Why does pulsed laser-deposited amorphous NiOx serve as an excellent electrode material for revolutionizing glucose detection?

TL;DR

Amorphous NiOx shows unique electrochemical properties for glucose detection, with surface changes linked to improved performance.

Contribution

The paper reveals a novel charge transfer mechanism and surface phase evolution in amorphous NiOx for glucose sensing.

Findings

Amorphous NiOx exhibits a high diffusion coefficient for glucose detection in alkaline medium.

Oxidation potential shifts correlate with surface nickel hydroxide phases during glucose oxidation.

Pulsed laser-deposited amorphous NiOx shows negligible current variation with glucose concentration.

Abstract

Amorphous materials offer distinct properties, such as specific electronic states, a multitude of surface dangling bonds, unsaturated coordination, and enhanced charge transfer, that may improve their electrochemical performance compared with their nano and bulk counterparts. Given their intriguing characteristics, herein, we report a revolutionary electrochemical response of amorphous NiOx to glucose, which is confirmed through cyclic voltammetry measurements in an alkaline medium. To investigate this, amorphous NiOx was grown on a commercially available screen-printed electrode using pulsed laser deposition. The amorphous nature of NiOx was confirmed using transmission electron microscopy, while nickel with multi valances was confirmed using an X-ray photoelectron microscopy. As the glucose concentration varied in the alkaline medium, a negligible change in current values is observed, whereas a systematic change is observed in oxidation potential Ep in the CV plot. The diffusion coefficient estimated by fitting the experimental data to the Randles–Sevcik expression is observed to be one order higher than that of the reported NiOx electrodes. The negligible change in current values and the high diffusion coefficient observed herein indicate a charge transfer process that might occur on the electrode surface. However, changes observed in the oxidation potential indicate a surface concentration of active species/phases (viz. α-Ni(OH)2, β-Ni(OH)2, β-NiOOH and γ-NiOOH) that drives the electrochemical reactions responsible for glucose oxidation. Various mechanisms proposed herein based on the theoretical models suggest that the surface modifications of the electrode material are a first-order process that gradually evolve due to the formation of multiple phases, i.e., the formation of various nickel hydroxide species.

Amorphous materials offer distinct properties viz. specific electronic states, multitude of surface dangling bonds, unsaturated coordination, enhanced charge transfer that may improve electrochemical performance compared to their other counterparts.

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