Spatial Surface Charge Engineering for Electrochemical Electrodes

Lingyun Xie,Hedong Chen,Guofu Zhou,Xingyu Wang,Lujia Rao,Yinping Qian,Richard Nötzel,Peng Wang,Hongjie Yin

doi:10.1038/s41598-019-51048-5

Lingyun Xie, Hedong Chen + Show 7 more

Open Access

https://doi.org/10.1038/s41598-019-51048-5

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Abstract

We introduce a novel concept for the design of functional surfaces of materials: Spatial surface charge engineering. We exploit the concept for an all-solid-state, epitaxial InN/InGaN-on-Si reference electrode to replace the inconvenient liquid-filled reference electrodes, such as Ag/AgCl. Reference electrodes are universal components of electrochemical sensors, ubiquitous in electrochemistry to set a constant potential. For subtle interrelation of structure design, surface morphology and the unique surface charge properties of InGaN, the reference electrode has less than 10 mV/decade sensitivity over a wide concentration range, evaluated for KCl aqueous solutions and less than 2 mV/hour long-time drift over 12 hours. Key is a nanoscale charge balanced surface for the right InGaN composition, InN amount and InGaN surface morphology, depending on growth conditions and layer thickness, which is underpinned by the surface potential measured by Kelvin probe force microscopy. When paired with the InN/InGaN quantum dot sensing electrode with super-Nernstian sensitivity, where only structure design and surface morphology are changed, this completes an all-InGaN-based electrochemical sensor with unprecedented performance.

Highlights

Electrochemical electrodes are prime examples of materials with functional surfaces
The InN/InGaN samples are alternately immersed for 150 seconds in 0.1 and 1 M KCl aqueous solutions
On the sample surfaces this translates into an undulated surface morphology, seen in top-view scanning electron microscopy (SEM)

Summary

Introduction

Electrochemical electrodes are prime examples of materials with functional surfaces. One of their key applications is as electrochemical sensors. The superior performance has been assigned to the presence of a high density of intrinsic, positively charged donor states on the InN surface[27,28] together with the zero-dimensional electronic properties of the QDs26 These sensing electrodes have been operated together with conventional Ag/AgCl reference electrodes, limiting the realization of compact sensor devices. We demonstrate a stable, all-solid-state, epitaxial InN/InGaN-on-Si reference electrode upon a sophisticated interplay of structure design, surface morphology and surface charge. Such an all-solid-state reference electrode allows compact and robust, easy to maintain all-solid-state miniaturized sensors and sensor arrays, removing all the difficulties associated with liquid-filled reference electrodes.

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