significantly improve the detection limit of the developed sensor by approximately 100 times compared with that of the cyclic voltammetric technique. The limit of detection of this sensor was 83 µM (S/N = 3), and wide linearity of the standard curve for methanol concentrations ranging from 0.1 to 1000 mM was achieved. Finally, this proposed sensor was successfully applied to detect methanol in fruit and vegetable beverage samples.

Methanol electrooxidation at NiCl2–FeCl3–graphite intercalation compound affected by ozone treatment

A graphite intercalation compound (GIC) incorporating nickel(II) and iron(III) chlorides (NiCl2–FeCl3–GIC) has been prepared, and the effect of ozone treatment on its catalytic activity towards methanol electrooxidation has been examined. The NiCl2–FeCl3–GIC was synthesized by a molten salt method, combining purified flaky graphite with the anhydrous metal chlorides. The obtained product was then modified with gaseous ozone. The crystalline structures and morphologies of the investigated compounds have been characterized by XRD and SEM/TEM techniques, respectively, and the results of these analyses have shown that ozone treatment of NiCl2–FeCl3–GIC contributes to changes in its structure and morphology. The process of methanol oxidation at both original and ozone-modified NiCl2–FeCl3–GIC electrodes has been examined in an alkaline electrolyte by means of cyclic voltammetry and a potentiostatic method. Electrochemical results have revealed that NiCl2–FeCl3–GIC exhibits activity towards the process of methanol electrooxidation. Furthermore, it has been proved that the electroactivity and durability of NiCl2–FeCl3–GIC are significantly increased following its ozone modification.

Atomic Fe sites doped two-dimensional (001) TiO2 nanosheets as an effective photo-response support in methanol electro-oxidation

The anode supports of direct methanol fuel cell (DMFC) directly affect the energy conversion efficiency between methanol fuel and electric energy. Semiconductor-based supports have nice photoelectric property for photo-assisted electrocatalytic methanol oxidation, making it be a kind of promising support of Pt. However, the rapid recombination of semiconductor photogenerated carriers limits the methanol oxidation ability of Pt. Herein, the two-dimensional (2D) (001) TiO2 nanosheets doped by a small amount of atomic iron were prepared by a reproducible impregnation method as the anode support to decrease the recombination rate. The atomic iron sites doped 2D (001) TiO2 nanosheets electrode has a high electrocatalytic performance for methanol oxidation under UV light-excitation, which is 2.7 times higher than that in dark and 4.8 times than that of non-doped electrode. The nice activities of atomic iron sites doped 2D (001) TiO2 nanosheets can be attributed to the introduction of atomic iron which are beneficial for the separation of photogeneration carriers and producing more photogenerated holes for the generation of strong oxidizing hydroxyl radicals (•OH). During the process of electrocatalytic methanol oxidation, •OH can not only promote the photocatalytic methanol oxidation, but also attenuate the inactivation of Pt poisoned by COads. These results provide a strategy to further ameliorate the photo-assisted electrocatalytic property for methanol oxidation.

Anion Exchange and Water Dynamics in a Phosphonium-Based Alkaline Anion Exchange Membrane Material for Fuel Cells: An Electrochemical Quartz Crystal Microbalance Study.

The anion exchange and water dynamics of a phosphonium-based alkaline anion exchange membrane (AAEM) during the methanol oxidation process have been studied with the electrochemical quartz crystal microbalance (EQCM). The viscoelastic effects of the phosphonium-based AAEM in water and the optimal film thickness for EQCM analysis were identified by acoustic impedance analysis. The phosphonium-based AAEM exhibited stronger mechanical toughness in water when compared to a quaternary-ammonium-based membrane that was studied previously. From the simultaneous measurement of the electrochemical response and the frequency changes of the quartz crystal oscillator, water ingress/egress to/from the AAEM film was found to accompany the hydrogen adsorption/desorption, Pt oxidation process, and methanol oxidation process. The in situ study of AAEM films helps illustrate the critical role that water transport plays in electrochemical processes during the operation of anion exchange membrane fuel cells. The generated CO32- and HCOO-, during methanol oxidation, were absorbed into the AAEM film, replacing the OH- in the film, as shown by the decrease in frequency after one potential cycle. The exchange of OH- by CO32- and HCOO- was found to be reversible. These results provide insights into the anion exchange processes in membranes and emphasize the importance of characterizing the hydrated membranes under electrochemical conditions.

