This project is completed by Dr. Vitaly Svetovoy at the University of Twente.

In heterogeneous catalysis, gas bubbles forming at the surface of a catalyst block its overall efficiency. Gaseous (nano)bubbles can form spontaneously, but they can also controllably generated by an external applied potential. The electrolytically generated bubbles can have dimensions from nanometers up to many micrometers. Nanobubbles with typical femtoliter volumes have been reported to be stable at the solid-liquid interface for days. On the other hand, electrolytically generated nano- and microbubbles grow with time and eventually detach as a result of buoyancy. Electrochemical control of the catalytic surface enables manipulation of the gas bubbles and therewith allows optimizing the efficiency of the catalytic surface.

In this project, we will investigate the gas evolution under electrolytic conditions, but choose for an alternate (AC) current: then both O2 and H2 will be produced, in stoichiometric mixture. Under certain conditions this knalgas inside the bubble will react, leading to an explosive reaction. It is unclear under what condition this reaction will happen and what triggers it.

The project is closely related to the project “Microscopic study of the initial stages of electrolytic gas production at catalytic surfaces” by Zandvliet et al: There a PhD student will look into electrolytically generated bubbles with DC. Many devices will jointly be used in the postdoc of this student will co-supervise the PhD student of that other project.

Project leader: Prof. Detlef Lohse

In heterogeneous catalysis, gas bubbles forming at the surface of a catalyst block its overall efficiency. Gaseous (nano)bubbles can form spontaneously, but they can also controllably be generated by an external applied potential. The electrolytically generated bubbles can have dimensions from nanometers up to many micrometers. Nanobubbles with volumes in the range of 10² – 10⁸ nm³ have been reported to be stable at the solid-liquid interface for days. On the other hand, electrolytically generated nano- and microbubbles grow with time and eventually detach as a result of buoyancy. Electrochemical control of the catalytic surface enables manipulation of the gas bubbles and therewith allows optimizing the efficiency of the catalytic surface.

In this project, we will investigate the gas evolution under electrolytic conditions, with the primary aim to control the formation of bubbles and their release from a catalytic active surface. Moreover, in addition to the formation, coalescence, growth and detachment, we will also investigate damage induced by the bubbles at the interface. Complementary techniques are used, including optical interference-enhanced reflection microscopy, attenuated infrared spectroscopy and atomic force microscopy, both in the conventional imaging mode but also employing high-speed AFM spectroscopy.

Project leader: Prof. Harold Zandvliet

This project is completed by Dr. Matteo Lulli at the University of Twente.

In heterogeneous catalysis, gas bubbles often form at the catalyst, blocking its efficiency. In their smallest known form the bubbles come as so-called surface nanobubbles. These are only a few femtoliters in volume and can stay at the interface as long as several hours or even days. The formation of surface nanobubbles can not only occur through (catalytic) chemical reactions, but also through electrolysis or when the interface experiences gas super-saturation by the change of the solvent, or of the temperature, or by pressure reduction.

Very similar to surface nanobubbles are surface nanodroplets that are liquid nanoscale domains on the solid surface in contact with an immiscible bulk liquid. Also these are relevant in catalytic reactions that produce an oil phase in an aqueous environment or vice verse.

In this project we want to better understand the properties and dynamics of surface nanobubbles and surface nanodroplets with the help of Lattice Boltzmann simulations in order to capture both the dynamics of single surface nanobubbles and nanodroplets and their collective dynamics (Ostwald ripening).

This project is the Lattice Boltzmann numerical counterpart to the experimental project “Surface nanobubbles and surface nanodroplets” and to the MD/theoretical project “Surface nanobubbles and surface nanobubbles: Theory and numerics for dynamics and collective effects.”

Project leader: Prof. Detlef Lohse

In heterogeneous catalysis, gas bubbles often form at the catalyst surface, hindering its efficiency. In their smallest known form, the bubbles come as so-called surface nanobubbles. These are only a few femtoliters in volume and can stay at the interface as long as several hours or even days. The formation of surface nanobubbles can occur not only through (catalytic) chemical reactions, but also through electrolysis, or when the interface experiences gas super-saturation due to a change of the solvent or in the temperature, or by pressure reduction.

Very similar to surface nanobubbles are surface nanodroplets, which are liquid nanoscale domains on the solid surface in contact with an immiscible bulk liquid. Also these are relevant in catalytic reactions that produce an oil phase in an aqueous environment or vice versa.

