Full runner electrolyzer stack for industrial-current-density NOx−-mediated ammonia synthesis from air and water
Wei Liu, Yang Lv, Honghui Ou, Jiayi Zhang, Yumei Ren, Mengyang Xia, Yang Li, He Li, Xiaoling Ren, Huagui Hu, Guidong Yang
Abstract
Plasma-electrochemical tandem conversion with NOx− 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 NOx− 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 NOx− conversion efficiency (>95%), high Faradaic efficiency (>91%), and long-term stability (>200 h) under industrial-relevant current densities. Electrolyzers operating efficiently at industrial current densities offer promise but face challenges for practical NOx− -to-ammonia conversion. Here, the authors report a full runner electrolyzer stack that enhances mass transfer in porous electrodes for NOx− reduction at high current densities.