Nickel Catalysts Get a Boost from Halogen Friends
The Challenge
Nickel catalysts lag behind noble metals in hydrogen oxidation reactions (HOR) within alkaline environments, boasting only 1-2% of their activity. The underlying reasons remained elusive—until now.
Breakthrough Research
Recent studies have uncovered the pivotal role of anions in enhancing nickel-based catalysts. Specifically, Br⁻ and Cl⁻ ions have emerged as game-changers.
The Mechanism
- Adsorption Boost: Br⁻ and Cl⁻ ions adhere to the catalyst's surface, facilitating hydrogen transfer and improving reaction efficiency.
- Oxidation Prevention: These ions also block OH⁻ from attaching, delaying nickel oxidation.
Performance Gains
- 13% Increase in HOR activity for NiMoOₓ catalysts.
- 40 mV Delay in nickel oxidation onset.
The Downside
Not all anions are beneficial. SCN⁻ ions, classified as pseudohalogens, poison the catalyst by binding too tightly, diminishing its effectiveness.
Practical Applications
Utilizing Cl⁻-modified NiMoOₓ catalysts in alkaline anion exchange membrane fuel cells yields impressive results:
- Peak Power Density: 234.3 mW cm⁻²—24% higher than unmodified NiMoOₓ.
Conclusion
This research underscores the critical role of anion adsorption in optimizing nickel-based catalysts, paving the way for more practical and efficient applications.