Evaluation of the Specific Capacitance of High-Entropy Oxide-Based Electrode Materials in View of Their Use for Water Desalination via Capacitive Method

Abstract

Water pollution and scarcity are serious concerns for the growing world population. To meet the ever-pressing demand of fresh water, a variety of desalting techniques of seawater have been developed. Due to its environmental friendliness, high efficiency, easy regeneration of the electrodes, ambient operating pressure, and low operating potential suitable for the use in remote areas, the capacitive deionization (CDI) method is one of the most sustainable among them. This work focuses on the preparation of high-entropy oxides (HEOs) and carbon/HEO composites and the evaluation of their specific capacitance in view of their possible use as CDI electrode materials. CrMnFeCoNi-HEO, having spinel structure (sHEO), is obtained in the form of nanoparticles (NPs) and nanofibers (NFs) by the sol–gel method and electrospinning, respectively. Composite NFs with embedded sHEO NPs or MgCoNiCuZn-HEO NPs with rock-salt structure (rHEO) are also produced. In the 5–100 mV s−1 scan rate range, the specific capacitance improves in the order C/rHEO NFs (8–32 F g−1) ≅ sHEO NPs (9–32 F g−1) < sHEO NFs (8–43 F g−1) < C/sHEO NFs (12–66 F g−1). The highest capacitance is obtained when the beneficial contributions of the carbon matrix and smaller-sized HEO NPs are synergistically coupled.

Evaluation of electrospun spinel-type high-entropy (Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)3O4, (Cr0.2Mn0.2Fe0.2Co0.2Zn0.2)3O4 and (Cr0.2Mn0.2Fe0.2Ni0.2Zn0.2)3O4 oxide nanofibers as electrocatalysts for oxygen evolution in alkaline medium

“…They consist of grains with a polyhedral shape and sizes ranging from a few tens to hundreds of nm, attached to each other to form a porous three-dimensional (3D) structure, as typical of several electrospun oxides. 60,6369 Since the size of as-spun NFs constitutes a geometric constraint for the development of HEO grains, their size is generally smaller (and their size distribution usually narrowe 60,70 ) than that obtained under the same heat treatment conditions with other synthesis techniques, including SG (compare HEO grains in Figure 1e and k). Moreover, as demonstrated in Figure S5, the grains can be easily detached from each other.…”

Charge Storage Mechanism in Electrospun Spinel‐Structured High‐Entropy (Mn0.2Fe0.2Co0.2Ni0.2Zn0.2)3O4 Oxide Nanofibers as Anode Material for Li‐Ion Batteries

“…[29] Among them, (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 ) 3 O 4 , first synthesized in 2018 via a solid-state method, [30] has received great attention. [31][32][33][34][35][36][37][38] A charge/discharge capacity of 1235 mAh g −1 (at 20 mA g −1 ), the highest among all known HEOs, has been reported for (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 ) 3 O 4 nanoparticles synthesized via a surfactant-assisted hydrothermal method [35] (Cr,Mn,Fe,Co,Ni) HEO prepared by the oxidation of high-entropy CrMnFeCoNi alloy powders delivers a reversible capacity of 597 mAh g −1 and shows a capacity retention of 86% after 1200 cycles at 2 A g −1 . [39] The stability of (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 ) 3 O 4 synthesized by solid state reaction (402 mAh g −1 capacity after 300 cycles at 0.5 A g −1 ) has been attributed to the amorphization process occurred during the initial discharging.…”