Patent Application: US-14559808-A

Abstract:
new multifunctional aromatic copolymers bearing pyridine or pyrimidine units either in the main chain or side chain and single wall carbon nanotubes or multi wall carbon nanotubes as side chain pendants have been prepared . these multifunctional materials will combine both high proton and electrical conductivity due to the existence of polar pyridine or pyrimidine groups and carbon nanotubes within the same chemical structure . the prepared multifunctional materials can be used in the catalyst ink of the electrodes in high temperature pem fuel cells .

Description:
the present invention relates to the development of new multifunctional polymeric materials ( structures 1 and 2 ) comprising copolymers and homopolymers bearing main or side chain pyridine or pyrimidine with multi wall or single wall carbon nanotubes . the structures of the materials are given below . g can be the same or different and is selected from the group consisting of : a =— ch 2 , — cf 2 , - phenyl , none ; or a salt thereof ; and q is nh or o ; m is a number between 1 to 18 ; and z is a number between 0 . 01 to 0 . 25 . g can be the same or different and is selected from the group consisting of : a =— ch 2 , — cf 2 , - phenyl , none ; or a salt thereof ; and q is nh or o ; m is a number between 1 to 18 ; and y is a number between 0 . 01 to 0 . 25 . the above multifunctional material ( structures 1 - 2 ) were prepared via high temperature polycondensation reaction of pyridine or pyrimidine containing diols , single wall or multi wall carbon nanotubes modified diols and various aromatic difluorides . the present invention relates to a method for implementing membrane electrode assemblies using the new multifunctional materials as described herein . the method for implementing of membrane electrode assembly includes ( a ) a gas diffusion and current collecting electrode component , ( b ) a reaction layer component comprising of a catalyst and a multifunction material which can act as paths for electron and proton conduction ( structures 1 - 2 ) and ( c ) pt alloy electrocatalysts for enhanced co tolerance and oxygen reduction reaction activity . the electrically conducting substrate is selected from a combination of woven carbon cloth ( such as toray fiber t - 300 ) or paper ( such as the toray tgp - h - 120 ), previously wet - proofed using tfe based solutions ( dupont , usa ). the typical porosity of this carbon substrate is between 75 - 85 %. the wet proofing is achieved with a combination of dip coating for fixed duration ( between 30 sec to 5 min ) followed with drying in flowing air . such a wet proofed substrate can be coated with a gas diffusion layer comprising of select carbon blacks and ptfe suspension . the choice of carbon blacks used in this layer range from ketjen black to turbostratic carbons such as vulcan xc - 72 ( cabot corp , usa ) with typical surface areas in the range of 250 to 1000 m 2 / gm . the deposition can be applied with a coating machine such as gravure coaters from euclid coating systems ( bay city , mich ., usa ). a slurry composition comprising of carbon black and ptfe ( poly tetrafluoro ethylene ) in aqueous suspension ( such as dupont tfe - 30 , dupont usa ) is applied to a set thickness over the carbon paper or cloth substrate with the aid of the coating machine . typical thickness of 50 - 500 microns is used . pore forming agents are used to prepare this diffusion layer on the carbon conducting paper or cloth substrate . careful control of the pore formers which consist of various combinations of carbonates and bicarbonates ( such as ammonium and sodium analogs ) affords control of gas access to the reaction zone . this is achieved by incorporation of these agents in the slurry mixture comprising of carbon black and ptfe suspension . typical porosity rendered in this fashion differs from anode and cathode electrode and is in the range of 10 - 90 %. coated carbon substrates containing the gas diffusion layers are sintered to enable proper binding of components . this can be achieved using thermal treatment to temperatures significantly above the glass transition point for ptfe , usually in the range 100 to 350 ° c . for 5 to 30 minutes . on the surface of the above mentioned gas diffusion layer , an additional layer comprising of a carbon supported catalyst , multifunction conducting elements ( structure 1 - 2 ), pore forming agents , is added using a variety of methods comprising of spraying , calendaring and or screen printing . typical steps first include appropriate choice of the electrocatalyst based on anode or cathode electrodes . for the anode , pure pt or pt in conjunction of another transition metal such as ru , mo , sn is used . this is motivated by the formation of oxides on these non noble transition metals at lower potentials to enable oxidation of co or other c 1 moieties which are typical poisons in the output feed of fuel reformers ( steam reformation of natural gas , methanol , etc .). the choice of electrocatalyst included pt and second transition element either alloyed or in the form of mixed oxides . the choice is dependent on the application based on choice of fuel feed - stock . the electrocatalysts are in the form of nanostructured metal alloys or mixed oxide dispersions on carbon blacks ( turbostratic carbon support materials usually ketjen black or similar material ). for the cathode , electrocatalysts which are relatively immune from anion adsorption and oxide formation are preferred . the choice of the alloying element ranges between available first row transition elements , typically ni , co , cr , mn , fe , v , ti , etc . previous studies have shown that adequate alloying of these transition elements with pt results in deactivation of pt for most surface processes ( lowering of surface workfunction ) ( mukerjee and urian 2002 ; teliska , murthi et al . 2003 ; murthi , urian et al . 2004 ; teliska , murthi et al . 2005 ). this renders the surface largely bare for molecular oxygen adsorption and subsequent reduction . the electrocatalyst can be obtained from commercial vendors such as columbian chemicals ( marrietta , ga ., usa ), cabot superior micro - powders ( albuquerque , n . mex ., usa ). the typical weight ratio of the catalyst on carbon support being 30 - 60 % of metal on carbon . second step involves preparation of slurry using a combination of electrocatalyst in a suspension containing solubilized form of the multifunction material ( structures 1 - 2 ). additionally , pore forming components based on a combination of carbonates and bicarbonates are added in a ratio of 5 - 10 % by weight . the ratio of the components has a variation of 10 - 30 % within choice of each component enabling a total catalyst loading 0 . 01 to 0 . 5 mg of pt or pt alloy / cm 2 . the application of the slurry is achieved via a combination or exclusive application of calendaring , screen printing or spraying . catalyst application so achieved in the form of a reaction layer is followed by third step which comprises of sintering and drying of electrode layer . in this step the electrodes are subjected to a two step process which initially involves drying at 160 ° c . for about 30 minutes followed by sintering at temperatures in the range of 150 - 350 ° c . for a time period in the range of 30 minutes to 5 hours . to prepare membrane electrode assemblies ( meas ), a sandwich of anode membrane and cathode electrodes is placed in an appropriate arrangement of gasket materials , typically a combination of polyimide and polytetrafluorethylene ( ptfe , dupont , usa ). this is followed by hot pressing with a hydraulic press or other similar device . pressures in the range of 0 . 1 to 10 bars are applied with platen temperatures in the range of 150 to 250 ° c . for time periods typically in the range of 10 to 60 minutes . the prepared membrane electrode assemblies have thickness in the range of 75 to 250 micro meters . this allows for a final assembly of the membrane electrode assembly . the polymer electrolyte that is used for the preparation of these meas is selected from the us patents applications 20060909151049 , 20060909152523 , 20060909154641 and 20060912150631 . baughman , r . h ., a . a . zakhidov , et . al . 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