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This review explores how cobalt-based electrocatalysts control selectivity in the oxygen reduction reaction (ORR). Understanding catalyst structure is key to directing the two-electron (2e-) pathway for hydrogen peroxide production or the four-electron (4e-) pathway for fuel cells.

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Area of Science:

  • Electrochemistry
  • Materials Science
  • Catalysis

Background:

  • The oxygen reduction reaction (ORR) is crucial for energy conversion devices like fuel cells and batteries.
  • ORR can proceed via two distinct pathways: a two-electron (2e-) pathway producing hydrogen peroxide (H2O2) or a four-electron (4e-) pathway producing water (H2O).
  • Controlling the selectivity of these pathways is essential for practical applications.

Purpose of the Study:

  • To review the structure-selectivity relationships of cobalt-based electrocatalysts for the ORR.
  • To provide insights into rationally designing catalysts for specific ORR pathways (2e- or 4e-).
  • To summarize current understanding and suggest future research directions in ORR electrocatalysis.

Main Methods:

  • Review and discussion of existing literature on cobalt-based electrocatalysts for ORR.
  • Analysis of reaction mechanisms and selectivity evaluation methods for ORR.
  • Focus on cobalt porphyrins as model systems for structure-selectivity studies.

Main Results:

  • Cobalt-based electrocatalysts can be engineered for high selectivity towards either the 2e- or 4e- ORR pathway.
  • Specific structural features of cobalt catalysts significantly influence ORR selectivity.
  • Cobalt porphyrins serve as excellent models for elucidating fundamental structure-activity relationships in ORR.

Conclusions:

  • Understanding the structural factors governing ORR selectivity is critical for catalyst design.
  • Cobalt-based catalysts offer a versatile platform for developing selective ORR electrocatalysts.
  • This review provides a foundation for designing advanced molecular and material catalysts for targeted ORR applications.