Abstract
Since polybenzimidazole (PBI) is often used in the aerospace industry, high-temperature fuel cells, and in redox flow batteries, this research investigated the surface modification of PBI film with 253.7 and 184.9 nm UV photo-oxidation. As observed by X-ray photoelectron spectroscopy (XPS), the oxygen concentration on the surface increased up to a saturation level of 20.2 ± 0.7 at %. With increasing treatment time, there were significant decreases in the concentrations of C-C sp2 and C=N groups and increases in the concentrations of C=O, O-C=O, O-(C=O)-O, C-N, and N-C=O containing moieties due to 253.7 nm photo-oxidation of the aromatic groups of PBI and reaction with ozone produced by 184. 9 nm photo-dissociation of oxygen. Because no significant changes in surface topography were detected by Atomic Force Microscopy (AFM) and SEM measurements, the observed decrease in the water contact angle down to ca. 44°, i.e., increase in hydrophilic, was due to the chemical changes on the surface.
Highlights
Interfacial properties are a key aspect for the optimization of fuel cell membrane electrode assemblies [10] and redox flow batteries [7,8,9] to increase the conductivity and uptake of the proton carrier; the concentration of the polar groups on the polymer backbone must be maximized [11]
Since ozone is linked to a broad array of health threats [14], the exiting gas was passed through a solution of saturated KI in order to react with the ozone before emission into the vacuum hood
For six sets of samples treated with UV photo-oxidation (Figure 2), the oxygen concentration increased up to a saturation level of 20.2 ± 0.7 at %, the carbon concentration decreased by around the same amount, and there were no significant changes in the nitrogen concentration
Summary
[3], and aerospace industries, where PBI may be exposed to ozone and UV radiation [4]. Technologies 2020, 8, x; doi: FOR PEER REVIEW www.mdpi.com/journal/technologies. To increase the hydrophilicity of the PBI surface, this research investigated the UV photo-oxidation of PBI with low-pressure Hg lamps which emit both 253.7 and 184.9 nm photons. The 184.9 nm radiation is absorbed by oxygen and breaks the molecular bond to form ground state O (3P) atoms [12] at a threshold wavelength of 242.4 nm [13]. Using atmospheric pressure of O2, ozone is produced by reaction (1) involving a stabilizing molecule (M), which is the oxygen molecule in this study
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