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(597c) Spontaneous Electric Fields Play a Key Role in Thermochemical Catalysis at Metal-Liquid Interfaces

Roman, Y., MIT
Surendranath, Y., Massachusetts Institute of Technology
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 general methods for wirelessly monitoring and controlling spontaneous electrical polarization at conductive catalysts dispersed in liquid media. By combining electrochemical and spectroscopic measurements, we demonstrate that proton and electron transfer from solution controllably, spontaneously, and wirelessly polarize Pt surfaces during thermochemical catalysis. We employ liquid-phase ethylene hydrogenation on a Pt/C catalyst as a thermochemical probe reaction, and observe that the rate of this non-polar hydrogenation reaction 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. Across these vastly disparate reaction media, we observe quantitatively similar scaling of ethylene hydrogenation rates with the Pt open-circuit electrochemical potential (EOCP). These results isolate the role of interfacial electrostatic effects from medium-specific chemical interactions, and establish that spontaneous interfacial electric fields play a critical role in liquid-phase heterogeneous catalysis. We combine mechanistic experiments with transition state theory to elucidate the rigorous thermodynamic origin of this electrostatic phenomenology, and conclude that EOCP—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 thermochemical catalysis at solid|liquid interfaces.