Fuel cell anode catalyst performance can be stabilized with a molecularly rigid film of polymers of intrinsic microporosity (PIM)

There remains a major materials challenge in maintaining the performance of platinum (Pt) anode catalysts in fuel cells due to corrosion and blocking of active sites.</p

Polymer of intrinsic microporosity (PIM-7) coating affects triphasic palladium electrocatalysis

A film of the polymer of intrinsic microporosity PIM-7 is coated onto a glassy carbon electrode and the resulting effects on electron transfer reactions are studied for three different types of processes: (i) aqueous solution based, (ii) solid state surface immobilised, and (iii) electrocatalytic processes on electrodeposited palladium. The effects on reactivity for hydroquinone oxidation in aqueous phosphate buffer are shown to be linked to microporosity causing a slightly lower rate of mass transport without detrimental effects on electron transfer and reaction kinetics. Next, water-insoluble microcrystalline anthraquinone is immobilised directly into the PIM-7 film and shown to give a chemically reversible reduction process, which is enhanced in the presence of PIM-7, when compared to the case of anthraquinone immobilised directly onto bare glassy carbon. Electrodeposition of a film of nano-palladium is demonstrated to give catalytically active electrodes for the reduction/oxidation of protons/hydrogen, the reduction of oxygen, and for the oxidation of formic acid and methanol. With the PIM-7 film applied onto palladium, a mechanical stabilisation effect occurs. In addition, both the hydrogen insertion and the hydrogen evolution reactions as well as formic acid oxidation are enhanced. Effects are discussed in terms of PIM-7 beneficially affecting the interfacial reaction under triphasic conditions. The microporous polymer acts as an interfacial “gas management” layer

Polymer of Intrinsic Microporosity (PIM-7) Coating Affects Triphasic Palladium Electrocatalysis

A film of the polymer of intrinsic microporosity PIM-7 is coated onto a glassy carbon electrode and the resulting effects on electron transfer reactions are studied for three different types of processes: (i) aqueous solution based, (ii) solid state surface immobilised, and (iii) electrocatalytic processes on electrodeposited palladium. The effects on reactivity for hydroquinone oxidation in aqueous phosphate buffer are shown to be linked to microporosity causing a slightly lower rate of mass transport without detrimental effects on electron transfer and reaction kinetics. Next, water-insoluble microcrystalline anthraquinone is immobilised directly into the PIM-7 film and shown to give a chemically reversible reduction process, which is enhanced in the presence of PIM-7, when compared to the case of anthraquinone immobilised directly onto bare glassy carbon. Electrodeposition of a film of nano-palladium is demonstrated to give catalytically active electrodes for the reduction/oxidation of protons/hydrogen, the reduction of oxygen, and for the oxidation of formic acid and methanol. With the PIM-7 film applied onto palladium, a mechanical stabilisation effect occurs. In addition, both the hydrogen insertion and the hydrogen evolution reactions as well as formic acid oxidation are enhanced. Effects are discussed in terms of PIM-7 beneficially affecting the interfacial reaction under triphasic conditions. The microporous polymer acts as an interfacial “gas management” layer.</p

Intrinsically microporous polymer slows down fuel cell catalyst corrosion

The limited stability of fuel cell cathode catalysts causes a significant loss of operational cell voltage with commercial Pt-based catalysts, which hinders the wider commercialization of fuel cell technologies. We demonstrate beneficial effects of a highly rigid and porous polymer of intrinsic microporosity (PIM-EA-TB with BET surface area 1027 m2 g−1) in accelerated catalyst corrosion experiments. Porous films of PIM-EA-TB offer an effective protective matrix for the prevention of Pt/C catalyst corrosion without impeding flux of reagents. The results of electrochemical cycling tests show that the PIM-EA-TB protected Pt/C (denoted here as PIM@Pt/C) exhibit a significantly enhanced durability as compared to a conventional Pt/C catalyst. Keywords: Electrocatalysis, Fuel cells, Membrane, Stabilization, Corrosio

Charge Transfer Hybrids of Graphene Oxide and the Intrinsically Microporous Polymer PIM-1

Nanohybrid materials based on nanoparticles of the intrinsically microporous polymer PIM-1 and graphene oxide (GO) are prepared from aqueous dispersions with a re-precipitation method, resulting in the surface of the GO sheets being decorated with nanoparticles of PIM-1. The significant blueshift in fluorescence signals for the GO/PIM-1 nanohybrids indicates modification of the optoelectronic properties of the PIM-1 in the presence of the GO due to their strong interactions. The stiffening in the Raman G peak of GO (by nearly 6 cm^{-1}) further indicates p-doping of the GO in the presence of PIM. Kelvin probe force microscopy (KPFM) and electrochemical reduction measurements of the nanohybrids provide direct evidence for charge transfer between the PIM-1 nanoparticles and the GO nanosheets. These observations will be of importance for future applications of GO-PIM-1 nanohybrids as substrates and promoters in catalysis and sensing

