In order to investigate the synergetic effects of biochar structure and AAEM species on the reactivity of biochar, the H2O activation of the cyclone air-gasified rice husk biochar was studied in the one-stage fluidized bed/fixed bed reactor. The details in the transformation of biochar structures and the properties of AAEM species were analyzed by FTIR, Raman and ICP-AES, respectively. The specific reactivity of biochar was determined in a ther-mogravimetric analyzer. The results indicated that those most marked synergetic effects of biochar structure and AAEM species on the H2O-activated reactivity of biochar were observed in the temperature range from 750 degrees C to 850 degrees C. During the H2O-activation reaction, the biochar reactivity would be improved due to the increase of surface oxygen containing functional groups (i.e., R-OH and -COO) and small aromatic ring structures in biochar catalyzed by the AAEM species. The improvement in the reactivity of air-gasified biochar by the H2O-activation is mainly in the initial carbon conversion (<15%) at 800 degrees C. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.