Polymer-based porous catalytic membranes for controlled hydrogen release from liquid chemical hydrogen carriers

This work investigates polymer-based porous catalytic membranes as structured reaction environments for controlled hydrogen release from liquid chemical hydrogen carriers, i.e. liquid compounds that store hydrogen and release it by chemical reaction. The approach is motivated by the challenge of hydrogen storage, since molecular hydrogen is difficult to store and handle efficiently in its gaseous form, whereas liquid-phase storage concepts offer a safer and potentially more practical alternative for transport and on-demand supply. In such systems, however, hydrogen must be released again in a controlled manner at the point of use, which makes catalytically active reaction environments for regulated gas generation a central requirement. Rather than treating membranes as passive catalyst supports, the thesis examines them as catalytically active porous media whose functional behaviour is governed by the interplay of catalyst accessibility, pore structure, wettability, gas-liquid distribution, and operating mode. A central aim of the study was to develop a broader understanding of the membrane-reactor design space by deliberately varying key system dimensions, including carrier chemistry, catalyst system, membrane fabrication route, and reactor operation mode, in order to identify which structure-transport relationships are general, which are regime-dependent, and how these findings can inform design suggestions and limitations of porous membrane contactor concepts. Ammonia borane was used as a strongly gas-evolving model system to establish the governing relationships between membrane structure, transport, and reactor behaviour. Membranes derived from blending of Nickle nanopowder with different additive formulations were used to investigate these relationships and to carry out the first cross-flow studies of the membrane contactor concept. The results showed that apparent hydrogen-release performance is shaped not only by catalyst presence, but also by how effectively liquid reactant can access active sites and how efficiently product gas can leave the pore network. Building on this framework, an in situ palladium nanoparticle membrane platform was developed to transfer and further assess the concept in cross-flow and subsequently in flow-through operation. Cross-flow experiments showed that directional hydrogen release through the membrane is feasible in principle, but that robust operation requires deliberate control of catalyst placement, wetting behaviour, and resistance against unwanted liquid penetration. Flow-through operation revealed hydrogen release rate and pressure drop across the membrane as coupled feasibility metrics and showed a morphology-dependent trade-off between higher hydrogen output and greater hydraulic robustness. The palladium membrane platform was further transferred to formic acid dehydrogenation under mild aqueous conditions. Although the resulting productivity was not sufficient for practical decentralized application, this part helped define the limitations of the concept in a more chemistry- and stability-sensitive regime. In addition, an excursus toward electrochemical porous-media systems showed that the transport-centred design logic developed here is also relevant for related catalyst-layer architectures in water electrolysis. Overall, the dissertation establishes porous catalytic membranes as reaction-active transport architectures and develops a transferable design-oriented framework for assessing the potential, limitations, and tuneable variables of membrane contactor/reactor concepts for controlled hydrogen release.