NASICON (Na 3 Zr 2 Si 2 PO 12 )-based gas sensors capable of detecting various gases (CO 2 , NO 2 , Cl 2 , VOC and so on) have so far been developed by many researchers. In this study, planar-type gas sensors using a NASICON disc attached with Pt mixed with Bi 2 O 3 as a sensing electrode (Pt(nBi 2 O 3 ), n (0.01~30): the amount of Bi 2 O 3 addition (wt%)) and Pt as a reference electrode were fabricated, and their sensing properties to CO and H 2 were examined in the operating temperature range of 25~300ºC in dry and wet air. The sensors obtained were denoted as Pt(nBi 2 O 3 )/Pt. All Pt(nBi 2 O 3 )/Pt sensors fabricated responded to CO at all operating temperatures tested, and the magnitude of CO response increased with a decrease in the operating temperature. In addition, the magnitude of CO response largely depended on the additive amounts of Bi 2 O 3 to the Pt sensing electrode. The increase in the additive amount of Bi 2 O 3 to the Pt sensing electrode (0.01 ≤ n ≤ 1) enhanced markedly the magnitude of CO response, 90% response time and CO selectivity against H 2 . The Pt(1Bi 2 O 3 )/Pt sensor showed a linear relationship between the CO response and the logarithm of CO concentration (1~3000 ppm) in dry air at 25C and the CO selectivity against H 2 was enhanced in wet air, in comparison with those observed in dry air. The interfacial layer, which was formed between the NASICON and the Pt(1Bi 2 O 3 ) electrode, was suggested to play an important role in improving of the CO-sensing properties.

NASICON (Na 3 Zr 2 Si 2 PO 12 )-based solid electrolyte-type sensors equipped with various metal oxides (MO)-added Pt sensing electrode (SE, Pt(nMO) (n: MO additive amount in wt%) and Pt counter electrode (CE, Pt) on the same side of the NASICON disc were fabricated and their (Pt(nMO)/Pt sensors) CO-sensing properties were examined at 25-300°C. The Pt(15Bi 2 O 3 )/Pt sensor showed the largest CO response with a change in electromotive force to a positive direction (positive response) at 25°C, while the Pt(15CeO 2 )/Pt sensor showed the largest negative CO response at 25°C. The CO response of the Pt(15CeO 2 )/Pt sensor seems to be determined by mixed potential at the triple phase boundaries (TPBs) containing the electrochemical reactions of CO oxidation and oxygen reduction. X-ray photoelectron spectroscopy of the Pt(15Bi 2 O 3 ) SE before and after exposure to CO indicated a slight reduction of Bi 3+ after the exposure to CO. Therefore, the additional electrochemical reactions containing the reduction of Bi 2 O 3 were anticipated to occur at the TPBs of the Pt(15Bi 2 O 3 ) SE, which resulted in the large positive CO response of the Pt(15Bi 2 O 3 )/Pt sensor. Furthermore, the addition of 15 wt% CeO 2 to Pt CE of the Pt(15Bi 2 O 3 )/Pt sensor largely enhanced the magnitude of CO response and attained relatively excellent CO selectivity against H 2 .

Radical-substituted radical cation salts are exotic species that are potentially applicable as spin building blocks for molecular magnets. We recently found that these species, which are derived from a diphenyldihydrophenazine (DPP) framework, are stable under aerated conditions at room temperature. Of these species, nitronyl nitroxide (NN • )-substituted DPP •+ tetrachloroferrate (NNDPP ••+ ؒFeCl 4 -) showed antiferromagnetic interaction at low temperature (<150 K), whereas the tetrabromoferrate salt NNDPP ••+ ؒFeBr 4 -exhibited a magnetic phase transition at 6.7 K to produce a bulk ferrimagnet. Both salts had very similar molecular structures. The difference in the magnetic properties was ascribed to the difference in molecular packing structures. A significant difference in these two salts was observed at the (NNDPP ••+ )-(NNDPP ••+ ) intermolecular contact, including the oxygen atom of the nitroxide moiety; NNDPP ••+ ؒFeCl 4 -had a serious antiferromagnetic O-O (nitroxide oxygen, 3.02 Å) intermolecular contact, whereas NNDPP ••+ ؒFeBr 4 -had a ferromagnetic O-HC (2.53 Å) intermolecular contact.

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