atomic-level energy storage mechanism of cobalt hydroxide electrode for pseudocapacitors - battery energy storage

With high capacitance and long cycle performance, cobalt hydroxide is a promising electrode material for super capacitor.
However, the energy storage/conversion mechanism of cobalt hydroxide is still vague at the atomic level.
Here, we reveal how cobalt hydroxide is used as an electrode for a super capacitor under operating conditions.
We found that the high specific capacitance and long cycle life of the cobalt hydroxide involve the complete modification of the electrode morphology, which is generally considered unfavorable, but in fact has little effect on the performance.
The conversion during charging/discharging does not have any large-scale structural evolution, but there are some minor shuffling or adjustments to the atomic/ionic species.
The results not only reveal the potential of the super capacitor to a large extent depends on the potential structural similarity of the switching phase, but also pave the way for future material design of the super capacitor, battery and hybrid equipment.
Our previous work has shown that electroplating is an ideal synthesis method for the preparation of adhesives
Free electrode with better performance.
In this work, CFP is used as a substrate.
Before preparation, the CFP was cleaned by ultrasonic wave with acetone, ethanol and distilled water for 30 min respectively. Co(OH)
Electrodeposition film in aqueous solution containing 1. 2u2009M Co(NO)(
Analytical reagents (AR), ≥99.
0%, Xilong Chemical Co. , Ltd. , Ltd. ).
The deposition process is in the traditional three-at 45 °c-
CFP composed of electrode electrolytic units (2u2009cm in area)
Platinum counter electrode (2u2009cm in area)
As well as the reference of saturated mercury electrode.
The deposition potential is controlled at-0. 9u2009V for 60u2009min.
The electric product process of Co (OH)
The film can be expressed as: After deposition, double-
Dry in a vacuum oven at 60 °c for 12 hours.
Quality of deposited Co (OH)
Measurement of weight difference before and after electroplating by micromeasurementbalance (
Sadores BT125D)
The accuracy is 0. 01u2009mg.
Prepare the surface morphology of the electrode, measured after bathing at 15 min 1 µm in KOH, after XAS, and studied using SEM (
Hitachi SU8000 scanning electron microscope operating under 2 kv.
A detailed study of structural features was conducted by transmission electron microscopy (
Justice and Equality Movement arm 1300 S high
Resolution TEM image of electron diffraction pattern and open field in selected area and Libra 200 HT Mc Cs (BF)images).
Check specific areas by using automatic JW-N adsorption measurements
BK132F instruments from Vivo gb sci.
Scientific instruments.
The Fourier transform infrared spectrum was obtained from the Perkin Elmer spectrum B instrument. X-
Optoelectronic energy spectrum (XPS)
Get spectrum from ESCALAB-
250 instruments with a single-color Al Kα radiation source and a hemisphere detector with an energy resolution of 0. 1u2009eV. The Co(OH)
Use X-
Ray diffraction (
Rigaku d/MAX2500 = month. 54u2009nm).
For more detailed information, X-
Co prepared (OH)
The electrode is collected in the Shanghai synchronous radiation device, and the BL14B1 beam line with an electronic energy of 2 ggev.
Electro-chemical measurement on computer
Controllable constant potential meter (
CHI660E, Shanghai CH Instrument Company)with a three-
The electrode battery is electrolyte in KOH aqueous solution.
The working electrode is Co (OH).
The platinum sheet and the saturated mercury electrode were used as the reverse electrode and the reference electrode respectively.
Electrolyte (1u2009M KOH)
From high school.
Purity particles of KOH (AR, ≥85.
0%, national pharmaceutical chemical reagent company. , Ltd. )
By adding 56 grams of pellets to 1 liter of distilled water.
Before the electrical activity is measured, Co (OH)
Soak in the electrolyte for 15 minutes, allowing OH to penetrate into the mezzanine space.
Activated carbon (AC)
The preparation methods of electrodes are as follows: AC, ethylene-propylene Black, nafion (wt%: 85:10:5)
A small amount of ethanol was prepared by stirring for 6 h to produce a uniform paste.
Press this paste on the Ni foam and make an AC electrode. A two-
Electrode cell structure is used to measure the performance of asymmetric SC in 1 m KOH aqueous solution.
