Beyond Photosynthesis: H 2 O/H 2 O 2 /O 2 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 H 2 O 2 generation with efficient bioelectrochemical H 2 O 2 consumption. Specifically, the BPEC is composed of a Mo-modified BiVO 4 (Mo:BiVO 4 ) 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 H 2 O oxidation can be carried out at the Mo-BiVO 4 photoanode to produce H 2 O 2 , followed by electroenzymatic reduction of H 2 O 2 to H 2 O by HRP with the help of a bis-Pyr-ABTS redox mediator at the biocathode. Besides, in response to the insufficient Faradaic efficiency of H 2 O 2 generation at the photoanode, the functional Co/CNTs catalysts, possessing prominent electrocatalytic selectivity toward two-electron O 2 reduction (electron transfer number = 2.6), are modified on the biocathode, thus clearly defining effective H 2 O/H 2 O 2 /O 2 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 cm 3 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.