Short-term memory in electric double-layer capacitors

Shared by various physical, chemical, and biological systems, fractional-order dynamics assert that the present state of a system is the result of not only the applied stimulus but also its past history. Consequently, in fractional-order systems, there exists a system-specific, input-dependent memory kernel. In this study, we demonstrate experimentally the existence of a memory effect in electric double-layer capacitors which are known to exhibit a fractional-order behavior through their non-single, distributed internal time constants. This is performed by showing variance in the discharge patterns of the device into a constant resistor after being charged to the same steady-state voltage and steady-state electric charge, first by using a step voltage and then using a linear voltage sweep. We observe a short-term memory effect in the transient regime which eventually fades out with time. This was attributed to the input-modulated device impedance and was confirmed mathematically.