Deposition and electrochemical activity of Pt-based bimetallic nanocatalysts on carbon nanotube electrodes

This article reports an approach to prepare bimetallic Pt–M (M = Fe, Co, and Ni) nanoparticles as electrocatalysts and examines their electrochemical activities in 1 M sulfuric acid. The approach consists of chemical oxidation of carbon nanotubes (CNTs), two-step refluxing, and subsequent thermal reduction in hydrogen atmosphere. Three bimetallic pairs of Pt–M catalysts are found to deposit well onto CNT surface, forming Pt–M/CNT composites. The electrochemical behavior of Pt–M/CNT electrodes was investigated in 1 M H2SO4 using cyclic voltammetry (CV) and ac electrochemical impedance spectroscopy. The active surface coverage (=electrochemical surface area/geometric surface area) of Pt–M catalysts is significantly enhanced, i.e., Pt–Co (85.1%) > Pt–Ni (80.4%) > Pt–Fe (76.2%) > Pt (26.3%). This enhancement of electrochemical activity can be attributed to the fact that the introduction of Co and Ni may reduce the required potential for water electrolysis and thus the associated carbon oxidation, thereby contributing to hydrogen adsorption. Equivalent circuit analysis indicates that charge transfer resistance accounts for (i) the major proportion of the equivalent serial resistance of Pt–M/CNT electrodes, and (ii) Pt–Co and Pt–Ni catalysts not only improves the electrochemical capacitance but also lowers the equivalent serial resistance. The results shed some light on how use of Pt–M/CNT composite would be a promising electrocatalyst for high-performance fuel cell applications.