Alkaline Direct Methanol Fuel Cells Research Articles

Pd supported on 3D graphene aerogel as potential electrocatalyst for alkaline direct methanol fuel cells

Direct methanol fuel cells (DMFCs) have been shown potential interest in several portable electronics for “green” power generation, however their large-scale commercial production are mostly hampered due to the low activity and high cost of the anode catalysts. In the present study, we report a facile, environmentally friendly, and cost-effective Pd supported on 3D graphene aerogel (Pd/GA) by one step freeze-casting process. The as-synthesized Pd/GA was broadly characterized by XRD, Raman, SEM, and TEM. Morphology observations show that 3D-porous cellular structure of Pd/GA with uniform distribution of 10 nm Pd nanoparticles on the surface of graphene sheets. Based on structural merits, the performance of Pd/GA has been investigated as an anode catalyst for alkaline DMFCs. Pd/GA catalyst shows significantly superior electrocatalytic performance, abnormally high poison tolerance, and stability as compared to the conventional Pd/ carbon black (Vulcan XC-72R) with the same loading (∼20%) of Pd.The superior electrocatalytic performance of Pd/GA towards methanol oxidation can be used in practical application as a promising anode material for DMFCs.

Atomically deviated Pd-Te nanoplates boost methanol-tolerant fuel cells.

The methanol crossover effect in direct methanol fuel cells (DMFCs) can severely reduce cathodic oxygen reduction reaction (ORR) performance and fuel efficiency. As a result, developing efficient catalysts with simultaneously high ORR activity and excellent antipoisoning methanol capability remains challenging. Here, we report a class of Pd-Te hexagonal nanoplates (HPs) with a Pd20Te7 phase that simultaneously overcome the activity and methanol-tolerant issues in alkaline DMFC. Because of the specific arrangement of Pd atoms deviated from typical hexagonal close-packing, Pd-Te HPs/C displays extraordinary methanol tolerance with high ORR performance compared with commercial Pt/C. DFT calculations reveal that the high performance of Pd-Te HPs can be attributed to the breakthrough of the linear relationship between OOH* and OH* adsorption, which leaves sufficient room to improve the ORR activity but suppresses the methanol oxidation reaction. The concurrent high ORR activity and excellent methanol tolerance endow Pd-Te HPs as practical electrocatalysts for DMFC and beyond.

Porous Pd‐PdO Nanotubes for Methanol Electrooxidation

AbstractPalladium (Pd) nanostructures are highly active non‐platinum anodic electrocatalysts in alkaline direct methanol fuel cells (ADMFCs) and their electrocatalytic performance relies highly on their morphology and composition. Herein, a facile high‐temperature pyrolysis method to synthesize high‐quality Pd‐palladium oxide (PdO) porous nanotubes (PNTs) by using Pd(II)‐dimethylglyoxime complex (Pd(II)‐DMG) nanorods as a self‐template is reported. The chemical component of pyrolysis products highly correlates with pyrolysis temperature. The electrochemical measurements and density functional theory calculations show the existence of PdO enhances the electroactivity of metallic Pd for both methanol oxidation reaction (MOR) and carbon monoxide oxidation reaction in alkaline media. Benefiting from its one‐dimensionally porous architecture and evident synergistic effect between PdO and Pd (e.g., electronic effect and bifunctional mechanism), Pd‐PdO PNTs achieve a 3.7‐fold mass activity enhancement and improved durability for MOR compared to commercial Pd nanocrystals. Considering the simple synthesis, excellent activity, and long‐term stability, Pd‐PdO PNTs may be highly promising anodic electrocatalysts in ADMFCs.

