Pms. Monk et al., PULSED ENHANCEMENT OF THE RATE OF COLORATION FOR TUNGSTEN TRIOXIDE BASED ELECTROCHROMIC DEVICES, Electrochimica acta, 43(16-17), 1998, pp. 2349-2357
The rate of electrochromic coloration within tungsten oxide-based opti
cal devices may be enhanced considerably by applying a progression of
potentiostatically-controlled current pulses rather than applying a co
ntinuous current. The rate of coloration depends strongly on the pulse
length employed, the optimum duration depending on the pulse amplitud
e. An additional advantage of this pulsing procedure is to enhance the
durability of electrochromic devices by decreasing the prevalence of
undesirable electrolytic side reactions such as the formation of molec
ular hydrogen gas. The effects of interrupting the current (pulses) is
attributed to the formation of a thin layer of bronze having a large
insertion coefficient x on the electrolyte-facing side of the WO3. The
relationship between optimum pulse width t for rapid coloration when
using a pulse height of V-a are analyzed in terms of the Faughnan and
Crandall model of potentiostatic ion movement through WO3, obeying the
formulations for electro-bleaching. It is inferred that the rate of b
ronze dissipation between the voltage pulses dominate the overall kine
tic V-a-i-t behavior observed. (C) 1998 Elsevier Science Ltd. All righ
ts reserved.