• Journal of the Korean Electrochemical Society
• /
• v.6 no.2
• /
• pp.119-129
• /
• 2003

The Langmuir adsorption isotherms of the over-potentially deposited hydrogen (OPD H) fur the cathodic $H_2$ evolution reaction (HER) at the poly-Au and $Rh|0.5M\;H_2SO_4$ aqueous electrolyte interfaces have been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift $(0^{\circ}{\leq}{-\phi}{\leq}90^{\circ})$ for the optimum intermediate frequency corresponds well to that of the fractional surface coverage $(1{\geq}{\theta}{\geq}0)$ at the interfaces. The phase-shift profile $({-\phi}\;vs.\;E)$ for the optimum intermediate frequency, i.e., the phase-shift method, can be used as a new electrochemical method to determine the Langmuir adsorption isotherm $({\theta}\;vs.\;E)$ of the OPD H for the cathodic HER at the interfaces. At the poly-Au|0.5M $H_2SO_4$ aqueous electrolyte interface, the equilibrium constant (K) and the standard free energy $({\Delta}G_{ads})$ of the OPD H are $2.3\times10^{-6}$ and 32.2kJ/mol, respectively. At the poly-Rh|0.5M $H_2SO_4$ aqueous electrolyte interface, K and ${\Delta}G_{ads}$ of the OPD H are $4.1\times10^4\;or\;1.2\times10^{-2}$ and 19.3 or 11.0kJ/mol depending on E, respectively. In contrast to the poly-Au electrode interface, the two different Langmuir adsorption isotherms of the OPD H are observed at the poly-Rh electrode interface. The two different Langmuir adsorption isotherms of the OPD H correspond to the two different adsorption sites of the OPD H on the poly-Rh electrode surface.

• Polymer(Korea)
• /
• v.36 no.2
• /
• pp.169-176
• /
• 2012

Based on our experience in developing resistive humidity sensor, interdigital gold electrodes with different fingers and gaps have been fabricated on a glass epoxy (GE) substrate using screen printing techniques. The basic structure of the electrode consisted of a 3-, 4- and 5-fingers with gaps of 310 and 460 ${\mu}m$. Gold electrode/GE was prepared by first printing silver nanopaste, followed by consecutive electroless plating of Cu, Ni and then Au. Copolymer of [2-(methacryloyloxy)ethyl] dimethyl benzyl ammonium chloride (MDBAC) and methyl methacrylate (MMA) was used as a humidity-sensing polyelectrolyte, which was fabricated by a screen printing method on the Au electrode/GE substrate. The flexible humidity sensor showed acceptable linearity between logarithmic impedance and relative humidity in the range of 20-95%RH, low hysteresis of 1.5%RH, good response and recovery time of 75 sec at 1 V, 1 kHz, and $25^{\circ}C$. Electrode construction had a significant influence on the humidity-sensing characteristics of polymeric humidity sensors. The activation energy between electrode and ion conducting polyelectrolyte plays an important role in explaining the differences of humidity sensing characteristics such as temperature dependence, sensitivity, linearity and hysteresis.