A bi-functional cobalt-porphyrinoid electrocatalyst: balance between overpotential and selectivity

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Cobalt porphyrins are known electrocatalysts for oxygen reduction and hydrogen evolution.
• Reducing overpotential in these reactions is crucial for energy applications.

Purpose of the Study:

• To synthesize a cobalt porphyrin with electron-withdrawing groups to lower overpotential for O2 reduction and H2 evolution.
• To investigate the catalytic mechanisms and selectivity of the modified cobalt porphyrin.

Main Methods:

• Synthesis of a cobalt porphyrin featuring two electron-withdrawing groups.
• Electrochemical characterization of the synthesized porphyrin for O2 reduction and H2 evolution.

Main Results:

• Oxygen reduction selectivity shifted to a 2-electron pathway, producing hydrogen peroxide (H2O2) instead of lowering overpotential.
• The Co(I) state was inactive for H+ reduction; catalysis of H2 evolution required reduction of a Co(III)-H species to Co(II)-H.

Conclusions:

• Electron-withdrawing groups can alter the selectivity of cobalt porphyrin-catalyzed oxygen reduction.
• The mechanism of hydrogen evolution by cobalt porphyrins involves specific cobalt-hydride intermediates and oxidation states.