Syntheses And Characterizations Of Sulfonated Polymeric Electrolytes Based Matrix Mixed Membranes For Proton Exchange Membrane Fuel Cell

Energy depletion and environmental degradation are the two most urgent issues currently confronting humanity.As fossil fuel usage increases in lockstep with global pollution,it will be unable to supply growing energy needs by continuing to consume traditional fossil fuels without environmental damage.Therefore,renewable,and innovative clean energy sources are being developed,and significant efforts have been made in this sector during the last few decades.Solar energy,hydroelectric energy,nuclear energy,geothermal energy,and hydrogen energy are some of the emerging renewable energy sources.Owing to their high energy density and ecologically friendly combustion products,hydrogen is regarded as one of the best choices among all energy sources for resolving energy-related issues.Utilizing hydrogen as raw material,proton exchange membrane fuel cells(PEMFCs)can convert its chemical energy into electrical energy in high efficiency with zero-carbon emission.Therefore,it is taken as a crucial solution for alternative energy technology.The proton exchange membrane(PEM)is a core component of PEMFCs.So,one of the most important challenges in this field is to find proton conducting electrolytes that are both facilely fabricated and efficient enough for PEMs to use.In this dissertation,efficient proton-conductive electrolytes have been developed that are pivotal in the PEM fuel cell.Firstly,a sulfonated polyamide(PA-PhSO3H)with in-built-SO3H moieties was facilely synthesized by the one-pot acylation polymeric combination of-SO3H functionalized phenylenediamine and triple-symmetrical 1,3,5-benzenetricarbonyl chloride.Investigations of electrochemical impedance spectroscopy measurements revealed that the sulfonated polyalide-based electrolyte displays a proton conductivity up to 8.85×10-2 S cm-1 at 80℃ under 98%relative humidity(RH),which is more than 2 orders of magnitude higher than that of its-SO3H-free analogue that is 6.30×10-4 S cm-1 at the same condition.Therefore,it was further made into matrix-mixed membranes after mixing with polyacrylonitrile(PAN)in different ratios.The analyses results based on the electrochemical impedance spectroscopy measurement system revealed that its conductivity can reach up to 4.90×10-2 S cm-1 under practical operation conditions at 80℃ and 98%RH the value of which is even comparable with those of commercial-available proton-conductive electrolytes being used in PEM fuel cells at the same condition.Additionally,the continuous test shows the sulfonated polyamide-based matrix-mixed membrane possesses long-life reusability.Then,in order to enhance the concentration of the-SO3H group in the fabricated polymers,the reactant of 4,4-diamino-2,2-biphenyldisulfonic acid was used to replace the reactant of-SO3H functionalized phenylenediamine,and a new polyamide was synthesized with a similar process as the first work.The analogue material was also synthesized by utilizing the reactants benzidine and triple-symmetrical 1,3,5-benzenetricarbonyl chloride.The synthesized sulfonated polyamide named PA-(PhSO3H)2,demonstrated a proton conductivity of 5.54×10-2 S cm-1 at 98%RH and 80℃ after being characterized using different analytical methods and EIS measurements.In comparison to its-SO3H-free counterpart,the results revealed that its proton conductivity was also increased two orders of magnitude,that is 2.38×10-4 S cm-1 under identical conditions.The synthesized materials were subsequently used for the fabrication of matrix-mixed membranes,which served as electrolytes in PEMFC.EIS investigations of the matrix-mixed membrane using electrochemical impedance spectroscopy equipment revealed that the material’s conductivity may reach up to 5.82×10-2 S cm-1 at 80℃ and 98%RH,a value that exceeds that of many other proton-conductive electrolytes available commercially.In the last work,through the polymeric coupling of hexachlorocyclotriphosphazene(HCCP)and sulfonate p-phenylenediamine,a sulfonated polyphosphazene with in-built-SO3H moieties(PP-PhSO3H)was readily achieved.Characterization showed that it is an amorphous polymer with exceptional stability.The synthesized PP-PhSO3H has a proton conductivity of up to 6.64×10-2 S cm-1 at 80℃ and 98%RH,as determined by proton conductivity measurements.This result is also about two orders of magnitude more than the comparable value for its-SO3H-free counterpart,PP-Ph,that is 1.72×10-4 S cm-1 which was measured under similar conditions.As a result,matrix-mixed membranes(labeled PP-PhSO3H-PAN)were fabricated by mixing PP-PhSO3H and PAN in varying proportions to evaluate their potential use in the PEM fuel cell.When the weight ratio of PP-PhSO3H/PAN is 3:1(designated as PP-PhSO3H-PAN(3:1)),its proton conductivity may reach up to 5.05×10-2 S cm-1 at 80 ℃ and 98%RH,which is equivalent to proton-conductive electrolytes already used in PEM fuel cells.In addition,the continuous test reveals that the PP-PhSO3H-PAN(3:1)is reusable for an extended period.These works demonstrate that,utilizing the facile polymeric reactions with the sulfonated module as precursors,highly effective proton-conductive matrix-mixed membranes for PEM fuel cells can be achieved.