Unveiling the charge storage mechanism in VN thick electrode for on-chip micro-supercapacitors The fabrication of miniaturized IoT networks [2]. Till now, the best candidate fulfilling all the criteria electrochemical energy storage devices via are micro-supercapacitors (MSC) based on pseudocapacitive materials where fast redox reaction occurs near the surface of production-compatible microfabrication the electrode material, providing higher energy densities than techniques is challenging for the next carbon-based MSCs, at higher charge/discharge rates compared generation of Internet of Things technology. to Li based micro-batteries. Vanadium nitride (VN) material [3] clearly demonstrated outstanding pseudocapacitive properties This work focuses on the collective fabrication (> 700 F g) in aqueous electrolyte and sputtered bi-functional-1 of high-performance micro-supercapacitors VN thick film was shown to be an intrinsically efficient current based on sputtered bi-functional vanadium collector and electroactive material for on-chip MSCs facilitating the scaling up of the technology to pilot production line. To nitride thick films, acting both as electrode explain their remarkably high areal and volumetric capacitances, material and as current collector. Since the the charge compensation mechanism was investigated using charge/discharge behavior of the proposed a combination of operando/in situ techniques. electrode in aqueous electrolyte was still METHODS AND RESULTS unclear (pseudocapacitive or not),in situ/ Prior to the VN deposition, a SiN layer was deposited to protect operando characterization techniques 3 4 the silicon wafer from the chemical etching by aqueous KOH were applied on sputtered VN films, thus electrolyte. Then, the VN films were prepared by DC-reactive unveiling the charge storage mechanism. magnetron sputtering at different temperature to tune the specific surface of the VN films, and different thicknesses were attained depending on the deposition time. The charge storage process The Internet of Things (IoT) is a revolutionary technology aimedoccurring in sputtered VN films was investigated using an arsenal at creating an ecosystem of interconnected devices to improveof characterization techniques such as operando X-Ray Absorption our daily lives [1]. Autonomy and mobility are crucial parametersSpectroscopy (XAS),in situAtomic Force Microscopy (AFM) and with respect to powering IoT micro-devices, and energy storageex situ X-ray Photoelectron Spectroscopy (XPS) coupled with systems capable of delivering high energy density at high charge/Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) discharge rates are a fundamental prerequisite for next-generationand Electron Energy Loss Spectroscopy (EELS). FIGURE 1 36