Nickel-Based\nMembrane Electrodes Enable High-Rate\nElectrochemical Ammonia Recovery

Wastewater\ncontains significant amounts of nitrogen that can be\nrecovered and valorized as fertilizers and chemicals. This study presents\na new membrane electrode coupled with microbial electrolysis that\ndemonstrates very efficient ammonia recovery from synthetic centrate.\nThe process utilizes the electrical potential across electrodes to\ndrive NH₄⁺ ions toward the hydrophilic nickel\ntop layer on a gas-stripping membrane cathode, which takes advantage\nof surface pH increase to realize spontaneous NH₃ production\nand separation. Compared with a control configuration with conventionally\nseparated electrode and hydrophobic membrane, the integrated membrane\nelectrode showed 40% higher NH₃–N recovery rate\n(36.2 ± 1.2 gNH₃–N/m²/d) and 11%\nhigher current density. The energy consumption was 1.61 ± 0.03\nkWh/kgNH₃–N, which was 20% lower than the control\nand 70–90% more efficient than competing electrochemical nitrogen\nrecovery processes (5–12 kWh/kgNH₃–N). Besides,\nthe negative potential on membrane electrode repelled negatively charged\norganics and microbes thus reduced fouling. In addition to describing\nthe system’s performance, we explored the underlying mechanisms\ngoverning the reactions, which confirmed the viability of this process\nfor efficient wastewater–ammonia recovery. Furthermore, the\nnickel-based membrane electrode showed excellent water entry pressure\n(∼41 kPa) without leakage, which was much higher than that\nof PTFE/PDMS-based cathodes (∼1.8 kPa). The membrane electrode\nalso showed superb flexibility (180° bend) and can be easily\nfabricated at low cost (<20 $/m²).