Optimizing the conditions of multi-walled carbon nanotubes surface activation and loading metal nanoparticles for enhanced hydrogen storage Maryam Aghababaei, Ali Asghar Ghoreyshi * , Kourosh Esfandiari Chemical Engineering Department, Babol Noshirvani University of Technology, Shariati Street, Babol, Iran highlights  KOH activation has positive effect on porous structure and H 2 uptake of MWCNTs.  Optimization of MWCNT activation condition results in enhancement of H 2 uptake.  Cobalt and lithium doping could improve H 2 uptake through spillover mechanism.  Decomposition of H 2 molecules to atoms causes better migration to adsorbent cavities.  Lithium doping revealed the ability of this metal to enhance H 2 uptake of MWCNTs. article info Article history: Received 16 March 2020 Received in revised form 19 June 2020 Accepted 21 June 2020 Available online xxx Keywords: Hydrogen storage MWCNT KOH activation Metal doping Spillover abstract In this study, the effect of surface activation of multi-walled carbon nanotubes (MWCNTs) by KOH along with loading of cobalt and lithium nanoparticles on the surface of MWCNTs are investigated. In the first step, surface activation parameters, i.e. MWCNT/KOH weight ratio, activation temperature, and activation time are optimized to give the highest hydrogen uptake. According to obtained results, the optimum synthesis conditions are MWCNT/KOH weight ratio of 1:5, 800  C, and 1 h of activation duration. Afterward, cobalt and lithium metal nanoparticles are doped discretely on the surface of activated nano- tubes. It is demonstrated that amounts of loaded cobalt and lithium metals are 5.5 and 1.9% wt, respectively. In addition, it is revealed that the amount of hydrogen storage ca- pacity for cobalt-loaded and lithium-loaded MWCNTs are 1.06% wt. and 1.33% wt., respectively (at 278 K) which are higher than the capacity of pristine and activated MWCNT samples. © 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Introduction Nowadays, greenhouse gases produced from massive com- bustion of fossil fuels become an environmental concern and hence considerable research efforts have been devoted to alternative sources of fuels to decrease carbon emission to the atmosphere. Among energy sources, hydrogen is a proper alternative to fossil fuels due to its high abundance, low weight, clean combustion, and environmental compatibility. Nevertheless, the low efficiency of hydrogen storage for essential applications is the major challenge to the future development of this clean fuel. In general, researchers are interested in three methods of hydrogen storage: storage at * Corresponding author. E-mail address: aa_ghoreyshi@nit.ac.ir (A.A. Ghoreyshi). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (xxxx) xxx https://doi.org/10.1016/j.ijhydene.2020.06.201 0360-3199/© 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Aghababaei M et al., Optimizing the conditions of multi-walled carbon nanotubes surface activation and loading metal nanoparticles for enhanced hydrogen storage, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2020.06.201