Electrochemical and Chemical Treatment Methods for Enhancement of Oxygen Reduction Reaction Activity of Pt Shell-Pd Core Structured Catalyst

Abstract

Based on the accelerated durability test protocol (ADT, rectangular wave, 1.0V (3s)-0.6V (3s), 10,000 cycles, at 80°C), a high activation protocol (HAP) was developed as an electrochemical treatment method using rectangular wave potential cycling for a carbon supported Pt shell-Pd core structured catalyst (Pt/Pd/C), which mitigated the decay of electrochemical surface area (ECSA) and enhanced the mass activity for oxygen reduction reaction (ORR). It was found that a longer holding time and a less cycle number (300s and 30 cycles) compared with those used for the ADT protocol (3s and 10,000 cycles) effectively suppressed the ECSA decay and enhanced the ORR mass activity. A potential in the range of 0.2 to 0.6V was suitable as the lower limit potential of the HAP protocol for the ORR activity enhancement when the upper limit potential was fixed at 1.0V. Furthermore, H2-O2 and Cu-O2 chemical treatment methods, which chemically realize the HAP performed on GC electrode, were developed, where the equilibrium potentials of Cu/Cu2+, hydrogen and oxygen were utilized for surface oxidation and reduction of Pd and Pt. Both methods mitigated the ECSA decay and enhanced the ORR mass activity, and the Cu-O2 chemical treatment method gave a higher mass activity. These chemical treatment methods are useful for mass-production of highly active Pt core-shell structured catalyst.