The Effect of Cross-linking Technique on Membrane Performance for Direct Methanol Alkaline Fuel Cell Application

In this study, anion exchange membranes (AEM) based on poly(vinyl alcohol) (PVA) were prepared by two different cross-linking techniques and the effects of application sequence of thermal and chemical cross-linking technique on properties of AEM were investigated. Poly(ethylene glycol) diglycidly ether (PEGDGE) was used as a chemical cross-linking agent instead of the commonly used glutaraldehyde (GA). Evaluation of the fuel cell-related properties of the prepared membranes showed that the technique of cross-linking and the application sequence of techniques affected the properties of membranes. Promisingly, it was found that the membranes prepared by firstly chemical cross-linking and then thermal cross-linking at 150˚C (PPP150) exhibited high ionic conductivity (47 mS/cm), membrane selectivity values (89 x104 S.s/cm3) and sufficient mechanical strength. These encouraging results indicate that AEMs-based on PVA cross-linked by chemical technique with PEGDGE and then thermal technique may be considered as a promising membrane for Direct Methanol Alkaline Fuel Cell (DMFC) applications.

Cell performance of direct methanol alkaline fuel cell (DMAFC) using anion exchange membranes prepared from PVA-Based block copolymer

Direct methanol alkaline fuel cells (DMAFCs) with anion exchange membranes (AEMs) have the potential to address many of the problems faced by their acidic counterparts made with proton exchange membranes. Polyvinyl alcohol (PVA) is a candidate material for polymer electrolyte membranes (PEMs) for DMAFCs due to its excellent methanol barrier properties. In this study, PVA-based PEMs for a DMAFC process were prepared from PVA-based block copolymers with varying glutaraldehyde (GA) cross-linker concentrations. The properties and DMAFC performance of the PVA-block type PEMs at various concentrations of methanol were measured and compared with a commercially available AEM, Neosepta® AMX.A single cell DMAFC test using the PEM cross-linked with 0.01 vol% GA and AMX produced the maximum power of 99.6 mW/cm2 and 15.2 mW/cm2, respectively. When the methanol concentration was increased to 10 wt%, the PEM produced 94.8 mW/cm2, while AMX produced significantly less power at 7.7 mW/cm2 under the same conditions. Even at the high methanol concentration of 30 wt%, the PEM produced 42.2 mW/cm2, while AMX did not generate any power under the same conditions.

Quaternized chitosan-based anion exchange membrane for alkaline direct methanol fuel cells

We synthesized a novel quaternized anion exchange membrane (AEM) that exhibits high ionic conductivity and structural stability, even under high pH conditions, by copolymerizing a chitosan-based membrane with vinylimidazole derivatives. During the process, a quaternized poly[O-(2-imidazolyethylene)-N-picolylchitosan (QPIENPC) was synthesized by modifying chitosan with a 4-pyridinecarboxaldehyde derivative and then copolymerizing the modified chitosan with 1-vinylimidzaole. The results revealed that the degree of quaternization is correlated with ionic exchange capacity, water absorption ability, linear expansion ratio, and hydroxide conductivity of the resulting membrane. The QPIENPC membrane was characterized by a high ionic conductivity of 10.15mScm−1, 14 times greater that of the unfunctionalized chitosan membrane, as well as by low water absorption ability (36.17%) and linear expansion ratio (20.49%) at 80°C. An alkaline direct methanol fuel cell (ADMFC) was fabricated using the prepared QPIENPC membrane as an anion exchange electrolyte membrane, with PtRu/C and Pt/C as the anode and cathode, respectively. The performance of this ADMFC is promising even under high pH conditions, with the peak power density of 10.42mWcm−2 and corresponding current density of 28.76mAcm−2. Moreover, the thermochemical and mechanical strengths of the QPIENPC membrane were higher than those of the chitosan membrane.

