Palladized dysprosium fluoride nanorods as a new performance catalyst in direct methanol fuel cell

Fuel cells are a new type of batteries that produce electricity from a continuous source of alcohols as long as fuel is inserted. In this study, decorated palladium nanoparticles (PdNPs) on dysprosium fluoride (DyF₃) nanorods (DyFNRs)‐multiwalled carbon nanotubes (MWCNTs) were used for electrooxidation of methanol. DyFNRs were synthesized by the hydrothermal method, and the proposed multifunctional catalyst (DyFNRs/MWCNT‐PdNPs) was identified by several methods such as X‐ray diffraction, elemental mapping images, field emission scanning electron microscopy, energy dispersive analysis of X‐rays, and transmission electron microscopy which demonstrated a uniform distribution and high dispersion of the PdNPs on the supports. The electrocatalytic activity toward methanol electrooxidation on glassy carbon electrode (GCE) with DyFNRs/MWCNT‐PdNPs (DyFNRs/MWCNT‐PdNPs/GCE) was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Experimental results showed a high improvement in oxidation potential and peak current of methanol electrooxidation by DyFNRs/MWCNT‐PdNPs in comparison to DyFNRs and PdNPs. The values of the catalytic rate constant (k) and physical dimension (D_s) for methanol oxidation on the DyFNRs/MWCNT‐PdNPs/GCE catalyst were calculated 0.008 s^?1 and 1.43, respectively. Moreover, the order of reaction was determined to be 0.43 and 0.13 for CH₃OH and NaOH, repectively. Finally, the synthesized catalyst was evaluated in direct methanol fuel cell (DMFC). The single DMFC with proposed anodic catalyst, DyFNRs/MWCNT‐PdNPs, indicated a power density of 4.4 mW·cm^?2 at a current density of 18 mA·cm^?2 in alcohol (1 M) and NaOH (1 M).     

High-performance core–shell PdPt@Pt/C catalysts via decorating PdPt alloy cores with Pt

A core–shell structured low-Pt catalyst, PdPt@Pt/C, with high performance towards both methanol anodic oxidation and oxygen cathodic reduction, as well as in a single hydrogen/air fuel cell, is prepared by a novel two-step colloidal approach. For the anodic oxidation of methanol, the catalyst shows three times higher activity than commercial Tanaka 50 wt% Pt/C catalyst; furthermore, the ratio of forward current I_f to backward current I_b is high up to 1.04, whereas for general platinum catalysts the ratio is only ca. 0.70, indicating that this PdPt@Pt/C catalyst has high activity towards methanol anodic oxidation and good tolerance to the intermediates of methanol oxidation. The catalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The core–shell structure of the catalyst is revealed by XRD and TEM, and is also supported by underpotential deposition of hydrogen (UPDH). The high performance of the PdPt@Pt/C catalyst may make it a promising and competitive low-Pt catalyst for hydrogen fueled polymer electrolyte membrane fuel cell (PEMFC) or direct methanol fuel cell (DMFC) applications.     

Carbon-ceramic supported bimetallic Pt–Ni nanoparticles as an electrocatalyst for electrooxidation of methanol and ethanol in acidic media

The electrooxidation of methanol and ethanol was investigated in acidic media on the platinum–nickel nanoparticles carbon-ceramic modified electrode (Pt–Ni/CCE) via cyclic voltammetric analysis in the mixed 0.5 M methanol (or 0.15 M ethanol) and 0.1 M H₂SO₄ solutions. The Pt–Ni/CCE catalyst, which has excellent electrocatalytic activity for methanol and ethanol oxidation than the Pt–Ni particles glassy carbon modified electrode (Pt–Ni/GCE), Pt nanoparticles carbon-ceramic modified electrode (Pt/CCE) and smooth Pt electrode, shows great potential as less expensive electrocatalyst for these fuels oxidation. These results showed that the presence of Ni in the structure of catalyst and application of CCE as a substrate greatly enhance the electrocatalytic activity of Pt towards the oxidation of methanol and ethanol. Moreover, the presence of Ni contributes to reduce the amount of Pt in the anodic material of direct methanol or ethanol fuel cells, which remains one of the challenges to make the technology of direct alcohol fuel cells possible. On the other hand, the Pt–Ni/CCE catalyst has satisfactory stability and reproducibility for electrooxidation of methanol and ethanol when stored in ambient conditions or continues cycling making it more attractive for fuel cell applications.     

