Methanol Electro-oxidation Reaction Research Articles

Determination of component drags coefficients in direct methanol fuel cell

Direct Methanol Fuel Cell (DMFC) system is considered as one of the most important clean and sustainable energy generation system. This system generates energy by electro oxidization of methanol however, this reaction is not fully completed. Consequently, the efficiency of the system is lower than expected. Studies in literature generally assume a fully completed methanol electrooxidation reaction (MOR) however, since MOR is not fully completed in this system. Thus, it is significant to consider the reaction intermediates. Therefore, this study focused on evaluating some critical parameters such as diffusion coefficients, component drag coefficients, and activation energies by considering reaction intermediates forms from MOR at the operating conditions. According to the experimental data, the properties of electroosmotically dragged substances in an operating DMFC system were investigated. First, the polarization curve was obtained, and then the system was run at constant current density for mid-term experiments. Next, the effect of the changes in DMFC operating conditions on performance was examined. Accordingly, component drag coefficients at 55 °C for methanol and water were obtained as 0.000246 and 3.1, respectively.

Engineering PtCu nanoparticles for a highly efficient methanol electro-oxidation reaction.

Achieving a highly efficient and durable methanol electro-oxidation catalyst in acid media is critical for the practical utilization of direct methanol fuel cells (DMFCs) at the commercial scale. Herein, we report a facile and effective one-pot strategy for the synthesis of carbon-supported PtCu alloy nanoparticles (PtCu NPs) with a Pt-rich surface, small particle size and uniform dispersion. The as-prepared PtCu NPs with the optimal alloy composition (Pt2Cu) exhibit a significantly improved electrochemical methanol oxidation reaction performance in terms of a high activity, superior CO tolerance and remarkable durability, in contrast to those of commercial Pt/C catalysts in acid media. Particularly, the Pt2Cu/C catalyst exerts a 4.5 times enhancement in the mass activity and a larger If/Ib value compared to those of commercial Pt/C (Pt/Ccomm). The enhanced catalytic activities can be ascribed to the high utilization of Pt and the high index facets of the surface. Also, the addition of Cu downshifts the d-band center of Pt and improves the CO tolerance during the methanol oxidation reaction process. This work provides an efficient strategy for designing desired Pt-based alloys for various catalytic reactions.

Structure engineering of PtCu3/C catalyst from disordered to ordered intermetallic compound with heat-treatment for the methanol electrooxidation reaction

Structure engineering of PtCu3/C catalyst from disordered to ordered intermetallic compound with heat-treatment for the methanol electrooxidation reaction

Electrocatalytic performance impact of various bimetallic Pt-Pd alloy atomic ratio in robust ternary nanocomposite electrocatalyst toward boosting of methanol electrooxidation reaction

The low-loading of precious platinum (Pt) metal electrocatalysts development by alloying with less expensive of earth-abundant transition metals exhibiting high electrocatalytic activity and durability performance towards methanol oxidation reaction (MOR) for new generation sustainability of direct methanol fuel cell (DMFC) application has aroused increasing consideration. In this typical study, the as-prepared ternary nanocomposite electrocatalysts with controllable composition of the bimetallic Pt-Pd alloy nanoparticles (NPs) in acidic media were synthesized through a facile one-step hydrothermal-assisted formic acid reduction reaction. The main study on the critical impact of the bimetallic Ptx-Pdy alloy atomic ratio (x-y = 1:1, 2:3, 3:7, 1:4, 1:9) in the as-prepared ternary RGO/bimetallic Ptx-Pdy alloy/0.90CeO2 nanocomposite electrocatalyst upon its suitability as anode electrocatalyst towards the electrocatalytic performance of MOR was thoroughly evaluated at constant operating conditions. The results clearly demonstrated that the compositions of the bimetallic Pt-Pd alloy NPs can be easily adjusted by varying the Ptx-Pdy alloy atomic ratio that can contribute to the significant impact on the electrocatalytic activity of MOR in DMFC. Upon increase in the composition of Pd from the bimetallic Pt-Pd alloy atomic ratio of 1:1 to 2:3 led to increased electrocatalytic activity, long-term stability, durability cycles and charge transfer resistance with respect to the MOR. However, it was continuously decrease with further increase of the Pd proportion in the Pt-Pd alloy NPs atomic ratio of 3:7 to 1:9. The maximum peak current density of the MOR (39.83 mA cm-2) was obtained in the present research work for the as-synthesized ternary nanocomposite electrocatalyst with the bimetallic Pt-Pd alloy atomic ratio of 2:3. The as-synthesized ternary nanocomposite electrocatalyst with low noble Pt content through the alloying strategy could promotes practically employed as anode electrocatalyst under acidic media in DMFC application.

