REVIEW Synthesis and applications of molybdenum (IV) oxide Caleb A. Ellefson • Oscar Marin-Flores • Su Ha • M. Grant Norton Received: 11 May 2011 / Accepted: 30 August 2011 / Published online: 16 September 2011 Ó Springer Science+Business Media, LLC 2011 Abstract Molybdenum dioxide (MoO 2 ) is a transition metal oxide with unusual metal-like electrical conductivity and high catalytic activity toward reforming hydrocarbons. This review covers the synthesis techniques used to fabri- cate MoO 2 in a variety of morphologies and particle sizes. Processing from molybdenum ore and reduction from MoO 3 are also covered, with emphasis on reduction mechanisms and kinetic considerations. Discussions of various solution-based and gas phase synthesis techniques shed light on strategies to achieve various unique mor- phologies, which leads into a brief discussion of nanoscale MoO 2 . Nanoscale MoO 2 is of interest for important tech- nological applications including catalysts for partial oxi- dation of hydrocarbons, solid oxide fuel cell anodes, and high-capacity reversible lithium ion battery anodes. Introduction Molybdenum may be most well known as an alloying element in various steels, such as 316 stainless steel and most high strength steels, where it is used to improve corrosion resistance. However, molybdenum compounds have long been in use for a variety of applications. Molybdenum disulfide, MoS 2 , is a solid lubricant because of its weakly bonded layered crystal structure, similar to graphite. High temperature furnace elements are commonly made of molybdenum disilicide (MoSi 2 ). Although molybdenum has oxidation states ranging from ?2 to ?6, oxides exist mainly in two forms: molybdenum (IV) and molybdenum (VI) oxide. Hexavalent MoO 3 is the principal product of MoS 2 roasting, and is also the main molybdenum compound added in steel production. It is also of interest as a semiconductor [1], a field-emitter [2], an electrochomic material [3, 4], photochromic material [5], and a gas sensor [6–8]. Tetravalent MoO 2 exhibits metal- like electronic conductivity [9] because of the existence of delocalized electrons in its valence band [10]. Recently, MoO 2 has garnered much interest for rechargeable lithium ion battery (LIB) anodes [e.g., 9]. Both MoO 3 and MoO 2 have been used extensively as a catalyst in hydrocarbon reforming processes [e.g., 11–13]. In particular, MoO 2 has been shown to be coke resistant [14] and sulfur tolerant [15] during the partial oxidation of hydrocarbons. Because of its electronic conductivity, MoO 2 also has potential as an anode material for fuel flexible solid oxide fuel cells [e.g., 16, 17]. This review focuses on a comparison of synthesis methods of MoO 2 and an overview of current research efforts in specific application areas. Molybdenum (IV) oxide synthesis techniques This section will present a review of MoO 2 synthesis techniques. First, the mineral processing of molybdenum ores is briefly considered. Then, direct hydrogen reduction of MoO 3 will be discussed in detail. We will describe hydrothermal and ambient temperature solution based methods, non-solution methods, and because of special interest, research into nanoscale MoO 2 will be reviewed. C. A. Ellefson  M. G. Norton (&) School of Mechanical and Materials Engineering, Washington State University, P.O. Box 642920, Pullman, WA 99164-2920, USA e-mail: norton@mme.wsu.edu O. Marin-Flores  S. Ha Voiland School of Chemical Engineering and Bioengineering, Washington State University, P.O. Box 642710, Pullman, WA 99164-2710, USA 123 J Mater Sci (2012) 47:2057–2071 DOI 10.1007/s10853-011-5918-5