Disentangling the Janus-faced effects of cations in electrocatalysis

Area of Science:

• Electrochemistry
• Surface Science
• Physical Chemistry

Background:

• Cation identity and concentration significantly impact electrocatalytic processes.
• Current understanding often oversimplifies cation roles as solely promotional or inhibitory.
• The hydrogen evolution reaction (HER) in alkaline media serves as a model system to investigate these complexities.

Purpose of the Study:

• To elucidate the mechanistic basis for the dual (promoter-inhibitor) effects of cations in electrocatalysis.
• To identify the key factors governing cation-induced transitions in electrocatalytic activity.
• To develop a theoretical framework explaining cation behavior at electrode-solution interfaces.

Main Methods:

• Investigated the hydrogen evolution reaction (HER) in alkaline media.
• Developed a theoretical model incorporating cation position within the electric double layer.
• Analyzed the influence of cation size and adsorption strength on electrocatalytic kinetics.

Main Results:

• Observed that cation concentration can either promote or inhibit HER activity, depending on cation identity, electrode material, and pH.
• Proposed that cation position (diffuse layer vs. inner Helmholtz plane) dictates their influence on the local electric field and reaction kinetics.
• Demonstrated that the competition between these two cation states explains activity inversions.

Conclusions:

• Cation position in the electric double layer is the critical determinant of their promoter-inhibitor behavior in electrocatalysis.
• The developed mechanistic rationale accounts for the observed Janus-faced effects of cations.
• The framework is applicable to other electrocatalytic reactions on negatively charged surfaces, including CO2 reduction.