(485f) Particle Size Effect On Electrocatalyst Stability

Development of advanced electrocatalysts for PEMFCs and electrolyzers requires improvement in both catalytic activity and stability.  While so far the focus has been placed on catalytic activity and significant progress has been made in the past decade, it still remains elusive how to enhance the stability of catalysts working under hostile electrochemical environment.  Recent work found that commercial catalysts with platinum (Pt) nanoparticles of 2 to 3 nm in size are not stable under PEMFC operation conditions, where migration and dissolution/re-deposition of Pt surface atoms result in substantial losses of surface area, activity and power density.  Using bigger particles can provide better stability, which however will lead to reduced mass activity.  Therefore, it is important to optimize the particle size to achieve a fine balance between catalytic activity and catalyst stability.

    Here we report a systematic investigation of particle size effect on the stability of Pt electrocatalysts for the oxygen reduction reaction (ORR).  Instead of using commercial catalysts with broad particle size and shape distributions, we developed an organic solution approach to synthesize monodisperse and uniform Pt nanoparticles of various particle sizes (2 - 10 nm).  The obtained Pt nanoparticles were supported on high-surface-area carbon, and the employed organic surfactants were removed by simple low-temperature thermal treatment.  Electrochemical studies by rotating disk electrode revealed that the catalyst stability improves with increasing particle size.  Moreover, volcano-type dependence of catalytic performance on particle size was established, with an intermediate particle size of 5 nm reaching the fine balance between activity and stability, showing the highest mass activity after extensive potential cycling.