Mechanistic insight into methanol electro-oxidation catalyzed by PtCu alloy

In this work, we have performed density functional theory (DFT) calculations to investigate the methanol electro-oxidation reaction (MOR) catalyzed by the Pt, PtCu alloy and Cu. The complex reaction networks, including the intermediate dehydrogenation, water dissociation and anti-poison reaction steps, are systematically investigated to explore the mechanisms. At the standard condition of pH = 0 and zero potential, for Cu, most dehydrogenation steps along the favorable pathway are endergonic, making it less active in MOR. For the Pt and PtCu alloy, their dehydrogenation steps are mainly exergonic, but the formed CO intermediate binds too tightly on Pt, that can accumulate on active sites to poison the electro-catalyst. The CO can be consumed by the thermodynamic reaction with OH*, which comes from water dissociation. DFT calculation shows alloying the Pt with Cu could not only reduce the free energy barrier for binding between CO* and OH*, but also assist the water dissociation to produce more OH* for that anti-poison reaction. That makes the PtCu alloy more active than the pure Pt electrode in experiment. The results reveal the importance of anti-poison reaction and water dissociation in MOR, which could be applied to the rational design of more active alloy electro-catalysts in future. In methanol electro-oxidation reaction, theoretical calculation shows alloying the Pt with Cu could promote the anti-poison reaction of binding between CO* and OH*, which makes it more active than the pure Pt electrode.

Electrocatalytic Oxidation of Methanol over An Electrode with Ni‐MOF‐74 Catalyst

AbstractDeveloping non‐noble metal catalysts for methanol oxidation in fuel cells is of importance. In this work, Ni‐MOF‐74 was synthesized through a simple solvothermal method and fully characterized. The as‐made Ni‐MOF‐74 modified carbon paste electrode (Ni‐MOF‐74/CPE) was applied for methanol electrooxidation reaction in 0.1 M NaOH solution. Ni‐MOF‐74 had high electrochemical stability and exhibited good electrocatalytic property for methanol oxidation, a mechanism for the reaction was proposed, the current density increases impressively on Ni‐MOF‐74/CPE compared with carbon paste electrode, and a really high catalytic rate constant (kcat) of 8.1×105 cm3 ⋅ mol−1 ⋅ s−1 was obtained in this work. The given results indicate that Ni‐MOF‐74 can be a promising candidate of electrocatalysts for direct methanol fuel cells (DMFCs).

Synergistic CoFe-Fe5C2 nanocrystal wrapped in N-doped carbon/carbon nanotubes as enhanced and CO-resistant electrocatalyst for methanol oxidation

