Abstract
The influence of microstructural or structural defects is seldom investigated in pseudocapacitive electrodes. Indeed, most of the synthesized materials do present defects at every scales which contribute to the improvement of the charge storage. In this study VN thin films were deposited by reactive magnetron sputtering. The as-deposited VN films were compared with similar films implanted with arsenide cations (As+) with energies ranging from 20 keV up to 150 keV. The influence of the ionic implantation on the structure and microstructure of the pristine films was characterized by several techniques. The initial curing of the internal stress of as-deposited VN films observed for low implantation energies was lost with increasing implantation energy. Concomitantly, the electrochemical behaviors of the VN films were investigated. All the VN films show a pseudocapacitive behavior at 2 mV.s−1. At low scan rates, the as-deposited film exhibits the highest areal capacitance (45 mF.cm−2) which drastically decreases upon increasing the scan rate. Only 30% of the initial capacitance is maintained at 100 mV.s−1. Despite lower capacitances at 2 mV.s−1, As+ implanted VN films exhibit better capacitance retention in the same conditions, i.e. up to 65% of the initial capacitance is maintained at 100 mV.s−1. The contributions coming from surface and subsurface reactions have been determined which enable to propose possible origins for the changes occurring in charge storage mechanisms upon ion implantation.
Highlights
Since the early evidencing of RuO2 electrode peculiar behavior in HClO4 aqueous electrolyte [1], pseudocapacitive materials have been the topic of extensive investigations
300 nm-thick sputtered vanadium nitride (VN) films were deposited by reactive DC sputtering
The presence of intra and inter columnar porosities due to feather like microstructure suggests that a large part of the film is affected by As+ implantation the change in VN microstructure was difficult to image from transmission electron microscopy
Summary
Since the early evidencing of RuO2 electrode peculiar behavior in HClO4 aqueous electrolyte [1], pseudocapacitive materials have been the topic of extensive investigations Their capacitive-like elec trochemical signatures such as rectangular shape cyclic voltammograms (CVs) are due to specific fast and reversible Faradaic surface and subsurface reactions [2] as it has been demonstrated for MnO2 [3,4,5], FeWO4 [6] or VN [7] electrodes among others. Cm− 2) have been recently reported owing to high surface area coming from inter-columnar and intra-columnar porous structures [17] Apart from their practical use as efficient electrodes in microsupercapacitors, VN thin films are interesting model electrodes for more fundamental investigations since they do not require the use of conductive additives neither polymeric binders to be electrochemically tested [7,13]. We show for the first time the implantation of Arsenic cations (As+) in sputtered VN films in order to create defects and determine their in fluence on the electrochemical behavior of VN electrodes in 1 M KOH electrolyte
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