Rational Design of Co(II) Dominant and Oxygen Vacancy Defective CuCo₂O₄@CQDs Hollow Spheres for Enhanced Overall Water Splitting and Supercapacitor Performance

Abstract

The hierarchical CuCoO@carbon quantum dots (CQDs) hollow microspheres constructed by 1D porous nanowires have been successfully prepared through a simple CQDs-induced hydrothermal self-assembly technique. XPS analysis shows the CuCoO@CQDs possesses the Co(II)-rich surface associated with the oxygen vacancies, which can effectively boost the Faradaic reactions and oxygen evolution reaction (OER) activity. For example, the as-synthesized 3D porous CuCoO@CQDs electrode exhibits high activity toward overall electrochemical water splitting, for example, an overpotential of 290 mV for OER and 331 mV for hydrogen evolution reaction (HER) in alkaline media have been achieved at 10 mA cm, respectively. Furthermore, an asymmetric supercapacitor (ASC) (CuCoO@CQDs//CNTs) delivers a high energy density of 45.9 Wh kg at 763.4 W kg, as well as good cycling ability. The synergy of Co(II)-rich surface, oxygen vacancies, and well-defined 3D hollow structures facilitates the subsequent surface electrochemical reactions. This work presents a facile method to fabricate energetic nanocomposites with highly reactive, durable, and universal functionalities.

Highly Hydrophilic Carbon Dots' Decoration on NiCo2O4 Nanowires for Greatly Increased Electric Conductivity, Supercapacitance, and Energy Density

“…According to the X‐ray diffraction (XRD) patterns in Figure c, this carboneous product is amorphous and has no obvious effect on crystallization of NiCo 2 O 4 during the synthesis. Furthermore, as shown in Figure S4b (Supporting Information) the Ni 2p spectra consist of two spin–orbit doublets (2p 1/2 and 2p 3/2 ) and their shake‐up satellites, in which the fitting peaks at 854.4 and 871.9 eV are contributed to Ni 2+ as well as the other fitting peaks at 855.9 and 874.0 eV are indexed to Ni 3+ , respectively, confirming the presence of both Ni 2+ and Ni 3+ . Similarly, the Co 2p spectra in Figure S4c (Supporting Information) also consist of the contributions of Co 2+ (779.8 and 794.8 eV) and Co 3+ (780.8 and 796.0 eV), respectively …”

Synthesis of ultrathin Co2AlO4 nanosheets with oxygen vacancies for enhanced electrocatalytic oxygen evolution

“…As shown in Fig. 3c, two obvious peaks of Co 2p 3/2 and Co 2p 1/2 can be split into two spin-orbit doublets, which can be assigned to Co 3+ (780.5 and 795.7 eV) and Co 2+ (782.1 and 797.4 eV), respectively [26,27]. Based on the peak area, the ratio of Co 2+ /Co 3+ on the surface of VO-rich Co 2 AlO 4 was determined to be 1.78, which was much higher than that of pristine Co 2 AlO 4 (0.84).…”

“…. ARTICLES (Table S1) [27,33,[41][42][43][44][45][46][47][48][49][50][51][52][53][54][55]. The results indicated that the VO-rich Co 2 AlO 4 possessed a high OER kinetics.…”

“…Based on the peak area, the ratio of Co 2+ /Co 3+ on the surface of VO-rich Co 2 AlO 4 was determined to be 1.78, which was much higher than that of pristine Co 2 AlO 4 (0.84). This is because that the formation of oxygen vacancies was balanced by the conversion of Co 3+ to Co 2+ [27].…”

“…S9), further proving that more Co 2+ sites were presented in the VO-rich Co 2 AlO 4 . It has been known that oxygen vacancies usually play a very important role in the enhancement of OER activity [21,24,25,27,33]. We carried out density function theory calculations for Co 2 AlO 4 and VO-rich Co 2 AlO 4 , respectively.…”