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A highly sensitive electrochemical sensor for the detection of ascorbic acid (AA) was first fabricated using network-like carbon nanosheets (NCN) as an enhanced electrode modifier. Novel carbon nanosheets were synthesized from willow catkin via a high temperature carbonization and chemical activation process with the aid of potassium hydroxide (KOH). The formation of porous and interconnected structures of the resulting product was characterized by various experiment techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and nitrogen isothermal adsorption–desorption technique. The network-like carbon nanosheet modified glassy carbon electrode (NCN/GCE) exhibited excellent electrocatalytic activity for the electrochemical oxidation of ascorbic acid owing to the unique network-like and partially graphitic structure. The amperometric curve of AA on the NCN/GCE showed a quick current response, a fine linear consistency of the peak current with the concentration of AA, a low detection limit and an excellent selectivity. Based on these excellent properties, a new sensing platform was developed and verified by the determination of ascorbic acid in commercial injections.

Considering the good ability of MnO2 for the breakage of the HO–OH bond in H2O2, we employed C@TiO2 nanowire supported MnO2 as a novel catalyst for H2O2 electroreduction. The morphology and phase structure of the MnO2/C@TiO2 electrode are characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffractometry. The catalytic activity of the MnO2/C@TiO2 electrode for H2O2 electroreduction is investigated by means of cyclic voltammetry and chronoamperometry. The catalyst exhibits a high catalytic activity and good stability in the electrochemical reaction process. The oxidation current density is higher than 200 mA cm−2 at −0.7 V in 1.6 mol dm−3 H2O2. The popular price, abundant reserves, and promising electrocatalytic performance make it a viable catalyst for H2O2 electroreduction.

In this work, an FeOOH/Ag/ZnO shell/core array electrode was prepared by electro-depositing FeOOH on Ag decorated ZnO nanorod arrays. Some characterization methods, including X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy were used to study the structure and surface morphologies of FeOOH/Ag/ZnO. The results suggest that Ag particles are homogeneously distributed on ZnO nanorods, and FeOOH is well-distributed on the surface of Ag/ZnO nanorod arrays. When evaluated as a supercapacitor electrode material, the FeOOH/Ag/ZnO shell/core array electrode exhibits a high specific capacitance of 376.6 F g−1 at a charge/discharge current density of 1 A g−1, and 70.3% specific capacitance is retained after 1000 cycles. The superior pseudo-capacitive properties of FeOOH/Ag/ZnO shell/core arrays are attributed to the unique shell/core structure. First, the ZnO nanorod arrays as skeleton loading active materials can provide a large surface to volume for easy access of electrolyte ions. Second, the Ag decorated on ZnO nanorods can improve the electrical conductivity of the as-prepared electrode, which can provide fast electron transfer for faradaic reactions. The results confirm that FeOOH/Ag/ZnO shell/core arrays are advantageous as electrochemical energy storage materials.

Electrolysis of water to obtain hydrogen is a practical way to transform surplus electrical power into clean and sustainable hydrogen fuels. A series of molecular [M(bztpen)(sol)]2+ (M = Ni, Co, and Fe) complexes (bztpen = N-benzyl-N,N′,N′-tris(pyridine-2-ylmethyl)ethylenediamine) have been reported to be efficient electrocatalysts for H2 production from water reduction. Density functional calculations were performed to explore the reaction mechanisms of water reduction, catalyzed by these three catalysts. The calculations showed that [NiII(bztpen)]2+ and [FeII(bztpen)]2+ have quite similar mechanisms, involving four major steps, namely, one electron reduction, proton-coupled electron transfer, protonation of a pyridine ligand, and H–H bond formation. However, in contrast with [FeII(bztpen)]2+, [NiII(bztpen)]2+ prefers to be hexa-coordinated with a water molecule bound, and the dissociation of this water molecule is required to generate a more reactive penta-coordinated species. For [CoII(bztpen)]2+, the mechanism involves three steps, namely, two sequential proton-coupled electron transfer processes, followed by H–H bond formation. For all three catalysts, the first reduction is the rate-limiting step, and the H–H bond formation has a very facile barrier.

Cuprous(I) oxide (Cu2O) carries high theoretical specific capacitance (2247.6 F g−1), however, the amount of research about the supercapacitive performance of Cu2O is relatively small compared with other transition metal oxides. A composite of metal and metal oxide could improve the electrochemical performance efficiently. In this work, the results of XRD and XPS demonstrate that CuO/Cu2O/Cu is prepared successfully via a facile, eco-friendly, one-step template-free growth process. SEM figures show that cubic CuO/Cu2O/Cu uniformly and densely covers a skeleton of nickel foam. The binder-free CuO/Cu2O/Cu electrode exhibits excellent supercapacitive performance with a high specific capacitance of 878 F g−1 at a current density of 5 mA cm−2 (1.67 A g−1), when the current density is enlarged ten times (50 mA cm−2 (16.7 A g−1)), the specific capacitance still remains at 545 F g−1. Furthermore, we have first successfully constructed a CuO/Cu2O/Cu//AC asymmetric supercapacitor, which can achieve an energy density of 42 W h kg−1 at a power density of 0.44 kW kg−1. The good electrochemical performance and simple accessibility prove that the as-prepared CuO/Cu2O/Cu/NF electrode has a potential application in electrochemical capacitors.

