From sunlight to fuels: hybrid PEC–PBEC systems for methanol and methane generation in ALGAESOL Carlos Hurtado 1 , Ana Fleitas 2 , André Martins 2 , Daniele Molognoni 2 , Pau Bosch 2 , Eduard Borràs 2 , Oriol Pérez-De-Gregorio 3 , Miguel González 4 , Daniel Alaustrey 4 , Ainhoa Cots 1 * 1 Sunlight Conversion & Management Area, 2 Bioelectrochemical Systems Area, 3 Photonics & Vision Area, 4 Advanced Engineering Area, *Corresponding author(acots@leitat.org) Leitat Technological Center, c/ de la Innovació 2, Terrassa (Barcelona) SPAIN The ALGAESOL project aims to develop sustainable, solar-driven pathways for converting CO 2 into value-added fuels —primarily methanol and methane— by integrating photoelectrochemical (PEC) and photobioelectrochemical (PBEC) approaches. The project focuses on the scalable development of critical components for both systems ((photo)(bio)electrodes), as well as their subsequent integration into a functional reactor under solar irradiation. The PEC system targets methanol production and is built based on a stable photoanode coupled to a dark cathode. The photoanode has been fabricated through three scalable techniques —screen printing, electrodeposition, and deposition— allowing for flexibility in adaptation to different industrial manufacturers. The metal oxide-based semiconductor is both doped and decorated with non-platinum group metal (non-PGM) co-catalysts, optimizing charge separation and surface kinetics under simulated solar conditions. For the PEC cathode, a spray-coated material has been developed to facilitate abiotic CO 2 reduction to methanol, managing to maintain a current density of 3 mA.cm -2 for over 100 hours. Future work will focus on faradaic efficiency improvements, and selectivity optimization. The PBEC system targets methane production using a dedicated biocathode coupled to the photoanode. The biocathode, hosting a specialized microbial consortium predominantly composed of hydrogenotrophic methanogenic archaea, achieves current densities of 1.2 mA·cm -2 with stable operation over extended periods. The biocathode showed methane production rates of 0.42 ± 0.03 L CH 4 /L/day. Future work will explore methane production by coupling the photoanode to the biocathode. Although the integration of the components into PEC and PBEC systems remains a challenge, significant progress has been made in the conceptual and technical design of the reactor architectures capable of accommodating both technologies (photoanode-cathode and photoanode-biocathode). This includes the co- design of fluidics, light input distribution, and electrochemical interfaces. Additionally, a customized optical solar concentrator system is being developed to enhance light harvesting and ensure optimal energy efficiency under varying sunlight conditions. Together, these developments represent an important step forward in demonstrating the feasibility of hybrid PEC and PBEC systems for distributed fuel production from CO 2 and sunlight. The ongoing work has the potential to combine systems that addresses both, environmental and energy challenges in a circular economy framework.
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