Emulsion-based electrolytes for sustainable electrocatalytic synthesis and efficient product recovery in zero-gap electrolyzers

Electrochemical hydrogenation in zero-gap cells has emerged as a promising, sustainable, and scalable route to produce fine chemicals. However, the poor aqueous solubility of many organic substrates in water typically necessitates the employment of volatile organic compound catholytes, raising environmental and health concerns, and complicating downstream product recovery. Together, these aspects may impede the technical implementation of organic synthesis based on zero-gap electrolysis. In this work, we introduce a strategy that combines aqueous emulsions with zero-gap electrolyzers, eliminating volatile organic compounds and simplifying downstream processing. The two-phase system allows for substrate separation from the catholyte under mild centrifugal forces, demonstrating the potential for technically robust, continuous separation using established industrial methods such as static or decanter-based systems. We use the hydrogenation of phenylacetylene to styrene and ethylbenzene as a model reaction that is particularly challenging because of the apolar nature of phenylacetylene and show that surfactant selection and the emulsification process critically influence emulsion stability and overall conversion. Significantly, we highlight that zero-gap electrolyzer-based synthesis can be conducted with emulsions. By combining the scalability of proton exchange membrane zero-gap electrolyzers with the simplified downstream processing of emulsions, we make a promising first step toward more scalable and sustainable electrocatalytic synthesis.