Methanol production from CO2 reduction over Ni/TiO2 catalyst

Photocatalytic reduction of carbon dioxide into methanol fuel over the Ni-doped TiO2 catalyst has been investigated. The experiments were carried out in a 50 ml batch reactor under UV irradiation. Ni/TiO2 photocatalysts were prepared by an impregnation method. The properties of the catalyst were characterized by X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse reflectance (UV–DR). Moreover, the effect of reaction time and Ni loading on the methanol conversion were investigated. The result indicated that the maximum of methanol production was obtained after the irradiation of 3 h and slightly reduced due to the methanol oxidation process. The Ni loading catalyst showed the higher methanol concentration than that over undoped TiO2 because Ni could trap the electron during irradiation and reduce electron–hole pair recombination by the p–n junction of TiO2. The highest methanol production rate of 272.45μmol/gcat was obtained over 4% wt Ni/TiO2 catalyst, which was 20 times higher methanol production rate than that over the commercial TiO2 catalyst (P25). Moreover, the stability of catalysts could be recycled four times with high activity of CO2 reduction to methanol. Therefore, 4% wt. Ni/TiO2 catalyst, low cost, showed better potential and activity in reducing CO2 emission to the environment.

Hole-supply-rate-controlled methanol-gas-sensing reaction over p-type Co3O4/single-walled carbon nanotube hybrid structures

Co3O4/single-walled carbon nanotube (Co3O4/SWCNT) hybrid structures are fabricated, and their methanol sensing properties and related sensing principles are systematically investigated. A series of Co/SWCNT nanohybrid structures are deposited on silicon dioxide substrates by a co-arc discharge process and converted to Co3O4/SWCNT nanohybrid structures by subsequent methanol treatment and oxidation processes. The morphologies and structures of the nanohybrid composites are investigated by scanning electron microscopy, transmittance electron microscopy, X-ray diffraction, and Raman spectroscopy. The effect of the nanohybrid film thickness and the Co3O4: SWCNT ratio in the films on their physical and gas sensing properties are systematically examined. The best methanol-sensing performance is observed upon measurement at 300 °C for the material fabricated by deposition for 15 min and oxidized at 500 °C. The enhanced gas-sensing performance of the hybrid nanostructures is analyzed to prove that the high carrier supply rate from the transducer determines the reaction rate on the receptor surface (providing the receptor can accommodate the oxygen ionosorption). The hybrid sensor structures also exhibit low detection limit of 50 ppb, good selectivity, repeatability, and long-term stability, demonstrating their potential for practical application to methanol sensing.

A highly efficient photocatalytic methanol fuel cell based on non-noble metal photoelectrodes: Study on its energy band engineering via experimental and density functional theory method

Photocatalytic fuel cell (PFC) is considered as a new energy source due to its cooperative conversion capacity of both solar energy and chemical energy. In this work, a highly efficient ZnO/BiVO4 photoanode is synthesized on fluorine-doped tin oxide (FTO) by continuous electrodeposition and hydrothermal method. Then, a visible-light driven dual photoelectrode photocatalytic methanol fuel cell (PMFC) consisted of the ZnO/BiVO4 photoanode and Cu2O photocathode is designed and constructed. Electrochemical results show that the short-circuit current density (Jsc), the open-circuit voltage (Voc) and the maximum power output (Pmax) of the prepared PMFC can reach 5.18 mA/cm2, 0.82 V and 0.91 mW/cm2 under simulated solar irradiation, respectively. Surface photovoltage (SPV) transients reveal the charge transporting dynamics in semiconductor heterojunction, and photoelectrochemical experiments further confirmed the light-induced methanol oxidation and oxygen reduction process. Under illumination, an interior potential difference between n-type ZnO/BiVO4 and p-type Cu2O actuate the electrons on the photoanode to transfer through the external circuit to photocathode, combining with the holes and generating electricity. The built-in electric field from the ZnO (002) surface to the BiVO4 (001) surface is confirmed based on the theoretical calculation of density functional theory (DFT).