Structurally ordered PtFe intermetallic embedded in N-doped carbon as a highly active and durable electrocatalyst for oxygen reduction reaction

The structurally ordered PtM with surface coating layers strategy has drawn increasing attention. In this work, we synthesize a structurally ordered PtFe@NC-X-PDA catalyst modified with nitrogen-doped carbon coating layers by confined space annealing strategy. Compared with the current commercial Pt/C catalyst, the structurally ordered PtFe@NC-X-PDA catalyst shows better catalytic activity and stability. Especially, the mass activity and specific activity of the synthesized PtFe@NC-0.06-PDA sample with the optimized poly-dopamine feeding mass content (0.06 g) exhibit 9.95 and 11.53 times higher than that of commercial Pt/C catalyst. In addition, after 20,000 CV cycles, the PtFe@NC-0.06-PDA sample achieves the minimum activity loss (7%). The PtFe alloy catalyst with the different thickness NC shell (PtFe@NC-X-PDA) possesses the enhanced ORR activity and stability owing to the protection of nitrogen carbon shell (NC) and the strong electronic interaction of the ordered PtFe NPs. The improved ORR activity and stability of the structurally ordered PtFe@NC-X-PDA catalyst provide a promising direction for the development of fuel cells.     

Nitrogen doped carbon layer coated platinum electrocatalyst supported on carbon nanotubes with enhanced stability

Enhancement in durability of electrocatalyst is still one of the most important issues in polymer electrolyte fuel cells (PEFCs). Here, we report a structurally coated electrocatalyst supported on carbon nanotubes (CNT), in which platinum (Pt) nanoparticles are coated by nitrogen doped carbon (NC) layers. CNT/NC/Pt/NC shows comparable electrochemical surface area (ECSA) and oxygen reduction reaction (ORR) activity to the non-coated electrocatalyst (CNT/NC/Pt), indicating that NC layer on Pt nanoparticles almost negligibly affects the activities of electrocatalyst; while, CNT/NC/Pt/NC exhibits a higher Pt stability due to the unique structure, in which the Pt nanoparticles are stabilized by the NC layers and Pt aggregation is decelerated proved by TEM measurement. Maximum power density of CNT/NC/Pt/NC reached 604 mW cm^?2 with Pt loading of 0.1 mg_Pt cm^?2, which only decreases by 7% compared to CNT/NC/Pt (650 mW cm^?2). The electrochemical analysis and fuel cell test illustrate that NC layer on Pt nanoparticles enhances the durability without serious deterioration of fuel cell performance.     

Methanol electro-oxidation on Pt/C modified by polyaniline nanofibers for DMFC applications

In the present study, in order to achieve an inexpensive tolerable anode catalyst for direct methanol fuel cell applications, a composite of polyaniline nanofibers and Pt/C nano-particles, identified by PANI/Pt/C, was prepared by in-situ electropolymerization of aniline and trifluoromethane sulfonic acid on glassy carbon. The effect of synthesized PANI nanofibers in methanol electrooxidation reaction was compared by bare Pt/C by different electrochemical methods such as; cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry. Scanning electron microscopy (SEM) was also employed to morphological study of the modified catalyst layer. The test results reveal that introduction of PANI nanofibers within catalyst layer improves the catalyst activity in methanol oxidation, hinders and prevents catalyst from more poisoning by intermediate products of methanol oxidation and improves the mechanical properties of the catalyst layer. SEM images also indicate that PANI nanofibers placed between platinum particles and anchor platinum particles and alleviate the Pt migration during methanol electrooxidation.     

Novel palladium-decorated molybdenum carbide/polyaniline nanohybrid material as superior electrocatalyst for fuel cell application

