Inhibiting the Oxygen Reduction Reaction Kinetics on Carbon Fiber Epoxy Composites Through Diazonium Surface Modification-Impacts on the Galvanic Corrosion of Coupled Aluminum Alloys

Abstract

We report on the chemical modification of carbon fiber reinforced polymer (CFRP) composites by the electrochemical reduction of 4-nitrophenyl (NP) and 4-nitroazobenzene (NAB) diazonium salts. The electrochemically assisted modification of the exposed carbon fibers was accomplished using cyclic voltammetry from 0.6 to −0.5 V (vs Ag QRE) for 25 cycles in deaerated acetonitrile containing 0.1 M tetrabutylammonium tetrafluoroborate (NBu4BF4) and 5 mM aryldiazonium salt. Raman spectra of the modified composites confirmed the formation of stable 4-NP and 4-NAB adlayers. The influence of diazonium surface pretreatment on the oxygen reduction reaction (ORR) kinetics was assessed by measuring the voltametric curves for dissolved oxygen reduction on unmodified and chemically modified composites in naturally aerated 0.5 M Na2SO4. The adlayers are believed to reduce the kinetically controlled current for the ORR by blocking reactive surface sites for O2 chemisorption. Results show the adlayers are stable during a 7-day continuous neutral salt spray (NSS) exposure and the extent of galvanic corrosion on trivalent chromium process (TCP) conversion-coated aluminum alloys is significantly reduced when joined with a surface treated composite. The extent of carbon corrosion and microstructural degradation of carbon fibers is also reduced by the organic adlayers.