Een holistische en gestructureerde ontwerpstrategie voor schaalbare en energie-efficiënte foto(electro)chemische reactoren

In the context of the escalating climate crisis, developing sustainable technologies to reduce industrial greenhouse gas emissions has become a scientific and moral obligation. According to the latest reports from the European Environment Agency, Europe emitted 2908 megatons of CO₂-equivalents in 2023. Offsetting this amount would require planting an additional 60 to 291 million hectares of forest, what is simply unfeasible given Europe's land constraints. The chemical industry is a major contributor to these emissions and urgently requires innovative, energy-efficient solutions. Photo(electro)chemical reactors offer a promising pathway, as they mimic natural photosynthesis to convert light energy into stable, energy-dense compounds, enabling the sustainable valorisation of captured CO₂ and biomass. Despite their potential, photoreactors remain largely absent at industrial scale due to limitations in efficiency, scalability, and cost. At the heart of this challenge lies a mismatch in the transport of photons, charge carriers, and molecules, which ultimately limits the technology's efficiency. Conventional strategies have attempted to improve these transport phenomena, primarily through materials engineering. However, such targeted interventions often produce trade-offs that inadvertently exacerbate other limitations. For example, increasing catalyst layer thickness may improve light absorption but hinders charge transport and static mixing elements enhance external mass transfer at the expense of high pressure drops. Moreover, solutions that perform well at laboratory scale often fall short in scalability and cost-effectiveness. These interdependencies call for a holistic integrated design methodology that simultaneously addresses all relevant transport limitations while ensuring scalability and economic viability. Achieving this requires a multidisciplinary perspective, as conventional material engineering approaches alone fall short. This doctoral thesis presents such an approach, i.e. a novel geometry-driven design strategy for photo(electro)chemical (PEC) reactors, whereby intelligent structuring is used to synergistically enhance light management, charge separation, and mass transport. This hypothesis was explored through a proof-of-concept study employing repetitive, translucent photocatalyst layers. These structures are designed to improve internal transport by enhancing light penetration, reducing charge diffusion distances, and increasing active surface area. Optical characterisation and PEC performance measurements reveal that the stacking of nanometre-thin layers leads to a 7.5-fold improvement in performance, while using 2.5 times less catalyst compared to a single thick-layer configuration. These results validate the premise that internal transport can be optimised by geometric design, without modifying the catalyst material. Building upon this, the repetitive translucent photocatalyst layer reactor performance was evaluated for the continuous-flow PEC upcycling of benzyl alcohol to benzaldehyde. The analysis revealed that the recombination of charge carriers remained a dominant bottleneck in thick single layer systems, while photon and internal mass transport were not limiting. The multilayer thin-film geometry effectively mitigated this bottleneck while maintaining excellent light absorption properties, resulting in a 2.8-fold increase in reaction rate compared to a conventional single thick-layer design. However, external mass transfer limitations persisted, even at increased flow rates. This underscores the need for reactor geometries that also facilitate convective transport. To improve the external mass transfer, transparent 3D-printed gyroid structures were introduced for the first time in photoreactors. A variety of gyroid configurations were fabricated using stereolithographic 3D printing with optically clear resins. Their performance was assessed via a benchmark photochemical reaction, i.e. singlet oxygen-mediated degradation of diphenyl anthracene, supported by hydrodynamic and optical simulations. The results were striking since the reactors demonstrated plug-flow behaviour and an optimal balance between light and mass transport. The most effective designs achieved energy efficiencies up to two orders of magnitude higher than most systems in current literature, while maintaining competitive space-time yields. This highlights the potential of gyroid-based reactors as a new class of scalable, energy-efficient, and manufacturable photochemical devices. In conclusion, this PhD thesis delivers a comprehensive and practical response to one of the main barriers in photo(electro)chemical reactor engineering, i.e., how to overcome all major transport limitations without sacrificing cost or scalability. By introducing a holistic, geometry-based design concept, this work provides a blueprint for the next generation of photo(electro)chemical reactors that are not only scientifically innovative, but also industrially viable.