Electric Fields, Not Just Voltage, Steer Catalytic Reactions

Because overpotential can also induce polarization, change intermediate coverage, or restructure the electrode surface, the team needed a test reaction where they could control coverage experimentally while keeping structural transformations minimal. Together with Dr. Francisco Sarabia, they chose CO oxidation on a Pt(111) single-crystal surface.

Doctoral student Caroline Aschendorf adsorbed a known amount of carbon monoxide onto the platinum surface, then oxidatively stripped it at a fixed step potential. This yielded a continuous current-versus-coverage dependence at constant potentials. Repeating the transients across different temperatures and performing electrochemical Arrhenius analysis — both as a function of step potential and of CO coverage — let the researchers extract apparent activation parameters for a Faradaic reaction against two independent control variables.

What does CO coverage reveal?

Sarabia said: "Another unique angle of this study comes from the fact that the coverage can give direct access to the local chemical potentials of the electrons. This way, we can change the degree of interfacial polarization independently from the applied potential and study how it impacts the activation parameters."

Aschendorf explained that different CO binding motifs on Pt(111) rearrange local charge in the chemical bonds, directly affecting the work function and electron chemical potential. Nobel laureate Gerhard Ertl had observed this effect under ultrahigh vacuum; the team wanted to test whether it modulates the electrochemical potential of zero total charge — and the kinetics with it. Measuring that potential across CO coverages, they found a dependence that qualitatively matches Ertl's work function changes.

What did the measurements show?

The two factors pulled in opposite directions:

• Raising the applied potential lowered the apparent activation energy — a stronger driving force helps the reaction proceed.
• Holding the potential constant but widening the gap between it and the potential of zero total charge raised the apparent activation energy.

The researchers found indications that water reorientation in the interfacial double layer drives these changes. Reaction speed, in short, depends not only on how much potential you apply but on how that potential redistributes charge and alters chemical potentials in the surrounding environment, including the double layer.

What changes for the field?

The result gives electrochemists a long-sought link between the potential of zero charge and the kinetics of a Faradaic reaction. More studies are needed to dissect other kinetically relevant effects at the interface, and the team frames its conclusions accordingly. But the method — independent control of potential and field — offers a new way to dissect such interplays in detail.

For practitioners, the practical payoff is design freedom: future catalysts and electrodes could deliberately strengthen or weaken electric fields to tune both activity and selectivity in complex multistep reactions, helping lower the cost of green hydrogen.

Publication: Caroline J. Aschendorf et al., "Disentanglement of interfacial electric fields and electrochemical potential gradients reveals a multidimensional kinetic landscape," Nature Chemistry (2026). DOI: 10.1038/s41557-026-02290-8.

By Marcus Bennett