Microalgae-Based Hybrid Biophotoelectrode for Efficient Light Energy Conversion.

Photosynthetic microorganisms are promising candidates for sustainable energy production in photobio-electrochemical systems. However, integrating them with electrodes is challenging due to the compartmentalized nature of photosynthetic organelles. Microalgae, in particular, have a more complex cell structure than cyanobacteria, leading to low electron transfer rates and compromising electrochemical communication. In this study, we propose a hybrid biophotoelectrode that integrates intact microalgae cells with a WO₃ semiconductor electrode using polydopamine for cell entrapment and charge transfer enhancement. The biophotoelectrode delivers photocurrents of up to 24 μA cm^-2 under visible light illumination with an incident light power below 6.0 mW cm^-2. The photoelectrode performance and the origin of electron flow are investigated, confirming a substantial contribution of immobilized microalgae to the overall photocurrent. We present a proof-of-concept application of the microalgae-based hybrid electrode in combination with a formate dehydrogenase biocathode for the implementation of a biophoto-electrochemical cell for the conversion of CO₂ to formate assisted by light. The system demonstrates the potential for coupling photosynthetic processes with bioelectrochemical conversion, achieving efficient and sustainable production of value-added chemicals. These findings advance our understanding of photosynthetic cell-electrode interactions in hybrid systems, offering insights for developing photobio-electrochemical devices and innovative conversion strategies for waste products.