Surface morphological structures and electrochemical activity properties of iridium–niobium binary alloy electrodes

• An Ir–23Nb alloy has the best oxidation capability among other Nb concentrations.
• The reason is the Ir–23Nb has a large surface area which results from Ir + Ir3Nb.
• An Ir–23Nb glucose sensor detects glucose much better than an Ir glucose sensor.

The electrochemical activities of Ir–Nb binary alloys were investigated as functions of the alloy compositions, crystal structures, and surface morphologies for a hydrogen peroxide and ascorbic acid redox reaction. High activities for the redox reaction of hydrogen peroxide were observed when pure Ir and an alloy with a composition of 77 at% Ir–23 at% Nb (Ir–23Nb) were used. Tests on eight electrodes—Ir, Ir–13Nb, Ir–17Nb, Ir–23Nb, Ir–30Nb, Ir–43Nb, Ir–62Nb, and Nb—showed that at a constant potential difference of 0.7 V vs. Ag/AgCl, the Ir–23Nb electrode had the best hydrogen peroxide oxidation capability: 9.2 μA/mm2 for 2 mM hydrogen peroxide. Apart from Nb, Ir–23Nb gave the best performance in terms of preferential hydrogen peroxide oxidation against ascorbic acid. Subsequently, the Ir and Ir–23Nb electrodes were used for the fabrication of amperometric glucose sensors. We first coated the two electrodes with a γ-aminopropyltriethoxysilane membrane and then with a glucose oxidase membrane. Tests on the Ir and Ir–23Nb electrode glucose sensors showed that the latter had better glucose detection capability than the former: 0.226 μA/(mm2 mM) for the Ir–23Nb sensor with 1.67 mM glucose. We investigated the relationship between the electrode responses to both hydrogen peroxide and ascorbic acid and the electrode surface structures.