Herein, a new metal organic framework MOF derived CoFe-Fe5C2 nanoparticles embedded nitrogen doped graphitized carbon/ nitrogen doped carbon nanotubes (CoFe-Fe5C2@NC/CNTs) heterostructures is successfully achieved through calcination in dicyandiamide atmosphere using Co/Fe-MOF as a precursor. The morphologies display that CoFe and Fe5C2 are uniformly dispersed in the framework of nitrogen doped carbon and dicyandiamide forms NCNTS using cobalt as a graphitization catalyst. The as prepared CoFe-Fe5C2@NC/CNTs hybrids exhibit remarkable specific properties of 60.23 mA cm−2 and small Tafel slope of 106.2 mV dec−1 in potential window from 0.4 V to 0.9 V towards methanol electro- oxidation reaction (MOR) in alkaline solution. At the same time, it realize more excellent stability comparing to that of CoFe-Fe5C2@NC electrocatalyst, which attributed to the interconnected ion/electron channels of abundant interfaces anchored nitrogen doped carbon nanotubes and the thin layer nitrogen doped graphitized carbon anchor the ultra-fine Fe5C2 and CoFe particles accelerating the charge transport. More importantly, CoFe-Fe5C2@NC presents 94.6% retention of initial MOR activity during CO poisoning test. This strategy will provide new ideas for the control of the composite structure of transition metal carbides using MOF derivatives, and provide technical support for the development of efficient and CO-resistant non noble metal electrocatalysts.

PdZrO2/rGO-FTO as an effective modified anode and cathode toward methanol electro-oxidation and hydrogen evolution reactions

In the present work, Pd/rGO and PdZrO2/rGO nanostructures were synthesized in a single step by hydrothermal method. Synthesized nanostructures containing 20 wt% Pd nanoparticles were characterized and approved using Fourier-transform infrared spectroscopy, x-ray diffraction, field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, and transmission electron microscopy techniques. The performance of Pd and PdZrO2 hybridized with rGO as catalysts were investigated and compared in the process of hydrogen production by water electrolysis and also in the process of electricity generation by methanol oxidation in the fuel cell. The activity and stability of synthetic nanocatalysts were evaluated using cyclic voltammetry, LSV, and chronoamperometry. The results showed that the presence of ZrO2 in the nanostructure increases the current density and reduces the overvoltage of the catalytic process. For methanol oxidation reaction, PdZrO2/rGO catalyst displays 92 mA cm–2 current density in alkaline media. For hydrogen evolution reaction, the Tafel slope of 52 mV dec–1 and overpotential of −0.198 V at the current density of 10 mA cm−2 were obtained in alkaline media. Also, due to high stability, this catalyst can be recommended as an optimal catalyst for industrial processes.

Platinum nanoparticles/phosphotungstic acid nanorods anchored poly(diphenylamine) nanohybrid coated electrode as a superior electro-catalyst for oxidation of methanol

Solvation of energy crises is the need of the era which urges for alternate energy resources. Direct methanol fuel cells (DMFCs) are an integral part of alternate energy and fuel concerns. This study demonstrates the facile fabrication of polydiphenylamine/phosphotungstic acid/platinum (PDPA/PTA/Pt) nanocomposites modified electrode via electrodeposition method for efficient electro-oxidation of methanol in acidic medium. The physicochemical characterization of PDPA/PTA/Pt nanocomposite modified electrode morphology using SEM with EDX mapping, and crystallinity behavior was examined using powder XRD analysis. The morphology of the PDPA/PTA/Pt nanocomposites demonstrates that the size of Pt nanospheres is ~200 nm, and the size of PTA nanorods is ~300 nm in the PDPA matrix. The electrochemical properties were also evaluated using cyclic voltammetry, chronoamperometric and electrochemical impedance studies techniques. The PDPA/PTA/Pt nanocomposite modified electrode showed superior electrocatalytic activity, higher current density (14.807 mA cm−2), longer stability and durability (30 min), and excellent catalytic poisoning tolerance to carbonaceous species accumulation towards methanol electro-oxidation reaction (MEOR), which is because of the synergistic existence of Pt nanospheres and PTA nanorods with PDPA matrix which enhances the electron transfer. The obtained results proved that the developed electro-catalyst is an excellent alternative for efficient MEOR in fuel cells applications.

