Pt-CeO(x) nanowire (NW)/C electrocatalysts for the improvement of oxygen reduction reaction (ORR) activity on Pt were prepared by a combined process involving precipitation and coimpregnation. A low, 5 wt % Pt-loaded CeO(x) NW/C electrocatalyst, pretreated by an optimized electrochemical conditioning process, exhibited high ORR activity over a commercially available 20 wt % Pt/C electrocatalyst although the ORR activity observed for a 5 wt % Pt-loaded CeO(x) nanoparticle (NP)/C was similar to that of 20 wt % Pt/C. To investigate the role of a CeO(x) NW promotor on the enhancement of ORR activity on Pt, the Pt-CeO(x) NW interface was characterized by using hard X-ray photoelectron spectroscopy (HXPS), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). Microanalytical data obtained by these methods were discussed in relation to atomistic simulation performed on the interface structures. The combined techniques of HXPS, TEM-EELS, and atomistic simulation indicate that the Pt-CeO(x) NW interface in the electrocatalyst contains two different defect clusters: Frenkel defect clusters (i.e., 2Pt(i)(••) - 4O(i)″ - 4V(o)(••) - V(Ce)″″) formed in the surface around the Pt-CeO(x) NW interface and Schottky defect clusters (i.e., (Pt(Ce)″ - 2V(O)(••) - 2Ce(Ce)') and (Pt(Ce)″ - V(O)(••))) which appear in the bulk of the Pt-CeO(x) NW interface similarly to Pt-CeO(x) NP/C. It is concluded that the formation of both Frenkel defect clusters and Schottky defect clusters at the Pt-CeO(x) NW heterointerface contributes to the promotion of ORR activity and permits the use of lower Pt-loadings in these electrocatalysts.
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To develop the state‐of‐the‐art polymer membrane fuel cells. Both maximization of oxygen reduction reaction (ORR) activity on Pt cathode and minimization of Pt content in the cathode are required. For this challenge, the defect interface on oxide support was modified by proton beam irradiation method. Pt‐CeOx nanowire/C (Pt/C = 0.02) was fabricated using the proton beam irradiation method. Since the radical density generated by proton beam irradiation is two orders of magnitude greater than that of electron beam irradiation, the CeOx nanowire surface was fully converted to a thin layer of Pt‐O‐Ce bonds under proton beam irradiation. The ORR activity observed for fabricated sample with above active surface layer was higher than that of conventional Pt/C (Pt/C = 0.2) and comparable to that of Pt‐CeOx nanowire/C (Pt/C = 0.2) fabricated by conventional methods. From the combination of microanalysis characterization and surface atomistic simulation, we concluded that the Pt‐O‐Ce bond was formed on defect‐rich regions of the CeOx nanowire and this leads to a maximized ORR activity on the fabricated sample. Based on all experimental data, it is concluded that the surface modification of CeOx nanowire support using proton beam irradiation is useful for a lowering the Pt content of the cathode with high ORR activity.
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