Suitable Conditions for the Use of Vanadium Nitride as an Electrode for Electrochemical Capacitor

Abstract

Vanadium nitride has displayed many interesting characteristics for its use as a pseudocapacitive electrode in an electrochemical capacitor, such as good electronic conductivity, good thermal stability, high density and high specific capacitance. Thin films of VN were prepared by D.C. reactive magnetron sputtering. The electrochemical stability of the films as well as the influence of dissolved oxygen in 1 M KOH electrolyte were investigated. In order to avoid material as well as electrolyte degradation, it was concluded that vanadium nitride should only be cycled between −0.4 and −1.0 V vs. Hg/HgO. After a 24 hours stabilization period, the prepared VN thin film showed an initial capacitance of 19 mF.cm −2 and a capacity retention of 96% after 10000 cycles. Furthermore, dissolved oxygen in the electrolyte was demonstrated to cause self-discharge up to a potential above −0.4 V vs. Hg/HgO, where VN was shown to be unstable. Additionally, the presence of oxygen was shown to shift the open circuit potential of a VN electrode to about 0 V through self-discharge processes. Electrochemical capacitors are currently being developed to complement other energy storage or conversion systems such as batteries and fuel cells. In the past two decades, several electrode materials have been investigated. The mostly studied materials include carbons, 1-8 conducting polymers 9-12 as well as pseudocapacitive 13 transition metal oxides such as ruthenium dioxide 14-18 and manganese dioxide. [19][20][21][22][23][24] In the effort to improve the performance of electrochemical capacitors, a widely used approach has been to develop synthetic methods to develop nanomaterials that are believed to lead to increased energy density and higher rate capability. 14,23,[25][26][27][28] Another approach has been to investigate the charge storage properties of novel materials. Accordingly, several research groups considered materials such as MXenes 29,30 and transition metal nitrides. [31][32][33][34][35][36][37] In the latter class of compounds, molybdenum nitride was firstly investigated 32,33,35,38,39 and in the past decade a great deal of attention has focused on other nitrides with an intensive focus on vanadium nitride 37,40-58 as a consequence of the impressive capacitance of 1340 F.g −1 reported for nanosized VN particles in 1 M KOH. 58 Indeed, VN is an interesting electrode material due to this high reported specific capacitance coupled with its close to metallic electronic conductivity (1.18 S.m −1 ), 59 high density (6.13 g.cm −3 ) and high melting point (2619 K). 59The hypothesis proposed by Choi et al.58 to explain such a high specific capacitance of VN, is that, in addition to electrochemical double layer capacitance, successive fast reversible redox reactions are taking place, involving surface oxide groups and OH − ions from the electrolyte. This hypothesis was supported by the observation of surface oxide via ex-situ XPS 58 and FTIR 41,58 post cycling measurements.While most studies concentrated on new synthesis of VN with the goa...

On Chip Interdigitated Micro‐Supercapacitors Based on Sputtered Bifunctional Vanadium Nitride Thin Films with Finely Tuned Inter‐ and Intracolumnar Porosities

“…The cyclic voltammogram (CV) shape looks like rectangular with one broad redox wave at −0.6 V (oxidation peak) and −0.7 V (reduction peak) versus Hg/HgO (Figure SI1F – inset, Supporting Information): although not perfectly rectangular shape, such capacitive envelope allows us to extract the pseudocapacitance value. Similar results have already been observed either with thin film or composite electrodes …”

“…Figure SI1F (Supporting Information) clearly showed the suitable electrochemical conditions to measure the performance of VN thin films as an electrode for micro‐supercapacitor based on TMN thin films. According to the work performed by Bélanger and co‐workers, the electrochemical window has to be limited in‐between −1 and −0.4 V versus Hg/HgO in order to provide a fair capacitance retention: in Figure SI1F (Supporting Information), the capacitance retention was higher than 80% after 3000 cycles at a scan rate of 25 mV s −1 in 1 m KOH. While VN thin film was tested between −1.2 and 0 V versus Hg/HgO (Figure SI1F – inset, Supporting Information), the capacitance retention quickly faded to 25% after only 100 cycles.…”

“…RuO 2 thin films have been deposited by direct current reactive sputtering technique in 2001 but the reported capacitance values of the RuO 2 films stay very low due to the dense morphology and the nonhydrous form of the thin film electrodes. Magnetron sputtering deposition technique has been recently used to synthesize metal carbide for nanoporous carbon or TMN thin films . While the studies on TMN were focused on the suitable electrochemical conditions to characterize the electrode performance, no information about the electrode porosity has been reported.…”

Uakitite, VN, a New Mononitride Mineral from Uakit Iron Meteorite (IIAB)

“…In general, the crystal structure and properties of well-known synthetic VN (or δ-VN) have been studied in detail [29,30,40,42,44,51,62,[64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82]. It is a cubic NaCl-type structure (Fm-3m, a ≈ 4.135 Å, Z = 4).…”

Preparation of Vanadium Nitride Using a Thermally Processed Precursor with Coating Structure

“…It can be widely used as iron and steel additive [1,2], electrode [3,4], catalyst [5,6], superconductor [7], and coating [8,9]. The frequent application of VN, as an important steel additive, can be ascribed to its beneficial effect on fine grain and precipitation strengthening, which can improve the comprehensive performance of steel and reduce the cost of the smelting process by using nitrogen to reduce the vanadium content of steel [10].…”