Free-standing graphene oxide and carbon nanotube hybrid papers with enhanced electrical and mechanic performance and their synergy in polymer laminates

Hybrid nanomaterials fabricated by the heterogeneous integration of 1D (carbon nanotubes) and 2D (graphene oxide) nanomaterials showed synergy in electrical and mechanical properties. Here, we reported the infiltration of carboxylic functionalized single-walled carbon nanotubes (C-SWNT) into free-standing graphene oxide (GO) paper for better electrical and mechanical properties than native GO. The stacking arrangement of GO sheets and its alteration in the presence of C-SWNT were comprehensively explored through scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. The C-SWNTs bridges between different GO sheets produce a pathway for the flow of electrical charges and provide a tougher hybrid system. The nanoscopic surface potential map reveals a higher work function of the individual functionalised SWNTs than surrounded GO sheets showing efficient charge exchange. We observed the enhanced conductivity up to 50 times and capacitance up to 3.5 times of the hybrid structure than the GO-paper. The laminate of polystyrene composites provided higher elastic modulus and mechanical strength when hybrid paper is used, thus paving the way for the exploitation of hybrid filler formulation in designing polymer composites

Platinum Nanoparticle Inclusion into a Carbonized Polymer of Intrinsic Microporosity: Electrochemical Characteristics of a Catalyst for Electroless Hydrogen Peroxide Production

The one-step vacuum carbonization synthesis of a platinum nano-catalyst embedded in a microporous heterocarbon (Pt@cPIM) is demonstrated. A nitrogen-rich polymer of an intrinsic microporosity (PIM) precursor is impregnated with PtCl62− to give (after vacuum carbonization at 700 °C) a nitrogen-containing heterocarbon with embedded Pt nanoparticles of typically 1–4 nm diameter (with some particles up to 20 nm diameter). The Brunauer-Emmett-Teller (BET) surface area of this hybrid material is 518 m2 g−1 (with a cumulative pore volume of 1.1 cm3 g−1) consistent with the surface area of the corresponding platinum-free heterocarbon. In electrochemical experiments, the heterocarbon-embedded nano-platinum is observed as reactive towards hydrogen oxidation, but essentially non-reactive towards bigger molecules during methanol oxidation or during oxygen reduction. Therefore, oxygen reduction under electrochemical conditions is suggested to occur mainly via a 2-electron pathway on the outer carbon shell to give H2O2. Kinetic selectivity is confirmed in exploratory catalysis experiments in the presence of H2 gas (which is oxidized on Pt) and O2 gas (which is reduced on the heterocarbon surface) to result in the direct formation of H2O2. View Full-Tex

pH-induced reversal of ionic diode polarity in 300nm thin membranes based on a polymer of intrinsic microporosity

“Ionic diode” (or current rectification) effects are potentially important for a range of applications including water purification. In this preliminary report, we observe novel ionic diode behaviour of thin (300 nm) membranes based on a polymer of intrinsic microporosity (PIM-EA-TB) supported on a poly-ethylene-terephthalate (PET) film with a 20 μm diameter microhole, and immersed in aqueous electrolyte media. Current rectification effects are observed for half-cells with the same electrolyte solution on both sides of the membrane for cases where cation and anion mobility differ (HCl, other acids, NaOH, etc.) but not for cases where cation and anion mobility are more alike (LiCl, NaCl, KCl, etc.). A pH-dependent reversal of the ionic diode effect is observed and discussed in terms of tentatively assigned mechanisms based on both (i) ion mobility within the PIM-EA-TB nano-membrane and (ii) a possible “mechanical valve effect” linked to membrane potential and electrokinetic movement of the membrane as well as hydrostatic pressure effects

Intrinsically microporous polymer retains porosity in vacuum thermolysis to electroactive heterocarbon

Vacuum carbonization of organic precursors usually causes considerable structural damage and collapse of morphological features. However, for a polymer with intrinsic microporosity (PIM-EA-TB with a Brunauer–Emmet–Teller (BET) surface area of 1027 m2g–1), it is shown here that the rigidity of the molecular backbone is retained even during 500 °C vacuum carbonization, yielding a novel type of microporous heterocarbon (either as powder or as thin film membrane) with properties between those of a conducting polymer and those of a carbon. After carbonization, the scanning electron microscopy (SEM) morphology and the small-angle X-ray scattering (SAXS) Guinier radius remain largely unchanged as does the cumulative pore volume. However, the BET surface area is decreased to 242 m2g–1, but microporosity is considerably increased. The new material is shown to exhibit noticeable electrochemical features including two pH-dependent capacitance domains switching from ca. 33 Fg–1 (when oxidized) to ca. 147 Fg–1 (when reduced), a low electron transfer reactivity toward oxygen and hydrogen peroxide, and a four-point-probe resistivity (dry) of approximately 40 MΩ/square for a 1–2 μm thick film