Architecture of porous CoS1.097-C composite nanowire for efficient oxygen reduction reaction

Design and preparation of efficient and low cost electrocatalysts for the oxygen reduction reaction (ORR) is vitally important for the commercialization of alkaline direct methanol fuel cell (ADMFC). Herein, porous CoS1.097-C composite nanowire is prepared by one-step in-situ pyrolyzing Co-nitrilotriacetic acid (Co-NTA) precursor in Ar atmosphere with adding S powder. The obtained CoS1.097-C composite nanowire gathered by carbon encapsulated CoS1.097 nanoparticles are further analyzed by FT-IR, XRD, SEM, TEM, Raman, BET and XPS. The optimized CoS1.097-C composite nanowire catalyst shows the onset potential of 0.90 V and half-wave potential of 0.79 V with the acquired tafel slope of 57.7 dec−1 for ORR in 0.1 M KOH. Further studies indicate that the effective four-electron pathway contributes to excellent ORR activity. Moreover, the CoS1.097-C composite nanowire catalyst exhibits good durability and methanol tolerance over the commercial Pt/C. This work provides a general strategy for developing carbon-based transition metal sulfide nanocomposite as cathode in ADMFC.

Cobalt oxyhydroxide and carbon dots modified by platinum as superior electrocatalyst for methanol oxidation

The engineering of electrocatalysts with high performance for methanol oxidation reaction (MOR) is of great urgency for the development of direct methanol fuel cells (DMFCs). Here, we designed and fabricated cobalt oxyhydroxide and carbon dots modified by platinum (Pt-CoOOH-CDs/C) hybrids with low content of Pt (13 wt%) as electrocatalyst, which exhibit high activity (856.3 mA·mg−1Pt), stability (3 h) and better anti-poisoning ability for MOR. The Pt-CoOOH-CDs/C was synthesized by precipitate method followed with photochemical deposition. In the catalytic system, the Pt nanoparticles serve as the active center toward MOR, CoOOH-CDs use as the co-catalyst to oxidize CO-like poisonous species to CO2 on neighbouring Pt sites, and the cost-efficient carbon black enhances the conductivity for the system. The cost-efficient Pt-CoOOH-CDs/C system with improved kinetics for anodic methanol oxidation has promising application in alkaline DMFCs.

Carbide-Derived Carbon/Carbon Nanotube Composite Catalysts Doped with Nitrogen and Transition Metals for Anion Exchange Membrane Fuel Cells

Developing a non-precious metal catalyst (NPMC) to replace Pt on the cathode of polymer electrolyte fuel cells is currently one of the most important challenges in electrocatalysis.1 In the recent years, incorporating transition metals, such as iron or cobalt into a nitrogen-doped carbon nanomaterial, thus forming active sites for the oxygen reduction reaction (ORR), has been shown to be a promising strategy for NPMC design. The debate on the exact active sites and the mechanism of the ORR in this type of catalysts is still ongoing, but many advances have been made by studying the effect of catalyst precursors (the sources for the carbon, nitrogen and transition metals) on the ORR activity of the final catalyst. Carbide-derived carbons (CDC) are carbon materials synthesized by removal of metals from metal carbides. By careful selection of synthesis conditions, the CDCs can be tuned to have specific pore size distributions and degrees of disorder. As a continuation of our previous work,2,3 where we studied nitrogen and transition metal doped highly microporous CDCs (M-N-CDC), we have now incorporated multiwall carbon nanotubes (MWCNT) into the M-N-CDC catalyst to form a composite catalyst (M-N-comp).4 The catalysts were synthesized in a two-step pyrolysis procedure: first the CDC was ball-milled along with iron(II)acetate and 1,10-phenanthroline. This mixture was pyrolyzed and then MWCNTs along with dicyandiamide and another amount of iron(II)acetate were added. The surface morphology and elemental composition of the final catalysts were investigated with scanning electron microscopy, N2 physisorption, inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy along with rotating disk electrode (RDE) and single-cell anion-exchange membrane fuel cell (AEMFC) studies to give a thorough characterization of the physico-chemical properties of the catalysts and the relationships between them. The addition of MWCNTs was revealed to add mesoporosity as the MWCNTs filled the space in between the highly microporous CDC grains, thus increasing the ORR activity by providing more active sites and also facilitating mass transport. The ORR onset potential for the best catalyst, which had a CDC-to-CNT ratio of 2:1 in RDE mode was 0.99 V vs RHE in 0.1 M KOH and the maximum power density using this catalyst in a H2/O2 AEMFC with Tokuyama A201 anion exchange membrane was 120 mW cm‒2. However, the catalyst with lowest CDC-to-CNT ratio (1:2), which had more negative onset potential in RDE testing, performed better at higher current densities in the AEMFC and reached a maximum power density of 160 mW cm‒2, likely due to better mass transport in the thick catalyst layer. The best catalysts exceeded the activity of commercial Pt/C in both RDE and AEMFC testing, showing the excellent potential of CDC-based catalysts to replace costly Pt in AEMFC devices. References A. Sarapuu, E. Kibena-Põldsepp, M. Borghei, and K. Tammeveski, Electrocatalysis of Oxygen Reduction on Heteroatom-doped Nanocarbons and Transition Metal-Nitrogen-Carbon Catalysts for Alkaline Membrane Fuel Cells, J. Mater. Chem. A, 6, 776-804 (2018).S. Ratso, I. Kruusenberg, M. Käärik, M. Kook, R. Saar, P. Kanninen, T. Kallio, J. Leis, and K. Tammeveski, Transition Metal-Nitrogen Co-doped Carbide-Derived Carbon Catalysts for Oxygen Reduction Reaction in Alkaline Direct Methanol Fuel Cell, Appl. Catal. B Environ., 219, 276–286 (2017).S. Ratso, I. Kruusenberg, M. Käärik, M. Kook, L. Puust, R. Saar, J. Leis, and K. Tammeveski, Highly Efficient Transition Metal and Nitrogen Co-doped Carbide-Derived Carbon Electrocatalysts for Anion Exchange Membrane Fuel Cells, J. Power Sources, 375, 233–243 (2018).S. Ratso, M. Käärik, M. Kook, P. Paiste, V. Kisand, S. Vlassov, J. Leis, and K. Tammeveski, Iron and Nitrogen Co-doped Carbide-Derived Carbon and Carbon Nanotube Composite Catalysts for Oxygen Reduction Reaction, ChemElectroChem (2018). doi:10.1002/celc.201800132. Figure 1

