Fabrication of nanosheet-assembled hollow copper–nickel phosphide spheres embedded in reduced graphene oxide texture for hybrid supercapacitors

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Abstract

Nanosheet-assembled hollow copper–nickel phosphide spheres encapsulated in reduced graphene oxide were synthesized for hybrid supercapacitor.

Abstract

Owing to their metalloid characteristics with high electrical conductivity, transition metal phosphides (TMPs) have attracted considerable research attention as prospective cathodes for hybrid supercapacitors. Unfortunately, they usually exhibit low rate performance as well as poor longevity, which does not meet the demands of hybrid supercapacitors. The nanocomposite constructed from reduced graphene oxide (rGO) and TMPs with a highly porous nature can effectively overcome the above-mentioned issues, greatly widening their utilization. In this work, we fabricated nanosheet-assembled hollow copper–nickel phosphide spheres (NH-CNPSs) by the controllable phosphatizing of copper–nickel–ethylene glycol (CN–EG) precursors. Then, porous NH-CNPSs were embedded in rGO texture (NH-CNPS–rGO) to form a unique porous nanoarchitecture. The obtained NH-CNPS–rGO has several advantages benefiting as the cathode electrode, such as (i) the hollow structure as well as porous nanosheets are conducive to fast electrolyte diffusion, (ii) the electrical conductivity of NH-CNPS is further enhanced when coupled with the rGO texture, hence promoting electron transfer in the whole structure, (iii) wrapping NH-CNPSs within the rGO texture endows the nanocomposite with much better structural stability, resulting in longer durability of the electrode, And (iv) the porous structures generated in the nanocomposite provide a perfect space for reducing the mass transfer resistance and accessing the electrolyte, thereby boosting the reaction kinetics. The tests demonstrated that the optimal NH-CNPS–rGO electrode revealed a capacity of up to 1075 C g ⁻¹, a superior rate capacity, and exceptional longevity of 94.7%. Moreover, a hybrid supercapacitor (NH-CNPS–rGO‖AC) equipped with the NH-CNPS–rGO-cathode electrode and activated carbon (AC)-anode electrode represented a satisfactory energy density of 64 W h kg ⁻¹ at 801 W kg ⁻¹ and amazing longevity (91.8% retention after 13 000 cycles), which endorses the promising potential of NH-CNPS–rGO for high-efficiency supercapacitors. This research showcases an appropriate method to engineer hollow TMP–rGO nanocomposites as effective materials for supercapacitors.

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Improved synthesis of graphene oxide.

Daniela C Marcano, Dmitry V Kosynkin, Jacob M. Berlin … (2010)

An improved method for the preparation of graphene oxide (GO) is described. Currently, Hummers' method (KMnO(4), NaNO(3), H(2)SO(4)) is the most common method used for preparing graphene oxide. We have found that excluding the NaNO(3), increasing the amount of KMnO(4), and performing the reaction in a 9:1 mixture of H(2)SO(4)/H(3)PO(4) improves the efficiency of the oxidation process. This improved method provides a greater amount of hydrophilic oxidized graphene material as compared to Hummers' method or Hummers' method with additional KMnO(4). Moreover, even though the GO produced by our method is more oxidized than that prepared by Hummers' method, when both are reduced in the same chamber with hydrazine, chemically converted graphene (CCG) produced from this new method is equivalent in its electrical conductivity. In contrast to Hummers' method, the new method does not generate toxic gas and the temperature is easily controlled. This improved synthesis of GO may be important for large-scale production of GO as well as the construction of devices composed of the subsequent CCG.