Steering acidic oxygen reduction selectivity of single-atom catalysts through the second sphere effect

Area of Science:

• Catalysis
• Materials Science
• Biomimetic Chemistry

Background:

• Natural enzymes exhibit high catalytic efficiency due to specific second-sphere interactions.
• Current synthetic methods lack versatility in modifying the second spheres of heterogeneous catalysts.

Purpose of the Study:

• To design an enzyme-mimetic single cobalt-nitrogen-4 (Co-N$_{4}$) atom catalyst with a functionalized second sphere.
• To enhance the selectivity of the oxygen reduction reaction (ORR) towards hydrogen peroxide (H$_{2}$O$_{2}$) production.

Main Methods:

• Synthesis of a Co-N$_{4}$ single-atom catalyst with a pendant amine group using 1,3-dipolar cycloaddition.
• Investigation of reaction mechanisms using proton inventory studies and theoretical calculations.
• Evaluation of catalytic performance for the oxygen reduction reaction under acidic conditions.

Main Results:

• The pendant amine group effectively acts as a proton relay, facilitating the protonation of O$_{2}$ to OOH on the Co-N$_{4}$ active site.
• The catalyst selectively promotes the 2e$^{-}$ pathway of the ORR, leading to H$_{2}$O$_{2}$ production.
• Achieved an optimal H$_{2}$O$_{2}$ selectivity of 97% ± 1.13%, a 3.46-fold enhancement compared to the bare Co-N$_{4}$ catalyst (28% ± 1.75%).

Conclusions:

• The developed enzyme-mimetic catalyst demonstrates a highly effective strategy for tailoring catalytic activity and selectivity.
• This approach bridges the gap between enzymatic and heterogeneous catalysis, offering a new avenue for catalyst design.
• The functionalized second sphere is crucial for enhancing proton transfer and directing the ORR pathway for efficient H$_{2}$O$_{2}$ synthesis.