Methanol Electro-oxidation Reaction Research Articles

Ni/NiO coated on multi-walled carbon nanotubes as a promising electrode for methanol electro-oxidation reaction in direct methanol fuel cell

In the current work, non-precious Nickel/Nickel oxide (Ni/NiO) and Ni/NiO/multi-walled carbon nanotube (Ni/NiO/MWCNT) composites were synthesized by combustion method for methanol oxidation. The fabricated catalysts were characterized by XRD, EDS, SEM, and TEM. From TEM micrographs, Ni/NiO with the particle size in the range of 20–30 nm was synthesized and uniformly embedded on MWCNTs with a diameter of 10–40 nm. It was found from the EIS results that the Ni/NiO/MWCNT has a lower charge transfer resistance than Ni/NiO, indicating a faster electron transfer from the Ni/NiO/MWCNT to methanol and faster reaction kinetics. The Ni/NiO/MWCNT catalyst showed a maximum peak current density of 15.94 mA cm−2 (49.81 mA mg−1) in peak potential of 0.43 mV (at room temperature) and long-term stability, showing good electrocatalytic activity. Also, DMFC single cell test based Ni/NiO/MWCNT anode catalyst showed a maximum power density of 41.8 mW cm−2, indicating its promising application in DMFC.

Synthesis of carbon nanofibers/poly(para-phenylenediamine)/nickel particles nanocomposite for enhanced methanol electrooxidation

Several studies have been conducted on direct methanol fuel cells (DMFCs) to resolve major issues such as the high cost of the catalyst and the poisoning of the electrode. Herein, a low-cost catalyst based on nickel particles (NiPs), carbon nanofibers (CNF) and poly(para-phenylenediamine) (PpPD) was carried out using a simple electrochemical method. The morphology and structure of the nanocomposite electrodes are characterized by field-emission gun scanning electron microscopy coupled with an energy dispersive X-ray detector, X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. The effects of various parameters such as the PpPD film thickness and the NiPs content on the electrocatalytic performance of CPE/CNF/PpPD/NiPs are evaluated which lead to the optimized composition. The results of the methanol electrooxidation reaction at room temperature showed that the optimized CPE/CNF/PpPD/NiPs nanocomposite exhibits a high catalytic activity (Ip = 38.11 mA cm−2), good stability and durability for more than 6 h in comparison with CPE/CNF/NiPs. These findings truly highlight the synergetic effect of CNF/PpPD in enhancing the electrochemical activity and stability and the vast potential of CPE/CNF/PpPD/NiPs as low-cost catalyst and electrodes for DMFCs.

One-step synthesis of unique catalyst Ni9S8@C for excellent MOR performances

A novel Ni9S8/C electrocatalyst for methanol oxidation reaction (MOR) is synthesized by a simple, cost-effective and one-pot strategy. The electrocatalyst Ni9S8 composed of micro and nanoparticles encapsulated inside carbon layers serves as carbon-supporter and fast ion and electron mobilization through the Ni9S8/C support materials. The sizes of Ni9S8/C nanoparticles range from 2.4 to 7.99 nm, reveals large surface area availability with plenty of active sites for electro-oxidation of methanol. The oxidation performance of electrocatalyst is determined in different solution of methanol and alcohol at various scan rates. At a scan rate of 50 mV s−1, the Ni9S8/C catalyst delivers total 52 mA cm−2 current density for 1.75 V potential (vs RHE) for 1 M KOH and 0.5 M methanol. The electrocatalyst shows low Rct circle and linear chronoamperometric graph for 5000 s, which demonstrate the outstanding stability of the electrocatalyst for methanol electro-oxidation reaction.

