Self-assembled two-dimensional copper oxide nanosheet bundles as an efficient oxygen evolution reaction (OER) electrocatalyst for water splitting applications

A high activity of a two-dimensional (2D) copper oxide (CuO) electrocatalyst for the oxygen evolution reaction (OER) is presented. The CuO electrode self-assembles on a stainless steel substrate via chemical bath deposition at 80 °C in a mixed solution of CuSO4 and NH4OH, followed by air annealing treatment, and shows a 2D nanosheet bundle-type morphology. The OER performance is studied in a 1 M KOH solution. The OER starts to occur at about 1.48 V versus the RHE (η = 250 mV) with a Tafel slope of 59 mV dec−1 in a 1 M KOH solution. The overpotential (η) of 350 mV at 10 mA cm−2 is among the lowest compared with other copper-based materials. The catalyst can deliver a stable current density of >10 mA cm−2 for more than 10 hours. This superior OER activity is due to its adequately exposed OER-favorable 2D morphology and the optimized electronic properties resulting from the thermal treatment

Direct growth of 2D nickel hydroxide nanosheets intercalated with polyoxovanadate anions as a binder-free supercapacitor electrode

A mesoporous nanoplate network of two-dimensional (2D) layered nickel hydroxide Ni(OH)2 intercalated with polyoxovanadate anions (Ni(OH)2–POV) was built using a chemical solution deposition method. This approach will provide high flexibility for controlling the chemical composition and the pore structure of the resulting Ni(OH)2–POV nanohybrids. The layer-by-layer ordered growth of the Ni(OH)2–POV is demonstrated by powder X-ray diffraction and cross-sectional high-resolution transmission electron microscopy. The random growth of the intercalated Ni(OH)2–POV nanohybrids leads to the formation of an interconnected network morphology with a highly porous stacking structure whose porosity is controlled by changing the ratio of Ni(OH)2 and POV. The lateral size and thickness of the Ni(OH)2–POV nanoplates are ∼400 nm and from ∼5 nm to 7 nm, respectively. The obtained thin films are highly active electrochemical capacitor electrodes with a maximum specific capacity of 1440 F g−1 at a current density of 1 A g−1, and they withstand up to 2000 cycles with a capacity retention of 85%. The superior electrochemical performance of the Ni(OH)2–POV nanohybrids is attributed to the expanded mesoporous surface area and the intercalation of the POV anions. The experimental findings highlight the outstanding electrochemical functionality of the 2D Ni(OH)2–POV nanoplate network that will provide a facile route for the synthesis of low-dimensional hybrid nanomaterials for a highly active supercapacitor electrode

Two-dimensional layered hydroxide nanoporous nanohybrids pillared with zero-dimensional polyoxovanadate nanoclusters for enhanced water oxidation catalysis

The oxygen‐evolution reaction (OER) is critical in electrochemical water splitting and requires an efficient, sustainable, and cheap catalyst for successful practical applications. A common development strategy for OER catalysts is to search for facile routes for the synthesis of new catalytic materials with optimized chemical compositions and structures. Here, nickel hydroxide Ni(OH)2 2D nanosheets pillared with 0D polyoxovanadate (POV) nanoclusters as an OER catalyst that can operate in alkaline media are reported. The intercalation of POV nanoclusters into Ni(OH)2 induces the formation of a nanoporous layer‐by‐layer stacking architecture of 2D Ni(OH)2 nanosheets and 0D POV with a tunable chemical composition. The nanohybrid catalysts remarkably enhance the OER activity of pristine Ni(OH)2. The present findings demonstrate that the intercalation of 0D POV nanoclusters into Ni(OH)2 is effective for improving water oxidation catalysis and represents a potential method to synthesize novel, porous hydroxide‐based nanohybrid materials with superior electrochemical activities

Phase Tuning of Nanostructured Gallium Oxide via Hybridization with Reduced Graphene Oxide for Superior Anode Performance in Li-Ion Battery: An Experimental and Theoretical Study

