Beyond Photosynthesis: H2O/H2O2/O2 Self-Circulation-Based Biohybrid Photoelectrochemical Cells for Direct and Sustainable Solar-to-Fuel-to-Electric Power Conversion

Solar-to-fuel conversion followed by secondary utilization in fuel cells provides an appealing approach to alleviating global energy shortages but is largely restricted by the complex design of power systems and the development of functional catalysts. Herein, we presented a biohybrid photoelectrochemical cell (BPEC) to implement sustainable solar-to-fuel-to-electric power conversion in a single compartment, by ingeniously combining reliable photoelectrochemical H₂O₂ generation with efficient bioelectrochemical H₂O₂ consumption. Specifically, the BPEC is composed of a Mo-modified BiVO₄ (Mo:BiVO₄) photoanode and a horseradish peroxidase (HRP)/pyrene-modified 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (bis-Pyr-ABTS)/carbon nanotubes with an encapsulated Co nanoparticle (Co/CNTs) biocathode. Upon photoexcitation, two-electron H₂O oxidation can be carried out at the Mo-BiVO₄ photoanode to produce H₂O₂, followed by electroenzymatic reduction of H₂O₂ to H₂O by HRP with the help of a bis-Pyr-ABTS redox mediator at the biocathode. Besides, in response to the insufficient Faradaic efficiency of H₂O₂ generation at the photoanode, the functional Co/CNTs catalysts, possessing prominent electrocatalytic selectivity toward two-electron O₂ reduction (electron transfer number = 2.6), are modified on the biocathode, thus clearly defining effective H₂O/H₂O₂/O₂ self-circulation in this device. This developed BPEC obtains an open-circuit potential of 1.03 ± 0.02 V and a maximum power density of 0.18 ± 0.02 mW cm^-2. Moreover, inspired by the particular advantage of enzymatic biofuel cells for easy miniaturization, an enclosed "sandwich-like" BPEC of approximately 1 cm³ size is fabricated and delivers a power output of 0.13 ± 0.03 mW cm^-2. Our work represents a controllable approach for meaningful solar energy utilization, beyond traditional artificial photosynthesis, and can further provide a significant paradigm shift in building an energy-sustainable society.