It can be seen in Figure (a) that H2 yield during MgH2 hydrolysis in deionised water (curve labelled as "H2O") is very low, amounting 1.5 and 3% after 5 and 10 minutes, respectively, from the reaction start. The H2 yield significantly increases when introducing organic acids ("AA", "CA", "OA"), even if their concentration is as low as 1 wt.% (Figure (a)). The increase of acid concentration to 2 wt.% (Figure (b)) and further to 3 wt.% (Figure (c)) results in the significant increase of the maximum H2 yield which exceeds 60 and 90%, respectively. The effects of different organic acids on the maximum H2 yield are rather close, with slightly higher yield for the acetic acid. The maximum H2 yield increases approximately linearly with the increase of the acid concentration (in wt. %), or Acid/MgH2 weight ratio, approaching 100% when the concentration is equal to or above 3 wt.%, or the weight ratio Acid/MgH2 ≥ 6 (Figure ). When considering Acid/MgH2 molar ratio (or acid molar concentration) (Figure (a)), the corresponding dependencies become different when the H2 yield increases slower for the acids which have lower molecular weight (Table ). For the latter ("OA" and "AA"), the increase of the H2 yield with the increase of the molar ratio / acid concentration becomes nonlinear slowing down when the molar ratio / concentration increases. The 100% hydrogen yield can be achieved at the Acid/MgH2 molar ratio of 0.9, 2.0 and 2.7 for the citric, oxalic and acetic acid, respectively.