Synthesis of Carbon-Supported Intermetallic Pt₅Ce Compound Nanoparticles via a Water-Based Impregnation Route

Abstract

A water-based impregnation synthesis route was used to obtain carbon-supported Pt–Ln (Ln: lanthanide metal) nanoparticles, which are expected to be among the most active catalysts toward the oxygen reduction reaction (ORR) but have previously been successfully prepared only in environments without H2O or O2 because of the strong oxophilicity of Ln. In the present work, a mechanistic study of the formation of Pt–Ln nanoparticles was conducted using Pt/C (Pt nanoparticles supported on carbon) and CeCl3 as starting materials, and the synthesized Pt–Ce/C particles were characterized in terms of their microstructure and their electrocatalytic activity toward the ORR. The results suggested that the impregnation-prepared powder contained Pt, CeO2, and CeCl3 (or hydrated CeCl3) and that these compounds transformed into Pt–Ce and CeOCl when heated under flowing dilute H2 gas. Microstructural analysis clarified that the obtained Pt–Ce nanoparticles (average size: 5.5 nm) were of the intermetallic Pt5Ce phase (P6/mmm, CaCu5 type, a = 0.5368 nm, c = 0.4383 nm) and that byproduct CeOCl was removed by successive washing. Carbon powders supporting Pt5La, Pt5Sm, Pt–Gd (Pt5Gd and Pt2Gd), and Pt3Tb nanoparticles were similarly obtained.

Atomically Ordered Pt5La Nanoparticles as Electrocatalysts for the Oxygen Reduction Reaction

“…Therefore, preparing Pt–L alloy nanoparticles (NPs) through chemical reduction using a relatively simple procedure is challenging. To synthesize ordered intermetallic Pt–L nanoalloys, several approaches, such as chemical reduction with hydrogen gas at high temperatures, strong reducing agents, electrolytic reduction, alkali vapor method, and gas-phase reduction, have been used. Recently, Hu et al prepared a series of Pt–rare earth (RE) nanoalloys (RE = Gd, Ce, and Tb) with a particle size of 2–14 nm using a chemical synthesis approach .…”

Platinum‐Rare Earth Alloy Electrocatalysts for the Oxygen Reduction Reaction: A Brief Overview

“…Besides, the NPs produced comprise the Pt‐REM alloy surrounded by a Pt‐rich shell, with higher ORR activity and stability than the Pt/C reference material. An example is given by Itahara et al [35b] . at the Toyota Central R&D Labs, Japan, who have synthesized Pt 5 Ce/C electrocatalysts using a top‐down approach: CeCl 3 was impregnated onto commercial Pt/C (Tanaka, 28.7 % wt .…”

“…An example is given by Itahara et al . [35b] at the Toyota Central R&D Labs, Japan, who have synthesized Pt 5 Ce/C electrocatalysts using a top‐down approach: CeCl 3 was impregnated onto commercial Pt/C (Tanaka, 28.7 % wt . Pt)by heat‐treatment at 850 °C for 2 h under Ar/4 %H 2 atmosphere.…”

Synthesis of a Hexagonal-Phase Platinum–Lanthanide Alloy as a Durable Fuel-Cell-Cathode Catalyst

“…10,11 Very recently, innovative syntheses of PtLn alloy catalysts were achieved on carbon supports in the presence of cyanamide 17 or chlorinated salts. 26 Despite the progress that has been made, the membrane electrode assembly (MEA) performance of the PtLn alloy catalysts that is highly relevant to practical PEMFC applications has been rarely demonstrated until now. 18 Here, we demonstrate that the conventional and industrially relevant impregnation approach is capable of easy synthesis of carbon-supported hexagonal-phase intermetallic Pt 5 Ln (Ln = La, Ce, Pr, and Nd) alloy nanoparticle catalysts, which is distinctively different from reported methods that often require O 2 /H 2 O-free conditions or additives.…”

“…To date, several effective approaches have been developed to synthesize PtLn alloy catalysts, including physical metallurgical methods, magnetron sputtering, , wet chemical synthesis, , microwave synthesis, strong chemical reduction with Na or triethyl borohydride, and electrodeposition . These methods, however, still face a few challenging problems for practical applications, such as the use of complicated equipment and the requirements of harsh preparation conditions (H 2 O/O 2 -free). , Very recently, innovative syntheses of PtLn alloy catalysts were achieved on carbon supports in the presence of cyanamide or chlorinated salts . Despite the progress that has been made, the membrane electrode assembly (MEA) performance of the PtLn alloy catalysts that is highly relevant to practical PEMFC applications has been rarely demonstrated until now …”