Pd and Pd@PdO core–shell nanoparticles supported on Vulcan carbon XC-72R: comparison of electroactivity for methanol electro-oxidation reaction

Nanomaterials based on Pd nanoparticles supported on Vulcan carbon (XC-72R) were prepared by the organometallic approach in one-pot and mild conditions (3 bar hydrogen and room temperature) using Pd(dba)2 (bis (dibenzylideneacetone) palladium (0)) as metal source and hexadecylamine (HDA) as stabilizer. High-resolution transmission electron microscopy (HR-TEM) evidenced the presence of well-dispersed Pd nanoparticles of ca. 4.5 nm mean size onto the carbon support (Pd/HDA/C). Scanning and transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) allowed to determine the chemical composition of the nanomaterials. When the Pd/HDA/C nanomaterial was submitted to heating treatment (ht) at 400 °C under air (referred as Pd/HDA/C@air-ht), X-ray photoelectron spectroscopy (XPS) and HR-TEM/STEM-EELS analyses suggested the presence of interactions between PdO and Pd(0) as a result of the formation of Pd@PdO core–shell nanoparticles. The highest oxidation current magnitude during methanol oxidation reaction is ascribed to the heat-treated material, linked with a better electron and mass transfer processes at the electrode interface. This can be attributed to electronic interactions at the core–shell formed, which might promote different redox processes at the electrode interface during CH3OH deprotonation in the alkaline electrolyte.

Superior catalytic performance of NiCo2O4 nanorods loaded rGO towards methanol electro-oxidation and hydrogen evolution reaction

In this work, a cost-effective ternary metal oxide nanorods, NiCo2O4, and embedding in reduced graphene oxide, NiCo2O4/rGO, as electrocatalysts were synthesized to use in direct methanol fuel cells (DMFCs) and hydrogen generation. For methanol oxidation reaction, NiCo2O4/rGO catalyst displayed the maximum current density of 9.6 and 16.2 mA cm−2 at 290 and 310 K, respectively in alkaline media. For hydrogen evolution, the Tafel slope of 49 mV dec−1 and 61 mV dec−1 and onset overpotential of 69 mV and 120 mV were obtained for NiCo2O4/rGO and NiCo2O4, respectively. The volume of evolved hydrogen obtained about 4 ml and 9 ml for NiCo2O4 and NiCo2O4/rGO, respectively, which are consistent with the polarization curves. The presence of rGO as a conductive material and the synergistic effect between Ni2+ and Co3+ ions are effective for electrocatalytic efficiency of the catalyst. The excellent performance of catalysts suggests their potentials for energy production.

Platinum Electrocatalysts Deposited onto Composite Carbon Black–Metal Oxide Support

New nanostructured Pt/(SnO2/C)-electrocatalyst (20 wt % Pt) is synthesized via platinum chemical deposited onto composite SnO2/C-support microparticles (4 wt % Sn). The composite support was prepared beforehand using unique method of the tin electrochemical deposition onto disperse carbon black particles. It was shown by X-ray diffraction and transmission electron microscopy that the platinum and tin oxide nanoparticles distributed over the carbon surface are sized 2.4 and 2.9 nm, respectively. Electrochemical measurements showed the obtained catalyst to approach the commercial Pt/C HiSPEC 3000 catalyst (20 wt % Pt) with respect to its mass-activity in the oxygen electroreduction reaction and to be superior thereto as for the electrochemically active surface area, stability in stress test, and activity in methanol electrooxidation reaction. The peculiarities in electrochemical behavior of the synthesized Pt/(SnO2/C)-electrocatalyst can be explained by the SnO2 nanoparticle effect on the platinum nanoparticle nucleation/growth, as well as presence of Pt–SnO2–C triple junction nanostructure at the surface. The Pt/SnO2 contact provides stable platinum-to-support adhesion and asserts bifunctional catalysis mechanism of the methanol electrooxidation. And the Pt/C junctions provide for electron supplying/retraction to or from the platinum nanoparticles.

Fine Control over the Compositional Structure of Trimetallic Core-Shell Nanocrystals for Enhanced Electrocatalysis.

