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

Toshiyuki Mori; Ke Tong; Shunya Yamamoto; Shipra Chauhan; Tomohiro Kobayashi; Noriko Isaka; Graeme Auchterlonie; Roger Wepf; Akira Suzuki; Shigeharu Ito; Fei Ye

doi:10.1021/acsomega.2c03348

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

ACS Omega. 2022 Jul 14;7(29):25822-25836. doi: 10.1021/acsomega.2c03348. eCollection 2022 Jul 26.

Authors

Toshiyuki Mori¹, Ke Tong^{1

2}, Shunya Yamamoto³, Shipra Chauhan¹, Tomohiro Kobayashi⁴, Noriko Isaka⁵, Graeme Auchterlonie⁶, Roger Wepf⁶, Akira Suzuki¹, Shigeharu Ito⁷, Fei Ye⁸

Affiliations

¹ Center for Green Research on Energy and Environmental Materials, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan.
² Center for High Pressure Science, State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
³ Takasaki Advanced Radiation Research Institute, National Institute for Quantum and Radiological Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma 370-1292, Japan.
⁴ Neutron Beam Technology Team, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
⁵ Transmission Electron Microscopy Station, NIMS, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
⁶ Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, Queensland 4072, Australia.
⁷ Department of Creative Engineering, National Institute of Technology Tsuruoka College, 104 Sawada, Inoka, Tsuruoka, Yamagata 997-8511, Japan.
⁸ Department of Materials Science and Engineering, Southern University of Science and Technology, No. 1088, Xueyuan Road, Shenzhen, Guangdong 518055, China.

Abstract

A Pt-nanocoated layer (thickness of approx. 10-20 nm) with Pt-O-Ce bonds was created through the water radiolysis reaction on a CeO _x nanowire (NW), which was induced by electron beam irradiation to the mixed suspension of K₂PtCl₄ aqueous solution and the CeO _x NW. In turn, when Pt-nanocoated CeO _x NW/C (Pt/C ratio = 0.2) was used in the cathode layer of a membrane electrode assembly (MEA), both an improved fuel cell performance and stability were achieved. The fuel cell performance observed for the MEA using Pt-nanocoated CeO _x NW/C with Pt-O-Ce bonds, which was prepared using the electron beam irradiation method, improved and maintained its performance (observed cell potential of approximately 0.8 V at 100 mW cm^-2) from 30 to 140 h after the start of operation. In addition, the activation overpotential at 100 mA cm^-2 (0.17 V) obtained for MEA using Pt-nanocoated CeO _x NW/C was approximately half of the value at 100 mA cm^-2 (0.35 V) of MEA using a standard Pt/C cathode. In contrast, the fuel cell performance (0.775 V at 100 mW cm^-2 after 80 h of operation) of MEA using a nanosized Pt-loaded CeO _x NW (Pt/C = 0.2), which was prepared using the conventional chemical reduction method, was lower than that of MEA using a Pt-nanocoated CeO _x /C cathode and showed reduction after 80 h of operation. It is considered why the nanocoated layer having Pt-O-Ce bonds heterogeneously formed on the surface of the CeO _x NW and the bare CeO₂ surface consisting of Ce⁴⁺ cations would become unstable in an acidic atmosphere. Furthermore, when a conventional low-amount Pt/C cathode (Pt/C = 0.04) was used as the cathode layer of the MEA, its stable performance could not be measured after 80 h of operation as a result of flooding caused by a lowering of electrocatalytic activity on the Pt/C cathode in the MEA. In contrast, a low-amount Pt-nanocoated CeO _x NW (Pt/C = 0.04) could maintain a low activation overpotential (0.22 V at 100 mA cm^-2) of MEA at the same operation time. Our surface first-principles modeling indicates that the high quality and stable performance observed for the Pt-nanocoated CeO _x NW cathode of MEA can be attributed to the formation of a homogeneous electric double layer on the sample. Since the MEA performance can be improved by examining a more effective method of electron beam irradiation to all surfaces of the sample, the present work result shows the usefulness of the electron beam irradiation method in preparing active surfaces. In addition, the quantum beam technology such as the electron beam irradiation method was shown to be useful for increasing both performance and stability of fuel cells.