Development of a method for quantification of active site density and turnover frequency of electrocatalysts

Abstract

Carbon-supported single-atom metal catalysts (SACs) offer great potential for achieving high catalytic performance in a number of electrocatalytic reactions. Although remarkable advances have recently been achieved in their synthesis and electrochemical applications, further development has decelerated by a lack of fundamental and empirical understanding of their intrinsic catalytic properties, i.e., active site density (SD) and turnover frequency (TOF). Here we develop an in situ SD quantification method by adopting cyanide anion as a probe molecule. Using a sensitive spectrophotometry, we can interconnect the amount of cyanide, which is irreversibly adsorbed on the Fe-Nx moieties on a model Fe-N-C catalyst, with electrocatalytic deactivation in an oxygen reduction reaction (ORR). Their correlation yields markedly surface-sensitive and metal-specific values of SD and TOF. Notably, this analytical strategy demonstrates its versatile applicability in the estimation of activity descriptors for a series of transition/noble metal SACs and potentially for bulk nanoparticles in a wide pH range of electrolytes. This will enable to understand the structure-activity relationship at an atomic-level even for SACs, and offer clear experimental clues for their rational designs.