Dense and entangled carbon nanotubes (CNTs) directly grown on the carbon cloth (CC) have been employed as hierarchical supercapacitor electrodes in neutral aqueous electrolyte of Na₂SO₄. XPS and Raman results show the CNTs with large amounts of oxygen functionalities and high degree of disorder, respectively, after treatment of electrochemical oxidation. The voltammograms and galvanostatic charge/discharge are performed to probe the capacitive characteristics of CNTs/CC electrode. Moreover, the symmetric supercapacitor of CNTs/CC exhibits an excellent cyclability over 10 000 cycles and high energy density of 27.8 Wh kg⁻¹, with a wide cell potential of 2 V and a large specific capacitance of 210 F g⁻¹.

A cost-effective and simple electroplating technique has been developed to prepare layered manganese oxide (MnO₂) arrays as a promising material for solar hydrogen production and waste-water cleaning through photoelectrochemical (PEC) process. The microstructure of these MnO₂ nanosheets can be referenced to Birnessite-type, as characterized by Raman spectra and transmission electron microscopy. The bandgap energy of the as-grown nanosheets determined from UV-vis spectroscopy is about 2.1 eV. Mott–Schottky plots show the flat band potential of the MnO₂ nanosheets to be −0.01 V and a donor concentration of 4.68 × 10²⁰ cm⁻³. Remarkable photocurrent in response to visible light is observed in the presence of hole acceptors, such as sodium formate and methanol, which efficiently suppress the recombination loss of electron–hole pairs from localized d–d transitions within manganese ion. Meanwhile, the transient photocurrent–time responses and the effect of different hole acceptors on PEC activity are studied with an increase of respective hole acceptor concentration, and the results reveal the critical role in the process of absorption and decomposition of the hole acceptor. Significantly, the MnO₂ nanosheets exhibit an incident photon-to-electron conversion efficiency of 7% in response to the monochromatic wavelength of 400 nm, which is comparable to that from hematite (α-Fe₂O₃). These results demonstrate the nanoporous MnO₂ nanosheets have great potential in solar hydrogen applications and organic pollutant cleaning.

A hierarchical p-type Cu₂O film with nano/microspheres on copper foil is successfully synthesized via a facile and cost-effective liquid reduction route through transformation of a lotus-like CuO/Cu(OH)₂ nanosheet/nanowire structure. Various sizes of sphere-like Cu₂O are transformed from CuO nanosheets and Cu(OH)₂ nanowires by chemically reducing the oxides from Cu²⁺ to Cu¹⁺ in a solution of ascorbic acid at a low temperature of 60 °C. Mott–Schottky analysis shows the flat band potential of the sphere-like Cu₂O film to be −0.11 V and an acceptor concentration of 2.7 × 10²⁰ cm⁻³. A direct band gap of 2.02 eV in Cu₂O film is determined by incident photon-to-electron conversion efficiency measurements. Significantly, this hierarchical Cu₂O photocathode exhibits remarkable photoelectrochemical activity in visible light. These results demonstrate that the Cu₂O film with nano/microspheres has great potential in solar hydrogen applications.