This study demonstrates the facile synthesis of palladium nanoparticles (PdNPs) decorated molybdenum carbide/polyaniline (MoC/PANI) nanohybrid material using a hydrothermal method followed by a high-temperature carbonization process. As-synthesized MoC/PANI/PdNPs nanohybrid material was characterized using high-resolution transmission electron microscopy, X-ray photoelectron spectrometry, X-ray diffractometer, and field-emission scanning electron microscopy techniques. The developed nanohybrid material was coated over a screen-printed carbon electrode (SPE) to fabricate MoC/PANI/PdNPs/SPE and applied for the efficient electrooxidation of methanol (MeOH) under alkaline medium using cyclic voltammetry and chronoamperometry techniques. The electrochemical behaviour of the developed electrode showed excellent electrocatalytic activity towards the oxidation of MeOH with high durability. The electrooxidation capability of the prepared electrode was compared with commercial 10% Pd/C and other recently reported electrocatalysts. The MoC/PANI/PdNPs/SPE showed superior electrocatalytic property due to specific surface morphology, intense surface area, and higher-mass activity over MoC/PdNPs/SPE, and Pd/C/SPE modified electrodes. Therefore, the fabricated MoC/PANI/PdNPs/SPE is proved to be an excellent electrocatalyst and alternative electrode material for direct MeOH fuel cell (DMFCs) applications in future energy technology.     

Structured multilayered electrodes of proton/electron conducting polymer for polymer electrolyte membrane fuel cells assembled by spray coating

Membrane electrode assemblies (MEAs) for fuel cell applications consist of electron conductive support materials, proton conductive ionomer, and precious metal nanoparticles to enhance the catalytic activity towards H₂ oxidation and O₂ reduction. An optimized connection of all three phases is required to obtain a high noble metal utilization, and accordingly a good performance. Using polyaniline (PANI) as an alternative support material, the generally used ionomer Nafion^® could be replaced in the catalyst layer. PANI has the advantage to be electron and proton conductive at the same time, and can be used as a catalyst support as well. In this study, a new technique building up alternating layers of PANI supported catalyst and single-walled carbon nanotubes (SWCNT) supported catalyst is introduced. Multilayers of PANI and SWCNT catalysts are used on the cathode side, whereas the anode side is composed of commercial platinum/carbon black catalyst and Nafion^®, applied by an airbrush. No additional Nafion^® ionomer is used for proton conductivity of the cathode. The so called spray coating method results in high power densities up to 160 mW cm⁻² with a Pt loading of 0.06 mg cm⁻² at the cathode, yielding a Pt utilization of 2663 mW mg_Pt⁻¹. As well as PANI, supports of SWCNTs have the advantage to have a fibrous structure and additional, they provide high electron conductivity. The combination of the new technique and the fibrous 1-dimensional support materials leads to a porous 3-dimensional electrode network which could enhance the gas transport through the electrode as well as the Pt utilization. The spray coating method could be upgraded to an in-line process and is not restricted to batch production.     

Conducting polymer-coated stainless steel bipolar plates for proton exchange membrane fuel cells (PEMFC)

Stainless steel satisfies many of the requirements for proton exchange membrane (PEM) fuel cell bipolar plates except its corrosion under fuel cell operating conditions. Metal oxide formation leads to contact resistance, and metal dissolution can cause contamination of the membrane electrode assembly (MEA). These problems can be solved by coating stainless steel plates with corrosion resistant and conductive layers. In this study, 304 stainless steel was coated electrochemically with the conducting polymers polyaniline (PANI) and polypyrrole (PPY). Cyclic voltammetry was used for the polymerization and deposition of these polymers. The polymer-coated stainless steel plates were tested for corrosion and contact resistance under PEM fuel cell conditions, which showed improved corrosion resistance with acceptable contact resistance.     

The formation of wrapping type Pt–Ni alloy on three-dimensional carbon nanosheet for electrocatalytic oxidation of methanol

In this paper, the PtNi alloy was embedded into the surface layer of three-dimensional carbon nanosheets (CNSs) with a special layered structure. We controllably adjusted the ratio of Pt/Ni to form large particle alloy with Pt coating Ni and a small number of hollow PtNi alloy pellets. The electro-catalytic methanol oxidation activity and durability of the catalysts were estimated by cyclic voltammetry and chronoamperometric techniques. The results indicated that the doping of Ni effectively improved the activity and anti-poisoning of the catalyst in the methanol electrocatalytic oxidation reaction (MOR). Transmission electron microscopy (TEM), Raman spectroscopy, nitrogen adsorption-desorption techniques, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to explore the composition, morphology and structure of these catalysts. It is discovered that the Pt–Ni/CNSs (2:1) sample exhibits the best MOR activity with a peak current density of 15.03 mA cm^?2 at the forward scan due to the excellent lamellar structure, good crystallinity and abundant pore structure of CNSs, which is benefit to form ultrahigh specific surface area, superb electron and ionic conductivity.     

