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A Rh−Sn nanoparticle is achieved by combinatorial approaches for application as an active and stable electrocatalyst in the oxygen reduction reaction. Both metallic Rh and metallic Sn exhibit activities too low to be utilized for electrocatalytic reduction of oxygen. However, a clean and active Rh surface can be activated by incorporation of Sn into a Rh nanoparticle through the combined effects of lateral repulsion, bifunctional mechanism, and electronic modification. The corrosion-resistant property of Rh contributes to the construction of a stable catalyst that can be used under harsh fuel cell conditions. Based on both theoretical and experimental research, Rh−Sn nanoparticle designs with inexpensive materials can be a potential alternative catalyst in terms of the economic feasibility of commercialization and its facile and simple surfactant-free microwave-assisted synthesis.

Ionic resistance and double layer capacitance of catalyst layer (CL) variations with the thickness of the cathode CL were estimated by electrochemical impedance spectroscopy (EIS) using the modified transmission-line model (TLM). 0.1–0.4 mgPt cm−2 of commercial 20, 40, and 60 wt% Pt/C catalysts were used to control cathode CL thicknesses. The catalyst with a low Pt to C ratio was favorable for maximum power density when the catalyst loaded was ≤0.2 mgPt cm−2, and the catalyst with a high Pt to C ratio was favorable when catalyst loading was ≥0.3 mgPt cm−2. The electrochemical surface areas of 20, 40, and 60 wt% Pt/C were different, whereas the Pt utilization of these catalysts was similar. Modified TLM under the non-faradaic condition was used for an easy estimate of the ionic resistance and double layer capacitance of the CL. Moreover cell inductance, electrolyte resistance, and the charge transfer resistance of crossovered H2 were used for a precise estimate. The ionic resistances and double layer capacitances of the CL were linearly proportional to CL thickness regardless of the Pt to C ratio.