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

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 K 2 PtCl 4 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 CeO 2 surface consisting of Ce 4+ 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 sho...

Super Hygroscopic Non‐Stoichiometric Cerium Oxide Particles as Electrode Component for PEM Fuel Cells

“…Thanks to its unique property, CeO 2 has been investigated as a promoter of the Pt/C catalyst for enhancing the oxygen concentration on the cathode surface and the ORR catalytic activity, leading to increase low‐temperature fuel cell performances. The enhanced performance obtained with the CeO 2 addition in the cathode layer is also due to the strong interaction between Pt and the oxide particles and to a better stability and durability of the composite catalysts [22–25] . However, it was demonstrated that cerium ions can get soluble in water during fuel cell operation, migrating out of the ionomer or binder, resulting in the loss of scavenging effect.…”

“…The enhanced performance obtained with the CeO 2 addition in the cathode layer is also due to the strong interaction between Pt and the oxide particles and to a better stability and durability of the composite catalysts. [22][23][24][25] However, it was demonstrated that cerium ions can get soluble in water during fuel cell operation, migrating out of the ionomer or binder, resulting in the loss of scavenging effect. In addition, these positive cerium ions (Ce 3 + or and Ce 4 + ) in water can establish ionic interaction with the anionic sulfonic groups of the membrane, reducing its proton conductivity.…”