Pt-based multimetallic nanocrystals (NCs) have attracted tremendous research interest because of their excellent catalytic properties in various electrocatalysis fields. However, the development of rational synthesis approaches that can give multimetallic NCs with desirable compositional structures is still a radical issue. In the present work, we devised an efficient strategy for the systematic control of the spatial distribution of constituent elements in Pt-based trimetallic core-shell NCs, through which NCs with distinctly different compositional structures, such as Au@PdPt, Au@Pd@Pt, AuPd@Pt, and AuPdPt@Pt core-shell NCs, could selectively be generated. The adjustment of the amount of a reducing agent, hydrazine, which can provide control over the relative reduction kinetics of multiple metals, is the key to the selective formation of NCs. Through extensive studies on the effect of the compositional structure of the trimetallic NCs on their catalytic function toward the methanol electro-oxidation reaction, we found that the Au@Pd@Pt NCs exhibited considerably enhanced catalytic performance in comparison to the other trimetallic NCs as well as to their binary counterparts, a commercial catalyst, and reported Pt-based nanocatalysts due to the optimized surface electronic structure. The present strategy will be useful to design and construct multicomponent catalytic systems for various energy and environmental applications.

Highly Active and CO-Tolerant Trimetallic NiPtPd Hollow Nanocrystals as Electrocatalysts for Methanol Electro-oxidation Reaction

Pt-based catalysts for methanol fuel electro-oxidation typically suffer from CO intermediate poisoning. Herein, we incorporated secondary Ni element into PtPd hollow nanocrystals (HNCs) to fabricat...

Promotion effects of CeO2 with different morphologies to Pt catalyst toward methanol electrooxidation reaction

In the present work, CeO2 nanocrystals with three well-defined morphologies including nanooctahedra, nanosphere and nanocube are synthesized and used as the promoter to Pt catalyst toward methanol electrooxidation reaction (MOR). The promotion effects of the CeO2 nanocrystals are investigated through electrochemical techniques including cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). Results indicate that the promotion effects are closely related to the nanostructure of CeO2 nanocrystals. Among the Pt-CeO2/C catalysts, Pt-CeO2/C-S catalyst with CeO2 nanosphere as the promoter shows the highest catalytic performance for MOR, which arises from both physical interaction and electronic effects between CeO2 and Pt. The loosened nanosphere structure with rough surface allows the Pt nanoparticles (NPs) to highly disperse onto the surface and thereby produce a strong physical interaction between Pt and CeO2. In addition, the change in the valence state from Ce4+ to Ce3+ generates abundant oxygen vacancies (VO) into the crystal lattice, and the increased vacancies lead to surplus electrons which would transfer from CeO2 to Pt. The increased electron density lowers the d-band center and thus improves the intrinsic activities (IA) of Pt. These data are used to discuss the role of physical interaction and electronic effects between the promoter and Pt and would be promising in designing the nanostructure of the Pt-based catalysts for DMFCs and other applications.

One-pot synthesis of efficient reduced graphene oxide supported binary Pt-Pd alloy nanoparticles as superior electro-catalyst and its electro-catalytic performance toward methanol electro-oxidation reaction in direct methanol fuel cell

The development of the clean synthesis of efficient bimetallic Pt-Pd alloy nanoparticles supported reduced graphene oxide (RGO) catalyst (RGO/Pt-Pd) through a facile, rapid, surfactant–free and novel one-pot process of chemical reduction-assisted hydrothermal reaction using formic acid as reducing agent have been introduced. The structural, elemental composition analysis and surface morphology of the as-prepared catalysts were extensively characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, energy dispersive x-ray spectroscopy (EDX), high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM), respectively. The electrochemical properties, catalytic activity and long-term stability performance of the RGO/Pt-Pd nanocomposite catalyst were employed by cyclic voltammogram and chronoamperometry. Furthermore, owing to the synergetic effects of Pt and Pd nanoparticles, the unique structure of Pt-Pd alloy nanoparticles and enhanced electron transfer by RGO, the as-synthesized RGO/Pt-Pd nanocomposite catalyst has demonstrated the enlarged electrochemical surface area (ECSA) (ECSA = 0.91 cm2), remarkably higher electro-catalytic activity (If = 59.6 mA/cm2) and enhanced stability as compared to RGO/Pt (If = 23.32 mA/cm2, ECSA = 0.18 cm2) and RGO/Pd (If = 8.65 mA/cm2, ECSA = 0.11 cm2) nanocomposite catalysts toward methanol oxidation reaction (MOR). This superior catalytic activity of the as-prepared RGO/Pt-Pd nanocomposite catalyst with facile and simple preparation approach is promising a great opportunity for the development of direct methanol fuel cell.