Effect of Pt-Mn nanoparticles supported on CNT in methanol electro-oxidation reaction, experimental, and theoretical studies

Effect of Pt-Mn nanoparticles supported on CNT in methanol electro-oxidation reaction, experimental, and theoretical studies

Facile synthesis of polyaniline/titanium carbide (MXene) nanosheets/palladium nanocomposite for efficient electrocatalytic oxidation of methanol for fuel cell application

Slow methanol oxidation reaction kinetics with current electrocatalysts is the major limitation to widespread application and development in direct-methanol fuel cells (DMFCs). The present work demonstrates a highly efficient electrocatalyst for methanol electrooxidation reaction (MEOR) using polyaniline/palladium/Ti3C2Tx (PANI/Pd/MXene) nanocomposite. The PANI/Pd/MXene nanocomposite was prepared using a one-pot electrochemical co-deposition technique with a pre-anodized screen-printed electrode (SPE) under acidic electrolyte solution containing Ti3C2Tx, aniline, and palladium chloride as precursors. The PANI/Pd/MXene nanocomposite was examined using FESEM, TEM, FT-IR, XPS, and cyclic voltammetric techniques. The electrochemical response of the PANI/Pd/MXene nanocomposite shows enhanced electrocatalytic response towards the oxidation of methanol, with a peak current density of 291 mA cm−2, approximately three times higher than Pd/MXene (106 mA cm−2). Furthermore, it was also stable up to 100 cycles. The electrochemically active PANI/Pd sites are incorporated with MXene nanosheets, facilitating a more efficient MEOR. This stimulating result was achieved due to the sturdy metal–support interactions between PANI/Pd and MXene nanosheets that provide maximum methanol adsorption on the electrode surface for efficient electrocatalytic oxidation. Thus, the Ti3C2Tx support tailors the metal electrocatalyst interface and surface properties, resulting in improved electrocatalytic performance. This study highlights a facile approach for designing MXene-supported noble metal electrocatalysts for MEOR in direct-methanol fuel cells.

The Effect of Tin Addition to Platinum Catalysts with Different Morphologies towards Methanol Electrooxidation in Alkaline Media

Direct methanol fuel cells (DMFCs) using anion exchange membranes have been attracting great interest. Thus, it is very important to develop electrocatalysts for methanol electrooxidation reaction (MEOR) in alkaline media. In this study, the effects of platinum nanoparticle morphology and presence of tin oxide in the electrocatalysts were investigated. Platinum and platinum-tin nanoparticles with cubic-like shape and (100) preferential orientation supported on carbon, Pt/C(100) and PtSnO2/C(100), were synthesized by the alcohol-reduction process using KBr as the shape-directing agent. Polycrystalline nanoparticles supported on carbon, Pt/C, and PtSnO2/C were also synthesized. The catalytic activity of the nanomaterials toward MEOR in alkaline media was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analysis showed cubic Pt nanoparticles and SnO2 dispersed on the carbon support. X-ray diffraction (XRD) showed peaks of SnO2 cassiterite and peaks of the face-centered cubic (FCC) structure of Pt. CV experiments showed that the maximum current density from MEOR on Pt/C(100) (current density of about 108 mA cm–2 mg–1 of Pt) is about 2.4, 2.1, and 1.1 times higher than on Pt/C, PtSnO2/C, and PtSnO2/C(100), respectively. The same trend was observed in CA experiments. The higher catalytic activity of Pt(100) might be related to the OHads species coverage on it. SnO2 increases the catalytic activity on polycrystalline platinum, probably due to the OHads species provided by it. On the other hand, for Pt(100), the presence of SnO2 results in a decrease of the catalytic activity towards MEOR.

Influence of Electrochemical Pretreatment Conditions of PtCu/C Alloy Electrocatalyst on Its Activity.

A carbon supported PtCux/C catalyst, which demonstrates high activity in the oxygen electroreduction and methanol electrooxidation reactions in acidic media, has been obtained using a method of chemical reduction of Pt (IV) and Cu (2+) in the liquid phase. It has been found that the potential range of the preliminary voltammetric activation of the PtCux/C catalyst has a significant effect on the de-alloyed material activity in the oxygen electroreduction reaction (ORR). High-resolution transmission electron microscopy (HRTEM) demonstrates that there are differences in the structures of the as-prepared material and the materials activated in different potential ranges. In this case, there is practically no difference in the composition of the PtCux-y/C materials obtained after activation in different conditions. The main reason for the established effect, apparently, is the reorganized features of the bimetallic nanoparticles’ surface structure, which depend on the value of the limiting anodic potential in the activation process. The effect of the activation conditions on the catalyst’s activity in the methanol electrooxidation reaction is less pronounced.

