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A freestanding, binder-free flexible polypyrrole: polystyrene sulfonate/cellulose nanopaper (PPy:PSS/CNP) electrode is successfully fabricated by a low-cost, simple, and fast vacuum filtration method for the first time. The hierarchical structure of CNP with high surface area and good mechanical strength not only provides a high electroactive region and shortens the diffusion distance of electrolyte ions, but also mitigates the volumetric expansion/shrinkage of the PPy during the charging/discharging process. The optimized PPy:PSS/CNP exhibits a high areal specific capacitance of 3.8 F cm −2 (corresponding to 475 F cm −3 and 240 F g −1 ) at 10 mV s −1 and good cycling stability (80.9% capacitance retention after 5000 cycles). The cyclic voltammetry curves of PPy:PSS/CNP at different bending angles indicate prominent flexibility and electrochemical stability of the electrode. Moreover, a symmetric supercapacitor device is assembled and delivers a high areal energy density of 122 μW h cm −2 (15 W h cm −3 ) at a power density of 4.4 mW cm −2 (550 mW cm −3 ), which is superior to other cellulose-based materials. The combination of high supercapacitive performance, flexibility, easy fabrication, and cheapness of the PPy: PSS/CNP electrodes offers great potential for developing the next generation of green and economical portable and wearable consumer electronics.

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Homing sequence derivation for nondeterministic finite state machines (NFSMs) has important applications in system testing and verification. Unlike prior methods based on explicit tree based search, in this work we formulate the derivation of a preset homing sequence in terms of a quantified Boolean formula (QBF). The formulation allows implicit NFSM representation and compact QBF encoding for effective computation. Different encoding schemes and QBF solvers are evaluated for their suitability to homing sequence derivation. Experimental results show the generality and feasibility of the proposed method.