Transition Metal and Nitrogen Co-Doped Carbide-Derived Carbon Catalysts for Oxygen Reduction Reaction in Alkaline Direct Methanol Fuel Cell

Finding viable alternative catalysts for the oxygen reduction reaction (ORR) is a key issue in modern electrocatalysis. Traditional Pt/C catalysts are not viable in the long term and thus much effort has been focused on non-precious metal catalysts (NPMCs). Metal-nitrogen doped carbon materials (MNCs) have emerged as the main candidate for replacing the platinum-based catalysts. Among these materials, carbide-derived carbon (CDC), which is a type of carbon materials produced by removing the metal atoms from a carbide lattice, stand out as exceptional candidates due to easily variable porosity. The specific surface areas of CDC materials can reach around 1000-2000 m2 g−1 and the textural characteristics can be tuned by selection of carbides and synthesis conditions, with reproducible large-scale syntheses already shown.1 In this work, we propose a method to introduce nitrogen and metals into a carbide derived carbon material with little loss of porosity using dicyandiamide (DCDA) and either cobalt or iron salts (Figure 1b). The CDC is derived from titanium carbide and then doped by pyrolyzing a mixture of the CDC, DCDA and either CoCl2 or FeCl3. The textural properties of the catalysts are probed with N2 physisorption, the morphology with scanning electron microscopy, the surface elemental composition with X-ray photoelectron spectroscopy (XPS) and the structure with Raman spectroscopy. The catalysts‘ activity towards ORR along with the stability during 1000 cycles and methanol tolerance in 0.1 M KOH is assessed using the rotating disk electrode (RDE) method and compared to that of commercial Pt/C catalysts (Figure 1a). The catalysts are also utilized in a alkaline direct methanol fuel cell (ADMFC)2 and an H2/O2 anion exchange membrane fuel cell (AEMFC). The catalysts are shown to retain their microporous structure after the pyrolysis with successful doping of up to 5.3 at.% of nitrogen into the surface layer of the materials as determined by XPS. The catalysts show excellent activity in 0.1 M KOH rivaling that of commercial platinum-based catalysts and are very stable during 1000 potential cycles, with the iron-based catalysts somewhat more active. Up to 3 M methanol concentration also has very minimal effect on the activity of the catalysts. In an ADMFC using the Fuma-Tech FAA3 membrane the MNC catalysts show better performance than Pt/C (Figure 1c) and in an AEMFC with the Tokuyama A201 membrane as the polymer electrolyte they also rival the Pt/C catalyst. Overall, we show that transition metal and nitrogen-doped CDCs present a viable alternative to commercial Pt/C catalysts for oxygen reduction in alkaline conditions and alkaline membrane fuel cells.

