Multi-shelled NiO hollow microspheres as bifunctional materials for electrochromic smart window and non-enzymatic glucose sensor

Abstract

A multi-shelled NiO hollow sphere was synthesized by a facile glucose-mediated hydrothermal route. The carbonaceous microsphere was utilized as a sacrificial template for the formation of multi-shells. All the shells were formed by a single pyrolysis step. The multi-shelled hollow sphere can provide enhanced active surface area and additional reactive sites, which facilitate faster ion intercalation and deintercalation, and play key roles in electrochromic devices and sensing application, including glucose sensing. Herein, we employed the as-synthesized material for electrochromic devices. As expected, NiO multi-shelled hollow microspheres exhibit a superior transmission modulation (ΔT = 47%) and yield a coloration efficiency of ~ 85.3 cm2 C−1, which is ~ 2.37 times higher than that of NiO microflakes which was synthesized in the absence of glucose. The geometry of the self-supported multi-shelled architecture ensures that the active faradaic sites can be in intimate contact with the electrolyte to enhance ionic diffusion. The observed colored and bleached switching time of multi-shelled hollow sphere is 6.7 s and 2.7 s respectively. A quasi-solid-state electrochromic device is also displayed with the aid of gel electrolyte with reversible color change from dark brown to transparent. Furthermore, the multi-shelled NiO displayed excellent catalytic activity towards non-enzymatic glucose sensing with a high sensitivity of 1646 ± 5 μA cm−2 mM−1 over a linear range of 2 μM–2.6 mM with a lowest detection limit of 1.5 ± 0.2 μM. Analysis on blood serum as a real biological sample reflects the practicability of the fabricated sensor. Developing hollow structured multi-shelled materials based on metal oxides will pave the way to design advanced electrode materials for electrochromic smart windows and non-enzymatic glucose sensors.