Phenomenological Descriptor-Based Characterization of Carbon Alloy ORR Catalysts

The development of carbon alloy ORR catalysts requires practical methods for their characterization and comparison. In this study, two carbon alloy ORR catalysts (CA and CA-Fe), together with a Pt/C reference, were characterized using rotating ring–disk electrode (RRDE) measurements over a range of catalyst loadings. The conventional RRDE metrics, the half-wave potential ( E 1/2 ) and hydrogen peroxide yield ( f H2O2 ), exhibit different loading dependences. As a result, direct comparison of catalyst characteristics becomes difficult. To address this limitation, we developed a descriptor-based characterization framework. It employs two phenomenological descriptors, k f2 and k s2 . They were derived from RRDE linear-sweep voltammetry within a simplified reaction–diffusion framework. The descriptor k f2 represents the overall tendency of H 2 O 2 formation. The second descriptor, k s2 , represents the overall disappearance of H 2 O 2 within the catalyst layer as reflected in the RRDE response. Both descriptors showed only small variations with catalyst loading and electrode rotation rate under the present experimental conditions. As a proof of concept, CA, CA-Fe, and Pt/C were mapped onto this descriptor space. Each catalyst occupied a distinct position. These results demonstrate that the framework provides a common basis for characterizing and comparing the catalyst systems examined in this study.