Surfactant-Mediated Interfacial Hydrogen Evolution Reaction

Abstract

Hydrogen is a highly promising clean energy source without greenhouse gas emissions. Liquid organic hydrogen carriers (LOHCs) offer a promising alternative for convenient storage and transportation. This study investigates the interfacial hydrogen evolution reaction between polymethylhydrosiloxane (PMH), a representative LOHC, and water, focusing on controlling reaction kinetics by modifying interfacial properties with surfactants. The hydrogen production rate at a planar interface between PMH and water catalyzed by sodium hydroxide revealed that surfactants such as Tween 20 and sodium dodecyl sulfate (SDS) can slow down the hydrogen formation by 5 to 20 times, possibly due to an overcrowded interface effect. In contrast, cationic surfactants, such as hexadecyltrimethylammonium bromide (CTAB) and other quaternary ammonium surfactants, act as pseudo phase-transfer catalysts and accelerate the hydrogen formation rate up to 3-fold at a concentration of 0.05 times their critical micelle concentration. As the PMH microdroplets were dispersed in the surfactant aqueous solution, the conversion yields of hydrogen with cationic surfactants reached up to 45%, which is significantly higher than the yields achieved with Tween 20 or SDS. The effects of the surfactant type were further confirmed by following hydrogen bubble growth in a single PMH droplet. Overall, our findings demonstrate that selecting an appropriate surfactant can provide an effective control over the interfacial reaction rate of dehydrogenation of LOHCs. This offers strategies for manipulating liquid-liquid interfaces and controlling in-demand hydrogen production.

Keywords: emulsion; hydrogen evolution reaction; phase-transfer catalysis; reacting droplet; surfactant.