Chonghoon Lee

Potentiometric CO2 gas sensor with lithium phosphorous oxynitride electrolyte

This work was supported by a grant from the National Science Foundation (EEC-9523358) with matching support from the State of Ohio and an Industrial Consortium.

Ceramic-based chemical sensors, probes and field-tests in automobile engines

The monitoring and control of combustion-related emissions is a top priority in many industries. The major methods used to detect combustion gases fall short of practical applications for in-situ measurements in industrial environments involving high temperature and chemical contaminants. The real challenge is not only to develop highly sensitive and selective sensors, but to maintain long-term stability in such aggressive environments. This article presents an overview of a multidisciplinary research effort in ceramic-based chemical sensors, highlighting opportunities as well as challenges. The group of sensors (CO, NOx, O2, and CO2) selected for this article can, in general, be used to determine the state of combustion in a wide variety of applications. Fabrication of sensor probes and their field-test results in automobile engines are also presented.

The origin of oxygen dependence in a potentiometric CO2 sensor with Li-ion conducting electrolytes

Abstract When the electrochemical cell arrangement of type III, O 2 , CO 2 , Au, Li 2 CO 3 ∣Li + conductor∣O 2 , reference ( a Li 2 O =constant) is used to measure the CO 2 concentration in air, the emf should depend only on the logarithmic concentration of CO 2 . In reality, however, the sensor response is also affected by the oxygen present in the environment. The oxygen dependence of the CO 2 sensing electrochemical cell originates from an influence of electronic conduction in the electrolyte. The theoretical change of emf with oxygen pressure, which is predicted from the modified emf-equation for the electrochemical cell with a mixed conducting electrolyte, agrees well with the measured emf change.

Mixed Ionic and Electronic Conduction in Li3PO4 Electrolyte for a CO2 Gas Sensor

An electrochemical CO 2 gas sensor using Li 2 CO 3 and Li 2 TiO 3 + TiO 2 as sensing and reference electrodes, respectively, and Li 3 PO 4 as the electrolyte is the subject of this paper. The sensor response to CO 2 gas showed a systematic deviation from the prediction of the Nemst equation at low p C O 2 . Based on the electromotive force (emf) measurement, the transference numbers of Li 3 PO 4 , a lithium-ion conductor, were estimated for different p C O 2 values, and the conduction domain boundary for Li 3 PO 4 separating n-type electronic conduction from ionic conduction was constructed. The conduction domain predicts that change in the Li activity in the sensing side of the cell drives the Li 3 PO 4 electrolyte to a mixed (n-type electronic and ionic) conduction region at low p C O 2 . Hebb-Wagner dc polarization measurements also indicate n-type electronic conduction in Li 3 PO 4 with a mixture of Li 2 CO 3 and gold as a reversible electrode. The transference numbers obtained from both the emf measurement and the Hebb-Wagner polarization measurements demonstrate that the origin of the non-Nernstian behavior of the CO 2 sensor is due to the lithium mass transport from the Li 2 CO 3 -sensing electrode to the Li 3 PO 4 electrolyte, resulting in nonstoichiometry of Li 3 PO 4 at temperatures above 500°C.

Mixed Ionic and Electronic Conduction in Li[sub 3]PO[sub 4] Electrolyte for a CO[sub 2] Gas Sensor

An electrochemical CO 2 gas sensor using Li 2 CO 3 and Li 2 TiO 3 + TiO 2 as sensing and reference electrodes, respectively, and Li 3 PO 4 as the electrolyte is the subject of this paper. The sensor response to CO 2 gas showed a systematic deviation from the prediction of the Nemst equation at low p C O 2 . Based on the electromotive force (emf) measurement, the transference numbers of Li 3 PO 4 , a lithium-ion conductor, were estimated for different p C O 2 values, and the conduction domain boundary for Li 3 PO 4 separating n-type electronic conduction from ionic conduction was constructed. The conduction domain predicts that change in the Li activity in the sensing side of the cell drives the Li 3 PO 4 electrolyte to a mixed (n-type electronic and ionic) conduction region at low p C O 2 . Hebb-Wagner dc polarization measurements also indicate n-type electronic conduction in Li 3 PO 4 with a mixture of Li 2 CO 3 and gold as a reversible electrode. The transference numbers obtained from both the emf measurement and the Hebb-Wagner polarization measurements demonstrate that the origin of the non-Nernstian behavior of the CO 2 sensor is due to the lithium mass transport from the Li 2 CO 3 -sensing electrode to the Li 3 PO 4 electrolyte, resulting in nonstoichiometry of Li 3 PO 4 at temperatures above 500°C.

Mixed Ionic and Electronic Conduction in Li_3PO_4 Electrolyte for a CO_2 Gas Sensor

An electrochemical CO 2 gas sensor using Li 2 CO 3 and Li 2 TiO 3 + TiO 2 as sensing and reference electrodes, respectively, and Li 3 PO 4 as the electrolyte is the subject of this paper. The sensor response to CO 2 gas showed a systematic deviation from the prediction of the Nemst equation at low p C O 2 . Based on the electromotive force (emf) measurement, the transference numbers of Li 3 PO 4 , a lithium-ion conductor, were estimated for different p C O 2 values, and the conduction domain boundary for Li 3 PO 4 separating n-type electronic conduction from ionic conduction was constructed. The conduction domain predicts that change in the Li activity in the sensing side of the cell drives the Li 3 PO 4 electrolyte to a mixed (n-type electronic and ionic) conduction region at low p C O 2 . Hebb-Wagner dc polarization measurements also indicate n-type electronic conduction in Li 3 PO 4 with a mixture of Li 2 CO 3 and gold as a reversible electrode. The transference numbers obtained from both the emf measurement and the Hebb-Wagner polarization measurements demonstrate that the origin of the non-Nernstian behavior of the CO 2 sensor is due to the lithium mass transport from the Li 2 CO 3 -sensing electrode to the Li 3 PO 4 electrolyte, resulting in nonstoichiometry of Li 3 PO 4 at temperatures above 500°C.