TY - JOUR
T1 - Chemically responsive microelectrochemical devices based on platinized poly(3-methylthiophene)
T2 - Variation in conductivity with variation in hydrogen, oxygen, or pH in aqueous solution
AU - Thackeray, James W.
AU - Wrighton, Mark S.
PY - 1986
Y1 - 1986
N2 - Microelectrochemical "transistors" can be prepared by connecting two closely spaced (approximately 1.2 μm) Au microelectrodes (0.1 μm thick X 2.4 μm wide X 50 μm long) with anodically grown poly(3-methylthiophene). The amount of poly(3-methylthiophene) used involves about 10-7-10-6 mol of monomer/cm2. Poly(3-methylthiophene) can be platinized by electrochemical reduction of PtCl42- at the pair of coated electrodes. The change in conductivity of poly(3-methylthiophene) with change in redox potential is the basis for amplification of electrical or chemical signals; the conductivity varies by 5-6 orders of magnitude upon change in potential from +0.2 (insulating) to +0.7 (conducting) V vs. SCE in aqueous electrolyte. The Pt equilibrates poly(3-methylthiophene) with the O2/H2O or H2O/H2 redox couples. [Poly(3-methylthiophene)/Pt]-based transistors are shown to be viable room-temperature sensors for O2 and H2 in aqueous solution. O2 reproducibly turns "on" the device, with 1 atm of O2/0.1 M HClO4/H2O showing 0.7-mA ID at a VD = 0.2 V; H2 reproducibly turns "off" the device, with 1 atm of H2/0.1 M HClO4/H2O showing less than 20-nA ID at a VD = 0.2 V, where VD (drain potential) is the applied potential between the two Au microelectrodes and ID (drain current) is the current that passes between the two microelectrodes. The turn "on" with O2 is complete within 2 min, and the turn "off" with H2 is complete within 0.3 min. A platinized microelectrode of a dimension similar to the microelectrochemical transistor shows only 1.0-nA reduction current upon exposure to 1 atm of O2; the current amplification of the transistor is thus a factor greater than 105. The transistor device can also reproducibly respond to pH changes in the pH range of 0-12, when there is a constant O2 concentration; there is a reproducible change in ID to alternate flow of a pH 5.5/pH 6.5 stream for over 10 h. The device responds to an injection of 10-6 L of 0.1 M HClO4 into an effluent stream of 0.1 M NaClO4 (flowing at 2.0 mL/min) within 4 s. Study of the resistance properties of [poly(3-methylthiophene)/Pt] vs. potential reveals that Pt has little effect on the intrinsic conductivity of poly(3-methylthiophene). Rather, the role of Pt is purely as a catalyst to allow equilibration of O2 and H2 with the polymer. The amount of Pt used is approximately 10-7 mol/cm2, and microscopy shows Pt to be present as particles of less than 0.1-μm size.
AB - Microelectrochemical "transistors" can be prepared by connecting two closely spaced (approximately 1.2 μm) Au microelectrodes (0.1 μm thick X 2.4 μm wide X 50 μm long) with anodically grown poly(3-methylthiophene). The amount of poly(3-methylthiophene) used involves about 10-7-10-6 mol of monomer/cm2. Poly(3-methylthiophene) can be platinized by electrochemical reduction of PtCl42- at the pair of coated electrodes. The change in conductivity of poly(3-methylthiophene) with change in redox potential is the basis for amplification of electrical or chemical signals; the conductivity varies by 5-6 orders of magnitude upon change in potential from +0.2 (insulating) to +0.7 (conducting) V vs. SCE in aqueous electrolyte. The Pt equilibrates poly(3-methylthiophene) with the O2/H2O or H2O/H2 redox couples. [Poly(3-methylthiophene)/Pt]-based transistors are shown to be viable room-temperature sensors for O2 and H2 in aqueous solution. O2 reproducibly turns "on" the device, with 1 atm of O2/0.1 M HClO4/H2O showing 0.7-mA ID at a VD = 0.2 V; H2 reproducibly turns "off" the device, with 1 atm of H2/0.1 M HClO4/H2O showing less than 20-nA ID at a VD = 0.2 V, where VD (drain potential) is the applied potential between the two Au microelectrodes and ID (drain current) is the current that passes between the two microelectrodes. The turn "on" with O2 is complete within 2 min, and the turn "off" with H2 is complete within 0.3 min. A platinized microelectrode of a dimension similar to the microelectrochemical transistor shows only 1.0-nA reduction current upon exposure to 1 atm of O2; the current amplification of the transistor is thus a factor greater than 105. The transistor device can also reproducibly respond to pH changes in the pH range of 0-12, when there is a constant O2 concentration; there is a reproducible change in ID to alternate flow of a pH 5.5/pH 6.5 stream for over 10 h. The device responds to an injection of 10-6 L of 0.1 M HClO4 into an effluent stream of 0.1 M NaClO4 (flowing at 2.0 mL/min) within 4 s. Study of the resistance properties of [poly(3-methylthiophene)/Pt] vs. potential reveals that Pt has little effect on the intrinsic conductivity of poly(3-methylthiophene). Rather, the role of Pt is purely as a catalyst to allow equilibration of O2 and H2 with the polymer. The amount of Pt used is approximately 10-7 mol/cm2, and microscopy shows Pt to be present as particles of less than 0.1-μm size.
UR - https://www.scopus.com/pages/publications/0010561812
U2 - 10.1021/j100283a016
DO - 10.1021/j100283a016
M3 - Article
AN - SCOPUS:0010561812
SN - 0022-3654
VL - 90
SP - 6674
EP - 6679
JO - Journal of Physical Chemistry
JF - Journal of Physical Chemistry
IS - 25
ER -