This work reports the development of an oil-immersed scanning micropipette contact method, a variant of the scanning micropipette contact method, where a thin layer of oil wets the investigated substrate. The oil-immersed scanning micropipette contact method significantly increases the droplet stability, allowing for prolonged mapping and the use of highly evaporative saline solutions regardless of ambient humidity levels. This systematic mapping technique was used to conduct a detailed investigation of localized corrosion taking place at the surface of an AA7075-T73 aluminum alloy in a 3.5 wt % NaCl electrolyte solution, which is typically challenging in the conventional scanning micropipette contact method. Maps of corrosion potentials and corrosion currents extracted from potentiodynamic polarization curves showed good correlations with the chemical composition of surface features and known galvanic interactions at the microscale level. This demonstrates the viability of the oil-immersed scanning micropipette contact method and opens up the avenue to mechanistic corrosion investigations at the microscale level using aqueous solutions that are prone to evaporation under noncontrolled humidity levels.
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...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.