Poly(arylene ether ketone) Copolymer Grafted with Amine Groups Containing a Long Alkyl Chain by Chloroacetylation for Improved Alkaline Stability and Conductivity of Anion Exchange Membrane

We report simple and controllable acetylation of poly(arylene ether ketone) (PK) followed by Menshutkin reaction (quaternization), to prepare a highly alkaline stable and conductive (phase-separated) anion exchange membrane (AEM). A long side alkyl chain grafted with ammonium groups facilitates decent hydrophilic/hydrophobic microphase separation. Prepared AEMs exhibited improved conductivity, alkaline stability, and water resistivity, because of well-designed membrane architecture. Under alkaline conditions, nucleophilic substitution reaction and/or Hofmann elimination reaction (β-hydrogen) are expected to protected by grafting of a large volumetric alkyl chain (C = 16) with amine groups responsible for steric hindrance. Suitably assessed PK-QD-48 AEM reveals 0.81 V open circuit voltage (OCV) corresponding to 25.53 mW cm–2 power density at 65 °C in alkaline direct methanol fuel cell (ADMFC) operation. The reported synthetic strategy offers a novel route for preparing highly conducting, and alkaline stabl...

Highly Zeolite-Loaded Polyvinyl Alcohol Composite Membranes for Alkaline Fuel-Cell Electrolytes.

Having a secure and stable energy supply is a top priority for the global community. Fuel-cell technology is recognized as a promising electrical energy generation system for the twenty-first century. Polyvinyl alcohol/zeolitic imidazolate framework-8 (PVA/ZIF-8) composite membranes were successfully prepared in this work from direct ZIF-8 suspension solution (0–45.4 wt %) and PVA mixing to prevent filler aggregation for direct methanol alkaline fuel cells (DMAFCs). The ZIF-8 fillers were chosen for the appropriate cavity size as a screening aid to allow water and suppress methanol transport. Increased ionic conductivities and suppressed methanol permeabilities were achieved for the PVA/40.5% ZIF-8 composites, compared to other samples. A high power density of 173.2 mW cm−2 was achieved using a KOH-doped PVA/40.5% ZIF-8 membrane in a DMAFC at 60 °C with 1–2 mg cm−2 catalyst loads. As the filler content was raised beyond 45.4 wt %, adverse effects resulted and the DMAFC performance (144.9 mW cm−2) was not improved further. Therefore, the optimal ZIF-8 content was approximately 40.5 wt % in the polymeric matrix. The specific power output was higher (58 mW mg−1) than most membranes reported in the literature (3–18 mW mg−1).

Preparation and characterization of quaternized poly(vinyl alcohol)/chitosan/MoS2 composite anion exchange membranes with high selectivity

In this study, a series of novel quaternized poly(vinyl alcohol)/chitosan/molybdenum disulfide (QPVA/CS/MoS2) anion exchange membranes (AEMs) were prepared for direct methanol alkaline fuel cell (DMAFC). The composite membrane was synthesized by adding different amounts of MoS2 nanosheets (0, 0.1, 0.2, 0.5 and 1wt%) into QPVA/CS mixture solution and using the solution casting method. The crystallinity, thermal and mechanical properties, ion conductivity and resistance to methanol of the QPVA/CS/MoS2 membranes were characterized by X-ray diffraction, thermogravimetric analysis, tensile testing, ion exchange capacity, and methanol permeability measurements, respectively. The MoS2 was homogeneously dispersed in the membranes. The mechanical strength of the composite membranes was enhanced with the addition of MoS2. With the addition of 1.0wt% MoS2, the QPVA/CS/MoS2 composite membrane has the lowest methanol permeability of 0.210×10−7cm2·s−1. This study confirmed that the novel QPVA/CS/MoS2 membrane would be a potential candidate for the application in DMAFCs.