Electrochemically synthesized polypyrrole/MWCNTs-Al2O3 ternary nanocomposites supported Pt nanoparticles toward methanol oxidation

As known, a good support enhances the activity and durability of any catalyst. In the current study, polypyrrole (PPY)/nanocomposite (MWCNTs and Al₂O₃) films were fabricated by electrochemical polymerization of pyrrole solution with a certain amount of nanoparticles on titanium substrates and were used as new support materials for Pt catalyst. The modified electrodes were characterized by Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX) techniques. High catalytic activity and long-time stability toward methanol oxidation of Pt/PPY–MWNTs-αAl₂O₃ catalyst have also been verified by cyclic voltammetry results and chronoamperometric response measurements. This catalyst exhibits a vehemently high current density (345.03 mA cm^?2) and low peak potential (0.74 v) for methanol oxidation. Other electrochemical measurements (electrochemical impedance spectroscopy (EIS), CO stripping voltammetry and Tafel test) clearly confirmed that Pt/PPY–MWNTs-αAl₂O₃/Ti electrode has a better performance toward methanol oxidation compared to the other electrodes and that can be used as a promising electrode material for application in direct methanol fuel cells (DMFCs).     

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.     

Enhancing methanol oxidation with a TiO2-modified semiconductor as a photo-catalyst

The direct methanol fuel cell (DMFC) is currently one of the most promising alternative power sources because of its high energy, simple design and operation. However, the DMFC still faces several problems, such as sluggish methanol oxidation and oxygen reduction, as well as a high methanol crossover. In other areas of study, it is well-known that methanol can be photocatalytically oxidized by wide band gap semiconductors under solar illumination. Methanol has been used in photocatalytic water splitting to enhance the performance of photo-electrochemical cells (PECs). Therefore, by combining photocatalytic and electro-catalytic mechanisms, methanol is expected to promote a new type of photo-assisted DMFC. In this work, the semiconductor TiO₂ was used as a photo-catalyst in a PEC using a methanol solution. A TiO₂ P25 suspension was cast onto carbon paper and then dried at 80 °C for 60 min. The photo-electrochemical measurements were carried out in a 3-arm electrochemical cell, using Pt wire as the counter electrode and Ag/AgCl as the reference electrode. Linear scan voltammetry (LSV) was carried out using a 20 V/400 mA potentiostat. The current densities of the electrode were monitored with and without simulated solar illumination. From the investigation, the current density of the TiO₂ electrode under solar illumination was higher than it was without solar illumination. However, the value is low due to the low activity of TiO₂ under visible light illumination. Further studies were carried out by combining TiO₂ with a carbon material and a noble metal alloy to maximize the current density. This modified photo-catalyst can be utilized in a new photo-assisted DMFC to produce higher electricity.     

Electronically conducting hybrid material as high performance catalyst support for electrocatalytic application

The electronically conducting hybrid material based on transition metal oxide and conducting polymer has been used as the catalyst support for Pt nanoparticles. The Pt nanoparticles loaded hybrid organic (polyaniline)–inorganic (vanadium pentoxide) composite has been used as the electrode material for methanol oxidation, a reaction of importance for the development of direct methanol fuel cells (DMFC). The hybrid material exhibited excellent electrochemical and thermal stability in comparison to the physical mixture of conducting polymer and transition metal oxide. The Pt nanoparticles loaded hybrid material exhibited high electrocatalytic activity and stability for methanol oxidation in comparison to the Pt supported on the Vulcan XC 72R carbon support. The higher activity and stability is attributed to the better CO tolerance of the composite material.     

A new durable and high performance platinum supported on Ag–Ni-porous coordination polymer as an anodic DMFC nano-electrocatalyst: DFT and experimental investigation

Due to the poor performance and intermediates poisoning of available catalysts in direct methanol fuel cells (DMFC), the researcher is confronted with a considerable challenge for obtaining modified electrocatalyst. Ag–Ni porous coordination polymer (ANP) as a new electrocatalyst supporter was synthesized by a hydrothermal method. To achieve favorable electrocatalyst for DMFC systems, platinum nanoparticles was deposited upon ANP by an electrochemical method and platinum supported on Ag–Ni porous coordination polymer (Pt-ANP) was formed. Fourier transform infrared spectroscopy (FTIR) analysis ensured correct synthesized of ANP and Pt-ANP. In addition, the morphologies investigation of ANP and Pt-ANP were carried out by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The FE-SEM images indicate that the platinum nanoparticles have been greatly deposited on ANP surface. Electrochemical behaviors of prepared catalyst for methanol oxidation were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) techniques. Electrochemical cyclic voltammetry tests (CV) indicate that the forward peak current density of Pt-ANP is about 105 mA/cm² which it is 33% more than the forward peak current density of pure Pt catalyst (70.21 mA/cm²). Moreover, electrochemical surface area (ECSA) of Pt-ANP is 26.42 m²/g_Pt. In addition, density functional theory (DFT) computations show that with the deposition of Pt upon ANP, the HOMO-LOMO energy gap of ANP has been decreased which they are suitable for electrochemical reactions. Theoretical results are greatly in accordance with the experiments. Based on the results, Pt-ANP could be a superior electrocatalyst for methanol oxidation.     