In this project we want to experimentally analyze and understand the properties and dynamics of surface nanobubbles and surface nanodroplets, using ultrafast imaging, AFM, and in-situ spectroscopic techniques. On the one hand, we aim to achieve at single nanobubble and single nanodroplet spectroscopy. On the other hand we want to understand collective effects of surface nanobubbles and surface nanodroplets, in particular the Ostwald ripening, which is related to their size distribution, surface coverage, and spatial arrangements.

Project leader: Prof. Detlef Lohse

In heterogeneous catalysis, gas bubbles often form at the catalyst, blocking its efficiency. In their smallest known form the bubbles come as so-called surface nanobubbles. These are only a few femtoliters in volume and can stay at the interface as long as several hours or even days. The formation of surface nanobubbles can not only occur through (catalytic) chemical reactions, but also through electrolysis or when the interface experiences gas super-saturation by the change of the solvent, or of the temperature, or by pressure reduction.

Very similar to surface nanobubbles are surface nanodroplets that are liquid nanoscale domains on the solid surface in contact with an immiscible bulk liquid. Also these are relevant in catalytic reactions that produce an oil phase in an aqueous environment or vice verse.

In this project we want to better understand the properties and dynamics of surface nanobubbles and surface nanodroplets with the help of molecular dynamics (MD) simulations and through developing a theoretical framework which is able to capture both the dynamics of single surface nanobubbles and nanodroplets and their collective dynamics (Ostwald ripening).

This project is the theoretical and numerical counterpart to the experimental project “Surface nanobubbles and surface nanodroplets”.

Project leader: Prof. Detlef Lohse

There is a substantial and increasingly important class of processes where a gaseous reaction product is produced on a catalyst surface in a liquid, like in photoelectrolysis where water is converted into hydrogen gas and oxygen under the influence of light. Wherever a gas bubble forms and covers part of the catalyst surface the reaction is inhibited and therefore it is crucial that these gas bubbles are transported away as fast as possible.

In this project we want to study new ways of transporting gas away from the catalyst surface by (i) controlling the bubble size, (ii) enhancing bubble nucleation and growth and (iii) controlling the fluid flow using bubble detachment and buoyancy.

We will conduct experiments in a unique experimental setup that allows for complete and independent control of pressure and supersaturation level during bubble nucleation, formation, and detachment from a micropatterned surface. More specifically, we will study how isolated bubbles grow in confinement, how they detach, and how much fluid they are able to advect. Next we will turn to how multiple growing bubbles influence each other as a function of their distance. And finally we will address how bubbles nucleate and grow on a photoelectrolytic surface.

Project leader: Prof. Devaraj van der Meer

The catalytic efficiency of metal nanoparticles is strongly influenced by the local environment of the metal nanoparticles. Are the metal nanoparticles accessible from all sides or is there partly a molecular transport barrier to and from the particle? In this project we will investigate the influence of the local metal nanoparticle environment by embedding metal nanoparticles in ceramic materials. Can substrates reach the metal nanoparticles or will they get stuck on the way? Using cleanroom-manufacturing methods, we will synthesize metal nanoparticles at the end of ceramic nanopores down to 5 nm wide, using different metal/ceramic combinations. The catalytic activity of the constructs will then be followed by optical methods. The final aim is to design a nanoscale geometry for optimal efficiency.

Project leader: Prof. Jan Eijkel

Surface nanobubbles are nanoscopic gaseous objects, which are formed mainly on hydrophobic surfaces. Although many catalytic processes taken place at the solid-liquid-gas interface, the implications of surface nanobubbles in the field of heterogeneous catalysis are totally not explored. A prominent example where surface nanobubbles may play a role is the catalytic hydrogenation of biomass-derived chemicals. In this project, we will develop a high-temperature, high-pressure Atomic Force Microscopy (AFM)-Vibrational Spectroscopy set-up to investigate the one pot hydrogenation reaction of levulinic acid into pentanoic acid over Ru/H-ZSM-5. To enable a detailed AFM investigation large coffin-shaped ZSM-5 crystals will be investigated and the presence and properties of the surface nanobubbles will be studied as a function of the surface roughness and Si/Al ratio (i.e., changing surface hydrophilicity). The latter will be realized by applying different post-treatments, while altering the hydrogenation conditions may affect the stability of the formed surface nanobubbles.

Project leader: Prof. Bert Weckhuysen