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The CO₂ adsorption on various Prussian blue analogue hexacyanoferrates was evaluated by thermogravimetric analysis. Compositions of prepared phases were verified by energy-dispersive X-ray spectroscopy, infra-red spectroscopy and powder X-ray diffraction. The influence of different alkali cations in the cubic <i>Fm</i>3<i>m</i> structures was investigated for nominal compositions <i>A</i>_2<i>/</i>3Cu[Fe(CN)₆]_2/3 with <i>A</i> = vacant, Li, Na, K, Rb, Cs. The Rb and Cs compounds show the highest CO₂ adsorption per unit cell, ~3.3 molecules of CO₂ at 20 &#176;C and 1 bar, while in terms of mmol/g the Na compound exhibits the highest adsorption capability, ~3.8 mmol/g at 20 &#176;C and 1 bar. The fastest adsorption/desorption is exhibited by the <i>A</i>-cation free compound and the Li compound. The influence of the amount of Fe(CN)₆ vacancies were assessed by determining the CO₂ adsorption capabilities of Cu[Fe(CN)₆]_1/2 (<i>Fm</i>3<i>m</i> symmetry, nominally 50% vacancies), KCu[Fe(CN)₆]_3/4 (<i>Fm</i>3<i>m</i> symmetry, nominally 25% vacancies), and CsCu[Fe(CN)₆] (<i>I</i>-4<i>m</i>2 symmetry, nominally 0% vacancies). Higher adsorption was, as expected, shown on compounds with higher vacancy concentrations.