Volcano plots in hydrogen electrocatalysis - uses and abuses

Area of Science:

• Surface Science
• Catalysis
• Physical Chemistry

Background:

• Sabatier's principle predicts a volcano-shaped relationship between rate constants and hydrogen adsorption energy for hydrogen evolution.
• Existing literature often presents such volcano plots, but a critical re-evaluation is needed.
• The role of oxide-covered metals in these plots requires careful consideration.

Purpose of the Study:

• To critically examine the validity of Sabatier's principle for hydrogen evolution reactions.
• To investigate the factors governing reaction rates beyond simple hydrogen adsorption energy.
• To propose an alternative theoretical framework for understanding catalytic activity.

Main Methods:

• Re-analysis of existing experimental data on hydrogen evolution rates and adsorption energies.
• Theoretical examination of reaction mechanisms and intermediate states.
• Focus on non-oxide covered metal catalysts.

Main Results:

• A universal volcano plot is not observed when oxide-covered metals are excluded from the analysis.
• Sabatier's principle is only one of several factors influencing the reaction rate.
• For many metals, the reaction rate does not decrease with highly exothermic hydrogen adsorption due to favorable intermediate states, with notable exceptions like nickel and cobalt.

Conclusions:

• The applicability of Sabatier's principle is limited and requires consideration of other mechanistic factors.
• Nickel's poor catalytic performance is attributed to compact 3d orbitals leading to low hydrogen overlap.
• A more comprehensive understanding of catalytic activity necessitates evaluating multiple reaction parameters.