PtNiAu Catalyst Nanoporous Shell for Fuel Cell Durability
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Solution Overview
Problem
Polymer electrolyte membrane fuel cells (PEMFCs) face challenges in minimizing platinum content while maintaining catalytic activity and durability, as existing electrocatalysts often require high platinum loading and are prone to degradation, leading to increased costs and performance loss over time.
Innovation Solution
The development of nanostructured catalysts with a composition of Pt x Ni y Au z, where x is between 27.3 and 29.9, y is between 63.0 and 70.0, and z is between 0.1 and 9.6, with gold incorporation improving mass activity and durability, either in the bulk or surface, before or after annealing and dealloying, to form nanoporous structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If platinum content is minimized to reduce cost, then catalyst cost decreases, but catalytic activity and durability deteriorate
Solution Approach 1:
The patent employs composite materials by creating a core-shell structure where a PtNi alloy core is combined with a gold shell. This composite structure allows the system to achieve high catalytic activity and durability with reduced platinum content, as the gold shell protects the PtNi core while maintaining catalytic function.
Solution Approach 2:
The patent applies local quality by creating a heterogeneous structure with different compositions in different regions - the PtNi alloy core provides catalytic activity while the gold shell provides protection. This spatial differentiation of properties allows the catalyst to simultaneously achieve low platinum content, high activity, and improved durability.
2Duration of action of stationary object
If gold is incorporated to improve durability, then mass activity retention improves, but initial catalyst cost increases
Solution Approach 1:
The patent applies beforehand cushioning by depositing a gold shell on the PtNi alloy core before the catalyst undergoes aging. This gold shell acts as a protective layer that prevents degradation of the PtNi core during accelerated aging, thereby cushioning against future performance loss and maintaining mass activity retention.
Solution Approach 2:
The composite PtNi-gold structure combines the high catalytic activity of PtNi alloy with the protective properties of gold. This composite material achieves improved durability and mass activity retention after aging, with the gold component protecting the platinum from degradation while maintaining cost-effectiveness through optimized composition.
3Quantity of substance
If nanoporous structures are formed to increase specific area, then catalyst cost per performance decreases, but manufacturing complexity increases
Solution Approach 1:
The patent employs porous materials by forming a nanoporous gold shell around the PtNi alloy core. This nanoporous structure dramatically increases the specific surface area of the catalyst, providing more active sites for reactions. The porous structure is achieved through controlled dealloying processes that create interconnected nanoscale pores.
Solution Approach 2:
The patent applies segmentation by dividing the catalyst into distinct functional regions - the PtNi alloy core and the nanoporous gold shell. This segmentation allows each component to perform its specific function optimally while the overall structure achieves high specific surface area. The dealloying process segments the alloy into a bicontinuous structure with interconnected pores.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The incorporation of gold into PtNi catalysts enhances the retention of mass activity, specific area, and performance after accelerated aging, improving durability and maintaining catalytic performance in fuel cell membrane electrode assemblies.
Implementation Method 1
PEMFC electrocatalysts often comprise platinum, a relatively expensive precious metal. It is typically desirable to minimize the platinum content in PEMFCs, increasing the catalyst activity per unit catalyst surface area (specific activity) and increasing the catalyst surface area per catalyst mass (specific surface area or specific area). The HOR and ORR occur on the catalyst surface
Implementation Method 2
Nanoporous electrocatalysts may have higher specific area, thereby reducing cost. Nanoporous catalysts are comprised of numerous interconnected nanoscale catalyst ligaments, and the surface area of a nanoporous material depends upon the diameter and volumetric number density of the nanoscale ligaments. Surface area is expected to increase as the nanoscale ligament diameter decreases and the volumetric number density increases.
Implementation Method 3
One method of forming nanoporous PEMFC electrocatalysts is via dealloying of a transition metal rich Pt alloy precursor, such as a PtNi alloy with 30 at.% Pt and 70 at.% Ni. During dealloying, the precursor is exposed to conditions where the transition metal is dissolved and the surface Pt has sufficient mobility to allow exposure of subsurface transition metal and formation of nanoscale ligaments, which separate the nanopores.
Data Source
Figure 1~2
Figure 3A~3C
Figure 3D~3E
AI summary
Catalysts comprising nanostructured elements comprising microstructured whiskers having an outer surface at least partially covered by a catalyst material having the formula PtxNiyAuz, wherein x is in a range from 27.3 to 29.9, y is in a range from 63.0 to 70.0, and z is in a range from 0.1 to 9.6. Catalyst described herein are useful, for example, in fuel cell membrane electrode assemblies.