Biomass-derived precious metal-free porous carbon: Ca-N,P-doped carbon materials and its electrocatalytic properties

The search for non-noble metal catalysts drive from biomass materials for oxygen reduction reactions (ORR) is highly desirable but challenging. Here, we have designed and synthesized three-dimensional hierarchical porous Ca-modified nitrogen and phosphorus co-doped carbon materials (Ca@NP6C4) derived from biomass hydrogel. Notably, the resulting Ca@NP6C4 material has high content of nitrogen (29.71 wt%)，and relatively high content percentage of pyridinic and graphitic nitrogen. As an efficient non-noble metal electrocatalyst, Ca@NP6C4 exhibits a high onset potential (0.94 V vs RHE) and a four-electron pathway for oxygen reduction reaction as well as good durability and outstanding methanol poisoning tolerance. Besides, it also performs as a good support for Pt particles (NPs). Pt/Ca@NP6C4 catalyst displayed remarkable catalytic performance and high stability for methanol electrooxidation reaction in acid medium. This work provides a feasible approach to develop cost-effective and highly efficient non-precious metal electrochemical catalysts for oxygen reduction.

Micro-Kinetic Modelling of the Electro-Oxidation of Methanol on Platinum

Methanol electro-oxidation reaction is a widely studied system due to its applicability in electrochemical devices for energy conversion, such as direct methanol fuel cells. Nevertheless, the effect of some kinetic parameters on the overall reaction rate is still unclear and the reaction mechanism is controversial. Herein we investigate the electro-oxidation of methanol on platinum by means of a micro-kinetic approach using the mean-field approximation. The resulting model, c.f. Figure 1, is based on data, namely spectroscopic and electrochemical, available in the literature, and translated into a set of ordinary differential equations. Simulations are carried out in comparison with experimental results, including cyclic voltammetry, chronamperometry and potential oscillations under galvanostatic control. The numerical simulations agree satisfactorily with the experimental results with a set of realistic reaction rates in the elemental reaction steps for the electrooxidation of methanol in platinum. The values of the rate coefficients show the adsorption of methanol and the first steps after the formation of formic acid as the fastest, while the desorption of bridge adsorbed formic acid and the chemical adsorption and desorption of methylformate as the fastest steps. Figure 1

Enhanced electrochemical performance of MnNi2O4/rGO nanocomposite as pseudocapacitor electrode material and methanol electro-oxidation catalyst

Binary transition metal oxides with encouraging electrocatalyst properties have been suggested as electrode materials for supercapacitors and methanol oxidation. Hence, in this work, a binary mixed metal oxide based on nickel and manganese (MnNi2O4) and its hybrid with reduced graphene oxide were synthesized by a one-step hydrothermal method. After physical and morphological characterization, the potential of these nanostructures was investigated for use as supercapacitor electrodes and methanol electro-oxidation. The results of the electrochemical analysis showed a substantial effect of adding rGO to the MnNi2O4. The MnNi2O4/rGO hybrid electrode supercapacitor exhibited good stability of 93% after 2000 consecutive CV cycles and a specific capacitance of 575 F g−1 at the current density of 0.5 A g−1. Furthermore, the application of this hybrid nanomaterial in the methanol electro-oxidation reaction (MOR) indicated its appropriate electrochemical efficiency and stability in methanol oxidation. Our results show that MnNi2O4/rGO can be considered as a promising electrode material for energy applications.