A low-cost nano-flake Co@carbon sponge (Co NF@carbon sponge) electrode is prepared by a simple sponge carbonization method coupled with direct Co growth on the carbon sponge surface using pulsed electrodeposition. The catalytic activity of sodium borohydride (NaBH4) electrooxidation in an alkaline medium are studied by cyclic voltammetry (CV) and chronoamperometry (CA). The Co NF@carbon sponge electrode reveals a unique three-dimensional (3D) nano-flake structure on the porous network skeleton with a large specific surface area and exhibits superior catalytic performance. The oxidation current density of the Co NF@carbon sponge electrode towards NaBH4 achieves 248 mA cm−2 in 1 mol L−1 NaOH and 0.12 mol L−1 NaBH4 solution at −0.55 V (vs. Ag/AgCl) accompanied with a considerable stability, which is remarkably higher than the electrocatalytic performance of NaBH4 oxidation obtained previously with non-noble metals as catalysts. The induced high catalytic activity greatly contributes to the excellent 3D nano-flake open structure and high electronic conductivity, which guarantees the full utilization of Co surfaces and allows the electrode to possess higher electrocatalytic performance. The novel Co NF@carbon sponge electrode is a hopeful anode with low cost and high performance for the application of fuel cells that employ NaBH4 as the fuel.

A novel Pd/polyaniline/CFC electrode is prepared by electroless deposition of palladium (Pd) onto three-dimensional polyaniline networks. The polyaniline matrix on the carbon fiber cloth (CFC) in the reduction state is electro-synthesized by cyclic voltammetry and has a lower vertex potential of −0.4 V vs. Ag/AgCl. The particle size of the Pd coated on the polyaniline chains is gradiently distributed. The as-prepared Pd/polyaniline/CFC electrode is characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FITR) and X-ray diffraction (XRD). The hydrogen peroxide (H2O2) electro-reduction reaction in H2SO4 solutions on the Pd/polyaniline/CFC electrode is investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results reveal that the electrode exhibited high catalytic activity and excellent stability in the strong oxidizing solution of H2O2 and H2SO4. Polyaniline itself shows electro-catalytic activity towards H2O2 to some extent involving the chemical–electrochemical (C–E) coupling mechanism.

In this work, RGO is decorated on MnO2 nanoflakes, which are electrochemically deposited on preformed C/TiO2 shell/core nanowire arrays to form a RGO/MnO2/C/TiO2 shell/core array electrode. Their structure and surface morphology are studied using X-ray diffraction analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman microscopy, scanning electron microscopy and transmission electron microscopy. The results suggest that a RGO layer was coated on the MnO2 nanoflakes, and the MnO2 nanoflakes have a well-distributed coverage on the surface of the C/TiO2 shell/core nanowire arrays. The RGO/MnO2/C/TiO2 shell/core arrays are evaluated as a supercapacitor electrode material, which exhibits a high specific capacitance of 822.3 F g−1 at a charge/discharge current density of 1 A g−1 and 87.4% specific capacitance retention after 5000 cycles. The superior pseudo-capacitive properties may be due to the unique shell/core structure and the decoration of RGO. The RGO decorated on MnO2 can provide partial double-layer capacitance; on the other hand, the RGO can improve the electrical conductivity of the electrode and alleviate the volume change of MnO2 during charge/discharge processes given its mechanical flexibility. Our results show that the RGO/MnO2/C/TiO2 electrode can be regarded as advantageous for electrochemical energy applications.

Nanowire-like Cu(OH)2 arrays, microflower-like CuO standing on Cu(OH)2 nanowires and hierarchical CuO microflowers are directly synthesized via a simple and cost-effective liquid–solid reaction. The specific capacitance of Cu(OH)2, CuO/Cu(OH)2 and CuO are 511.5, 78.44 and 30.36 F g−1, respectively, at a current density of 5 mA cm−2. Therefore, the Cu(OH)2/Cu-foil electrode displays the best supercapacitive performance. The capacitance retention reaches up to 83% after 5000 charge/discharge cycles with the columbic efficiency of ∼98%. More importantly, the nanowire Cu(OH)2 transformed into stable nanosheet CuO after about 600 constant current charge–discharge cycles. Additionally, we fabricate an asymmetric supercapacitor with nanowire Cu(OH)2/Cu-foil as a positive electrode, activated carbon (AC) as a negative electrode and 6 mol dm−3 KOH as electrolyte, which exhibits an energy density of 18.3 W h kg−1 at a power density of 326 W kg−1.

In this article, direct growth of Co3O4 with different morphologies on nickel foam is successfully achieved via a simple hydrothermal method by changing the volume ratio between ethanol and water. The morphology and structure of the as-prepared samples are examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The electrochemical performance of the Co3O4 electrodes is investigated as pseudocapacitor material by cyclic voltammetry and galvanostatic charge/discharge test in 3 mol L−1 KOH solution. Results show that the solvent composition plays an important role not only in the morphology but also in the capacitance. Co3O4 with a honeycomb structure obtained from the volume ratio of C2H5OH/H2O = 1 exhibits the highest capacitive performance, 2509.4 F g−1 at 1 A g−1 and 1754 F g−1 at 10 A g−1, which is much larger than that prepared in the pure water and pure ethanol solvent. The electrode also has a satisfactory cycling performance with capacity retention of 74% after 1000 cycles at 10 A g−1. The enhanced electrochemical performance is ascribed to the honeycomb nanostructure allowing facile electrolyte flow which speeds up electrochemical reaction kinetics. These findings may open up the opportunity for optimizing the hydrothermal synthesis conditions to control the morphology and performance of the products.