In recent years, there has been growing interest in utilization of urea in terms of disposal of industrial urea wastewater and renewable energy. Urea with high energy density of 16.9 MJ/L corresponding to 10.1 wt% of hydrogen is considered as an attractive material that can produce hydrogen as the sources for fuel cells [1]. Urea also has the advantages of stability, non-toxicity, and non-flammable properties [2]. Therefore, urea can be a good candidate for alternative fuel in DUFC systems where urea is electrochemically oxidized to nitrogen (N₂) and carbon dioxide (CO₂) at the anode [3]. It can be economically feasible to produce hydrogen because the cell voltage required for urea electrolysis (0.37 V) is much lower than the cell voltage required for water electrolysis(1.23V) [2].

Various types of catalysts such as Ti-Pt [5], Pt-Co [6], and Pd-Co [7] have been researched because the urea can be oxidized in neutral medium when noble metals are used. However, due to the low activity to electrochemical oxidation of urea and high cost of noble metals, nickel-based catalysts have been investigated extensively as anode catalyst in DUFC. Ni-Co bimetal results in reduced onset voltage and improved electrochemical properties, but Co has a disadvantage of indirect contribution to urea oxidation [8]. Therefore, sputtered bimetallic and inexpensive Ni-Pd, catalysts were studied as a cathode catalyst for DUFC application. Moreover, sputter process can be simple and reproducible depositing catalysts on substrate.

In this study, sputtered Ni-Pd catalysts on carbon substrate were prepared as an anode catalyst for DUFC platform. The morphologies and structural properties of Ni-Pd bimetals were analyzed by SEM and XRD, and the contents of Ni and Pd were measured by EDS. Thereafter electrochemical measurements have been performed on a three-electrode cell in 1M urea containing 0.33 M urea, and fuel cell testing was conducted using 0.33M urea or urine which is fed into flow channel as fuels. Detailed discussion on performance of Ni-Pd bimetal as anode catalyst in DUFC will be given.

References

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2. Boggs, B. K., King, R. L., & Botte, G. G. (2009). Urea electrolysis: direct hydrogen production from urine. Commun., (32), 4859-4861.
3. Wright, J. C., Michaels, A. S., & Appleby, A. J. (1986). Electrooxidation of urea at the ruthenium titanium oxide electrode. AIChE Journal, 32(9), 1450-1458.

4. Simka, Wojciech, et al. "Electrochemical treatment of aqueous solutions containing urea." of applied electrochemistry39.7 (2009): 1137-1143.
5. Huang, H., Fan, Y., & Wang, X. (2012). Low-defect multi-walled carbon nanotubes supported PtCo alloy nanoparticles with remarkable performance for electrooxidation of methanol. Acta, 80, 118-125.
6. Wang, Z., Du, Y., Zhang, F., Zheng, Z., Zhang, Y., & Wang, C. (2013). High electrocatalytic activity of non-noble Ni-Co/graphene catalyst for direct ethanol fuel cells. of Solid State Electrochem., 17(1), 99-107.
7. Xu, W., Zhang, H., Li, G., & Wu, Z. (2014). Nickel-cobalt bimetallic anode catalysts for direct urea fuel cell. Scientific reports, 4, 5863.

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.