Optimized V‐Doped Defective TiO₂/α‐(Fe₂O₃)_1‐x(Cr₂O₃)_x Heterojunctions for Photo‐Assisted Supercapacitor Devices: Insights on the Materials Integrity and Dual Conversion‐Storage Mechanism

Abstract

Energy conversion and storage integrated power units suffer from multiple engineering issues. Replacing two devices (solar cell and supercapacitor assembly) with one device (photo‐enhanced supercapacitor‐ PSC) requires materials with emerged dual solar‐electrochemical storage attributes. Herein, a propitious approach is developed to fabricate all visible light‐enhanced semisolid flexible PCS. Nanoflakes‐based p‐n junction α‐(Fe2O3)1‐x(Cr2O3)x photocathode is synthesized directly on industrial waste stainless steel mesh (316L‐SS). Alongside, three TiO2‐based electrodes are utilized as positive photoactive electrodes. Tuning the optical properties of TiO2 is displayed via doping with mixed valence vanadium (V4+/V5+) together with thermal hydrogen annealing. This is revealed via the reduction of the bandgap energy from 2.89 to 2.15 eV, which can be ascribed to the induced oxygen vacancies. The device can sustain up to 1.6 V potential window with 91% stability after 350 successive charge/discharge cycles with the possibility of performance regeneration to its 100% retention. An illustration of the photo‐storage mechanism is proposed based on the X–ray photoelectron spectroscopy, X–ray crystallography, and band position/alignment results. Quasi‐reversible water splitting/formation is concluded as the main storage mechanism in the semisolid state electrolyte under illumination conditions.

Compositionally variant bimetallic Cu–Mn oxysulfide electrodes with meritorious supercapacitive performance and high energy density

“…When the amount of manganese increases, the specific capacitance decreases, which may be attributed to the mechanical expansion of MnO 2 , despite the high theoretical specific capacitance of Mn. 9,13,25,67 Galvanostatic charge–discharge profiles (GCDs) were also recorded to assess the electrochemical performance of the C 3 M 1 OS, C 1 M 1 OS, and C 1 M 3 OS electrodes as a function of current density (1–10 A g −1 ) at a constant potential window of 0.48 V, Fig. 5(c)–(e).…”

“…Specifically, transition metal oxysulfides (TMOS) have been suggested as promising electrode materials for energy storage devices owing to their comparatively high specific capacitance and cycling stability. 4–15 Note that transition metal oxides (TMO) still suffer from some constraints of limited electrical conductivity and moderate cycling life despite their multivalence states, low cost, and high specific capacitance. At a current density of 1 A g −1 , the CuMnO 2 /GQD nanocomposite and CuMnO 2 nanoparticles exhibited capacities of 520.2 and 381.5 C g −1 , 16 respectively.…”

“…12 A composite of nickel–molybdenum oxyphosphides and oxysulfides (NMOP/NMOS) delivered a C sp of 338.7 F g −1 . 13 Electrodeposited iron–vanadium oxysulfide (Fe–VO–S) nanostructures on the SS substrate with an Fe : VO molar ratio of 2 : 1 showed a C sp of 217 F g −1 at 3 A g −1 . 14…”

Recent Advances in Photochargeable Integrated and All-in-One Supercapacitor Devices

“…Besides, the maximum specific capacitance of the ZnCo 2 O 4 //CuCo 2 S 4 -based devices was calculated as 448 F g −1 with photoassistance, whereas the specific capacitance under darkness was 340 F g x nanoflakes and a Vdoped TiO 2 -based photoanode was assembled using semisolid PVA−KOH electrolyte to build up a PSC device with an energy density of 2.30 μWh cm −2 at a power density of 1.28 mW cm −2 . 118 Bismuth-based organometallic-halide perovskite is also among the photoactive materials for all-in-one design. 99 Bismuth-based perovskites offer low toxicity compared with lead-based ones.…”

“…In their recent work, Prakash et al reported symmetric V 2 O 5 ||V 2 O 5 and asymmetric V 2 O 5 ||AC PSC devices where the asymmetric PSC device displayed an enhanced energy density from 3.6 to 9.8 Wh kg –1 at a power density of 29 W kg –1 under light illumination. In another recent study, a photocathode prepared from p–n junction α-(Fe 2 O 3 ) 1– x (Cr 2 O 3 ) x nanoflakes and a V-doped TiO 2 -based photoanode was assembled using semisolid PVA–KOH electrolyte to build up a PSC device with an energy density of 2.30 μWh cm –2 at a power density of 1.28 mW cm –2 . Bismuth-based organometallic-halide perovskite is also among the photoactive materials for all-in-one design .…”