Arylphosphonic Acid‐Functionalized Polyelectrolytes as Fuel Cell Membrane Material

Abstract

IntroductionThe growing awareness of diminishing fossil fuel reserves and man-made climate change has encouraged academic and industrial research into more efficient use of primary energy sources. Regarding efficiency in power generation, the single-step energy conversion in fuel cells (FC) is inherently superior to the multi-step internal combustion engine.[1] Fuel cells, like other electro-chemical energy devices, provide an electric current by physical detachment of a redox reaction into an oxidation and a reduction part, and separation of the resultant electron and ion flux using an ion-conductive solid electrolyte. To preserve over-all cell neutrality, the electrolyte has to facilitate an ion transport antagonistic to the electron movement. In the operant hydrogen-or methanol-powered fuel cell, the charge imbalance that results from electron transport is compensated by a cathode-wise proton transport via a proton conductive polyelectrolyte membrane (PEM) material. A fuel cell's power output is, therefore, coupled to the ReviewIn comparison to sulfonated polymers, phosphonic acid-functionalized polyelectrolytes possess higher proton conductivity at elevated temperatures, improved chemical and thermal stabilities, much lower water swelling, decreased fuel permeability, and enhanced proton conductivities in low hydration states. Arylphosphonic acid-functionalized polymers have been produced by the copolymerization of arylphosphonated monomers, as well as by various polymer-analogous functionalization reactions on high performance polymer backbones. Among the latter, the catalytic arylphosphonation of brominated high-performance polymers, such as poly(ethers), poly(sulfones), and poly(etherketones) represents an attractive and versatile synthetic route to arylphosphonic polyelectrolytes for application in polyelectrolyte membrane fuel cells (PEMFC). This review summarizes available syntheses of arylphosphonic acid-functionalized polymers, the data on such materials' membrane performance, and introduces special polyelectrolyte blends and new ionomers developed to meet the demands made on PEMFC membranes. electrolyte's proton conductivity under operating conditions, which explains the on-going effort to establish materials with suitable properties. Among the presently discussed fuel-cell types, [1] the polyelectrolyte membrane fuel cell (PEMFC) and the direct methanol fuel cell (DMFC) are considered best suited for portable and mobile applications, because of their high power densities, moderate operating temperatures of 60-120 8C, and accordingly short start-up times. The polyelectrolyte fuel cell scheme displayed in Figure 1 shows the PEMFC to basically resemble a 'gas battery', which derives an electric current from the catalytic oxidation of hydrogen on noble metal electrodes, e.g., Pt or Pt-Ru alloys. However, available PEMs' material properties limits fuel-cell operation to temperatures below 80 8C. Since noble metal electrodes' are prone to deactivation by fuelcontaminating trace CO below 120 8C, [2,3] pres...

Analysis of proton-conducting organic–inorganic hybrid materials based on sulphonated poly(ether ether ketone) and phosphotungstic acid via ASAXS and WAXS

“…Polyelectrolytes have gained considerable attention on account of their potential application as membranes for polyelectrolyte membrane fuel cell PEMFCs [1][2][3]. In this context, a lot of work has been done in order to synthesize polymers and copolymers bearing sulfonic and/or phosphonic groups due to their good proton-conductivity [1][2][3][4][5][6][7][8][9][10][11][12].…”

Porous Polymers: Enabling Solutions for Energy Applications

“…Since the C-P bond is stable against hydrolysis, phosphonic acid functionalized polymers seem for example a promising alternative to the binary PBI/H 3 PO 4 systems. [35][36][37][38] Also for such functionalized polymers it has been shown that the microstructure plays a significant role, as aggregation of phosphonic acid groups is necessary to obtain good proton transport properties in the dry state. [8] Polymer post-functionalization strategies like grafting or polymer reactions also showed to be a versatile pathway to achieve phosphonic acid based, phase separated morphologies.…”

Microwave-assisted Hirao reaction: recent developments

“…aryl-and vinyl-phosphonates, phosphine oxides and related derivatives) are compounds of practical importance in industry, agriculture, and medicine as well as in everyday life [34][35][36][37][38][39]. In addition to their applications as pesticides, detergents, or anticorrosive agents, these phosphorus-containing synthetic compounds Scheme 10 Pd/C-catalyzed synthesis of aryl diphenylphosphine oxides (28) in water Scheme 11 Ligand-free synthesis of arylphosphonates/phosphine oxides (30) have received a lot of attention both in drug research and in medicinal chemistry due to their great potential in combating diseases and pathological conditions, and curing parasitic infections [40].…”

“…Arylphosphonate scaffolds are used in designing fuel cell membranes [39] and materials with special optical properties [41][42][43]. Arylphosphonates are the phosphonic acids precursors, which can be used for their water-soluble properties and for the synthesis of mixed organic-inorganic materials [44,45].…”