Facile Preparation of Mesoporous Titanium Nitride Microspheres for Electrochemical Energy Storage Shanmu Dong, †,‡ Xiao Chen, †,‡ Lin Gu, § Xinhong Zhou, | Hongxia Xu, ‡ Haibo Wang, ‡ Zhihong Liu, ‡ Pengxian Han, ‡ Jianhua Yao, ‡ Li Wang, ‡ Guanglei Cui,* ,‡ and Liquan Chen ‡,⊥ Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, P. R. China, WPI Advanced Institute for Materials Research, Tohoku University, Sendai 9808577, Japan, Qingdao University of Science and Technology, Qingdao 266101, P. R. China, and Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China ABSTRACT In this study, mesoporous TiN spheres with tunable diameter have been fabricated via a facile template-free strategy. Under ammonia atmosphere, mesoporous TiO 2 spheres are directly converted into mesoporous TiN spheres with the addition of cyanamide to retain the original morphology. The electrochemical performance of the resultant mesoporous TiN spheres demonstrates that this material can be a promising electrode material for nonaqueous supercapacitors with high energy densities. KEYWORDS: titanium nitride • mesoporous spheres • cyanamide • template-free method • supercapacitors • electrochemical performance INTRODUCTION T itanium nitride (TiN) has drawn considerable atten- tion for its interesting properties and various applica- tions (1), such as abrasives and protective coating materials (2). Recent reports have found its potential use as catalyst (3-6), sensors for electroanalysis (7-9), superca- pacitors (10), and also a conductive additive for lithium-ion batteries with minor capacity (1, 11). During the past decades, substantial researches have been carried out for the synthesis of materials with porous nanostructures ben- eficial for energy storage applications (12-19), as these materials possess high surface/volume ratio, good acces- sibility of the pores, and a short distance of ion diffusion or mass transport. Therefore, it is reasonably expected that a mesostructure of TiN can be potential for enhancing its electrochemical performance for lithium batteries and su- percapacitor applications. TiN nanoparticles are often prepared from titanium oxide using nitrogen sources (such as ammonia or nitrogen) at high temperature (20-27). However, it is challenging to prepare mesoporous structure, because the collapse of the nanop- ores during conversion and recrystallization severely hinder the formation of mesoporous TiN (28). To address this issue, the general synthetic strategies have mostly relied on the use of multiple templates (28-33). Two recently reported pro- cedures intended for preparation mesoporous TiN deserve highlighting: (1) the use of SBA-15 and graphitic carbon nitride as sacrificial templates to fabricate 2D hexagonal mesoporous TiN/C composites (28), (2) the use of hollow Zn 2 TiO 4 spheres formed by nebulization as an in situ tem- plating to prepare hollow TiN mesoporous spheres (33). However, these approaches substantially require a tedious and time-consuming process of template formation and the necessity of template removal. Therefore, it is urgent to explore new template-free synthetic methods for preparing mesoporous nanostructure of TiN. Herein, we reported a facile route to directly converted TiO 2 mesoporous spheres into TiN mesoporous spheres under ammonia atmosphere using cyanamide to retain the morphology. In this approach, cyanamide plays a significant role in the procedure of ammonia reduction. First, cyana- mide confines the aggregate of spheres at high temperature, prevents the nanopores structure from collapse during re- crystallization (4), and finally thermally decomposes without additional purification. Second, cyanamide also serves as an excess of nitrogen source to promote the nitrogenization reaction during decomposition (21, 31). Therefore, TiN can be obtained with well-maintained mesoporous spheres structure. In addition, mesoporous TiN spheres offer an electronic conducting framework which can be expected to be an effective and fast charge-separation network desirable for the electrochemical energy storage application (34, 35). A highly effective electronic conducting network is expected to ensure a rapid electronic diffusion while the mesoporous structure can be favorable for accessible diffusion of elec- trolyte. Therefore, in the present study, the electrochemical * Corresponding author. E-mail: cuigl@qibebt.ac.cn. Received for review October 3, 2010 and accepted November 29, 2010 † These authors contributed equally to this work. ‡ Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences. § Tohoku University. | Qingdao University of Science and Technology. ⊥ Institute of Physics, Chinese Academy of Sciences. DOI: 10.1021/am100951h 2011 American Chemical Society ARTICLE www.acsami.org VOL. 3 • NO. 1 • 93–98 • 2011 93 Published on Web 12/10/2010