Core‐Shell Structured Cobalt Sulfide/Cobalt Aluminum Hydroxide Nanosheet Arrays for Pseudocapacitor Application

• Published in: Chemistry, an Asian journal an Asian journal, 2019-02, Vol.14 (3), p.446-453
• Main Authors: Cha, Ji‐Hyun, Park, Eun Bi, Han, Sang Wook, Kim, Young Dok, Jung, Duk‐Young
• Format: Article
• Language: English
• Subjects: Additives; Aluminum; Aluminum hydroxide; Aqueous solutions; Capacitance; Chemistry; cobalt; Cobalt sulfide; Core-shell structure; Electrochemical analysis; Electrochemical cells; electrochemistry; Electrode materials; Electrodes; Electrolytes; Electrolytic cells; Hydroxides; Nanosheets; Nanostructure; Organic chemistry; pseudocapacitors; Robustness (mathematics); Shell stability; Sodium sulfide; Substrates; surface modifications; Synthesis
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201801749

The direct synthesis of nanostructured electrode materials on three‐dimensional substrates is important for their practical application in electrochemical cells without requiring the use of organic additives or binders. In this study, we present a simple two‐step process to synthesize a stable core–shell structured cobalt sulfide/cobalt aluminum hydroxide nanosheet (LDH‐S) for pseudocapacitor electrode application. The cobalt aluminum layered double hydroxide (CoAl‐LDH) nanoplates were synthesized in basic aqueous solution with a kinetically‐controlled thickness. Owing to the facile diffusion of electrolytes through the nanoplates, thin CoAl‐LDH nanoplates have higher specific capacitance values than thick nanoplates. The as‐grown CoAl‐LDH nanoplates were transformed into core–shell structured LDH‐S nanosheets by a surface modification process in Na2S aqueous solution. The chemically robust cobalt sulfide (CoS) shell increased the electrochemical stability compared to the sulfide‐free CoAl‐LDH electrodes. The LDH‐S electrodes exhibited high electrochemical performance in terms of specific capacitance and rate capability with a galvanostatic discharge of 1503 F g−1 at a current density of 2 A g−1 and a specific capacitance of 91 % at 50 A g−1. Pseudocapacitor without sacrificing power capability: Core‐shell structured cobalt sulfide/cobalt aluminum layered double hydroxide electrodes were developed for pseudocapacitors via a direct synthesis process on 3D metal substrates. Sulfide modification is a facile and efficient way to enhance the electrical performance and stability of 3D nanostructured electrode materials. The specific capacitance of the modified electrode was more than 91 % of its initial capacitance, with discharge current densities ranging from 2 to 50 A g−1.