Electrocatalytic activity of nanoporous Pd and Pt: effect of structural features

The electrocatalytic activities of nanoporous palladium (npPd) and platinum (npPt) for oxygen reduction reaction (ORR) under alkaline conditions and hydrogen peroxide electrochemical reactions under neutral conditions were examined. npPd and npPt were prepared by the electrochemical deposition of each metal from the corresponding metal precursor in the presence of reverse micelles of Triton X-100, directing highly porous microstructures. The nanoporous catalysts showed excellent electrocatalytic activity for both the ORR and hydrogen peroxide electrochemical oxidation/reduction due to the increased active surface area. In particular, the npPd exhibited superior ORR activity (i.e., more positive onset and half-wave potentials, higher current density and greater number of electrons transferred) despite the smaller roughness factor than the npPt and commercial Pt. The catalytic activity for the hydrogen peroxide electrochemical reactions was also higher while using npPd (i.e., faster electrode reaction kinetics, increased current densities, etc.) compared to npPt. The higher catalytic activity of npPd than that of npPt suggests an advantage of the unique npPd structure, composed of nano- as well as micro-porosity, in facilitating mass transport through the porous metal layer. The npPd exhibited amperometric current responses, induced by the oxidation as well as reduction of hydrogen peroxide, linearly proportional to the hydrogen peroxide concentration with a rapid response time (<~2 s), high sensitivity, and low detection limit (<1.8 μM).