Programming Hydrogen Production via Controllable Emulsification/Demulsification in a Switchable Oil–Water System

Compositing stimuli-responsive polymers or microgels can provide material systems with the unique capability of being programmable under specific external signals. Herein we show that by using CO2-responsive microgels as carriers of metal nanocatalysts and stabilizers to disperse the immiscible liquid organic hydrogen carriers (LOHCs), organosilanes in water coreagents, we can achieve a programmable generation of hydrogen for safe and portable applications of hydrogen fuels. The solubility of the tertiary amine-based microgel particles in water can be switched through CO2 bubbling or vacuuming, allowing a controllable demulsification or emulsification of the LOHCs/water system. Microcompartments consisting of a porous microgel shell with nano catalysts and organosilane droplets can be broken and created on demand, resulting in a change of the oil/water interfacial area of over 3 orders of magnitude and a hydrogen generation rate increase of about 20-fold by forming the microcompartments. In addition, it was demonstrated that successive breaking/creating of the microcompartments can minimize the effect of the inevitable ripening and coalescence of oil droplets in the emulsion, providing a 3-fold increase in reaction rate. The microgels/nanocatalysts also show good stability and durability in repeated runs of the hydrogen generation. It is possible that controllably creating/breaking of the microcompartments containing smart microgels or polymer shells could become an important strategy to power up programmable or intelligent systems in the future.