Moisture‐Enabled Germination of Heat‐Activated Bacillus Endospores for Rapid and Practical Bioelectricity Generation: Toward Portable, Storable Bacteria‐Powered Biobatteries

Abstract Small‐scale battery‐like microbial fuel cells (MFCs) are a promising alternative power source for future low‐power electronics. Controllable microbial electrocatalytic activity in a miniaturized MFC with unlimited biodegradable energy resources would enable simple power generation in various environmental settings. However, the short shelf‐life of living biocatalysts, few ways to activate the stored biocatalysts, and extremely low electrocatalytic capabilities render the miniature MFCs unsuitable for practical use. Here, heat‐activated Bacillus subtilis spores are revolutionarily used as a dormant biocatalyst that can survive storage and rapidly germinate when exposed to special nutrients that are preloaded in the device. A microporous, graphene hydrogel allows the adsorption of moisture from the air, moves the nutrients to the spores, and triggers their germination for power generation. In particular, forming a CuO–hydrogel anode and an Ag 2 O–hydrogel cathode promotes superior electrocatalytic activities leading to an exceptionally high electrical performance in the MFC. The battery‐type MFC device is readily activated by moisture harvesting, producing a maximum power density of 0.4 mW cm −2 and a maximum current density of 2.2 mA cm −2 . The MFC configuration is readily stackable in series and a three‐MFC pack produces enough power for several low‐power applications, demonstrating its practical feasibility as a sole power source.