Polypyrrole‐Coated Hierarchical 3D Printed Graphene Electrodes for Reusable High‐Performance Biophotovoltaic System

Biophotovoltaic (BPV) systems use living photosynthetic organisms to generate electricity from sunlight, offering a clean and renewable energy source. Despite notable advances, further development toward practical applications remains limited by low current and power densities and insufficient system reusability. Here we report a hierarchical reduced graphene oxide (rGO) lattice electrode that was 3D printed and coated with polypyrrole (PPy) to serve as the BPV anode. The lattice geometry offers tunable porosity and high surface area to maximize BPV performance. PPy was electropolymerized onto the rGO framework via cyclic voltammetry, with the number of cycles optimized to achieve adequate PPy coverage, favorable cyanobacterial adhesion, and maximal photocurrent generation. The structural characteristics of the 3D printed lattice, particularly the number of voids, significantly influenced the photoresponse by modulating light penetration and mediator diffusion pathways. Two different BPV designs were tested using biofilm‐coated electrodes and a suspension‐based setup. The suspension‐based BPV delivered a peak power density of 40 μW cm −2 at 235 μA cm −2 . In a mediator‐free operation, we measured up to 300 μA cm −2 at a cyanobacterial loading of 25 μg mL −1 chlorophyll a, and the reusability of the 3D PPy/rGO electrode was also demonstrated for seven consecutive days.