The crystal phase of nanostructured metal oxide can be effectively controlled by the hybridization of gallium oxide with reduced graphene oxide (rGO) at variable concentrations. The change of the ratio of Ga₂O₃/rGO is quite effective in tailoring the crystal structure and morphology of nanostructured gallium oxide hybridized with rGO. This is the first example of the phase control of metal oxide through a change of the content of rGO hybridized. The calculations based on density functional theory (DFT) clearly demonstrate that the different surface formation energy and Ga local symmetry of Ga₂O₃ phases are responsible for the phase transition induced by the change of rGO content. The resulting Ga₂O₃–rGO nanocomposites show promising electrode performance for lithium ion batteries. The intermediate Li–Ga alloy phases formed during the electrochemical cycling are identified with the DFT calculations. Among the present Ga₂O₃–rGO nanocomposites, the material with mixed α-Ga₂O₃/β-Ga₂O₃/γ-Ga₂O₃ phase can deliver the largest discharge capacity with the best cyclability and rate characteristics, highlighting the importance of the control of Ga₂O₃/rGO ratio in optimizing the electrode activity of the composite materials. The present study underscores the usefulness of the phase-control of nanostructured metal oxides achieved by the change of rGO content in exploring novel functional nanocomposite materials

Preferentially oriented m-tuned WO3 thin-films photocatalysts for the multitargeted degradation of organic molecules

In this work, morphology-tuned tungsten oxide (m-tuned WO3) thin films are deposited on a glass substrate by a simple and cost-effective chemical bath deposition (CBD) method. The deposition pH is varied to tune the physicochemical properties of m-tuned WO3 thin films. The m-tuned WO3 thin films show an orthorhombic crystal structure with a preferred orientation along the (020) plane. The morphological study demonstrated the conversion of ‘rice hull’ to ‘interlocked nanosheets’ to ‘reticulated nanosheets composed of nanorods’ upon changing pH, highlighting the significant role of pH in m-tuned WO3 thin film synthesis. The m-tuned WO3 thin films show good absorption in the visible-light region (390–780 nm) of the solar spectrum. The m-tuned WO3 thin films are used for the visible light active photocatalytic degradation of organic molecules such as methylene blue (MB), rhodamine B (Rh B), and tetracycline hydrochloride (TC). The optimized m-tuned WO3 thin film shows maximum photocatalytic performance of 95, 94, and 86 % in 180 min for MB, Rh B, and TC, respectively. The present study demonstrates the usefulness of the CBD method for the deposition of m-tuned WO3 and improved photocatalytic performance

Highly efficient electro-optically tunable smart-supercapacitors using an oxygen-excess nanograin tungsten oxide thin film

A smart supercapacitor shares the same electrochemical processes as a conventional energy storage device while also having electrochromic functionality. The smart supercapacitor device can sense the energy storage level, which it displays in a visually discernible manner, providing increased convenience in everyday applications. Here, we report an electro-optically tunable smart supercapacitor based on an oxygen-rich nanograin WO3 electrode. The nanostructured WO3 electrode is dark blue in color in the charged state and becomes transparent in its discharged state with a high optical modulation of 82%. The supercapacitor has a specific capacitance of 228 F g(-1) at 0.25 Ag-1 with a large potential window (1.4 V). It is highly durable, exhibits good electrochemical stability over 2000 cycles, retains 75% of its initial capacitance, and exhibits high coloration efficiency (similar to 170 cm(2)/C). The excellent electrochromic and electrochemical supercapacitor properties of the electrode is due to the synergetic effect between nanograin morphology and excess oxygen. A smart-supercapacitor fabricated with an oxygen-rich nanograin WO3 electrode exhibits a superb combination of energy storage and highly-efficient electrochromic features in one device that can monitor the energy storage level through visible changes in color.ope

Calcium nitrate (Ca(NO3)2)-based inorganic salt electrode for supercapacitor with long-cycle life performance

A novel water-soluble inorganic Ca(NO3)2 salt electrode is investigated for its pseudocapacitance in an aqueous KOH electrolyte. Commercially available Ca(NO3)2 salt is directly used as the key electrode material. The supercapacitor electrode contains Ca(NO3)2 salt, carbon black, and polyvinylidene fluoride (PVDF) in a ratio of 80:10:10. The Ca(NO3)2-based electrode demonstrates an exceptionally long life cycling stability, and a reasonably sound specific capacitance of 234 F/g is obtained at a current density of 3 A/g. Via chemical and electrochemical reactions, the in-situ activation of the Ca(NO3)2 forms an intermediate CaO which contributes to the pseudocapacitance of the electrode. The electrode undergoes a reversible redox reaction between Cu2+ ??? Cu+ during the charge-discharge process. Superior rate capability and excellent specific capacitance retention of ???120% over 2000 cycles are achieved compared with other inorganic salt electrodes