Impact of electrode modifications on electrochemical ammonia stripping across activated carbon membrane electrodes

초록

Electrochemical ammonia stripping (electrochemically converting aqueous NH4+ to gaseous NH3) enables ammonia recovery with high selectivity from complex solutions. Although the membrane electrode (with a zero-gap between the electrode and membrane layers) can significantly improve ammonia recovery fluxes by reducing cathodic losses and physical distances, the impact of the electrode characteristics on determining ammonia recovery remains unclear. In this study, nickel-functionalized activated carbon (Ni/AC) membrane electrodes were evaluated by varying electrode thickness (as well as electrode loadings) and chemical properties (by oxidizing the electrode surface and blending conductive additives) to understand the impacts of physicochemical modifications of the electrode on ammonia recovery. The reduced electrode thickness (from 760 µm to 470 µm) demonstrated 42–69% improved ammonia recovery with 28–36% lower energy consumption, attributing to both improved electrochemical activities (reduced ohmic and charge transfer resistances) and the reduced physical distance. Electrode surface oxidation (by acid treatment) and carbon black (CB) blending both enhanced the ammonia recovery fluxes up to 97.9 ± 8.8 gNH₃-N/m²/day under high current densities, while no significant improvements were observed under moderate current densities. More oxygen functional groups (by acid treatment) and improved electrochemical conductivity (by CB blending) improved the electrochemical activities of the Ni/AC membrane electrode, which resulted in enhanced ammonia recovery performance. Overall, these results highlight that managing electrode thickness provides a critical architectural baseline for optimizing electrochemical stripping systems, while surface modifications offer vital complementary enhancements under high-current operating regimes.

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