Large oriented electric fields spontaneously arise at all solid-liquid interfaces via the exchange of ions and/or electrons with the solution. Although intrinsic electric fields are known to play an important role in molecular and biological catalysis, the role of spontaneous polarization in heterogeneous thermocatalysis remains unclear because the catalysts employed are typically disconnected from an external circuit, which makes it difficult to monitor or control the degree of electrical polarization of the surface. Here, we address this knowledge gap by developing methods to monitor and control spontaneous electrical polarization at conductive catalysts dispersed in liquid media. We present electrochemical and spectroscopic measurements demonstrating that proton and electron transfer from solution controllably, spontaneously, and wirelessly polarize Pt surfaces during thermochemical catalysis. We observe that the rate of liquid-phase olefin hydrogenation is significantly influenced by spontaneous electric fields generated by both interfacial proton transfer in water and interfacial electron transfer from organometallic redox buffers in a polar aprotic solvent. We combine mechanistic experiments with transition state theory to elucidate the rigorous thermodynamic origin of this electrostatic phenomenology, and conclude that <i>E<sub>OCP</sub></i>—a previously overlooked parameter in heterogeneous catalysis—warrants consideration in mechanistic studies of thermochemical reactions at solid-liquid interfaces, alongside chemical factors such as temperature, reactant activities, and catalyst structure. Indeed, this work highlights the value of applying electrochemical concepts to understanding liquid-phase thermochemical catalysis.

Spontaneous electric fields play a key role in thermochemical catalysis at metal-liquid interfaces

ACS Fall 2021

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