Synthesis of Pd and Nb–doped TiO2 composite supports and their corresponding Pt–Pd alloy catalysts by a two-step procedure for the oxygen reduction reaction

Abstract

Several Pd–composite Nb0.06Ti0.94O2 materials are synthesized by a two-step procedure, and employed as the Pt–Pd alloy catalyst support for the PEM fuel cell oxygen reduction reaction (ORR). These supports and their supported catalysts are characterized using analytical and electrochemical methods with respect to their material morphology, chemical/electrochemical stability, electronic conductivity as well as oxygen reduction reaction (ORR) mass activity/stability. For the supported Pt–Pd catalysts, the Pt–Pd nanoparticles adhered to both the Nb0.06Ti0.94O2 and composited Pd surfaces to form PtmPdn clusters. A possible synergetic interaction between the Pt–Pd alloy catalyst and its Pd–Nb0.06Ti0.94O2 composite support is believed to exist which enhances the ORR activity of these catalysts. The electronic conductivity of Nb0.06Ti0.94O2 can be greatly improved after forming composites with Pd to the desired levels required for electrocatalyst applications. Three supported Pt–Pd catalysts, 20 wt% Pt0.62Pd0.38/Pd10wt%–(Nb0.06Ti0.94O2)90wt%, 20 wt% Pt0.62Pd0.38/Pd30wt%–(Nb0.06Ti0.94O2)70wt%, and 20 wt% Pt0.62Pd0.38/Pd50wt%–(Nb0.06Ti0.94O2)50wt%, are synthesized and tested using both cyclic voltammetric and rotating disk electrode techniques with respect to their surface electrochemistry, ORR mass activity, and electrochemical stability. All three catalysts show higher Pt mass activity (>130 mA mgPt−1 at 0.9 V vs. RHE) than that of the baseline 47 wt% Pt C−1 carbon supported catalyst (110 mA mgPt−1). However, the durability of these catalysts needs to be further improved.