Reorientation of Magnetic Graphene Oxide Nanosheets in Crosslinked Quaternized Polyvinyl Alcohol as Effective Solid Electrolyte

This work aims to clarify the effect of magnetic graphene oxide (GO) reorientation in a polymer matrix on the ionic conduction and methanol barrier properties of nanocomposite membrane electrolytes. Magnetic iron oxide (Fe3O4) nanoparticles were prepared and dispersed on GO nanosheets (GO-Fe3O4). The magnetic GO-Fe3O4 was imbedded into a quaternized polyvinyl alcohol (QPVA) matrix and crosslinked (CL-) with glutaraldehyde (GA) to obtain a polymeric nanocomposite. A magnetic field was applied in the through-plane direction during the drying and film formation steps. The CL-QPVA/GO-Fe3O4 nanocomposite membranes were doped with an alkali to obtain hydroxide-conducting electrolytes for direct methanol alkaline fuel cell (DMAFC) applications. The magnetic field-reoriented CL-QPVA/GO-Fe3O4 electrolyte demonstrated higher conductivity and lower methanol permeability than the unoriented CL-QPVA/GO-Fe3O4 membrane or the CL-QPVA film. The reoriented CL-QPVA/GO-Fe3O4 nanocomposite was used as the electrolyte in a DMAFC and resulted in a maximum power density of 55.4 mW·cm−2 at 60 °C, which is 73.7% higher than that of the composite without the magnetic field treatment (31.9 mW·cm−2). In contrast, the DMAFC using the CL-QPVA electrolyte generated only 22.4 mW·cm−2. This research proved the surprising benefits of magnetic-field-assisted orientation of GO-Fe3O4 in facilitating the ion conduction of a polymeric electrolyte.

Methanol Oxidation on Ru- or Ni-Modified Pd-Electrocatalysts in Alkaline Media: A Comparative Differential Electrochemical Mass Spectrometry Study