Synthesis and optimization of PtRu/TiO2-CNF anodic catalyst for direct methanol fuel cell

Direct methanol fuel cell (DMFC) is a promising power source technology, but it has been unable to be successfully commercialized due to its high cost and low kinetic oxidation. Both problems stem from one of its main components, the catalyst. Therefore, this study is focused on determining and optimizing the electrocatalyst parameters of a high-performance DMFC. The electrocatalyst, PtRu/TiO₂-CNF, is produced by the deposition method and is subjected to electrochemical measurement and cyclic voltammetry (CV) to measure half-cell performance in a DMFC. The optimization process involved two main phases, a screening process followed by response surface methodology (RSM). The resulting optimum parameters were then used for the single cell performance testing. The results show that the mathematical model suggested by RSM is adequate for the optimization of the parameter levels. The optimum parameters suggested by RSM are a PtRu composition of 30.25% and a catalyst loading of 0.59 mg/cm², resulting in almost perfect agreement between the measured current density (603.06 mA/mg_PtRu) and the predicted value (600.63 mA/mg_PtRu). The current density obtained in this study is the highest among other researchers in the same field.     

Electrochemical impedance studies on carbon supported PtRuNi and PtRu anode catalysts in acid medium for direct methanol fuel cell

The anodic Pt–Ru–Ni/C and the Pt–Ru/C catalysts for potential application in direct methanol fuel cell (DMFC) were prepared by chemical reduction method. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were carried out by using a glassy carbon working electrode covered with the catalyst powder in a solution of 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄ at 25 °C. EIS information discloses that the methanol electrooxidation on the Pt–Ru–Ni/C catalyst at various potentials shows different impedance behaviors. The mechanism and the rate-determining step of methanol electrooxidation are changed with increasing potential. Its rate-determining steps are the methanol dehydrogenation and the oxidation reaction of adsorbed intermediate CO_ads and OH_ads in low (400–500 mV) and high (600–800 mV) potentials, respectively. The catalytic activity of the Pt–Ru–Ni/C catalyst is higher for methanol electrooxidation than that of the Pt–Ru/C catalyst. Its tolerance performance to CO formed as one of the intermediates of methanol dehydrogenation is also better than that of the Pt–Ru/C catalyst.     

Facile fabrication and electrocatalytic activity of Pt0.9Pd0.1 alloy film catalysts

A nano-thickness porous Pt_0.9Pd_0.1 alloy film with a greatly enhanced surface area were firstly synthesized at a glassy carbon electrode (GCE) using a facile cyclic voltammetry (CV) method. The atomic ratio of the alloy can be controlled by controlling the composition of the electrodeposition solution. We found that small amount of alloying Pd is an excellent catalytically enhancing agent for the Pt catalyst, and 10% Pd is the optimal. The structures of the Pt_0.9Pd_0.1 alloy film were characterized by FE-SEM, XPS, XRD and electrochemical techniques. It was found that the Pt_0.9Pd_0.1 film was in nanoporous structure and consisted of crystallites of 10.1 nm on average, leading to the modified electrode (Pt_0.9Pd_0.1/GCE) has an effective surface area as large as 790 times that of a corresponding bare Pt disk electrode. The Pt_0.9Pd_0.1/GCE exhibited significantly higher stability and catalytic activity for both of the methanol electro-oxidation reaction (MOR) and the oxygen electro-reduction reaction (ORR) than the correspondingly electrodeposited Pt modified GCE. The advantage can be attributed to the CV-prepared nano-porous structure on the electrode surface. This method and the prepared electrode can be expected to have promising applications in biosensors and fuel cells, etc.     