One-step preparation of graphitic carbon nitride/Polyaniline/Palladium nanoparticles based nanohybrid composite modified electrode for efficient methanol electro-oxidation

In this work, we report a simple one-step preparation of a novel graphitic carbon nitride/Polyaniline/Palladium nanoparticles (g-C3N4/PANI/PdNPs) based nanohybrid composite modified screen-printed electrode (SPE) for the efficient electro-oxidation reaction of methanol. g-C3N4/PANI/PdNPs nanohybrid structure was achieved by a single-step simultaneous electro-deposition method with an electrolyte solution containing palladium chloride, aniline, and g-C3N4 nanosheets. Structural and morphological characterizations depicted that the needle-shaped PANI and spherical shaped Pd NPs were deposited between g-C3N4 nanomatrix. The electrocatalytic behavior of the as-prepared nanohybrid composite modified SPE was assessed using cyclic voltammograms and chronoamperometric method, and it showed superior electro-oxidation and excellent catalytic performance over methanol oxidation compared to commercial 10% palladium loaded carbon black material and other previously reported electrode materials. These outcomes proved that the newly developed nanohybrid composite could be used as a potential electrocatalyst material for the direct methanol fuel cell applications.

Quantification of formaldehyde production during alkaline methanol electrooxidation

The alkaline methanol electrooxidation reaction (MOR) in alkaline direct methanol fuel cells is still very little understood with regard to its electrochemical behavior. Theoretically, when using a rotating disk (RDE) as working electrode, the limiting current from an electrochemical reaction increases with the rotation rate as described by Levich. Contrary to this principle, the current resulting from the alkaline MOR does not increase, but decreases with rotation rate. In this work, we investigate the reason for this phenomenon using the method described by Nash and modified by Belman to quantify formaldehyde, a reaction intermediate of the alkaline methanol electrooxidation. The amount of formaldehyde is in direct relation to the rotation rate, proving that the current density loss can originate from an intensified removal of formaldehyde into the bulk solution. We analyse the influence of the electrolyte and methanol concentration on the formation of formaldehyde in order to investigate which conditions support the complete oxidation pathway and suppress the incomplete oxidation to formaldehyde. The concentration ratio as well as the absolute concentrations are of great importance for the pathways taking place. A low electrolyte concentration leads to an increase of the formaldehyde but decreasing the methanol concentration results in an absence of formaldehyde in the bulk solution.

Methanol electrooxidation at nickel-modified rhodanine self assembled monolayer films: A new class of multilayer electrocatalyst

Nickel modified rhodanine (Rh) self-assembled monolayer films (Rh-SAM/Ni) were fabricated on copper from 10.0 mM Rh containing methanol. The films were characterized with the help of scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDX) techniques. The methanol oxidation activity of the Rh-SAM/Ni electrode was tested in 1.0 M methanol containing 0.1 M KOH solution using many electrochemical techniques. The results indicated that well-ordered and very homogeneously distributed Rh-SAM films were assembled over the copper surface. The rate of methanol electrooxidation reaction can be enhanced by modifying copper surface with Rh-SAM/Ni multi-layer film. The enhanced activity was related to increasing active sites over the surface for adsorption and oxidation of methanol as well as facilitating oxidation or desorption of adsorpted intermediates of the process. It was suggested that the Rh-SAM layer could be a candidate supporting material for fabricating direct methanol fuel cell (DMFCs) anodes.

Pt catalysts supported on lignin-based carbon dots for methanol electro-oxidation

Pt catalysts supported on lignin-based carbon dots are successfully prepared, and their catalytic performances for methanol electro-oxidation are investigated. Firstly, lignin-based carbon dots (Lg-CDs) are prepared by the acid etching of lignin carbonization products. Then, Pt catalysts supported on lignin-based carbon dots (Pt/Lg-CDs) are synthesized by the reduction of chloroplatinic acid in carbon dots solution. Although Pt/Lg-CDs catalysts aggregate obviously due to the deposition of Pt catalysts on the surface of Lg-CDs, the activity and stability of an optimal Pt/Lg-CDs-800 catalyst are still more outstanding than commercial Pt/C (40%Pt) and PtRu/C (30%Pt+15%Ru) catalysts for methanol electro-oxidation reaction (MOR) in acidic solutions. A large number of oxygen-containing groups on the surface of Lg-CDs-800 facilitate the uniform and stable deposition of Pt catalysts, and make the surface of more Pt catalysts expose to reaction system, thereby improving catalytic performance.

