The effect of cobalt-based catalysts, i.e. CoCl(2)(20 wt% Co)/Al(2)O(3) treated by different acids, on NaBH(4) hydrolysis was investigated. Five acids were used: oxalic acid, citric acid, acetic acid, sulfuric acid and hydrochloric acid. Two ways of acid treatment were considered: (i) ex-situ addition of acid to COCl(2)(20 wt% Co)/Al(2)O(3) at room temperature and (ii) in-situ addition by mixing COCl(2), Al(2)O(3) and acid (one-step process). Both ways showed that adding an acid to the catalyst contributed to an important increase of the catalytic activity towards the NaBH(4) hydrolysis. The best performances were obtained with the catalysts treated with either HCl or CH(3)COOH as the global activity of COCl(2)(20 wt% Co)/Al(2)O(3) was increased up to 50%. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.