Current density used for galvanostatic charge/discharge cycling does not seem to have a major influence on the device capacitance. Devices capacitance increase with the length of the SiNWs on the electrode has been improved up to 10 μF cm−2 by using 20-μm selleckchem SiNWs, i.e., ≈10-fold bulk silicon capacitance. This device exhibits 1.8% capacitance loss in 250 cycles with a maximum power density of 1.4 mW cm−2. As SiNWs growth by CVD with HCl gas enables to tune the NWs lengths without any limitation, the capacitance can be improved up to the wanted values by increasing the SiNWs length and density and by improving device design to avoid SiNWs constriction. Acknowledgments

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