Nickel and cobalt in situ grown in 3-dimensional hierarchical porous graphene for effective methanol electro-oxidation reaction

Here we report, an efficient, cheap and simple strategy to obtain electrocatalysts for methanol electro-oxidation reactions. Nickel encapsulated 3-dimensional hierarchical porous graphene and cobalt encapsulated 3-dimensional hierarchical porous graphene composites are obtained by ion exchange/activation method. The well dispersion of nickel and cobalt nanoparticles are observed inside the nickel encapsulated 3-dimensional hierarchical porous graphene and cobalt encapsulated 3-dimensional hierarchical porous graphene composites respectively. Graphene layer over the metals nanoparticles may suppress metal corrosion and enhance their catalytic performance for methanol electro-oxidation reactions. Nickel encapsulated 3-dimensional hierarchical porous graphene exhibits low onset potential of 0.32V (vs Ag/AgCl) and the highest current density of 147.108mAcm−2 at a low overpotential of 0.728V (vs Ag/AgCl). Similarly, cobalt encapsulated 3-dimensional hierarchical porous graphene shows lower onset potential of 0.45V (vs Ag/AgCl) and high current density of 10mAcm−2 at low overpotential of 0.62V (vs Ag/AgCl). More importantly, better methanol electro-oxidation reaction was recorded in 1M KOH and 0.75M methanol solution with a scan rate of 50mVs−1. The nickel-containing electrocatalyst show better performance than cobalt based electrocatalyst under same conditions.

Galvanic Replacement-Mediated Synthesis of Ni-Supported Pd Nanoparticles with Strong Metal-Support Interaction for Methanol Electro-oxidation.

Herein, well-defined Pd nanoparticles (NPs) developed on Ni substrate (Pd NPs/Ni) are synthesized via a facile galvanic replacement reaction (GRR) route performed in ethaline-based deep eutectic solvent (DES). For comparison, a Pd NPs/Ni composite is also prepared by the GRR method conducted in an aqueous solution. The Pd NPs/Ni obtained from the ethaline-DES is catalytically more active and durable for the methanol electro-oxidation reaction (MOR) than those of the counterpart derived from conventional aqueous solution and commercial Pd/C under alkaline media. Detailed kinetic analysis indicates that the unique solvent environment offered by ethaline plays vital roles in adjusting the reactivity of the active species and their mass transport properties to control over the genesis of the Pd NPs/Ni nanocomposite. The resulting Pd NPs/Ni catalyst possesses a homogeneous dispersion of Pd NPs with a strong Pd (metal)-Ni (support) interaction. This structure enhances the charge transfer between the support and the active phases, and optimizes the adsorption energy of OH- and CO on the surface, leading to superior electrocatalytic performance. This work provides a novel GRR strategy performed in ethaline-DES to the rational design and construction of advanced metal/support catalysts with strong interaction for improving the activity and durability for MOR.

Casting Nanoporous Platinum in Metal-Organic Frameworks.

Nanocasting based on porous templates is a powerful strategy in accessing materials and structures that are difficult to form by bottom-up syntheses in a controlled fashion. A facile synthetic strategy for casting ordered, nanoporous platinum (NP-Pt) networks with a high degree of control by using metal-organic frameworks (MOFs) as templates is reported here. The Pt precursor is first infiltrated into zirconium-based MOFs and subsequently transformed to 3D metallic networks via a chemical reduction process. It is demonstrated that the dimensions and topologies of the cast NP-Pt networks can be accurately controlled by using different MOFs as templates. The Brunauer-Emmett-Teller surface areas of the NP-Pt networks are estimated to be >100 m2 g-1 and they exhibit excellent catalytic activities in the methanol electrooxidation reaction (MEOR). This new methodology presents an attractive route to prepare well-defined nanoporous materials for diverse applications ranging from energy to sensing and biotechnology.

