Spontaneous voltage drop between EDLC electrodes, when it is kept under the open-circuit condition, is commonly called 'self-discharge' and is interpreted as a result of energy loss by the device. Three mechanisms of self-discharge were proposed: due to a leakage-current, faradaic reactions and charge redistribution. According to the law of energy preservation, if the voltage drop is associated with the energy loss, the energy would more likely be exchanged with the environment. While heat generation was measured during EDLC charging and discharging, the corresponding effect during storage under open-circuit conditions has not been reported. This may support the conclusion that voltage changes during 'self-discharge' are not related to a considerable energy loss. Moreover, it has been shown that a two-stage charging process, i.e. first galvanostatic charging followed by a potentiostatic charge redistribution, resulted in considerably slower potential changes when the device was switched to the open circuit. All discussed models were based on the assumption that the energy accumulated by EDLCs is proportional to the voltage in the second power, with capacitance (C/2) as the proportionality constant. However, it has been shown that during EDLC charging or discharging through a resistance R, equations valid for 'dielectric' and electrolytic capacitors, do not hold in the case of EDLCs. Consequently, the assumption that the energetic state of the EDLC is proportional at any time to the voltage in the second power may not be valid due to considerable variability of the 'constant' C. Therefore, voltage changes may not reflect the energetic state of the device.

Carbon (sp3)‐on‐carbon (sp2) materials have the potential to revolutionize fields such as energy storage and microelectronics. However, the rational engineering and printing of carbon‐on‐carbon materials on flexible substrates remains a challenge in wearable electronics technology. This study demonstrates the scalable fabrication of flexible laser‐induced graphene (LIG)‐boron doped diamond nanowall (BDNW) hybrid nanostructures for microsupercapacitors. Direct laser writing on polyimide film is tuned by the presence of BDNW powder where an appreciable absorbance of the BDNWs at the CO2 laser wavelength enhances the local film temperature. The thermal shock due to laser irradiation produces graphitized and amorphous carbon at the diamond grain boundaries which increases the thermal and charge transfer capacity between the LIG–diamond interfaces. The samples are further treated with O2 plasma to tune the wettability or to improve the microsupercapacitor device performance. The outstanding electrical characteristics of graphene, exceptional electrochemical stability of diamond, and essential contributions of oxygen‐containing groups result in a remarkable charge storage capacity (18 mF cm−2 @ 10 mV s−1) and cyclic stability (98% retention after 10 000 cycles) outperforming most state‐of‐the‐art LIG‐based supercapacitors. Furthermore, despite extreme mechanical stress, these microsupercapacitors maintain their outstanding electrochemical properties, thus holding promise for high‐power, flexible/wearable electronics.

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Here, we provide a detailed evaluation of photoluminescence (PL) as a comprehensive tool for phosphorene characterization with the emphasis on a prominent quantitative role of PL in providing fingerprint-like features due to its extreme sensitivity to the band structure details, anisotropy, disorder, external fields, etc. Factors such as number of layers, dimensionality, structural and chemical disorder, and environmental factors and their effect on phosphorene’s PL signal are reviewed and discussed. Applications of PL in monitoring phosphorene and its modifications, as well as potential impacts on the fields of chemical and biosensing, nanomedicine, and solar energy harvesting, are also elaborated.