Tuning oxygen reduction activity on chromia surface via alloying: a DFT study

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Economical electro-catalysts are crucial for advanced energy storage, particularly for the oxygen reduction reaction (ORR).
• Chromium compounds, specifically chromia (Cr₂ O₃), are explored as non-precious metal alternatives for ORR catalysis.
• Cr₂ O₃ is the most stable form of chromium oxide at room temperature.

Purpose of the Study:

• To investigate the effect of alloying hydroxylated Cr₂ O₃ surfaces with 17 different transition metals on the 4-electron oxygen reduction reaction (ORR).
• To identify optimal alloying elements for enhancing ORR activity in Cr₂ O₃-based catalysts.
• To explore the potential of Cr₂ O₃ and its alloys in corrosion prevention for stainless steels.

Main Methods:

• Density functional theory+U (DFT+U) calculations were employed.
• The 4-electron ORR on hydroxylated Cr₂ O₃ surfaces alloyed with 17 transition metals was simulated.
• The ORR overpotential was analyzed for each alloyed surface.

Main Results:

• Alloying Cr₂ O₃ with transition metals at the end of the first and second rows, such as Zinc (Zn), significantly lowered the ORR overpotential.
• Cadmium (Cd) alloying showed the highest ORR promotion but is unsuitable due to toxicity and cost.
• Alloying with early-to-mid row transition metals (e.g., Zr, Ti) generally resulted in higher and less varied ORR overpotentials.
• Cr₂ O₃'s role in stainless steel passivation and the potential benefit of early-to-mid row transition metal alloying for corrosion resistance were highlighted.

Conclusions:

• Transition metal alloying can tune the ORR activity of Cr₂ O₃ surfaces.
• Zn is identified as a promising, cost-effective, and less toxic alloying element for enhancing ORR on Cr₂ O₃.
• Alloying Cr₂ O₃ with early-to-mid row transition metals may improve the corrosion resistance of stainless steels by reducing the ORR rate.