LAUSR

Root nodules are agricultural-important symbiotic plant-microbe composites in which microorganisms receive energy from plants and reduce dinitrogen (N 2 ) 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 2 ) concentration gradient, which reconciles anaerobic N 2 fixation with O 2 -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 2 gradient of root nodules in the array. The wire array compatibly accommodates N 2 -fixing symbiotic bacteria, which receive energy and reducing equivalents from inorganic catalysts on microwires, and fix N 2 in the air into biomass and free ammonia. A N 2 reduction rate up to 6.5 mg N 2 per gram dry biomass per hour is observed in the device, about two orders of magnitude higher than the natural counterparts. Root nodules are of key importance in nitrogen fixation. Here, the authors report on an electrically powered artificial root nodule for nitrogen fixation made from silicon-based microwires which can accommodate nitrogen fixing symbiotic bacteria for fixing nitrogen into biomass and free ammonia.