Electricity-powered artificial root nodule.

Root nodules are agricultural-important symbiotic plant-microbe composites in which microorganisms receive energy from plants and reduce dinitrogen (N) into fertilizers. Mimicking root nodules using artificial devices can enable renewable energy-driven fertilizer production. This task is challenging due to the necessity of a microscopic dioxygen (O) concentration gradient, which reconciles anaerobic N fixation with O-rich atmosphere. Here we report our designed electricity-powered biological|inorganic hybrid system that possesses the function of root nodules. We construct silicon-based microwire array electrodes and replicate the O gradient of root nodules in the array. The wire array compatibly accommodates N-fixing symbiotic bacteria, which receive energy and reducing equivalents from inorganic catalysts on microwires, and fix N in the air into biomass and free ammonia. A N reduction rate up to 6.5 mg N per gram dry biomass per hour is observed in the device, about two orders of magnitude higher than the natural counterparts.