PH2OTOGEN’s photoreactor design using multiphysics modelling

In the PH2OTOGEN project, innovation drives our approach to rethinking hydrogen production. A key focus of our work is the development of a cutting-edge photoreactor system that efficiently combines sunlight and organic molecules to produce green hydrogen. Using advanced modelling techniques, our team is addressing complex challenges to ensure the reactor’s success under real-world conditions.

The photoreactor will operate by depositing hydrogen evolving particles (HEP) and oxidising particles (OP) onto transparent porous conductive substrates. These two substrates are arranged in a tandem configuration to form the photocatalyst sheet and exposed to concentrated solar light at irradiances reaching up to 25 suns (25 kW/m²). As the reactor operates, an electrolyte will circulate through the system, carrying dissolved and gaseous products, ensuring a continuous reaction cycle.

Overcoming the challenges of photoreactor design

However, achieving optimal performance with porous photoelectrodes exposed to such highly concentrated solar light comes with unique challenges:

• Light Transfer: The porous substrates’ fibres scatter light, limiting the absorption and transmission of light to the second photoelectrode.
• Heat Management: Concentrated solar light generates significant heat, which could alter the properties of the electrolyte, affect the reaction kinetics, and accelerate the degradation of the photocatalyst materials.
• Fluid Flow Dynamics: The formation of bubbles during gas evolution reactions creates a bubbly (two-phase) flow, complicating the system’s fluid dynamics.
• Charge Transport: The rate of chemical reactions occurring in porous media can be significantly different from those on non-porous surfaces. Hence, this effect must be considered in the model.
• Mass Transport: Ensuring the efficient diffusion of gases and ions is critical to maintaining high reaction rates.

Advanced modelling for precision

To navigate these challenges, PH2OTOGEN is developing a suite of advanced models. A zero-dimensional model is being developed to establish the theoretical efficiency limits by simplifying the system to its core components. This foundational approach is being complemented by a multidimensional multi-physics model that integrates heat, mass, and charge transfer with light transfer and fluid dynamics, offering a comprehensive understanding of the reactor’s behaviour.

The team is also employing a Monte Carlo ray-tracing model to analyse light scattering within the porous photoelectrodes to predict their reflectance, transmittance, and absorptance. This model will also help to pinpoint photon absorption locations, enabling precise optimisation of electron-hole pair generation and their alignment with electrochemical reactions.

Collaboration driving innovation

Collaboration across PH2OTOGEN’s areas of expertise is vital to the success of the photoreactor system. Quantitative data from other project teams feed directly into the modelling and design process, ensuring a holistic approach to innovation. By integrating these insights, the photoreactor is being developed with scalability and long-term sustainability in mind.

As this work progresses, the photoreactor system holds the promise of redefining hydrogen production and contributing significantly to the global shift toward renewable energy.

Sophia Haussener, Associate Professor at EPFL