Theory

Electrochemical stability window

These are the most important reactions that occur on any electrode in aqeous electrolyte.

The potentials given are the standard redox potentials for the conversion between H2/O2 <-> H2O. Platinum is a really good catalyst for HER/HOR so the onset for both reactions is respectively <0V and >0V but OER/ORR start at a significant overpotential of at least 0.2 V for the best catalysts.

1) Hydrogen evolution reaction (HER) @ <0 V vs. RHE

Acidic:

\[\mathrm{2 H^+ + 2e^-\rightarrow H_2}\]

Alkaline:

\[\mathrm{2 H_2O + 2e^-\rightarrow H_2 + 2 OH^-}\]

2) Hydrogen oxidation reaction (HOR) @ >0 V vs. RHE

What are the reactions for acidic and alkaline conditions?

3) Oxygen evolution reaction (OER) @ >>1.23 V vs. RHE

Acidic:

\[\mathrm{2 H_2O\rightarrow O_2 + 4 H^+ + 4 e^-}\]

Alkaline

\[\mathrm{4 OH^-\rightarrow O_2 + 2 H_2O+ 4 e^-}\]

4) Oxygen reduction reaction (ORR) @ <<1.23 V vs. RHE What are the reactions for acidic and alkaline conditions?

References

Some references that use similar materials (Fe, Co, molecular catalysts) as used in this LO1 class to compare. There is no need to read every paper, they only serve as reference materials.

Tutorial paper about cyclic voltammetry and electrochemistry

A Practical Beginner’s Guide to Cyclic Voltammetry

Reference about pH effect Effects of electrolyte pH on oxygen reduction properties using a cobalt porphyrin-coated carbon composite

References about molecular Fe/Co catalysts on different substrates

1. Electrocatalytic reduction of O2 and H2O2 by adsorbed Cobalt tetramethoxyphenyl porphyrin and its application for fuel cell cathodes

2. Electrocatalytic reduction of dioxygen by cobalt porphyrin-modified glassy carbon electrode with single-walled carbon nanotubes and nafion in aqueous solutions

3. Catalytic activity of cobalt and iron phthalocyanines or porphyrins supported on different carbon nanotubes towards oxygen reduction reaction

4. Metalloporphyrin-modified perovskite-type oxide for the electroreduction of oxygen

5. Electrochemical two-electron O2 reduction reaction toward H2O2 production: using cobalt porphyrin decorated carbon nanotubes as a nanohybrid catalyst

6. Asymmetric cobalt porphyrins for oxygen reduction reactions: Boosted catalytic activity by the use of triphenylamine

7. Effects of support material and electrolyte on a triphenylamine substituted cobalt porphyrin catalytic oxygen reduction reaction

8. Heterogeneous molecular Co–N–C catalysts for efficient electrochemical H2O2 synthesis