Probing monomer purity towards structural control of polybenzimidazole synthesis for fuel cell membranes


Companies / Organizations


Greater Copenhagen area

High temperature polymer electrolyte membrane fuel cells (HT-PEMFC) are constructed around phosphoric acid imbibed polybenzimidazole membranes. The polybenzimidazoles comprise a large family of engineering plastics, characterized by their superior thermomechanical properties. The most common derivative in this family of materials is poly(2,2′-(m-phenylene)-5,5′-bibenzimidazole) (m-PBI). It can be readily synthesized in polyphosphoric acid (PPA) by step-growth polymerization of isophthalic acid (IPA) and 3,3´-diaminobenzidine (DAB) in stoichiometric amounts. The polymer is subsequently isolated, purified and dissolved in an organic solvent (such as N,N-dimethylacetamide or N-methyl-2-pyrrolidone). Mechanically robust films are obtained by solution casting, and further equilibration in phosphoric acid yields the proton conducting membranes.

The physicochemical properties of the membrane depends on the degree of polymerization (molecular weight) and the structural purity of the obtained polymer. Both parameters are to a large extent determined by the monomer purity. Monomer impurities makes it difficult to accurately control the stoichiometry during synthesis, and inevitably introduces structural defects. Controlling the monomer purity is particularly challenging for DAB, which is highly oxidation sensitive.

The overall aim of this project is to correlate monomer purity with the quality of the obtained polymer. More specifically, the objectives are:

  • To synthesize m-PBI using monomers with a well-characterized assay
  • To characterize the obtained polymers with respect to molecular weight and structural purity
  • To correlate the molecular weight and structural purity of the polymer to the monomer assay

Proposed DTU institute: Energy (proposed supervisors): David Aili (, Chemistry (proposed supervisors): Charlotte Held Gotfredsen (

Company: Danish Power Systems (, contact person Allan Robertson Petersen (

Danish Power Systems, founded in 1994 and located north of Copenhagen, Denmark, is a dynamic development- and manufacturing company working in the fields of chemistry and energy with primary focus on fuel cells. The company currently has 24 employees.

Danish Power Systems works with a fuel cell technology called HTPEM (High Temperature Polymer Electrolyte Membrane fule cells) and manufactures the critical component called a MEA (Membrane Electrolyte Assembly) in which electricity is generated by a reaction between a hydrogen containing gas, typically based on methanol- and air.

Danish Power Systems is one of the very few companies in the world that can manufacture the material, polybenzimidazole (PBI), which the fuel cell’s polymer membrane is made of, making us incredibly competitive on the fuel cell market.

Danish Power Systems has established a number of excellent R&D relationships with leading universities and companies worldwide bringing us closer to the market. This gives us a unique understanding of the individual needs, specifications and requirements of our customers, and facilitates our effort in delivering state of the art customized technology to our customers. 

For general information, contact Hans Aage Hjuler, CEO (

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Danish Power Systems


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