Understanding and Controlling Nanoporosity Formation for Improving the Stability of Bimetallic Fuel Cell Catalysts

Abstract

Nanoporosity is a frequently reported phenomenon in bimetallic particle ensembles used as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. It is generally considered a favorable characteristic, because it increases the catalytically active surface area. However, the effect of nanoporosity on the intrinsic activity and stability of a nanoparticle electrocatalyst has remained unclear. Here, we present a facile atmosphere-controlled acid leaching technique to control the formation of nanoporosity in Pt-Ni bimetallic nanoparticles. By statistical analysis of particle size, composition, nanoporosity, and atomic-scale core-shell fine structures before and after electrochemical stability test, we uncover that nanoporosity formation in particles larger than ca. 10 nm is intrinsically tied to a drastic dissolution of Ni and, as a result of this, a rapid drop in intrinsic catalytic activity during ORR testing, translating into severe catalyst performance degradation. In contrast, O2-free acid leaching enabled the suppression of nanoporosity resulting in more solid core-shell particle architectures with thin Pt-enriched shells; surprisingly, such particles maintained high intrinsic activity and improved catalytic durability under otherwise identical ORR tests. On the basis of these findings, we suggest that catalytic stability could further improve by controlling the particle size below ca. 10 nm to avoid nanoporosity. Our findings provide an explanation for the degradation of bimetallic particle ensembles and show an easy to implement pathway toward more durable fuel cell cathode catalysts.

A selective and efficient electrocatalyst for carbon dioxide reduction

“…By selectively etching Al through dealloying, the remaining Ag atoms were reorganized to form a three-dimensional interconnected nanoporous structure. The dealloying process has been reported in a few alloyed systems 26,27 and the resulting materials have shown unique catalytic performance such as in fuel cells [28][29][30] and alcohol oxidation 31 . However, there is still no report on their catalytic properties for CO 2 reduction.…”

Organic-inorganic hybrid PtCo nanoparticle with high electrocatalytic activity and durability for oxygen reduction

“…While PtM alloy catalysts such as PtCo/C generally have much higher initial ORR activities than the Pt catalyst due to the electronic ligand effect of the electron transfer from the TM to Pt, they also rapidly degrade owing to the TM oxidation and dissolution. 5,26 The surface Pt can also be concomitantly oxidized owing to the collapse of its initial structure by the TM dissolution in the ADT. 59 As expected, both PtCo/C and PtCo/C-PNIPAM had much higher ORR activities compared with Pt/C (Supplementary Figure S11).…”

“…[23][24][25] In addition, the surface TM oxides are rapidly dissolved when the PtM nanoparticles are used as catalytic cathodes in acid electrolytes for ORR. 5,[26][27][28] These electrochemical and chemical dealloying phenomena are widely known to be critical factors for catalyst degradation.…”

Carbon-Supported Pt-Based Alloy Electrocatalysts for the Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells: Particle Size, Shape, and Composition Manipulation and Their Impact to Activity

“…Later, their group used this electrochemical dealloying method to prepare the core−shell structured PtNi/C catalysts and ternary Pt-based electrocatalysts; they obtained high ORR activities (>500 mA mg Pt −1 at 0.9 V under single-cell test) 261,265,266 and stable catalytic activity by keeping the particle size in the range of 5− 10 nm. 266 …”