High-performance quaternary PtRuIrNi electrocatalysts with hierarchical nanostructured carbon support

Abstract

The PtRuIrNi quaternary system is explored by a robotic dispenser and combinatorial optical screening method, and some active ternary and quaternary electrocatalysts for methanol oxidation in direct methanol fuel cells are discovered. When combinatorial screening is employed, pH change allows one to differentiate active catalysts using fluorescent acid–base indicators. A quaternary catalyst with Pt34Ru30Ir13Ni23 composition is found to be the most active, demonstrating superior electrochemical catalytic activity and stability for methanol oxidation compared to commercial Pt50–Ru50 binary catalyst. The effect of carbon support on methanol oxidation is also investigated using hollow mesoporous carbon (HMC), mesoporous CMK-3, and commercial Vulcan XC-72 as supporting materials for the quaternary composition. The newly developed PtRuIrNi/VC, PtRuIrNi/CMK-3, and PtRuIrNi/HMC catalysts exhibit an enhancement in activity of ca. 26–50% and demonstrate better electrochemical stability toward methanol oxidation than the Vulcan carbon-supported Pt50–Ru50 binary alloy catalyst. About half of the total improvement in catalytic activity is attributed to a new active quaternary catalyst composition, whose activity can be explained by a bifunctional mechanism, electronic effect, and stability effect occurring from addition of Ni and Ir. An additional boost amounting to the other half of the total enhancement is obtained from a unique hierarchical nanostructured carbon support with high surface area and pore volume, which favors not only homogeneous dispersion of small catalyst nanoparticles, but also fast mass transport in the catalyst layer.