Highly Durable and Conductive Tungsten Oxide Nanofiber Supports for Improved Oxygen Reduction Reactions
Authors: Kim Ga Yoon , Ryu Won-Hee 
Published: December 2020

Developing an efficient and sustainable electrocatalyst for facilitating sluggish oxygen reduction reaction (ORR) is a key issue for the realization of metal-air batteries and fuel cells. The platinum deposited carbon (i.e., Pt/C) is the most popular and widely adopted catalyst system for enhancing the ORR kinetics. Unfortunately, the practical use of Pt/C is severely limited by low electrochemical oxidation resistance and subsequent structural collapse of the carbon-based support materials, especially during dynamic cell operations.[1] Recently, alternative inorganic metal oxides (TiO2, WO3, etc.) have been spotlighted as catalyst support due to higher electrochemical robustness than carbon. However, other properties such as electronic conductivity and electrochemical catalyst-support interactions should be considered to perform as a support material for achieving a prominent performance of supported catalyst.[2]

Several methods for modulating the properties of metal oxides has been suggested to overcome their intrinsic limitation such as electronic and electrochemical features. Particularly, the off-stoichiometric metal oxides with oxygen-deficient structure have known to exhibit unique surface activity and electrical property. For example, tungsten oxide with low oxidation number, called black WO3-x, can offer several advantages such as (i) high electronic conductivity induced by reduced bandgap, (ii) high surface activity, (iii) improved ion mobility, and (iv) structural flexibility by generating free volumes.[3-7] However, the applicability and feasibility of WO3-x materials as a catalyst support have rarely been reported.

In this work, we successfully synthesize the black WO3-x nanofiber (NF) via electrospinning and subsequent reducing thermal treatments, and elucidate their performance as a Pt catalyst support material. Morphological and structural characterizations of the black WO3-x NF are carried out to investigate unique features of the WO3-x NF. It is noted that the Pt catalysts supported on black WO3-x nanofibers (Pt/black WO3-xNF) outperform the Pt/white WO3 NF reference in electrochemical ORR and prolonged cycle tests. We also demonstrate the origin of high durability and catalytic functions of the black WO3-x NF as catalyst support by using various Ex-situ characterizations.

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[2] P. A. Shinde, S. C. Jun, ChemSusChem
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[3] Na-Won Lee, Ji-Won Jung, Jun-Seo Lee, Hye-Yeon Jang, Il-Doo Kim, and Won-Hee Ryu, Electrochimica Acta, 2018, 263, 417-425.

[4] Na-Won Lee, Ki Ro Yoon, Jae Yun Lee, Yoonsu Park, Seongji Pyo, Ga-Yoon Kim, Don-Hyung Ha, and Won-Hee Ryu, ACS Applied Energy Materials, 2019, 2, 3513-3522.

[5] Won-Hee Ryu, Hope Wilson, Sungwoo Sohn, Jinyang Li, Xiao Tong, Evyatar Shaulsky, Jan Schroers, Menachem Elimelech, André D. Taylor, ACS Nano, 2016, 10, 3, 3257-3266

[6] Ji-Yong Eom, Sung-Jin Lim, Sang-Min Lee, Won-Hee Ryu and Hyuk-Sang Kwon, J. Mater. Chem. A, 2015, 3, 11183-11188

[7] Jiajia Song, Zhen-Feng Huang, Lun Pan, Ji-Jun Zou, Xiangwen Zhang, and Li Wang, ACS Catalysis, 2015, 5, 6594-6599