Liquid-Recirculation-Assisted Anion exchange membrane ammonia Electrolysis: Simultaneous Closed-Loop NH3 recovery and improved H2 purity

Ammonia (NH 3 ) as a hydrogen carrier is limited by the energy-intensive reconversion to high-purity hydrogen at the point of use. Anion exchange membrane (AEM) ammonia electrolysis offers a low-voltage, low-temperature alternative, but unreacted ammonia is emitted at the anode and crosses over to the cathode, degrading both efficiency and hydrogen purity. Here, two alternative recovery units—a pressurized tank and a wet scrubber—were independently integrated with an AEM electrolysis cell. With the pressurized tank, increasing the anode-side pressure from 1 to 10 bar reduced the outlet NH 3 concentration from 3.64 to 0.65 vol% (82.1 %) but increased the cell-electrical specific energy consumption (SEC) from 55.78 to 69.62 k ⁢ W ⁢ h ⁡ / k ⁢ g H 2 (24.8 %). At the matched 240 mA/cm 2 condition, the atmospheric-pressure wet scrubber reduced outlet NH 3 to approximately 0.475 vol% (87.0 %) with an SEC of 55.4 k ⁢ W ⁢ h ⁡ / k ⁢ g H 2 and maintained the outlet concentration at or below 0.50 vol% across the tested current range. The NH 3 -loaded solution was reused once as the anolyte with a 3.7 % increase in SEC at the matched current density, supporting proof-of-concept closed-loop reuse. A pH-dependent emission model indicated that NH 3 re-volatilization is strongly suppressed when the scrubbing-medium pH is around 6. Furthermore, a pressure-sensitivity analysis indicated that operation without a trans -membrane pressure differential avoids an additional pressure-driven NH 3 crossover, while the measured dry-gas composition corresponded to a bulk H 2 purity of 98.1–98.5 %. These results establish the wet scrubber as the simpler and more energy-efficient route for integrating NH 3 emission control, recirculation, and cathodic H 2 -purity improvement in modular or on-site ammonia-to-hydrogen systems.