Design of Al–Fe alloys for fast on-board hydrogen production from hydrolysis Kwang Sup Eom, ab Jae Young Kwon, ac Min Joong Kim a and Hyuk Sang Kwon * a Received 29th March 2011, Accepted 28th June 2011 DOI: 10.1039/c1jm11329a On-board hydrogen production from the hydrolysis of Al in alkaline water has received great attention because it eliminates the need for hydrogen storage. The Al powder, though providing high reaction rate in the hydrolysis, causes a serious problem of explosive danger when in contact with air or moisture, etc. Since the hydrogen generation rate increases linearly with the corrosion rate of Al to Al 3+ , an Al–Fe alloy, in which an electrochemically noble Al 3 Fe phase precipitates along grain boundaries, is designed, and hence causes fast hydrogen generation from the hydrolysis of Al in alkaline water by combined action of galvanic and intergranular corrosion. The Al alloy containing 1 wt% Fe increases the hydrogen generation rate 3.7 times compared with that of pure Al, in which 65% of the increase is due primarily to the galvanic corrosion between Al and Al 3 Fe phase, and 35% due to the increase in reaction area by intergranular corrosion. 1 Introduction Hydrogen has received much attention as a future energy source due to its clean, abundant and regenerative properties as well as its high energy density. It is very attractive that the chemical energy of hydrogen can be easily converted to electrical energy using a fuel cell such as a PEMFC (proton exchange membrane fuel cell). Currently, most hydrogen (more than 95%) is produced by steam or partial oxidation reforming of natural gas and coal gasification. 1 Since the raw materials used in the reforming processes are based on the fossil fuels resulting in CO 2 emission, it is essential to develop safe and economic hydrogen storage and production system to realize the hydrogen based economy society. Hydrogen storage using high-pressure vessels, 2 metal hydrides, 3 carbon nanotubes, 4 and metal organic frameworks 5 is not appropriate due primarily to their low hydrogen density and the associated safety and cost problems. 1,6,7 Recently, on-board hydrogen generation from the hydrolysis of Al and its alloys (e.g., Al, 8,12–19 Na, 9 Mg, 10 Zn, 11 etc.) has received great attention because it eliminates the need for hydrogen storage. The chem- ical reaction of the Al hydrolysis in alkaline solution, expressed by eqn (1), occurs according to the consecutive reactions repre- sented by eqn (2) and (3): 8 Al + 3H 2 O / Al(OH) 3 + 3/2H 2 (1) Al + 3H 2 O + NaOH / NaAl(OH) 4 + 3/2H 2 (2) NaAl(OH) 4 / NaOH + Al(OH) 3 (3) The hydrogen generation occurs more rapidly in higher concentrated NaOH solution due to the faster dissolution of aluminium hydroxide (Al(OH) 3 ) formed on the surface of Al into Al(OH) 4  . 15–17 Aluminium has relatively high density of hydrogen storage (3.7 wt% H 2 ), and it goes up to 5.5 wt% when the water produced from PEMFC operated by the hydrogen produced from the hydrolysis of Al is recycled into the hydrolysis of aluminium. 12 One kilogram of aluminium generates about 0.110 kg H 2 , or 1340 LH 2 (at 1 atm, 298  C). In the all the previous reports, 8,12–19 Al or its alloys in powder forms have been used for the hydrolysis of Al in alkaline solutions due primarily to the large surface area of the powders, leading to the fast reaction rate. However, the powders of Al and Al alloys need to be stored in high vacuum because they are dangerous and explosive when in contact with moisture and air. 8 Further, the Al powders are quite expensive due to complex manufacturing processes. Accordingly, the development of safe Al and Al alloys in such bulk forms as sheet or plate with a high performance of hydrogen generation has proven to be a challenge. It is evident from eqn (1) that the hydrogen generation rate increases in proportional to the corrosion rate or the oxidation rate of Al to Al 3+ . Accordingly, in order to increase the hydrogen generation rate in the hydrolysis of Al, the corrosion rate of Al should be increased. The corrosion rate of Al would be increased by precipitating an electrochemically noble phase such as Al 3 Fe, Al 3 Ni and Al 2 Cu, etc. along the grain boundaries, thereby causing a combined action of galvanic corrosion and intergranular corrosion in the Al alloy. Among the alloying elements, Fe is very cheap and contained in the range of 1–3 wt% as unwanted material in the wasted Al scraps. a Dept. of Materials Science and Engineering, KAIST, Daejeon, 305-701, Republic of Korea. E-mail: hskwon@kaist.ac.kr; Fax: +82-42-350-3321; Tel: +82-42-350-3326 b Fuel Cell Center, Korea Institute of Science and Technology (KIST), Seoul, 136-791, Republic of Korea. E-mail: eks192@kist.re.kr c Dept of Materials Science and Eng., University of Michigan, Ann Arbor, MI, 48109, USA. E-mail: jykwon@umich.edu This journal is ª The Royal Society of Chemistry 2011 J. Mater. Chem. Dynamic Article Links C < Journal of Materials Chemistry Cite this: DOI: 10.1039/c1jm11329a www.rsc.org/materials PAPER Downloaded by Korea Institute of Science and Technology / KIST on 01 August 2011 Published on 29 July 2011 on http://pubs.rsc.org | doi:10.1039/C1JM11329A View Online