Full runner electrolyzer stack for industrial-current-density NO_x⁻-mediated ammonia synthesis from air and water

Plasma-electrochemical tandem conversion with NO_x⁻ as intermediates promises a route for renewable ammonia (NH₃) synthesis from air and water. However, a critical challenge lies in developing electrolyzers capable of operating efficiently at large current densities. Here, we present a scalable membrane electrode assembly electrolyzer with a full runner design (MEA-FR) that achieves efficient NH₃ production at industrial current densities. Compared to conventional serpentine runner configuration, MEA-FR leveraging forced convection within porous electrodes achieves three-order-of-magnitude enhancement in NO_x⁻ mass transfer flux. This design, meanwhile, generates strong shear forces across the porous electrode, promoting rapid detachment of O₂ bubbles at the anode and reducing overpotential losses. Notably, MEA-FR exhibits a high Faradaic efficiency of 91.8 ± 1.4% for NH₃ synthesis at 500 mA cm⁻², significantly outperforming the serpentine runner counterparts (64.9 ± 1.1%). Furthermore, a scaled-up 4 × 25 cm² MEA-FR stack with four modular cells is assembled with rotationally symmetric bipolar plates, delivering high NO_x⁻ conversion efficiency (>95%), high Faradaic efficiency (>91%), and long-term stability (>200 h) under industrial-relevant current densities.