Forced filling and spontaneous draining of hydrophobic subnanoporous particles embedded in a cellulose-based composite for energy applications

Nanofluidics open new opportunities for water treatments, desalination and energy harvesting but also for energy storage. In the latter application, Heterogeneous Lyophobic Systems (LHS) stand as an original approach for quick storage of mechanical energy at interfaces.

LHS are ultrahydrophobic nanoporous or even sub-nanoporous particles in which a liquid, typically water, or brine, being forced in the pores by intrusion at high pressure (several hundreds of bars), is spontaneously extruded when the pressure drops, therefore releasing energy (see Fig. 1A). LHS are able to sustain large liquid flow rates with limited dissipation over multiple intrusion/extrusion cycles, which in other words, means large power densities.

Until now, LHS have been mainly studied in static regime, moreover, they are prepared as dense suspensions of ultra-hydrophobic nanoporous particles in water, an approach which gives a poor control of inter-particles voids and limits the full exploitation of intrusion/extrusion cycles within intra-particle nanopores. This project aims, on the one hand to initiate a new strategy to optimise the inter-particle structure by means of cellulose-based scaffold and on the other hand to contribute to the physical understanding of liquid transport mechanisms associated to LHS, in order to optimise their power densities.

The first expected breakthrough is the design of an innovative nano-composites made of hydrophobic zeolitic imidazolate framework (ZIF) sub-nanoporous particles (see Fig. 1B and 1C) structured with biosourced cellulose nanocrystals (CNC) (see Fig. 1D). The goal is to achieve mechanically resistant pellets of composite. To address the question of the dynamical behavior of LHS we developed a specific high pressure apparatus which gives the ability to characterise intrusion and extrusion phenomena on four decades of time scale.

The second breakthrough is the characterisation of wetting and dewetting dynamics within the hydrophobic sub-nanopore of ZIF particles trapped in the biosourced composite. Such measurement of transport phenomena in sub-nano confinement will contribute to the emerging field of angströfluidics.