Enhanced Electro-Oxidation of Urea Using Hollow Structured Nickel Manganese Oxide Catalysts

Abstract

The utilization of urea has attracted more attention due to its various applications such as fuel cell, hydrogen production, wastewater remediation, and electrochemical sensors. [1] Especially, urea is a crucial biomarker to detect various human metabolic disorders such as renal function and liver disease. Therefore, the measurement of the urea level plays an important role in monitoring metabolic activity of human. Electrochemical sensing method is considered one of the most promising technique for urea detection due to its simplicity and reliable sensing. [2] The enzyme-based catalyst is widely used for urea oxidation. However, the enzyme has the stability issue due to the denaturing of the enzyme. Hence, non-enzymatic biosensors by metal-based catalysts have been studied. Compared with noble metal catalysts, nickel-based catalysts are inexpensive and abundant. Furthermore, bimetallic nickel-based oxides (nickel cobalt oxide [3], nickel molybdenum oxide [4], and nickel manganese oxide [5]) have been developed for efficient urea oxidation reaction in alkaline medium. Despite many efforts to achieve higher catalytic effect with bimetallic oxides, the improvement of catalytic property of urea oxidation is still challenging due to the low exposure of active sites and low electrical conductivity The hollow structured catalyst can improve the performance of urea detection by providing structural stability of catalyst and facile transport channels for electrolyte with exploiting its inner and outer surface as active sites. With introducing the template-free hydrothermal method with SDBS, Ni-Mn-based oxide is synthesized. Due to the synergetic catalytic effect between NiO and MnO and morphological effect of hollow structure, higher oxidation current and lower onset potential could be achieved. In this study, nickel manganese oxide catalyst with the variation of Ni:Mn atomic ratios were synthesized by one-pot template-free hydrothermal method. Structure and morphologies of synthesized nickel and manganese oxide hollow structure were characterized by XRD and SEM. And the atomic ratio of nickel manganese oxide was confirmed by EDS. CV measurement was conducted in a three-compartment cell with a potentiostat 1M KOH with 0.33M urea. CA measurement was also performed to measure the selectivity and limit of detection. Detailed mechanism and discussion of the formation of structure and sensing properties of nickel manganese oxide catalyst will be presented.