Zirconia-Based Potentiometric Sensors Using Metal Oxide Electrodes for Detection of Hydrocarbons

Abstract

The non-Nernstian behavior of zirconia-based electrochemical cells with various metal oxide electrodes for 0–500 ppm C1-C4 hydrocarbons, hydrogen, and carbon monoxide was studied in the presence of 10% oxygen at 600°C. The cell using an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML1" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">In</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mo>O</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> electrode exhibited a largely negative electromotive force (emf) for propene but gave moderately negative emfs for hydrogen and carbon monoxide. The addition of 0.1 wt % <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML2" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">MnO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> to the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML3" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">In</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mo>O</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> electrode significantly improved the selectivity of the parent electrode for propene over hydrogen and carbon monoxide. The negative emf of the cell using the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML4" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">MnO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> -containing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML5" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">In</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mo>O</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> electrode for the hydrocarbons became enhanced as the carbon number of the hydrocarbon increased, the C-C linkage was unsaturated, and the chain structure was branched. This enhanced effect, as well as the addition effect of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML6" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">MnO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>,</mml:mo> </mml:math> was discussed on the basis of the measurements of the polarization curves of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML7" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">MnO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> -containing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML8" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">In</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mo>O</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> electrode for the hydrocarbons and oxygen and the nonelectrochemical oxidation of the hydrocarbons by oxygen. In addition, the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML9" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">MnO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> -containing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML10" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">In</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mo>O</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> electrode for the hydrocarbons was compared with an Au electrode with respect to sensitivity to the hydrocarbons and reproducibility of the sensing properties. © 2000 The Electrochemical Society. All rights reserved.