Exploration of Metal Oxide Catalysts for Direct Urine Fuel Cell and Gas Sensors for Its Condition Monitoring
Authors: Chung Yoonsung , Park Hyejin , Lee Eunji , Lee Seokhee , Woo Sungpil , Yoon Youngsoo , Kim Dong-Joo 
Published: February 2020

The technology to use hydrogen as an attractive energy resource is in development. However, storage of hydrogen is still considered as a major drawback. An alternative approach has been investigated to use light chemicals as a hydrogen source such as methanol, ammonia or urea (1-4). Urea is a non-toxic and low-cost industrial product as well as naturally exists in urine and waste water. Urea / urine fuel cell can be applied to treatment of waste water, animal waste, waste supplier of manned spaceship, power of electrical vehicles and portable equipment (3). Since the mechanisms of chemical reaction on urine conversion are not well understood, an economic method to rapidly evaluate the chemical species inside the fuel cell can provide insights to understand the mechanisms.

Among critical components to construct a fuel cell, catalyst can be an important material for urine/urea conversion. Nickel, an inexpensive transition metal, has been investigated as a catalyst for the urine / urea fuel cell. Boggs et al. (2) demonstrated the direct conversion of urine and urea to hydrogen using electrochemical oxidation with a nickel catalyst. Lan et al. (4) synthesized nanostructured nickel and applied it as an anode catalyst for fuel cells. Transition metal oxides also show catalytic processes due to their selectivity on oxidation, reduction and dehydrogenation (5). Electrochemical properties of nickel oxide has been studied to apply capacitors (6), electrochromic thin films (7), phenol degradation (8), and biosensors (9). Therefore, nickel oxide is considered as a potential catalyst of urea / urine oxidation.

In this study, nanostructured nickel oxide is synthesized using a hydrothermal method and a precipitation method with different morphology. The crystal structure and morphology after calcination are shown in Fig. 1 and Fig. 2, respectively.  Different ratios of mixtures with synthesized nickel oxide and graphene oxide are fabricated to films by electrophoretic deposition (EPD). Parameters in EPD were controlled to construct different hierarchical structures. The structural properties of the deposited nickel oxide layers are analyzed by using SEM and XRD.  Then, the catalytic effects were also investigated. The use of gas sensors to measure cell reaction will be performed to advance fundamental understanding of direct conversion of urine.  

This research was partially supported by Agency for Defense Development (ADD) as global corporative research and Auburn University IGP.

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Figure 1