Effect of nanoporous structure on enhanced electrochemical reaction

Geometric factors affecting the enhanced electrocatalysis on nanoporous Pt (L₂-ePt) were examined by electrochemical methods and computer simulations. The experimental results revealed that the electrochemical enhancement of O₂ and H₂O₂ does not come only from expansion of the active surface area (so-called roughness factor, f _R) of L₂-ePt. The presence of extra contribution was verified by the fact that significant enhancement in electrocatalytic reactions remained even after the effect of the f_R was eliminated from the electrochemical redox behavior of O₂ and H₂O₂ on L₂-ePt electrodes. Not only the voltammetric observation but also potentiometric pH responses of L₂-ePt suggested the presence of unique nanoporous effects other than the surface enlargement in regard to heterogeneous electrochemical reactions. L₂-ePt showed near Nernstian behavior, faster response time, and less hysteresis even if the real surface area was smaller than that of flat Pt. Increased residence time near the electrode surface due to extremely confined space of nanoporous structure was proposed as possible origins and examined by the Monte Carlo simulations of simple model electrodes. The theoretical approaches indicated that long residence time of reactant at electrode surface by confinement effect of the nanoporous environment well accounted for the experimental results.