Using Metal Cation to Control the Microstructure of Cobalt Oxide in Energy Conversion and Storage Applications

Abstract

Herein, a facile and efficient synthesis of microstructured Co3O4 for both supercapacitor and water‐splitting applications is reported. Metal cations (Fe3+, Cu2+) serve as structure‐directing agents regulating the structure of Co compounds, which are subsequently annealed to yield Co3O4. Detailed characterizations and density functional theory (DFT) calculations reveal that the in situ Cl‐doping introduces oxygen defects and provides abundant electroactive sites, and narrows the bandgap, which enhances the electron excitation of the as‐formed Co3O4. The as‐prepared Cl‐doped Co3O4 hierarchical nanospheres (Cl‐Co3O4‐h) display a high specific capacitance of 1629 F g−1 at 1 A g−1 as an electrode for supercapacitors, with excellent rate capability and cyclability. The Cl‐Co3O4‐h//activated carbon (AC) asymmetric supercapacitor (ASC) electrode achieves a specific capacitance of 237 F g−1 at 1 A g−1, with an energy density of 74 Wh kg−1 at a power density of 807 W kg−1 and even maintains 47 Wh kg−1 at the higher‐power density of 24.2 kW kg−1. An integrated electrolyzer for water‐splitting with Cl‐Co3O4‐h as both cathode and anode can be driven by Cl‐Co3O4‐h//AC ASC. The electrolyzer provides a high current density of 35 mA cm–2 at a cell voltage of 1.6 V, with good current density retention over 50 h.

A Self‐Reconstructed Bifunctional Electrocatalyst of Pseudo‐Amorphous Nickel Carbide @ Iron Oxide Network for Seawater Splitting

“…The mass activity (Figure 3g ) of NiFe‐PBA‐gel‐cal in freshwater is 66.3 A g –1 at an overpotential of 280 mV, which is approximately four times higher than that of NiFe‐PBA‐gel‐cal in simulated seawater, this may be due to the formation of hypochlorite attached to the surface of the network blocking combination with oxygen‐containing intermediates during the electrolysis. [ 43 , 44 , 45 ] The mass activity of NiFe‐PBA‐gel‐cal is also over ten times that of FeFe‐PBA‐gel‐cal. Turnover frequencies (TOFs) for NiFe‐PBA‐gel‐cal and FeFe‐PBA‐gel‐cal were also calculated by using the ECSA at different overpotentials (Figure 3e,f and Figure S5 , Supporting Information) based on the total deposited metal amount, a similar tendency as mass activity is observed for TOFs (Figure 3h ).…”

Plasma-Engineered N-CoOx Nanowire Array as a Bifunctional Electrode for Supercapacitor and Electrocatalysis

“…As displayed in Figure 4 d, our device realized a high energy density of 80.5 Wh/kg at the power density of 1.3 kW/kg, while the power density reached 25.4 kW/kg at the energy density of 43.7 Wh/kg. The comprehensive performance is superior or comparable to the recently reported Co 3 O 4 //carbon devices, such as Co 3 O 4 nanosheet (38.8 Wh/kg at 7.5 kW/kg) [ 41 ], Co-Co 3 O 4 (60.8 Wh/kg at 5.8 kW/kg) [ 42 ], Co 3 O 4 nanorod (34.1Wh/kg at 4 kW/kg) [ 43 ], Co 3 O 4 @C nanofiber (37.75 Wh/kg at 1.8 kW/kg) [ 44 ], Cl-doped Co 3 O 4 nanosphere (74 Wh/kg at 0.807 kW/kg, 47 Wh/kg at 24.2 kW/kg) [ 45 ], Co 3 O 4 nanoplate (66.1 Wh/kg at 1.652 kW/kg) [ 46 ], and Co 3 O 4 nanosheet (51.7 Wh/kg at 1.125 kW/kg, 34.7 Wh/kg at 33.75 kW/kg) [ 47 ].…”

Rational Design of Porous Nanowall Arrays of Ultrafine Co4N Nanoparticles Confined in a La2O2CN2 Matrix on Carbon Cloth for a High-Performing Supercapacitor Electrode

“…On the other hand, in the preliminary stage of the stability test, the electrochemical activation may occur, which would cause the improvement of the specific capacitance of the electrode at the first few hundreds of cycles. 51,52 To further understand the optimized faradic behavior of the Co 4 N@LOC/CC electrode, the kinetics of charge storage was studied by CV curves at scan rates of 5−60 mV s −1 (Figure S15 of the Supporting Information). The peak current (i) and scan rate (v) follow the relationship 53 = i av b (11) b is a parameter to distinguish the surface capacitive-controlled process (b = 1.0) and diffusion-controlled process (b = 0.5).…”

“…On one hand, we added some solutions several times to reduce the influence of the evaporation of the electrolyte on stability during the cycle stability test, which may distort the test system and lead to the fluctuation of capacitance. On the other hand, in the preliminary stage of the stability test, the electrochemical activation may occur, which would cause the improvement of the specific capacitance of the electrode at the first few hundreds of cycles. , …”