Are redox catalytic reaction rates accelerated in microdroplets on electrode surfaces?

TL;DR

This study investigates whether redox reactions in microdroplets on electrode surfaces are faster and finds no evidence of such acceleration.

Contribution

The paper challenges the assumption of reaction rate acceleration in microdroplets by providing a detailed numerical and experimental analysis.

Findings

Redox catalytic reactions in microdroplets on electrode surfaces do not show accelerated rates.

The triple phase boundary dynamics significantly affect reaction environments but do not enhance reaction rates.

Simulation and experimental data suggest a need to re-examine assumptions about microdroplet-induced acceleration.

Abstract

Homogeneous redox catalysis within electrochemically supported microdroplets immobilised on an electrode surface and bathed by an immiscible electrolyte solution is characterised using finite difference numerical methods, after conformal transformation of the physical problem. This is shown to be a challenging environment to simulate and model, not least due to the confinement of the heterogeneous electron transfer to the droplet/support/electrolyte boundary, and hence leading to acute convergent/divergent diffusion regimes. Reactivity at the triple phase boundary underpins both the spatial and temporal non-uniformity of the reacting droplet environment. Crucially, through comparison with experimental data reported in the literature, it is demonstrated that there is no droplet-induced acceleration of the redox catalytic reaction. Reasons for this discrepancy with literature are suggested. It is recommended that any inference of reaction rate acceleration through increased rate constants in microdroplets on surfaces be re-examined, lest the multi-dimensional dynamics at the three-phase boundary are unaccounted.

The online version contains supplementary material available at 10.1007/s10008-025-06283-4.

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