Ionic liquid-activated carbon composite materials for efficient ammonia removal from hydrogen: Experimental and molecular simulation studies

IL modified activated carbon adsorbents were prepared for trace NH 3 removal from H 2 . • 20%[Bmim]BF 4 /AC showed the best NH 3 adsorption. • The purified H 2 meets fuel cell standard with NH 3 below 0.1 μmol·mol –1 . • Anions adsorb electrostatically and cations synergistically capture NH 3 via H-bonds. • Small BF 4 – disperses fully in pores and outperforms larger anions in adsorption. Ammonia residue in hydrogen fuel significantly affects the durability of proton exchange membranes in fuel cells. To address the challenge of removing trace ammonia from hydrogen produced by ammonia decomposition, a series of activated carbon (AC)-based adsorbents modified with ionic liquids (ILs) were prepared. Based on the evaluation under a 200 mg·m –3 NH 3 /H 2 atmosphere, the 20%[Bmim]BF 4 /AC exhibited the best ammonia adsorption capacity. The ammonia concentration in purified H 2 can be reduced to below 0.1 μmol·mol –1 (0.0695 mg·m –3 ), which meets the fuel cell application standards. N 2 adsorption–desorption, scanning electron microscope and energy dispersive spectroscopy confirm that the ILs dispersed uniformly on AC, though they significantly reduced the specific surface area and pore volume of the support. Fourier transform infrared spectroscopy analysis combined with molecular simulations further clarified the adsorption mechanism, highlighting that the anions of ILs provide negatively charged regions for electrostatic adsorption of NH 3 , while the hydrogen atoms on the imidazole ring of cations form hydrogen bonds with NH 3 , synergistically enhancing ammonia adsorption. The theoretical NH 3 affinity order of pure ILs conflicts with experimental adsorption capacities, which is explained by anion size: small BF 4 – achieves full pore dispersion and high active site utilization, whereas larger anions block pore openings. Pore blockage ratio analysis confirms that well-distributed IL within pores dominates adsorption performance. Download: Download high-res image (109KB) Download: Download full-size image