This paper describes new actuators with cellulose nanofiber/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/ionic liquid (CNF/PEDOT:PSS/IL) structures. Devices containing these structures exhibit higher strain and maximum generated stress than those based on only PEDOT:PSS/IL. The new actuator system contains an electrode, which is an electrochemical capacitor, and which consists of both a faradaic capacitor (FC) and a small electric double-layer capacitor (EDLC), i.e., PEDOT:PSS. This combined capacitor plays the role of an FC and a base polymer, and the CNF skeleton is used in the place of carbon nanotubes (CNTs). This device therefore functions differently from traditional CNT/PVdF–HFP/IL actuators, which are only used as EDLC units and from PEDOT:PSS/vapor-grown carbon nanofibers (VGCF)/IL actuators, which are used as hybrid (FC and EDLC) units. The developed films are novel, robust, and flexible, and demonstrate potential as actuator materials for wearable energy-conversion devices. A double-layer charging kinetic model, which is similar to that previously proposed for PEDOT:PSS/CNT/IL actuators, is developed to explain the oxidation and reduction of PEDOT:PSS. This model successfully simulates the frequency-dependent displacement response of actuators.