The role of mechanically induced defects in carbon nanotubes to modify the properties of electrodes for PEM fuel cell

The characteristics and reactivity of two anodes based on Pt supported on carbon nanotubes (CNTs) without or with defects induced by ball-milling are studied by SEM, TEM, cyclic voltammetry (CV) and single-cell measurements using a flow of pure H2 or containing 50 ppm CO. It is evidenced that the presence of defects influences several properties and not only the dispersion of Pt particles. Therefore, the performances cannot be correlated neither with the geometrical surface area of Pt particles, neither with the electrochemical active surface area determined from CV tests. The presence of defects, enhancing the amount of surface functional groups on CNT, influences various aspects: (i) the efficiency of three-phase boundary and thus the transport of protons to or from the active metal particles, (ii) the resistance of electron transfer and (iii) the tolerance of the catalyst to CO poisoning. The latter is attributed to carbon functional groups in close contact with very small Pt particles favoring the reactivation of Pt sites poisoned by CO.