Oxygen Defects in Promoting the Electrochemical Performance of Metal Oxides for Supercapacitors: Recent Advances and Challenges

Abstract

and considered as indispensable energy storage devices because of their higher power density and greater life expectancy compared with their competitive counterparts such as batteries, fuel cells, and conventional capacitors. Significantly, owing to their distinct advantages including the simple and safe configuration, quick charge/discharge response, large power output, and long operating life (>100 000 cycles), SCs show a promising prospect in next-generation energy technologies, like smart and wearable electronics, quick charging cellphones, regenerative braking electric motors, and instant management of industrial power and energy. [20][21][22][23][24] Currently, there are three main categories of active materials employed to advance the electrochemical performance of SCs: i) carbonaceous matrix, ii) conducting polymers, and iii) metal oxides (MOs). With respect to the former two types, MOs, especially transition MOs, usually delivers a much higher specific capacitance, as their unique crystal structure, combined with the multiple oxidation states of metal ions, are both in favor of excellent charge storage capability. Sometimes, SCs assembled with MOs are also called pseudocapacitors (PCs), because different from carbon-based electrical double layer capacitors (EDLCs), they realize the charge storage via fast Faradaic redox and/or metal ion intercalation reactions. In this way, they could deliver substantially superior specific capacitances as high as 300-1200 F g −1 and offer 10-100 times larger energy density than that of EDLCs. [25][26][27][28][29] In recent years, various MO materials have been proposed as high-performance SCs electrodes, some of which the theoretical capacitances and common operating potential windows are summarized in Figure 1a,b. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Nevertheless, further practical applications of these SCs are severely hindered by the poor electrical conductivity and frustrating structural stability of semiconductive MOs. To address these issues, owing to the rapid advancement of nanotechnology, a series of nano-and meso-scale morphological engineering strategies have been proposed to boost the electrochemical performance of MOs, either by enlarging the electrochemical active surface area or by shortening the diffusion length of electrons/ions. [30][31][32] For instance, combining MOs with some other highly conductive substances such as carbonaceous materials and metals is validated to be a feasible Metal oxides (MOs) with multiple active sites are regarded as one of the most potential active materials for high-performance supercapacitor (SC) constructions. Engineering oxygen vacancies into MOs can effectively modulate their electronic properties, subtly induce impurity states in their bandgaps, and considerably optimize their electrical conductivity. Benefiting from these advantageous properties, the resultant oxygen-defective electrodes generally embed more electrochemical active sites and present better charge storage capability in co...

Oxygen Vacancy‐Engineered Ti−Mo−Ni Ternary Oxide Nanotubes as Binder‐Free Supercapacitor Electrodes with Exceptional Potential Window

“…To this end, oxygen vacancy engineering was shown to be an effective approach to enhance the electrical conductivity of TMOs. [27][28][29][30][31] One of the most commonly used methods to create oxygen vacancies is the thermal annealing of the material in a reducing atmosphere such as ammonia or hydrogen gases.…”

Laser Irradiation of Electrode Materials for Energy Storage and Conversion

“…Anion vacancies represent another intriguing structural defect of transition metal compounds with rising interest for energy-related applications. 24,76 The vacancies can decrease the valence state of the metal ions, thus contributing to an increased donor density. In this regard, the kinetics of redox reactions would be essentially improved, consequently boosting the electrochemical performance.…”

“…In this regard, the kinetics of redox reactions would be essentially improved, consequently boosting the electrochemical performance. 76 Traditionally, these vacancies are introduced by reducing the compounds at elevated temperatures that require a high thermal budget and long processing time. 14 Moreover, the controllability of these processes is generally poor.…”

Oxygen Defects in Nanostructured Metal‐Oxide Gas Sensors: Recent Advances and Challenges†

“…Reduction process is usually consisting of reductive gases or reducing agents ( e.g ., H 2 , NH 3 , NaBH 4 ), which can react with oxygen atoms to produce oxygen vacancies on the surface of metal oxides. [ 12,31 ] Generally, in comparison to thermal treatment in oxygen‐deficient environment, reduction process is an easier strategy to yield oxygen vacancies in metal oxides at relatively low temperature. For example, Wang et al .…”

“…In addition to self‐doping method, foreign atoms or ions doping strategy is also an effective approach to create unbalanced charge situations, which leads to the generation of oxygen vacancy in metal oxides. [ 12,38 ] For example, the pure and Cr‐doped WO 3 nanofibers were synthesized by a simple and facile electrospinning technique. [ 39 ] As shown in Figure 2a, when low valence Cr 3+ ion is replaced for a tungsten ion in Cr‐doped WO 3 sample, a center of Cr 3+ accompanied with oxygen…”