Enhanced methanol oxidation on PtNi nanoparticles supported on silane-modified reduced graphene oxide

Developing low cost, highly efficient, and long-term stability electrocatalysts are critical for direct oxidation methanol fuel cell. Despite huge efforts, designing low-cost electrocatalysts with high activity and long-term durability remains a significant technical challenge. Here, we prepared a new kind of platinum-nickel catalyst supported on silane-modified graphene oxide (NH₂-rGO) by a two-step method at room temperature. Powder X-ray diffraction, UV–vis spectroscopy, Raman, FTIR spectroscopy and X-ray photoelectron spectroscopy results confirm that GO was successfully modified with 3-aminopropyltriethoxysilane (APTES), which helps to uniformly disperse PtNi nanoparticles. Cyclic voltammetry, chronoamperometry, CO-stripping and rotating disk electrode (RDE) results imply that PtNi/NH₂-rGO catalyst has significantly higher catalytic activity, enhance the CO toxicity resistance, higher stability and much faster kinetics of methanol oxidation than commercial Pt/C under alkaline conditions.     

A graphite-coated carbon fiber epoxy composite bipolar plate for polymer electrolyte membrane fuel cell

A PEMFC (polymer electrolyte membrane fuel cell or proton exchange membrane fuel cell) stack is composed of GDLs (gas diffusion layers), MEAs (membrane electrode assemblies), and bipolar plates. One of the important functions of bipolar plates is to collect and conduct the current from cell to cell, which requires low electrical bulk and interfacial resistances. For a carbon fiber epoxy composite bipolar plate, the interfacial resistance is usually much larger than the bulk resistance due to the resin-rich layer on the composite surface.In this study, a thin graphite layer is coated on the carbon/epoxy composite bipolar plate to decrease the interfacial contact resistance between the bipolar plate and the GDL. The total electrical resistance in the through-thickness direction of the bipolar plate is measured with respect to the thickness of the graphite coating layer, and the ratio of the bulk resistance to the interfacial contact resistance is estimated using the measured data. From the experiment, it is found that the graphite coating on the carbon/epoxy composite bipolar plate has 10% and 4% of the total electrical and interfacial contact resistances of the conventional carbon/epoxy composite bipolar plate, respectively, when the graphite coating thickness is 50 μm.     

Nontrivial role of carbon nanofibers morphology in binderless Pt nanocatalyst supported electrode

Similar to conventional composite electrodes, developing binderless-based carbon nanostructured (CNs) electrodes for fuel cells requires particularly the optimisation of both the morphology and the density of the CNs. In this work, carbon nanofibers (CNFs) have been optimised and used as catalyst support for Pt nanoparticles (NPs). The nontrivial role of the CNFs on the catalytic behavior is clearly demonstrated. We have shown that for a similar amount, morphology and dispersion of the Pt NPs fabricated onto CNFs, the density of the latter and to a lesser extent their diameter are the main factors influencing the catalytic activity. For the particular case of CNFs considered in this work, an optimum activity toward methanol fuel cell reaction was obtained when Pt NPs were supported with CNFs synthesized with a C₂H₂/Ar ratio of 0.31.     

Solving Nafion poisoning of ORR catalysts with an accessible layer: designing a nanostructured core-shell Pt/C catalyst via a one-step self-assembly for PEMFC

A core-shell Pt/C@NCL300 catalyst with an accessible layer was designed to recover lost ORR activity and was constructed via a one-step self-assembly process in this paper. A thin porous layer derived from Nafion was first formed on the surface of Pt/C catalyst to create a shell. This first coating successfully separated the Nafion and Pt particles in the catalysts and reducing the negative impact of Nafion on ORR activity and enhancing the fuel cell performance. The newly fabricated Pt/C@NCL300 catalyst exhibited much higher specific activity than the original Pt/C catalyst in RDE tests under the same conditions and were comparable to the activity of Pt/C electrode without Nafion poisoning. Moreover, the fuel cell with Pt/C@NCL300 catalyst exhibited a higher power density without an obvious increase in proton transport and O₂ transport resistance compared to that of a Pt/C fuel cell with a low Pt loading. This result indicates that coating the Pt/C catalyst with a layer accessible for oxygen and protons is a promising way to effectively promote Pt-based catalysts that work under normal operating conditions.     