Electrosynthesis of dendritic palladium supported on Ti/TiO2NTs/Ni/CeO2 as high-performing and stable anode electrocatalyst for methanol electrooxidation

Liquid-fueled direct methanol fuel cell (DMFC) is highly promising for low-carbon transportation, but is hindered by high cost and short lifespan of conventional Pt-based electrocatalysts. Herein, we propose a new Pt-free catalyst strategy to exploit high-performing and stable electrocatalyst of DMFC, achieving enhanced electrocatalytic activity and high stability for methanol oxidation reaction (MOR) in alkaline media. A new Pt-free anode catalysts consisting of titanium/reduced-titanium dioxide nanotubes/nickel/cerium dioxide (Ti/r-TiO₂NTs/Ni/CeO₂) nanosupport and uniformly-dispersed Pd dendrites is successfully prepared by a facile three-step electrodeposition route without applying any template or surfactant. Noticeably, the as-prepared Ti/r-TiO₂NTs/Ni/CeO₂–Pd as an anode electrode exhibits superior activity than commercial Pd/C and other electrodes. The obtained large mass activity for Ti/r-TiO₂NTs/Ni/CeO₂–Pd electrode is 1752 mA mg_Pd^?1 for MOR. After successive CV tests of 1000 cycles, Ti/r-TiO₂NTs/Ni/CeO₂–Pd electrode still retained 88.9% of its initial current. The superior performance of Ti/r-TiO₂NTs/Ni/CeO₂–Pd attributes to the large surface area and excellent conductivity, as well as the synergistic effects among nanosupport and Pd dendrites. Therefore, this study will open a new door for high-performance fuel cell applications.     

Pt–Ni nanoparticles electrodeposited on rGO/CFP as high-performance integrated electrode for methanol oxidation

A novel carbon fiber paper loaded with reduced graphene oxide (rGO) was used as the substrate, on which Pt–Ni nanoparticles were electro-deposited as to prepare an integrated electrode by two electrochemical methods (cyclic voltammetry and square wave pulse). The electrochemical tests indicated two integrated electrodes had excellent performance towards methanol oxidation. Especially, Pt-Ni-CV(A)-rGO/CFP electrode showed the highest electrocatalytic activity, and mass activity reached 5.33 A·mg^?1_Pt, which was about 5.6 times that of the commercial Pt/C catalyst (JM). Further, after annealing under a reducing atmosphere, two electrodes exhibited completely different changes in the aspects of morphology and electrocatalytic performance. It can be attributed to the changes of element distribution and morphology of nanoparticles after annealing. The as-prepared Pt–Ni-rGO/CFPs composite electrode is promising for integrated electrode of proton exchange membrane fuel cells. This work opens an avenue for the preparation of high-performance integrated electrode.     

Glassy carbon electrode modified by Pd–Cu bimetallic nano-dendrites film decorated on the reduced graphene oxide using galvanic replacement as a low-cost anode in methanol fuel cells

Glassy carbon electrode (GCE) modified by reduced graphene oxide Cu–Pd nano-dendrimer (Pd-CuNDs-RGO/GCE) was prepared using electro-deposition and spontaneous displacement methods. Graphene oxide was put on the surface of GCE by drop-casting, then a thin film of reduced graphene oxide (RGO) was formed by electro-reduction at ?0.9 V. The copper nano-dendrimers (CuNDs) were electro-plated on RGO/GCE surface. Finally, Pd-CuNDs-RGO/GCE was prepared by the spontaneous replacement of CuNDs with palladium nanoparticles (PdNPs) in a dilute solution of palladium. The electrode surface was characterized using field-emission scanning electron microscopy (FESEM), X-ray energy diffraction (EDX) spectroscopy, and electrochemical techniques. The electrochemical behavior of the modified electrode in the oxidation of alkaline solution of methanol was investigated. The experimental conditions affecting the performance of the modified electrode in the methanol oxidation were studied and optimized. Finally, the proposed electrode has the onset potential of ?0.5 V and the ratio of i_f/i_b equal to 2.2, which confirms the high catalytic activity. The electrode has appropriate stability and shows about 86% of initial activity after 100 times testing.     

Electrochemical study of platinum deposited by electron beam evaporation for application as fuel cell electrodes

Platinum is the most used catalyst in electrodes for fuel cells due to its high catalytic activity. Polymer electrolyte and direct methanol fuel cells usually include Pt as catalyst in their electrodes. In order to diminish the cost of such electrodes, different Pt deposition methods that permit lowering the metal load whilst maintaining their electroactivity, are being investigated. In this work, the behaviour of electron beam Pt (e-beam Pt) deposited electrodes for fuel cells is studied. Three different Pt loadings have been investigated. The electrochemical behaviour by cyclic voltammetry in H₂SO₄, HClO₄ and in HClO₄ + MeOH before and after the Pt deposition on carbon cloth has been analysed. The Pt improves the electrochemical properties of the carbon support used. The electrochemical performance of e-beam Pt deposited electrodes was finally studied in a single direct methanol fuel cell (DMFC) and the obtained results indicate that this is a promising and adequate method to prepare fuel cell electrodes.     