The electrochemical oxidation of methanol on electrocatalysts is intensively investigated since direct methanol fuel cells (DMFCs) were proposed as a promising alternative as power source for mobile and back-up power applications. In DMFCs, methanol is oxidized at the anode and oxygen is reduced at the cathode to convert the chemical energy of the fuels to electric power. In recent years, the electrochemical oxidation of methanol in alkaline environment is rising in interest, because other electrocatalysts than the expensive platinum are feasible as anode and cathode catalysts in alkaline DMFCs. While multiple catalysts are feasible on the cathodic site, Palladium was proven to be a suitable substitute for Pt as anode catalyst for the electrochemical oxidation of alcohols in alkaline media [1], but needs further improvement to compete with Pt especially regarding methanol oxidation reaction. The catalytic activity of Pd catalysts was improved by alloying or mixing other metals (or metal oxides) to Pd [2,3] or by controlling the size and shape of Pd particles [4]. Besides high catalytic activity, the complete oxidation of methanol to CO2is of enormous interest, because the complete oxidation results in the highest possible faradaic efficiency with six electrons transferred per methanol molecule. In contrast, two or four electrons are transferred to the anode per methanol molecule, if methanol is not completely oxidized. Differential electrochemical mass spectrometry (DEMS) is used by different research groups to quantify a catalyst’s ability to completely oxidize methanol. While the methanol electrooxidation on Pt-based catalysts was investigated intensively via DEMS in acidic media, DEMS studies on Pd-based catalysts for methanol electrooxidation in alkaline media are rare. In former studies, we reported on PdXNi/C and PdXRu/C catalysts for methanol electrooxidation in alkaline media synthesized by wet-chemical reduction with sodium borohydride [2,3]. It was possible to show that these oxophilic metals have a positive effect on the catalytic activity towards methanol oxidation of Pd-based catalysts. Taking these studies into account, we herein investigated the influence of these metals on Pd-based electrocatalysts regarding methanol oxidation reaction via DEMS. Besides analyzing the product distribution from methanol bulk oxidation on PdXNi/C or PdXRu/C, the main interest of this work is to investigate how the addition of the metals to Pd influences the methanol oxidation mechanism and catalyst poisoning. Hence, standard electrochemical tests like cyclic voltammetry, chronoamperometry, COadsstripping or methanol adsorbate stripping were conducted in the DEMS flow cell. Figure 1 shows cyclic voltammograms and corresponding MS signals for produced CO2 (m/z = 44) and methyl formate (m/z = 60) for Pd/C, Pd5Ni/C and Pd3Ru/C during methanol electrooxidation. While both modified catalysts show higher current densities and lower onset potentials than Pd/C for the electrooxidation of methanol, the product distribution differs strongly depending on the added metal. For Ni-modified catalyst the formation of CO2 is significantly lower than for Pd/C. While the addition of Ni to Pd leads to a negative effect on the ability to completely oxidize methanol, Pd3Ru/C is able to oxidize methanol more efficiently to CO2 than Pd/C. For Pd3Ru/C, the CO2 formation is shifted to lower potentials while methyl formate is produced at higher potentials. This hints to a more selective production of CO2 at low potentials on Pd3Ru/C than on Pd/C or Pd5Ni/C. Besides DEMS experiments, measurements were carried out in dependence of methanol concentration or oxidation temperature using a 3-electrode setup with stationary electrolyte to determine the rate determining step and the activation energy of methanol electrooxidation on Pd/C and the modified catalysts. Fig. 1 – Methanol bulk oxidation on Pd/C, Pd5Ni/C and Pd3Ru/C investigated via cyclic voltammetry in a DEMS flow cell at 20 mV s-1 from 0.1 to 1.2 V (vs. RHE) with 0.1 M CH3OH + 0.5 M KOH solution as electrolyte. Corresponding mass spectrometry signals for CO2 (m/z 44) and HCOOCH3(m/z 60) are displayed to evaluate the product distribution during methanol oxidation reaction.

Methanol Oxidation in Alkaline Medium Using PtIn/C Electrocatalysts

Pt/C and PtIn/C with atomic ratios of 90:10, 70:30, and 50:50 were investigated for methanol electro-oxidation in alkaline media by using cyclic voltammetry (CV), chronoamperometry (CA), and direct methanol alkaline fuel cell (DMAFC). All electrocatalysts were synthesized using sodium borohydride method with 20 wt% of metals loading on carbon. X-ray diffraction (XRD) analysis revealed that bimetallic PtIn had faced centered cubic structure and, also, confirmed alloy formation for PtIn/C nanoparticles. Transmission electron micrographs showed metal nanoparticles with average particle size between 3.0 and 5.0 nm; however, the particle size increases when the In content was increased in PtIn/C. In the CV experiments, the onset potential of methanol electro-oxidation shifted to lower values as the indium content increased. Chronoamperometry experiments and direct methanol alkaline fuel cell suggested PtIn/C (70:30) as the most promising material for methanol electro-oxidation: this result could be explained by the presence of Pt and In in close contact (electronic effect) as the occurrence of oxy-hydroxy interactions.

