Bipolar electrochemistry is used as an economical, single‐step, and scalable process for the oxidation of a wireless graphite substrate, and the subsequent electrophoretic deposition of graphene oxide thin film on a second wireless substrate. An all‐solid‐state symmetric double‐layer capacitor (EDLC) using binderless reduced graphene oxide electrodes exhibited outstanding reversibility and capacitance retention over 18000 cycles, as well as superior capacitive behavior at far‐from‐dc frequencies (for example 45 and 47 μ F cm-2 ), effective capacitances at 75 and 189 Hz, respectively (computed using a series resonance network with ideal inductors), compared to 55 μ F cm-2 at close‐to‐dc (computed from cyclic voltammetry at 10 mV s-1 ). This makes the device well‐suited for ac filtering applications. A one‐hour thermal treatment of the electrodes at 900 °C under vacuum increased the capacitance 13‐fold (719 μ F cm-2 ) at close‐to‐dc, which decreased to 185 and 150 μ F cm-2 as the frequency was increased to 37 and 106 Hz, respectively These properties make this device suitable for both reasonable dc energy storage and higher frequency applications.

Summary This paper presents a facile and economic development of dye‐sensitized solar cells using a nonprecious counter electrode made from ball‐milled tellurium‐doped graphene (Te‐Gr) and a natural sensitizer extracted from Calotropis gigantea leaves. The prepared materials were characterized using various techniques, such as Raman spectroscopy, X‐ray diffraction (XRD), atomic force microscopy (AFM), impedance spectroscopy, and scanning electron microscopy with built‐in energy‐dispersive X‐ray spectroscopy (SEM with EDS). The electrochemical activity of the produced counter electrodes and the impedance of the fabricated cells were examined and discussed to devise plans for future enhancement of cell performance. A clear pattern of improvement was found when using cost‐effective Te‐Gr relative to the costly platinum counter electrodes, especially when compared with cells employing another natural sensitizer. The results show approximately 51% enhancement over chlorophyll‐based cells made from spinach, where the added advantage in our approach is the utilization of an abundant plant extract with little nutritional appeal.

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