We report a practical and efficient strategy for synthesizing hierarchical (meso- and macro-)porous NiO nano/micro spherical superstructures. First, β-Ni(OH)₂ microspheres were self-assembled based on the coalescence and Ostwald-ripening mechanisms during refluxing in an alkaline solution with Ni(NH₃)_x ²⁺ at 97 °C for 1 h under vigorous stirring. Second, hierarchical porous NiO microsphere superstructures were obtained from the precursor by a simple calcination procedure. The resulting superstructures comprised two-dimensional mesoporous NiO petal building blocks. Electrochemical data demonstrated that the hierarchical porous NiO nano/micro superstructures were capable of delivering a specific capacitance of 710 F g⁻¹ at 1 A g⁻¹ and offered a good specific capacitance retention of ca. 98% after 2000 continuous charge-discharge cycles. This indicates that we successfully met key requirements in terms of large specific energy density, high-rate capability and good electrochemical stability. We would expect our superstructures to be good candidates for a low-cost replacement for the state-of-the-art supercapacitor material RuO₂.

An advanced electrode for high-performance electrochemical capacitors has been designed by growing ultrathin mesoporous Co₃O₄ nanosheet arrays on the Ni foam support. This unique 3D electrode manifests exceptional supercapacitive performance with ultrahigh specific capacitance at high current densities and excellent cycling stability.

Biomass-derived carbon materials have received extensive attention as electrode materials for energy storage devices, including electrochemical capacitors, lithium–sulfur batteries, lithium-ion batteries, and sodium-ion batteries.

Nowadays, energy shortage is a serious socioeconomic problem. The recovery of biomass can make a very significant contribution in alleviating the burden on already-strained energy resources. Broad beans, which are abundant in amino acids and vitamins, are extensively cultivated worldwide. However, a large quantity of by-product, broad bean shells, remains unused and pollutes the environment from the incinerating and/or uncontrolled decomposition that results. In this paper, we report the synthesis of sulfur and nitrogen dual-doping porous carbon materials, for use as the electrode materials of energy storage devices, produced by carbonizing the shells of broad beans by a chemical activation. The specific capacitance of the as-prepared porous carbon material is as high as 202 F g⁻¹, with a superior cycling performance for electric double layer capacitors at a current density of 0.5 A g⁻¹. Furthermore, it also shows a stable performance for lithium ion batteries and sodium ion batteries, which suggests that it has a promising potential for wide applications in the field of energy storage devices.