Superior carbon belts from Spirogyra were explored for highly efficient extracellular electron transfer and microbial energy harvesting.

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Summary Microbial electrocatalysis showed great potential for waste energy harvesting and CO2 upgrading. The conventional electrodes with three‐dimensional (3D) architectures hold promise for efficient microbial electrocatalysis, but they were designed as macroporous structure with microfibers in all three dimensions, which could not concurrently improve the mass transfer and microbes penetration. In this study, a high‐performance 3D electrode assembled from bulk two‐dimensional (2D) structures derived from natural wood was fabricated by hydrothermal treatment for surface activation and followed by pyrolysis. This 2D/3D hybrid structure guaranteed high surface area and multi‐transportation‐pathways, which endowed the wood electrode attracted more bacterial cells, facilitated the interfacial electron transfer between cells and electrode. As a result, the wood electrode delivered 8.3 times higher power output (483 vs 52 mW/m2) and 3.1 times higher formic acid production (3.3 vs 0.8 mM) than conventional carbon cloth electrode in microbial electrocatalysis system. This work provided new strategy for high‐performance wood electrode fabrication and unveiled the mechanism of microbial electrocatalysis with natural biomass electrode.