Hydrogen Sensing with Thin-Filmed Copper Dicyanoanthraquinone Diimine Electrodes

Thin-filmed copper dicyanoanthraquinone diimines, (DCNAQI)Cu, were electrochemically deposited on conductive SnO₂ electrodes, and characterized in aqueous K_2SO4 solutions containing methyl viologen and ferricyanide. They behave like an n-type semiconductor with a potential window 1.0 ~ -l.0 V vs, SCE. Under bandgap excitation (4, 000 cm^-1), the conductance recorded with these electrodes was observed to be substantially enhanced, but very sensitive to the presence of hydrogen. A nearly linear relationship of conductance difference between light and dark against the partial pressure of hydrogen was obtained with most (DCNAQI)Cu electrodes. The adsorption of hydrogen at (DCNAQI)Cu surface follows a simple Langmuir isotherm with an equilibrium constant in the range 1.7 ~ 2.6 atm^-1, as manifested by conductance measurements. Despite possessing a relatively smaller adsorption equilibrium constant, (β-methyl-DCNAQI)Cu exhibits the greatest sensitivity to hydrogen. This extraordinary sensitivity is very likely attributed to the mediation of surface states, located near the valence band.