Dynamic Co(II)/Co(III) Cycle Driven by Outer- and Inner-Sphere Electron Transfer for Sustained Peroxymonosulfate...

Area of Science:

• Environmental Chemistry
• Electrochemistry
• Catalysis

Background:

• Transition metal catalysts in peroxymonosulfate (PMS) advanced oxidation processes (AOPs) face challenges due to sluggish M(n+1)+ reduction kinetics.
• This limits the commercialization of homogeneous AOPs.

Purpose of the Study:

• To elucidate a distinct Co(II)/Co(III) cycling mechanism in electrochemically enhanced PMS-AOPs.
• To investigate the role of electrochemical modulation on catalyst regeneration.

Main Methods:

• Utilized Co(II) as a model catalyst in an electrochemical system.
• Analyzed the Co(II)/Co(III) cycling mechanism, predominantly in the anodic region.
• Employed Gibbs free energy calculations to confirm process spontaneity.

Main Results:

• Identified anodic Co(III) generation and its role in disrupting dimerized hydrolysis products.
• Demonstrated outer- and inner-sphere electron transfer pathways for Co(III) reduction.
• Achieved superior yields of Co(IV)=O and sulfate radical (SO4•−) with high Co(II) mass activity.

Conclusions:

• The study presents a novel Co(II)/Co(III) redox cycling mechanism driven by anodic oxidation for sustained PMS activation.
• This mechanism offers a new perspective on transition metal regeneration in homogeneous catalysis for environmental remediation.