Metal-Nickel Oxyhydroxide Nanostructures on Carbon Clothes As Anode Catalysts for Direct Urea Fuel Cells
Authors: Yoon Jaesik , Lee Doohee , Lee Eunji , Yoon Young Soo , Kim Dong-Joo 
Published: February 2020

Existing energy sources based on fossil fuel is an obstacle for environmental sustainability, and there is a concern regarding the depletion of fossil fuel resources [1], [2]. Therefore, it is essential to develop new alternative energy sources. As a safe and effective method of generating power, the conversion of natural biomass to electricity in the form of direct biomass fuel cell (DBFC) has attracted significant attention due to its high efficiency and low emissions [3]. Among various DBFCs, direct urea fuel cell (DUFC) using urea in wastewater and urine as fuel has recently been validated as a clean energy device [4].
The overall power response of the DUFC mainly depends on the urea oxidation reaction (UOR), so it is vital to investigate the UOR catalysts. Ni-based catalysts, which are inexpensive and commonly used as UOR catalysts, have widely utilized for replacement of noble metals. The Ni/C electrode as an anode in the reported study achieved a power density of 1.7 mW/cm2 [5], and nanostructured Ni-based catalysts or bimetallic types of catalysts also have been implemented for better performances [6], [7]. However, the above studies proceeded in an alkaline medium, which makes it difficult to use actual wastewater or urine directly as a source for fuel cells application. Since the electrochemical features of nickel-based catalysts are based on the mechanism of electrooxidation from Ni2+ to Ni3+ in alkaline medium, the catalytic activity in neutral solutions is less well distinguished [8]. Thus, nickel-based catalysts essentially comprising Ni3+ ions will more efficiently improve the UOR performances even if a neutral atmosphere of urea solution is adopted.
In this study, the catalyst with a nanostructures array based on nickel oxyhydroxide with metal (metal-NiOOH) was prepared by using the electrospinning process for DUFC. The morphology and the structure of the metal-NiOOH catalysts were observed using scanning electron microscopy, Transmission electron microscopy, and X-ray diffraction methods. The metal-NiOOH catalyst used as the DUFC anode showed excellent UOR performances and power achievements in real human urine. A comprehensive investigation on the performances of metal-NiOOH and the function of internal Ni3+ ions as a catalyst in DUFC will be presented.
References

Suranovic, Steven. "Fossil fuel addiction and the implications for climate change policy." Global Environmental Change 23.3 (2013): 598-608.

Veziroğlu, T. Nejat, and Sümer Şahi. "21st Century’s energy: Hydrogen energy system." Energy conversion and management 49.7 (2008): 1820-1831.

Zhao, Xuebing, and J. Y. Zhu. "Efficient conversion of lignin to electricity using a novel direct biomass fuel cell mediated by polyoxometalates at low temperatures." ChemSusChem 9.2 (2016): 197-207.

Xu, Wei, et al. "Nickel-cobalt bimetallic anode catalysts for direct urea fuel cell." Scientific reports 4 (2014): 5863.

Lan, Rong, Shanwen Tao, and John TS Irvine. "A direct urea fuel cell–power from fertiliser and waste." Energy & Environmental Science 3.4 (2010): 438-441.

Ye, Ke, et al. "Facile preparation of three-dimensional Ni (OH) 2/Ni foam anode with low cost and its application in a direct urea fuel cell." New Journal of Chemistry 40.10 (2016): 8673-8680.

Guo, Fen, et al. "Preparation of nickel-cobalt nanowire arrays anode electro-catalyst and its application in direct urea/hydrogen peroxide fuel cell." Electrochimica Acta 199 (2016): 290-296.

Vedharathinam, Vedasri, and Gerardine G. Botte. "Direct evidence of the mechanism for the electro-oxidation of urea on Ni (OH) 2 catalyst in alkaline medium." Electrochimica Acta 108 (2013): 660-665.

Acknowledgement
This work was supported by Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD) and the Ocean University of China-Auburn University (OUC-AU) Grants program.