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The main properties of chars produced from corn stover, either by pyrolysis at 550°C (to produce biochar) or by hydrothermal carbonisation (to produce hydrochar), were studied. Carbonaceous materials were characterised by: SEM imaging, solid-state 13C NMR, FT-IR, Raman spectroscopy, and XPS. The following parameters were determined: elemental composition, cation exchange capacity, acid groups contents, BET, and yield. The hydrochar had a low ash content and low pH (4.7); recovery of C was high (57%), although only about half of the C was aromatic. Atomic O/C and H/C ratios in the hydrochar were higher than in the biochar. The same pattern was observed for the estimated concentration of carboxylic functional groups (0.07 compared with 0.04 mol/kg). The biochar had higher ash content than the hydrochar, and also higher pH (~10) (lime equivalence ~40 kg CaCO3/t). The C recovery (46%) was …