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[Display omitted] • E-waste can be strategically converted into energy-storing electrodes. • Interesting core–shell morphology is formed by a facile two-step synthesis process. • The optimized NiSe-120/Cu 4 O x -3 electrode shows an areal capacity of 138.27 µAh cm−2. • Excellent stability is achieved even after 50,000 charge–discharge cycles. • The C-type HSC device exhibits a good areal capacitance of 233.1 mF cm−2. Recently, for energy storage materials, various surfactant-less synthesis methods have been attaining extensive attention from researchers. Herein, we utilized the wasted desoldering copper wicks (E-waste) as the base substrate to synthesize hierarchical core–shell maze-corn-like nickel selenide/copper oxide (NiSe/Cu 4 O x) architectures by a facile two-step synthesis process. Initially, the Cu 4 O x nanorods (NRs) were grown directly over the surface of the flat braided E-waste copper wicks by thermal oxidation, followed by a facile electrodeposition method to coat the pre-existing Cu 4 O x NRs with NiSe nanoparticles. The optimized NiSe-120/Cu 4 O x -3 electrode exhibited superior electrochemical characteristics (138.27 µAh cm−2 at 4 mA cm−2) compared to the other electrodes, owing to the contribution of core and shell materials, and sustained an ultra-long cycling test of 50,000 charge/discharge cycles with an excellent capacity retention of 98.7%. Inspired by commercially available AA battery, the as-synthesized working electrode was coupled with activated carbon-coated nickel foam to fabricate a cylindrical-type (C-type) hybrid supercapacitor (HSC) device, with an areal capacitance of 233.1 mF cm−2 accompanied by an extraordinary cycling efficiency of 99.1%. Furthermore, the C-type HSC device exhibited maximum energy and power densities of 70.9 µWh cm−2 and 14,000 µW cm−2, respectively and it was tested by powering portable electronics for real-time application. [ABSTRACT FROM AUTHOR]

Porous carbon materials were synthesized by a simple one-step pyrolysis of disodium ethylenediamine tetraacetate (Na 2 EDTA) under different temperature (650, 750 and 850 °C). Several characterization technologies were employed to evaluate the as-synthesized samples. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy tests were carried out to study the electrochemical property of the samples. The capacitive deionization (CDI) performance of the three samples-based electrodes was investigated and compared. The obtained results showed that pyrolysis temperature played a key role in the formation of the final products with different pore structure and heteroatom content, such as nitrogen and oxygen. Electrochemical performance measurement revealed that 750 °C sample exhibited the highest specific capacitance, the smallest diffusive resistance and charge-transfer resistance, and good conductivity. The salt electrosorption capacity of 750 °C samples were 8.02 mg g−1 at a low initial concentration of NaCl solution (25 mg L−1) and 27.75 mg g−1 at a high initial concentration of NaCl (500 mg L−1). The outstanding CDI performance of 750 °C material can be contributed to its high specific surface area and suitable pore structure. As a low-cost and processable precursor, Na 2 EDTA exhibited promising application prospect in large-scale CDI process. • Na 2 EDTA was employed as nitrogen- and oxygen-rich carbon precursors to fabricate porous carbon material (PC) through one-step pyrolysis process. • The existence of large amount of alkaline –COONa functional groups in Na 2 EDTA exhibited self-activated effect during the pyrolysis process, which simplified the fabrication of PC materials and avoided the usage of pore-forming agent. • The PC sample under 750 °C pyrolysis temperature showed the highest specific surface and pore volume and then a satisfying electrosorption capacity (8.02 and 27.75 mg g−1 with 25 and 500 mg L−1 initial concentration of NaCl solution, respectively). • Excessive high N content in PC sample may have contribution to the specific capacitance but did not do much to the increase of electrosorption capacity. [ABSTRACT FROM AUTHOR]