In Situ and Operando Spectroscopy for Assessing Mechanisms of Gas Sensing

Abstract

The mechanistic description of gas sensing on inorganic, organic, and polymeric materials is of great scientific and technological interest. The understanding of surface and bulk reactions responsible for gas-sensing effects will lead to increased selectivity and sensitivity in the chemical determination of gases and thus to the development of better sensors. In recent years, spectroscopic tools have been developed to follow the physicochemical processes taking place in an active sensing element in real time and under operating conditions. Thus, the monitoring of the processes in "living" gas sensors is no longer an unsolvable problem. This Review gives an overview of in situ and operando spectroscopic techniques for the study of gas-sensing mechanisms on solid-state sensors.

Thin 2D: The New Dimensionality in Gas Sensing

“…Such a charge transfer affects the electrical resistance of the sensitive material, representing the response of the sensor [14]. Generally, for LHDs or MOX chemoresistive sensors, the presence of oxygen is crucial for this mechanism, because electron transfer occurs through chemisorption of the oxygen reactive species O 2 − , O − , O 2− , which react with the chemisorbed target gases [24]. Obviously, high operation temperatures (usually above 200 • C) are needed to obtain this.…”

A high-temperaturein situcell with a large solid angle for fluorescence X-ray absorption fine structure measurement

“…This cell also has no water-cooling system because the Kapton window temperature was kept at less than 373 K due to the high thermal conductivity of Al, even at a sample temperature of 703 K. The system can be applied to reaction analysis of solid oxide, bimetallic catalyst for fuel cells, [19][20][21][22] and in situ analysis of W oxide photo/electrochromic materials. 54,55 These powder samples are loaded into a small container made of BN or graphite and fixed to the heater.…”

“…10 Numerous in situ fluorescence XAFS experiments have been performed on the systems of fuel cell, corrosion, catalyst, and gas sensors. 5,6,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] In situ fluorescence XAFS cells require a large fluorescence window at a position sufficiently close to the sample to secure a large solid angle. When the polymer window is used for the in situ fluorescence XAFS measurements, it is difficult to realize the large solid angle because the fluorescence window temperature raises easily even if the peripheral region of the window is cooled by water flow owing to low thermal conductivity of polymer window material.…”

Halbleitergassensoren: Trockensynthese und Anwendung

“…[59] Der Sensormechanismus von Halbleitergassensoren ist theoretisch [21, 23-25, 27, 48] und experimentell mit spektroskopischen In-situ-sowie OperandoTechniken untersucht worden, mit denen physikalisch-chemische Prozesse in einem aktiven Sensorelement in Echtzeit und unter Betriebsbedingungen verfolgt werden konnten. [60] Einige Übersichtsartikel betonten außer den Materialeigenschaften (Kristallgröße, Agglomerierung, Sinterhälse) auch die Bedeutung von Strukturparametern (Porengröße, Filmmorphologie, Zugänglichkeit der Oberfläche). [55,61] Da diese Strukturparameter wechselseitig voneinander abhängen (z.…”

“…Für eine weitergehende Darstellung der Wirkungsweise von MO xHalbleitern als Gassensoren verweisen wir auf die zitierten Übersichtsartikel. [24,25,27,60] [3,21,23] Sein Sensorverhalten gegenüber Ethanol [21] und CO [24,25] ist beispielhaft für das Wechselspiel zwischen der auf der Oberfläche adsorbierten Spezies und der Leitfähigkeit im Metalloxidhalbleiter und lieferte die Grundlage für zwei allgemeine Beschreibungen [60] des Sensormechanismus: das Sauerstoffvakanz-(ReduktionsReoxidations-Mechanismus) [60,67] und das Ionosorptionsmodell. [21,24,25,68] Keines dieser beiden Modelle wird jedoch allen experimentellen Beobachtungen gerecht.…”