Platinum‐Based Nanowires as Active Catalysts toward Oxygen Reduction Reaction: In Situ Observation of Surface‐Diffusion‐Assisted, Solid‐State Oriented Attachment

Abstract

Facile fabrication of advanced catalysts toward oxygen reduction reaction with improving activity and stability is significant for proton-exchange membrane fuel cells. Based on a generic solid-state reaction, this study reports a modified hydrogen-assisted, gas-phase synthesis for facile, scalable production of surfactant-free, thin, platinum-based nanowire-network electrocatalysts. The free-standing platinum and platinum-nickel alloy nanowires show improvements of up to 5.1 times and 10.9 times for mass activity with a minimum 2.6% loss after an accelerated durability test for 10k cycles; 8.5 times and 13.8 times for specific activity, respectively, compared to commercial Pt/C catalyst. In addition, combined with a wet impregnation method, different substrate-materials-supported platinum-based nanowires are obtained, which paves the way to practical application as a next-generation supported catalyst to replace Pt/C. The growth stages and formation mechanism are investigated by an in situ transmission electron microscopy study. It reveals that the free-standing platinum nanowires form in the solid state via metal-surface-diffusion-assisted oriented attachment of individual nanoparticles, and the interaction with gas molecules plays a critical role, which may represent a gas-molecular-adsorbate-modified growth in catalyst preparation.

In Situ Transmission Electron Microscopy Study of Nanocrystal Formation for Electrocatalysis

“…There are seldom works which reported the gas‐phase synthesis of Pt‐based nanowire or the growth mechanism. So far only one study reported the dynamic gas‐phase formation of Pt NWs involving both surface diffusion and particle attachment along selective orientation . The growth process of free‐standing Pt NWs was divided into four stages as shown in Figure A: I) Pt precursors were reduced to form a great quantity of nuclei, II) Pt nuclei experienced initial growth to form grown Pt nanoparticles, III) Short Pt chains started to form, VI) Short Pt chains assembled into a longer NW.…”

“…In the past two decades, different dimensional nanocrystals with diverse shapes, size and structures have been achieved by using these ingenious methods. For example, Pt‐based nanocrystals have been synthesized from single atom to hundreds of nanometers in size, from hollow, core‐shell, sphere, cube, octahedra, icosahedra, to rod or wire, plate or sheet in morphology . Nevertheless, the understanding on the mechanism of nucleation, growth or formation of the nanocatalysts is still limited.…”

Platinum Group Nanowires for Efficient Electrocatalysis

“…In the work by Ma et al, they reported the growth mechanism at the atomic level with the help of in situ transmission electron microscopy (TEM). H 2 was used as the reduction source without introducing any structure‐directing agent . Isolated Pt nuclei with the diameter of few nanometers were grown in the primary stage.…”

High‐Performance Ordered PdCuFe/C Intermetallic Catalyst for Electrochemical Oxygen Reduction in Proton Exchange Membrane Fuel Cells

“…However, according to the volcano plot, the free energies of adsorption (ΔG) of the oxygenated species of oxygen (*OOH and *OH) for Pt are too high . One of the effective strategies for regulating the adsorption energy of the reaction intermediates is to develop Pt alloy nanocatalysts (alloys with transition metal elements)…”