The Role of Fluorinated Polymers in the Water Management of Proton Exchange Membrane Fuel Cells: A Review

As the hydrogen market is projected to grow in the next decades, the development of more efficient and better-performing polymer electrolyte membrane fuel cells (PEMFCs) is certainly needed. Water management is one of the main issues faced by these devices and is strictly related to the employment of fluorinated materials in the gas diffusion medium (GDM). Fluorine-based polymers are added as hydrophobic agents for gas diffusion layers (GDL) or in the ink composition of microporous layers (MPL), with the goal of reducing the risk of membrane dehydration and cell flooding. In this review, the state of the art of fluorinated polymers for fuel cells is presented. The most common ones are polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP), however, other compounds such as PFA, PVDF, PFPE, and CF4 have been studied and reported. The effects of these materials on device performances are analyzed and described. Particular attention is dedicated to the influence of polymer content on the variation of the fuel cell component properties, namely conductivity, durability, hydrophobicity, and porosity, and on the PEMFC behavior at different current densities and under multiple operating conditions.

Combined use of total fluorine and oxidative fingerprinting for quantitative determination of side-chain fluorinated polymers in textiles

Given their extensive production volumes and potential to form persistent perfluoroalkyl acids (PFAAs), there is concern surrounding the ongoing use of side-chain fluorinated polymers (SFPs) in consumer products. Targeted SFP quantification relies on matrix assisted laser desorption ionization-time-of-flight mass spectrometry, which suffers from poor accuracy and high detection limits. Alternatively, total fluorine (TF)-based methods can be used, but these approaches report concentrations on a “fluorine equivalent” basis (e.g. F/m2 in the case of textiles) and are incapable of elucidating structure/chain length, which is critical for predicting the identity and quantity of degradation products. Here a new method for comprehensive characterization of SFPs is presented, which makes use of the total oxidizable precursors assay for fingerprint-based structural elucidation, and combustion ion chromatography for TF quantification. When used in parallel, quantitative determination of SFPs (in units of mass of CnF2n+1/m2 textile) is achieved. Expressing SFP concentrations in terms of mass of side-chain (as opposed to fluorine equivalents) facilitates estimation of both the structure and quantity of PFAA degradation products. As a proof-of-principle, the method was applied to six unknown SFP-coated medical textiles from Sweden. Four products contained C6-fluorotelomer-based SFPs (concentration range 36-188 mg C6F13/m2), one contained a C4-sulfonamide-based SFP (718 mg C4F9/m2), and one contained a C8-fluorotelomer-based SFP (249 mg C8F17/m2).

Fluorinated polymers: evaluation and characterization of structure and composition

The proposed review represents the systematic analysis of modern methods and approaches for the characterization and structural evaluation of fluorinated polymers that have found a wide application as materials for chemical processing, chemically resistant components and coatings, pharmaceutical and electrical packaging, biomedical equipment, etc. The chemical composition of the polymers (fluorine content, its distribution inside the fluorinated materials, chemical bonds, presence of oxygen-containing groups) substantially influences on the operation properties (chemical resistance, adhesive, cohesive, optical, dielectrical, thermal, barrier, gas permeation) of the final polymeric products. Hence, it was of particularly importanсe to bond the emergence of specific features with the presence of fluorine in the chemical structure of polymer by means of related analytical techniques. Namely, we focused on spectral (IR, UV-VIS, NMR, XPS, EPR), chemical (elemental analysis), Secondary-ion mass spectroscopic (SIMS) and microscopic (AFM, SEM-EDX) methods emphasizing their general consideration and limitations as well as application for the in-depth characterization.

Photocatalytic antifouling coating based on carbon nitride with dynamic acrylate boron fluorinated polymers

Study on the preparation and properties of an environmentally friendly photocatalytic antifouling coating.