Modulating Electronic Structure of an Au‐Nanorod‐Core–PdPt‐Alloy‐Shell Catalyst for Efficient Alcohol Electro‐Oxidation

AbstractDirect alcohol fuel cells (DAFCs) utilize alcohol electro‐oxidation reactions (AORs) to provide electricity, where catalysts with optimal electronic structures are required to accelerate sluggish AORs. Herein, an electrocatalyst with an Au‐nanorod core and a PdPt‐alloy shell is designed. Its electronic structures are modulated through epitaxial growth of a PdPt‐alloy shell on the Au‐nanorod core, which exhibits a tensional strain effect and atomic steps. Three key problems of AORs are solved with this catalyst, including poor adsorption of alcohols on the catalyst, CO poisoning of the catalyst, and a high free energy barrier for the AORs. Taking methanol electro‐oxidation reaction (MOR) as an example, this catalyst shows 9.4 times higher mass activity than the market‐available Pt/C catalyst. Theoretic simulations prove that this catalyst has a low free energy barrier for the MOR, and strong adsorption of methanol but weaker adsorption of carbonaceous intermediates. The reasons behind this are the stretched geometric structure of the PdPt (100)‐alloy shell and the optimized electronic structure of catalytic sites on the catalyst surface. Meanwhile, efficient electro‐oxidation of ethanol, ethylene glycol, and glycerol is realized. This work paves the way to design and synthesize universal and efficient AOR catalysts for the construction of high‐performance DAFCs.

Defective PdRh bimetallic nanocrystals enable enhanced methanol electrooxidation

Although PdRh-based bimetallic nanocrystals have been demonstrated as effective catalysts for methanol electrooxidation, the impact of introduced Rh on CO poisoning resistance and consequently the catalytic activity is still lacking in-depth studies. In this work, defective PdRh bimetallic nanocrystals (PdRh NAs) with different composition ratios are synthesized. The prepared Pd3Rh1 NAs exhibit much higher peak current density and greater durability in comparison with the control sample of Pd1Rh1 NAs, Pd5Rh1 NAs, and the Commercial Pd/C. In addition, we observe that the introduced suitable amount of Rh plays a critical role in promoting the activity and stability of PdRh NAs for methanol electrooxidation reaction (MOR). This work provides an advanced MOR catalyst, and highlights that modulating both surface structure and chemical composition of catalysts is an effective route to realize catalytic property optimization.

Three dimensional nitrogen, phosphorus and sulfur doped porous graphene as efficient bifunctional electrocatalysts for direct methanol fuel cell

The development of efficient and durable bifunctional catalysts for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) is desirable but remains a great challenge. Herein, a series of new three-dimensional (3D) nitrogen, phosphorus and sulfur doped porous graphene (NPS G) were fabricated by facile and cost-effective strategy, as efficient bifunctional electrocatalysts for direct methanol fuel cell. To obtain superior ORR and MOR bifunctional catalytic activities, we optimized the doping amount of nitrogen, phosphorus and sulfur in catalysts. The resulting metal-free NPS G2 catalyst had a long-term stability, desirable four electron pathway and excellent methanol poisoning tolerance. Moreover, NPS G2 exhibited higher onset potential compared to other metal-free NPS G, and close to commerical Pt/C catalyst current density under the same conditions. In addition, a series of NPS G used as good supports for Pt nanoparticles. Pt/NPS G2 catalyst displayed remarkable electrochemical performance, better cyclic stability and tolerance in methanol electrooxidation reaction.

Enhanced Methanol Electro‐Oxidation Activity of Nanoclustered Gold

Size-selected 3nm gas-phase Au clusters dispersed by cluster beam deposition (CBD) on a conducting fluorine-doped tin oxide template show strong enhancement in mass activity for the methanol electro-oxidation (MEO) reaction compared to previously reported nanostructured gold electrodes. Density functional theory-based modeling on the corresponding Au clusters guided by experiments attributes this high MEO activity to the high density of exposed under-coordinated Au atoms at their faceted surface. In the description of the activity trends, vertices and edges are the most active sites due to their favorable CO and OH adsorption energies. The faceted structures occurring in this size range, partly preserved upon deposition, may also prevent destructive restructuring during the oxidation-reduction cycle. These results highlight the benefits of using CBDin fine-tuning material properties on the nanoscale and designing high-performance fuel cell electrodes with less material usage.