Efficient Pt-based nanostructured electrocatalysts for fuel cells: One-pot preparation,gradient structure,effect of alloying,electrochemical performance

This paper proposes an environmentally friendly one-pot synthesis approach for the PtCu and PtNi nanoparticles with the gradient structure on the carbon support. This method offers exceptional advantages over other approaches. Among them there is a surfactant-free synthesis, being low-temperature, simple, fast, and one-pot. The bimetallic electrocatalysts with a reduced platinum content for proton-exchange membrane fuel cells have been obtained. The proposed method is promising in terms of scaling and transition to commercial production. In this study, we first attempted to apply the gradient synthesis strategy to the PtNi/C catalysts in order to make this method versatile. We obtained the high-performance PtNi/C and PtCu/C catalysts, exhibiting the specific ORR activity higher than that of the commercial Pt/C catalyst by 3 and 4.6 times, respectively.     

Efficient synthesis of Pt3Co/NC alloy catalysts with enhanced durability and activity for the oxygen reduction reaction

Lack of catalytic performance, short life, and high cost are three main problems related to JM-Pt/C catalysts for proton exchange membrane fuel cells. The introduction of cheap transition metals improves catalytic performance while significantly reducing the cost of the catalysts. Here, we report the synthesis of Pt₃Co/NC alloy catalysts via coating and pyrolysis treatment. The agglomeration of nanoparticles during the high-temperature alloying process is significantly inhibited by coating with PANI. Remarkably, the obtained Pt₃Co/NC alloy catalysts exhibit excellent ORR catalytic performance and structural stability in 0.1 mol/L HClO₄. After 30,000 potential cycles, the mass activity and area-specific activity of Pt₃Co/NC alloy catalysts are 1.949 and 3.936 times higher, respectively, than that of JM-Pt/C with negligible performance loss. The strong metal-support interaction between N and Pt and the Pt-rich surface restrict the dissolution of Pt and Co, resulting in excellent stability. This synthesis approach provides an effective way to develop active and stable Pt alloy catalysts.     

Polyaniline/carbon black composite-supported iron phthalocyanine as an oxygen reduction catalyst for microbial fuel cells

Polyaniline/carbon black (PANI/C) composite-supported iron phthalocyanine (FePc) (PANI/C/FePc) has been investigated as a catalyst for the oxygen reduction reaction (ORR) in an air-cathode microbial fuel cell (MFC). The electrocatalytic activity of the PANI/C/FePc toward the ORR is evaluated using cyclic voltammogram and linear scan voltammogram methods. In comparison with that of carbon-supported FePc electrode, the peak potential of the ORR at the PANI/C/FePc electrode shifts toward positive potential, and the peak current is greatly increased, suggesting the enhanced activity of FePc absorbed onto PANI/C. Additionally, the results of the MFC experiments show that PANI/C/FePc is well suitable to be the cathode material for MFCs. The maximum power density of 630.5 mW m⁻² with the PANI/C/FePc cathode is higher than that of 336.6 mW m⁻² with the C/FePc cathode, and even higher that that of 575.6 mW m⁻² with a Pt cathode. Meanwhile, the power per cost of the PANI/C/FePc cathode is 7.5 times greater than that of the Pt cathode. Thus, the PANI/C/FePc can be a potential alternative to Pt in MFCs.     