The working electrode is prepared for Co (OH)
The AC electrodes mentioned above, they are put together, with porous non-
Woven fabric separator.
The activity of it was then studied by cyclic kVA.
Its charging/discharging capability was measured by electrostatic test.
The energy and power density of asymmetric capacitors are calculated as follows: = 0.
5 ×, = ×/, where (Whu2009kg)
Energy density and (Wu2009kg)
Power density. X-
Synchronous accelerator in Beijing (BSRF)
On the beamline 1W1B.
The BSRF storage ring has an electronic energy of 2.
250 of the beam of the YMMA 2 u2009 GeV band. A Si (111)double-
The crystal color meter is applied.
The beam size used at the sample position is about 900x300 u2009 μm.
For the electrochemical experiment, no data need to be collected and transmitted, and the fluorescence mode is adopted.
All data are collected at ambient temperature.
Curve fitting using Artemis and IFEFFIT software, using Co (OH)
And CoOOH data as the starting parameters.
Before collecting the XAS spectrum, the electrode cycles 30 times in three times
The electrode battery reaches a stable state.
The self of the electrochemical methodmade device ()
Cycle KVA is used from 0. 3 to 0. 4u2009V.
To satisfy the conditions for XAS sampling, we set the scan rate to 0. 4u2009mVu2009s.
Quickly obtained the spectrumEXAFS (QXAS)mode. Cobalt oxide (99.
995% of Alfa Aesar may contain up to 10% CoO)
The purchase is for reference. Spin-
The polarised DFT calculations are based on the hypercrystal cell method and Perdew-Burke Ernzerhof (PBE)
Functions implemented in the simulation package from scratch in Vienna (VASP, version 5. 4. 1).
We have (1), O (2, 2)and Co (3, 3, 3, 4)
With valence electrons expanding in plane waves with cutting
Shutdown energy of 520ev while the remaining electrons are replaced by PBE-Projector based
Enhanced wave potential.
Total energy and electron density are calculated using the density method of Dudarev.
Hubbard U-
Terms describing the interaction of the scene Cullen (
=-, That is, the difference between Cullen and the exchange parameters, hereinafter referred to as simple)
Added to the PBE feature.
We used the value of = 3.
3ev ev of Co atom obtained by Ceder.
Based on oxide formation energy and with the recent proposed description of the different cobalt oxide and hydroxide phases and CoOOH (ref. )and Co-doped NiOOH (ref. )surfaces.
We used a unit cell with two formula units (CoOH).
The equilibrium lattice constant is calculated, allowing the atomic position, lattice vector, and cell shape to relax when the residual force threshold is 0.
02 evevev and use the monkhorst-pack grid of 8 × 2-point sampling.
These calculation settings ensure the tight convergence of the equilibrium distance (better than 0. 001u2009Å).
The transition structure of the phase transition considered is located by using a light push elastic band algorithm using five images along each path.
The optimized lattice constants are used for the calculation of all push elastic bands performed at a constant volume.
Surface calculation using a sheet model with a ratio of chemical metrology along five low cuts
Exponential direction of β-Co(OH)(space group P-3m1): (0001); (10–10); (11–20); (01–12); and (10–14).
Each slab model contains four to six atomic Co (OH)
Layers, between the flat and center layers, there is a vacuum of 15 å, fixed to their large pieces of pbe u-
Optimal position, leaving at least two layers of slack on both sides of the plate, with a residual force threshold of 0. 03u2009eVu2009Å.
Displays the side and top views of the optimized geometry.
Calculation using 800ev ev aircraftwave cut-off and -
Point grids of 12 × 1, 10 × 8 × 1, 14 × 12 × 1, 8 × 4 × 1 and 12 × 4 × 1 (0001), (10–10), (11–20), (01–12)and (10–14)
The surface is respectively. This set-
Up ensures a tight convergence of energy for each atom at least 3mev mev.
The surface area of each plate given area 2 and free energy is calculated as = (−)
/2, where is the number of Co (OH)
The formula unit in the plate is the free energy of each formula unit of the ground state Bulk Co (OH)(space group 2).
We ignore the zero-point energy and entropy corrections of the sum, which are subsequently equal to the total energy and the sum of the discrete Fourier transform, respectively.
According to the requirements, the corresponding authors provided data supporting the results of this study.