A non-noble,low cost,multicomponent electrocatalyst based on nickel oxide decorated AC nanosheets and PPy nanowires for the direct methanol oxidation reaction

The multicomponent electrocatalyst is a low-cost composite material exhibiting excellent catalytic activity suitable for methanol oxidation reactions (MOR). In this work, we report a glassy carbon electrode modified nickel oxide nanospheres (NiO) decorated biomass-derived activated carbon (AC) nanosheets and polypyrrole (PPy) nanowire, electrocatalyst (NiO_AC@PPy/GCE) for direct methanol oxidation fuel cell (DMFC) application. The SEM micrographs reveal the nanosheets and nanowire-like morphology of AC and PPy decorated with NiO nanospheres which provide a high surface area with electrocatalytic activity, and stability for MOR. The NiO_AC@PPy/GCE exhibits a high current density of 551 mA/mg at a low onset potential of 0.5 V (vs Ag|AgCl) towards electro-oxidation of 0.5 M methanol (MeOH) in an alkaline medium. This superior performance of the NiO_AC@PPy/GCE over other reported metal-oxides based electrocatalysts is attributed to the synergistic effect of the NiO_AC@PPy electrocatalyst, wherein NiO provides electrocatalytic active sites for MOR via Ni²⁺/Ni³⁺ redox couple while the PPy and AC contribute towards the chemical stability and electrical conductivity of the electrode, respectively. The electrode shows 79% of capacity retention after 10,000 s of chronoamperometry displaying excellent chemical stability with reduced effect of CO intermediate poisoning at the electrode surface. This excellent stability and overall performance of the NiO_AC@PPy proves it as an ideal, low-cost non-noble electrocatalyst for DMFCs.     

Microfluidic direct methanol fuel cell by electrophoretic deposition of platinum/carbon nanotubes on electrode surface

Carbon nanotubes (CNTs) supported platinum (Pt) nanoparticles prepared via electrophoretic deposition are used as catalyst layer of a microfluidic direct methanol fuel cell (DMFC), to study the influence of catalyst layer materials and deposition methods on the cell performance. A Y‐shaped channel is designed and microfabricated. It is verified by cyclic voltammetric measurements that shows ca. 317.7% increase in the electrochemical active surface area for the electrode with CNTs over that without CNT. Scanning electron microscopy observations indicate the network formation within the electrode because of a 3‐D structure of CNTs, which could be beneficial to the increasing electrode kinetics and to the improvement in fuel utilization. Comparison between the DMFCs with and without CNTs as support shows that the proof‐of‐concept microfluidic DMFC with Pt/CNTs electrode is able to reach a maximum power density of 5.70 mW cm^?2 at 25 °C, while the DMFC with plain Pt electrode only has a maximum power density of 2.75 mW cm^?2. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of conditioning method on direct methanol fuel cell performance

We investigated the effect of the conditioning methods on improving the direct methanol fuel cell (DMFC) performance. The DMFC performance after the conditioning was measured using a newly developed single cell having an Ag/Ag₂SO₄ reference electrode, which is not influenced by methanol. As a result, we succeeded in developing an original two-step conditioning method in which the conditioning by fueling H₂ gas is conducted prior to a conventional DMFC conditioning. The anode and cathode characteristics after the two-step conditioning were measured with respect to a reference electrode. Based on the obtained i-E curves, the two-step conditioning is found to improve the methanol oxidation performance at the anode and also suppress the decline of the O₂ reduction performance at the cathode. The high DMFC performance based on the two-step conditioning is well explained by the anode and cathode characteristics.     

PtRu/C-Au/TiO2 electrocatalyst for a direct methanol fuel cell

Au/TiO₂ is added to a PtRu/C electrode to improve the performance of a direct methanol fuel cell (DMFC). A high-throughput-screening test is performed for the fast screening of the loading of Au/TiO₂ on PtRu/C. The electrochemically-active surface area of PtRu/C-Au/TiO₂ and PtRu/C is determined from cyclic voltammetry. In CO-stripping and methanol oxidation voltammetry, PtRu/C-Au/TiO₂ exhibits better activity for CO and methanol oxidation than PtRu/C. The performance of the DMFC is also improved by addition of Au/TiO₂ to the PtRu/C electrode. The CO adsorbed on Pt may move to the surface of the Au/TiO₂ by the interaction between PtRu/C and Au/TiO₂. The improved performance of the PtRu/C-Au/TiO₂ catalyst is explained in terms of preferential oxidation of CO or CO-like poisoning species that are generated during the oxidation of methanol on PtRu/C.