Ultrathin nitrogen doped carbon layer stabilized Pt electrocatalyst supported on N-doped carbon nanotubes

The enhancements in fuel cell performance and durability are crucial for the commercialization of polymer electrolyte fuel cells (PEFCs). Here, we deposit platinum nanoparticles on nitrogen doped carbon nanotubes (N-CNT) and continuously coat the electrocatalyst with nitrogen doped carbon (NC) layer derived from the carbonization of poly(vinyl pyrrolidone) (PVP). The NC-coated electrocatalyst shows stable electrochemical surface area (ECSA) during the potential cycling from 0.6 V to 1.0 V vs. RHE; while, the commercial and non-coated electrocatalysts lose 50% and 33% of initial ECSAs, respectively. Moreover, the NC-coated electrocatalyst shows higher oxygen reaction reduction (ORR) activity compared to non-coated electrocatalyst due to the additional nitrogen atoms in the electrocatalyst. The maximum power density of the coated electrocatalyst reaches 676 mW cm^?2 with Pt loading of 0.1 mg cm^?2, indicating that the mass power density of the electrocatalyst is one of the highest values in recently published literature. The NC layer is significantly important for simultaneous enhancements in durability and fuel cell performance.     

Fine-tuning catalytic performance of ultrafine bimetallic nickel-platinum on metal-organic framework derived nanoporous carbon/metal oxide toward hydrous hydrazine decomposition

Heterogeneous catalysts with a high performance as well as low cost is pivotal but still challenging for hydrous hydrazine (N₂H₄·H₂O) as a hydrogen storage material. Herein, bimetallic PtNi nanoparticles are well dispersed on nitrogen doped porous carbon/zirconia support (PtNi/NC-ZrO₂). PtNi/NC-ZrO₂ nanocatalysts could be responsive and completely for catalyzing hydrous hydrazine decomposition with a H₂ selectivity of 100% as well as a turnover frequency of 1716 h⁻¹ measured at 323 K, outperforming most heterogeneous metal catalysts. This is mainly attributed that bi-support NC-ZrO₂ can efficiently expedite the electron transfer to metallic NPs and re-construct the electronic structure bimetallic active sites for selectively catalyzing hydrous hydrazine decomposition.     

Novel single step electrochemical route to γ-MnO2 nanoparticle-coated polyaniline nanofibers: Thermal stability and formic acid oxidation on the resulting nanocomposites

γ-MnO₂ nanoparticles-coated polyaniline (PANI) nanofibers on carbon electrode were prepared by potentiodynamic electrochemical deposition of PANI and MnO₂ from a single pot. Higher thermal stability of the resulting nanocomposites and their activity for formic acid oxidation permits the realization of a platinum-free anode for formic acid fuel cells.     

Membrane electrode assembly with doped polyaniline interlayer for proton exchange membrane fuel cells under low relative humidity conditions

A membrane electrode assembly (MEA) was designed by incorporating an interlayer between the catalyst layer and the gas diffusion layer (GDL) to improve the low relative humidity (RH) performance of proton exchange membrane fuel cells (PEMFCs). On the top of the micro-porous layer of the GDL, a thin layer of doped polyaniline (PANI) was deposited to retain moisture content in order to maintain the electrolyte moist, especially when the fuel cell is working at lower RH conditions, which is typical for automotive applications. The surface morphology and wetting angle characteristics of the GDLs coated with doped PANI samples were examined using FESEM and Goniometer, respectively. The surface modified GDLs fabricated into MEAs were evaluated in single cell PEMFC between 50 and 100% RH conditions using H₂ and O₂ as reactants at ambient pressure. It was observed that the MEA with camphor sulfonic acid doped PANI interlayer showed an excellent fuel cell performance at all RH conditions including that at 50% at 80 °C using H₂ and O_2.     

Nafion/polyaniline composite membranes specifically designed to allow proton exchange membrane fuel cells operation at low humidity

A Nafion and polyaniline composite membrane (designated Nafion/PANI) was fabricated using an in situ chemical polymerization method. The composite membrane showed a proton conductivity that was superior to that obtained with Nafion^® 112 at low humidity (e.g. RH = 60%). Water uptake measurements revealed similarities between the Nafion^® 112 and Nafion/PANI membranes at different humidities. The high conductivity of the Nafion/PANI membrane at low humidity is hypothesized to be due to the existence of the extended conjugated bonds in the polyaniline; proton transfer is facilitated via the conjugated bonds in lower humidity environments allowing retention of the relatively high conductivity. Correspondingly, the performance of a single cell fuel cell containing the Nafion/PANI composite membrane is improved compared to a Nafion^® 112-containing cell under low humidity conditions. This is important for portable fuel cells, which are required to operate without external humidification.