The sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode remains as one of the main challenges for commercial viability of alkaline exchange membrane fuel cells (AEMFCs). It is therefore, of great interest to explore the development of electrocatalysts with superior activity and stability relative to the coinventional carbon supported Pt nanoparticles (NPs).
In this work we have studied the effects and evolution of structure and surface composition of Pt-Mn NPs on their electrocatalytic activity for the ORR in alkaline media. Pt-Mn NPs were synthesized using solvothermal methods and were supported on C via impregnation. An ordered intermetallic phase was obtained by heat treatment. We have investigated the crystalline structure of these NPs using X-ray diffraction (XRD) and their size, morphology and composition using TEM/STEM, EELS and EDX. Cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry were used to assess their electrocatalytic activity and stability.
The Pt-Mn NPs were electrochemically dealloyed in acidic media, through potential cycling, leading to the formation of a ~1nm thick Pt shell on an ordered Pt3Mn core. Enhanced mass and specific activity resulted by such electrochemical dealloying. The stability of the electrocatalyst was tested after 4,000 potential cycles in alkaline media following the DOE protocol (0.6-1.0 V vs reversible hydrogen electrode). In alkaline media, Mn surface segregation ensued, leading to a lower electrocatalytic activity when compared to the freshly dealloyed catalyst.