Comparison of the Electrochemical Response of Carbon-Fiber-Reinforced Plastic (CFRP), Glassy Carbon, and Highly Ordered Pyrolytic Graphite (HOPG) in Near-Neutral Aqueous Chloride Media

Abstract

Carbon-fiber-reinforced polymers (CFRP), being conductive, are capable of supporting cathodic oxygen reduction reactions (ORR) and thus promote galvanic corrosion when coupled to many metallic materials. Hence, understanding cathodic processes at carbon surfaces is critical to developing new strategies for the corrosion protection of multi-material assemblies. In the present work, the electrochemical responses of CFRP, glassy carbon, and HOPG (Highly Ordered Pyrolytic Graphite) have been evaluated in a quiescent 50 mM NaCl solution, and their respective activities towards ORR have been ranked. Employing the averages of the specific charges (CFRP, 129.52 mC cm−2; glassy carbon, 89.95 mC cm−2; HOPG, 60.77 mC cm−2) passed during 1 h polarization of each of the 3 carbon surfaces at −1000 mVSCE in the test media as a ranking criterion, the propensities of the 3 carbon surfaces (CFRP, GC, and HOPG) to support cathodic activities that can lead to anodic metal dissolution on galvanic coupling to metallic materials are ranked thusly; CFRP > GC > HOPG. This ranking is consistent with the trend of capacitance values obtained in this work: CFRP (19.5 to 34.5 μF cm−2), glassy carbon (13.6 to 85.5 μF cm−2), and HOPG (1.4 to 1.8 μF cm−2). A comparison of electrochemical data at potentials relevant to galvanic coupling to metals indicated that at these cathodic potential(s) the CFRP surface is the most electrochemically active of the studied carbon surfaces. On the basis of the values and trends of the electrochemical parameters evaluated, it is postulated that the observed differences in the electrochemical responses of these 3 carbon-rich surfaces to ORR are significantly due to differences in the proportions of edge sites present on each carbon surface. These results could provide valuable insights on plausible strategies for designing carbon surfaces and carbon fiber composites with reduced activity toward ORR for corrosion protection applications or enhanced activity towards ORR for energy applications.

Drop-cast gold nanoparticles are not always electrocatalytically active for the borohydride oxidation reaction

“…The comparison between GC and HOPG is possible due to the similar chemical makeup, surface functional groups, and (electro)chemical stability. 57,58 This CV displays a BOR current which is more constant per cycle, as expected for the BOR on a large number of NPs, and the a 1 and a 2 peaks are broader and less separated, likely due to the subtle variation of peak potentials on different NPs that make up the ensemble. This is also visible, albeit to a lesser extent, in the CV which results from summing up the currents of all of the NPs measured with SECCM (Fig.…”