The oxides of nitrogen and their detection in automotive exhaust

McFarland, John H.; Benton, C. S.

doi:10.1021/ed049p21

Cited by 5 publications

(2 citation statements)

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“…Because Au oxide forms at more cathodic potentials in base 45 than in acid and it has been reported that the onset of NO 2 reduction is similarly pH dependent, 46 a similar explanation of the mechanism of NO x oxidations on this basis is reasonable. The NO 2 oxidation apparently starts to occur at ͓Ϫ50 mV͔ before NO oxidation ͓at ϩ100 mV͔, and this is consistent with the NO 2 being a stronger acid and forming a HONO, NO 2 Ϫ , or other species with water which can easily be oxidized to NO 3 or NO 3 Ϫ . The reactions available to NO and the reaction of NO with oxygen to form NO 2 appear to be much slower than the reactions of NO 2 with water at the electrode surface.…”

Section: ͓No͑g͒] ͓No͑aq͒] ͓5͔supporting

confidence: 69%

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Amperometric Sensing of NO[sub x] with Cyclic Voltammetry

Roh

Stetter

2003

J. Electrochem. Soc.

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Cyclic voltammetry ͑CV͒ techniques were used to measure the concentration of nitric oxide ͑NO͒ and nitrogen dioxide (NO 2 ) in air using an amperometric gas sensor. A porous gold membrane working electrode in sulfuric acid electrolyte was used with a counter electrode of bare Pt wire and quasi-reference electrode of electrodeposited Pt on a Pt wire. The anodic peak current (i pa ) was proportional to the concentration of NO at various bias sweep rates. The limit of detection was about 4.8 ppm for NO in air or 31 ppm for NO 2 in air for the CV methods. A parameter related to the diffusion coefficient and membrane permeability can be determined from CV measurements and was at the high range, 2.4 ϫ 10 Ϫ4 cm 2 s Ϫ1 , of reported values of diffusion constants. Simple models of combined effects of gas and liquid mass-transport and electrokinetic current limiting mechanisms complicate explanation of observed currents with porous gas electrodes.Nitric oxide, NO, is a human hormone necessary for healthy metabolic processes at parts per billion levels, and NO inhalation is now used to treat some conditions, but at high levels it can damage the human respiratory system. 1 The U.S. Occupational Safety and Health Administration and Department of Labor recommended exposure limit is 25 ppm NO in air. Symptoms of excess NO exposure are eye, nose, and throat irritations, drowsiness, and unconsciousness. Chronic health effects are methemoglobinemia, central nervous system effects, and delayed lung damage. 2 NO is formed in processes of combustion and found in effluents from coal-fired power plants and automobiles. 3,4 NO 2 can also cause adverse health effects 5 and causes environmental impact when reacting with water vapor in the atmosphere to contribute to acid rain. Therefore, sensitive and selective detection methods for these gases are required.Detection methods from colorimetric to electrochemical have been reported for NO, and references to electroanalytical approaches 6-10 can be found, but it has been some time since the earliest amperometric gas sensors ͑AGS͒ for NO and NO 2 were reported 9 in this journal. This early commercial NO/NO 2 sensor had a large 25 cc electrolyte reservoir and a design adapted from the amperometric ethanol 11 and CO 12,13 sensors of the time that used a composite Pt/tetrafluoroethylene ͑TFE͒ porous fuel cell-type electrode. The early NO sensor replaced the working electrode ͑WE͒ of the CO sensor with a powdered Au/TFE composite electrode to avoid interference from CO. Selectivity was achieved by reducing NO 2 at a potential too cathodic for NO oxidation and too anodic for NO reduction. 6,9 Since then, this system for ambient NO/NO 2 detection has been studied and used in several different embodiments. Later an electrode of powdered Au on Nafion was built 14 and the performance of this system was characterized and compared 7 to a thin-film low surface area ͑LSA͒ Au electrode on Nafion, both at constant potential. It was found that the LSA electrode offered a faster response and parts per billion...

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Section: ͓No͑g͒] ͓No͑aq͒] ͓5͔supporting

confidence: 69%

“…2 NO is formed in processes of combustion and found in effluents from coal-fired power plants and automobiles. 3,4 NO 2 can also cause adverse health effects 5 and causes environmental impact when reacting with water vapor in the atmosphere to contribute to acid rain. Therefore, sensitive and selective detection methods for these gases are required.…”

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confidence: 99%