NiO Nanostructured Catalysts By AC EPD for Non-Enzymatic Urea Sensors

Abstract

Urea has attracted more attention because of its various potential applications such as hydrogen production, fuel cell, fertilizer, and electrochemical sensors.[1] In particular, as an end-product of human metabolism, urea is important for analyzing various metabolic disorders such as liver disease and renal function. Therefore, sensing the urea level is pivotal in monitoring human’s metabolic activity. Other areas including the environmental and food industries also demand accurate measurement of urea. [2] Amperometric sensing technique is considered one of the most promising method for urea sensing, since it provides a simple, fast, economic and reliable detection. [3] In the amperometric sensor, the ammonium ion can be oxidized by either enzyme or metal catalysts. However, enzyme-based sensors can have the stability issue owing to the denaturing of the enzyme. Recently, non-enzyme biosensors by metal-based catalysts have been widely studied. Various noble metals have been utilized as catalysts for urea oxidation. Metal oxides such as ZnO, CuO and NiO were also actively investigated because of low cost . Especially nickel oxide-based catalysts have shown excellent electrocatalytic properties. [4] To uniformly load such catalysts on electrodes, various techniques were utilized, such as electrodeposition [5], sputtering [6], brushing [7], spin coating [8], and EPD [9]. Among them, electrophoretic deposition (EPD) can offer versatile, simple, economic technique. It is also easy to adjust the coating thickness with achieving uniform coating even onto complex-shaped substrates by an electric field. [10] Larger surface area of the catalyst will lead to the higher oxidation current density, which makes easier detection of urea available. [9] By controlling direction and periodicity of the electric field, alternating current (AC) EPD can make tunable rearrangement of particles. [11] Therefore, tuned arrangement of nanostructured particles would control and potentially improve electrochemical properties of urea biosensor. In this study, NiO nanorods synthesized by hydrothermal method were loaded by EPD technique onto carbon fabric sensing area. In order to investigate the relation between catalytic activity and different morphologies controlled by AC EPD, parameters of frequencies, time and voltage were examined. Structure and morphologies of deposited NiO nanostructures were characterized by XRD and SEM. Cyclic voltammetric measurement was conducted in a three-compartment cell with a potentiostat 1M KOH with 0.33M urea. Chronoamperometric measurement was also performed to assess selectivity and limit of detection. Detailed mechanism and discussion of AC EPD and sensing properties of NiO rod/carbon fabric will be presented.