Study of physicochemical characterization of potassium-doped Nafion117 membrane and performance evaluation of air-breathing fuel cell in different alkali-methanol solutions

Direct methanol alkaline fuel cell (DMAFC) using a cation exchange membrane (CEM) was operated in passive condition and compared to passive direct methanol fuel cell (DMFC). A polymer electrolyte membrane for passive DMAFC was prepared by immersing Nafion117 membrane into KOH solution at temperature of 80 °C. The prepared membrane (potassium-doped Nafion117) exhibited higher mechanical properties and thermal stability than Nafion117. Ionic conductivity of K+ form Nafion117 membrane was measured to be lower than that for pristine Nafion117. Single cell in alkaline condition (passive DMAFC) exhibited better cell performance than that in the cell using Nafion117 in acidic condition (passive DMFC). The open circuit voltage (OCV) of passive DMAFC reached to about 1 V which was considerably higher than that for passive DMFC (0.45 V). The methanol crossover rate through membranes was also measured and the results implied that the potassium-doped Nafion117 membrane had lower permeability to methanol.

Quaternized poly(phenylene oxide) anion exchange membrane for alkaline direct methanol fuel cells in KOH‐free media

ABSTRACTA series of anion exchange membrane (AEM) electrolytes with quaternary ammonium moiety are fabricated from poly (phenylene oxide) for its application in alkaline direct methanol fuel cells (ADMFCs). In the first step, poly(phenylene oxide) (PPO) is successfully chloromethylated by substituting chloromethyl groups in the aryl position of polymer. In the second step, the chloromethylated PPO (CPPO) is further homogeneously quaternized and ion‐exchanged to form an AEM. From the second step, series of AEMs are prepared by changing the mole ratio of amine in relation to CPPO. The presence of quaternary ammonium group in the membrane was confirmed by elemental analysis. The fabricated membranes are subjected to cell polarization studies in ADMFCs, wherein quaternized poly(2,6‐dimethyl‐1,4‐phenylene oxide) (CPPO:amine of 1:8) membrane exhibits higher peak power density of 3.5 mW cm−2 when compared with the other ratios of CPPO:amine in the absence of KOH solution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43693.

Model-based analysis of water management at anode of alkaline direct methanol fuel cells

Alkaline direct methanol fuel cells (ADMFCs) produce water at the aqueous fed anode. This complicates water management at anode which is analysed in this study by modelling three extreme case scenarios assuming different conditions for water transport or removal. All scenarios include recycling of methanol solution at anode outlet to achieve high methanol efficiencies. One scenario reveals that high operation times and high methanol efficiencies necessitate active stabilisation of anodic water level since both water accumulation and depletion can take place depending on operation conditions. Another scenario shows that water level can be stabilised by adjusting cathodic evaporation and the corresponding water removal from the system. The results indicate that feeding cathode with water-saturated gas is detrimental for stabilising water level. The last scenario suggests the addition of a gas flow to anodic outlet to remove excess water for water level stabilisation. Minimization of additional methanol loss requires to reach high humidities by evaporation. The present paper reveals the impact of processes occurring in ADMFCs on anodic water management and indicates the necessity to quantify water transport through membrane. Knowledge of the influence of operation conditions on water level in the anodic loop are beneficial for design of ADMFC systems.

Facile synthesis of a mechanically robust and highly porous NiO film with excellent electrocatalytic activity towards methanol oxidation.

Considerable research is being conducted in searching for effective anode catalysts in alkaline direct methanol fuel cells (DMFCs). Although significant progress has been achieved, it is still challenging to prepare non-Pt catalysts with both excellent activity and good durability. Herein, a highly porous NiO film is developed by a facile and fast anodization approach. The anodic NiO film demonstrates a high surface area, large mesopore volume and small crystallite size, leading to facilitated adsorption of reaction species, easy electrolyte penetration and fast reaction kinetics. Furthermore, as anodic NiO is grown in situ on a metallic substrate with strong adhesion strength and good electrical contact, it can be used directly as an anode catalyst for methanol oxidation without the need to add any binder or conducting agent. Such an additive-free approach greatly expedites the catalyst preparation process. The anodic NiO shows lower methanol oxidation potential, higher oxidation current and better catalytic durability than most of the state-of-the-art Ni-based catalysts reported elsewhere. As anodization is a simple, low cost and easily scaled up method, the work described here provides an exciting direction to speed up the practical application of alkaline DMFCs.