Cerium Boosts Stability of Low-Platinum High-Entropy Alloy Catalysts for Acidic Oxygen Reduction Reaction

ACS Publications (Chemistry of Materials) USA

Overview

Researchers have significantly enhanced the stability of low-platinum high-entropy alloy (HEA) catalysts for the oxygen reduction reaction (ORR) in acidic media, a critical component for proton exchange membrane fuel cells (PEMFCs). By intrinsically alloying cerium (Ce) into the HEA lattice, they successfully suppressed the dissolution of transition metals and structural degradation. The reversible Ce3+/Ce4+ redox pair actively scavenges harmful radical species, leading to substantially improved catalyst longevity and offering a pathway to ultra-low platinum catalysts for more cost-effective and durable fuel cell technology.

In Depth

Background

Proton exchange membrane fuel cells (PEMFCs) represent a promising clean energy technology, yet their widespread commercialization is hampered by the high cost and insufficient durability of platinum-based catalysts for the oxygen reduction reaction (ORR) at the cathode. The development of low-platinum (low-Pt) catalysts is crucial for reducing costs while maintaining performance. High-entropy alloys (HEAs), characterized by the incorporation of multiple principal elements in near-equimolar ratios, have emerged as potent candidates due to their unique ‘cocktail effect’ and lattice distortion, which can lead to superior catalytic properties. However, a significant challenge for low-Pt HEA catalysts in the highly acidic environment of PEMFCs has been their instability, primarily manifesting as the dissolution of non-noble transition metals and structural degradation.

Key Findings / Results

This groundbreaking research introduces an innovative strategy to overcome the stability limitations of low-Pt HEA catalysts: the intrinsic alloying of cerium (Ce) directly within the HEA lattice. Unlike conventional approaches where cerium is often applied as an external oxide additive, this intrinsic integration provides a dual mechanism for enhanced catalytic stability:

• The HEA matrix effectively stabilizes the incorporated Ce atoms, which in turn significantly suppresses the leaching of other transition metal atoms from the catalyst structure. This preservation of structural integrity is critical for long-term operation.
• The reversible Ce³⁺/Ce⁴⁺ redox pair within the alloy actively captures and neutralizes detrimental reactive oxygen species (radicals), such as hydrogen peroxide, generated during the ORR. This scavenging action mitigates radical-induced degradation of the catalyst surface.

Through this intrinsic alloying approach, the new Ce-enhanced HEA catalyst demonstrated remarkable stability and sustained high ORR activity even under highly acidic conditions, comparable to or exceeding traditional Pt/C catalysts, but with significantly reduced platinum loading. This dual-functional design provides a robust solution for developing highly durable and cost-effective catalysts for fuel cell applications.

Technical Significance & Outlook

The intrinsic alloying of cerium into HEAs marks a significant conceptual and practical advancement in the design of ultra-low Pt catalysts. This strategy directly addresses the core challenges of cost and durability in PEMFCs, accelerating their path towards commercial viability and widespread adoption in the clean energy sector. The principles established in this study could be extended to other electrocatalytic reactions and various high-entropy material systems, fostering broader innovation in sustainable energy conversion technologies. Future work will focus on scaling up the synthesis methods, conducting extensive long-term durability tests under real-world operating conditions, and further optimizing the precise composition and structural parameters to achieve even higher performance and industrial applicability.