Pd nanoparticles supported on N and P dual-doped graphene as an excellent composite catalyst for methanol electro-oxidation

We synthesize a novel composite catalyst of Pd nanoparticles supported on N and P dual-doped graphene (N-P-G) for the methanol electro-oxidation reaction in alkaline medium. It is revealed that the Pd nanoparticles with a particle size of ∼4.59 nm uniformly distribute on the surface of N-P-G with a two-dimensional flake-like structure. The synergistic doping of N and P changes the electronic structure of graphene, increases the electron density of Pd and produces higher proportion of P-C bonds. This increases the metallic Pd content in the composite, enhances the combination of Pd nanoparticles with graphene, and produces more active sites. The Pd/N-P-G catalyst delivers a catalytic current density of 11.9 mA cm−2 in 1 M KOH with 1 M CH3OH at −0.2 V after the test duration for 3600 s, manifesting excellent electrocatalytic performance for methanol oxidation. These results may provide a new opportunity for the design of the Pd-based catalysts in the direct methanol fuel cells (DMFCs) technology.

Morphology effect of MnO2 promoter to the catalytic performance of Pt toward methanol electrooxidation reaction

Three MnO2 samples with different well-defined morphologies including nanoplates, nanorods and corallines are prepared through a simple chemical precipitation method and used as the promoter/support for Pt electrocatalysts (denoted as Pt/MnO2P, Pt/MnO2-R and Pt/MnO2C, respectively). The morphology effects of MnO2 to the catalytic properties of Pt for methanol oxidation reaction (MOR) are intensively investigated. Results show that the catalytic properties of Pt are strongly dependent on the morphology of the promoter. Pt/MnO2-R with MnO2 nanorods as the promoter shows the highest catalytic properties among the MnO2-promoted catalysts. The mass-specific activity and intrinsic activity of Pt in Pt/MnO2-R catalyst is 0.51 A mg−1Pt and 11.54 A m−2Pt, which is ca. 1.89 and 2.18 times that of commercial Pt/C catalysts (0.27 A mg−1Pt and 5.29 A m−2Pt), respectively. Change in the electronic structure of Pt is responsible for the enhancement in the catalytic properties of Pt/MnO2-R.

Electrocatalytic methanol oxidation over Cu, Ni and bimetallic Cu-Ni nanoparticles supported on graphitic carbon nitride

Ni, Cu and Cu–Ni nanostructures have been fabricated and homogeneously embedded on ultrathin two-dimensional (2D) carbon nitride (g-C3N4), and the surface morphology and composition of the resulting hybrid nanostructures were studied by XRD, TEM, HRTEM-elemental mapping, Raman spectroscopy and XPS. The new hierarchical hetero-structures dropcasted on GC anodes have been visualised by SEM and their catalytic performance have been examined in methanol electrooxidation reaction (MOR) under alkaline conditions. Nanosized Ni particles dispersed finely over g-C3N4 are very active electrocatalysts with MOR onset at potential 0.35 V and charge transfer resistance 0.12 kΩ. The stability of modyfied GC electrodes, examined under chronoamperometric conditions showed that for electrode loading with 4% (wt. %) of NiO the stable current density ca. 36 A g−1 (12 A cm2) was obtained during whole experiment (up to 160 min). For all catalyst studied the curent density obtained during MOR reaction was enhanced when electrode was iluminated by UV light λ∼400 nm, and the highest value were obtained for 4% Ni/CN catalyst ca. 127 A g−1 (22 A cm2). The Cu incorporation in the hybrid material evoke loss of activity mostly due to Cu+ irreversible reduction/oxidation to Cu° and Cu2+, CuO segregation and influencing electron transfer process which results in the increasing in the redox potential. These results represent an important step towards light-enhanced electro-reactive systems and sensors in which heterojunction formation can facilitate electron-hole separation and enable more efficient energy transfer.