Surface layer of Pt‐O‐Ce bonds on CeO_x nanowire with high ORR activity converted by proton beam irradiation

Abstract

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.

Active Pt-Nanocoated Layer with Pt–O–Ce Bonds on a CeOx Nanowire Cathode Formed by Electron Beam Irradiation

“…As mentioned in the Introduction, the authors successfully formed a Pt-nanocoated layer on the CeO x NWs using the proton irradiation method. Furthermore, our electrochemical measurements confirmed that the formation of Pt–O–Ce bonds together with fine Pt particles in this nanocoated layer enhances the ORR on the Pt/C cathode . However, it is impossible to prepare the cathode powder for MEA using a small amount of high-energy proton radiation emitted from the tip of a small glass capillary attached to the ion accelerator.…”

“…Furthermore, our electrochemical measurements confirmed that the formation of Pt–O–Ce bonds together with fine Pt particles in this nanocoated layer enhances the ORR on the Pt/C cathode. 57 However, it is impossible to prepare the cathode powder for MEA using a small amount of high-energy proton radiation emitted from the tip of a small glass capillary attached to the ion accelerator. Therefore, to obtain the necessary amount of cathode powder for fabrication of MEA, electron irradiation experiments were conducted by adding C 2 H 5 OH to a suspension consisting of K 2 PtCl 4 aqueous solution and CeO x NWs (C 2 H 5 OH/K 2 PtCl 4 molar ratio = 5), as in the case of proton irradiation experiments.…”

“…The peak at 71.1 eV is attributable to metallic Pt (Pt 0 ). The other extra peak located at a binding energy of 72.0 eV is labeled as Pt–O–X (X: Ce cation or oxygen vacancy) and corresponds to slightly ionized Pt. ,, This slightly ionized Pt peak, which is located midway between metallic Pt and Pt 2+ (i.e., PtO located at 72.6 eV), appeared in the Pt 4f spectrum due to the formation of Pt–O–Ce bonds at the interface between Pt and CeO x . Based on the results shown in Figure , the peak area ratio of Pt–O–X (X: Ce cation or oxygen vacancy) species when the peak area of metallic Pt species was 1 was 0.53, refer to Table .…”

“…To overcome this problem, the authors previously prepared a Pt-nanocoated CeO x NW/C cathode with Pt–O–Ce bonds using a proton beam irradiation method . In that previously published work, it was reported that the Pt-CeO x NW/C cathode with a Pt–O–Ce bonded nanocoating layer showed high ORR activity by electrochemical measurements.…”

“…To overcome this problem, the authors previously prepared a Pt-nanocoated CeO x NW/C cathode with Pt–O–Ce bonds using a proton beam irradiation method . In that previously published work, it was reported that the Pt-CeO x NW/C cathode with a Pt–O–Ce bonded nanocoating layer showed high ORR activity by electrochemical measurements. However, the amount of Pt-CeO x NW/C with a nanocoating layer on its surface that can be produced by using high-energy proton beams, which can only be generated using an ion accelerator, was very little.…”