Electrochemical workstation

X-ray diffraction (XRD) measurements to manifest the crystal structure of photocatalysts were carried out on a Bruker D8 Advance diffractometer with CuKa1 radiation. Transmission electron microscopy (TEM) to observe morphological characteristics of photocatalysts was performed on an FEI Tencai 20 microscope. X-ray photoelectron spectroscopy (XPS) to analyze the chemical state of photocatalysts was obtained using a Thermo ESCALAB250 instrument. Room-temperature photoluminescence spectra (PL) were obtained by an Edinburgh FI/FSTCSPC 920 spectrophotometer. UV-vis diffuse reflection spectra (UV/Vis DRS) to analyze optical properties of photocatalysts were operated by a Varian Cary 500 Scan UV/Vis system. Electrochemical tests were performed on a Shanghai Chenhua Electrochemical Workstation. The three-electrode cells contained a working electrode, a counter electrode (Pt plate), and a reference electrode (Ag/AgCl electrode).

The electrochemical performance of as-synthesized LiNi_xMg_0.08Mn_1.92−xO₄ samples was evaluated in CR2032 type coin cells using lithium metal as the anode and reference electrode. The working electrodes were fabricated by mixing active materials, carbon black and polyvinylidene fluoride (PVDF) binder in 1-methyl-3-pyrrolidone (NMP) solvent with a mass ratio of 8:1:1. The electrolyte was 1 M LiPF₆ that dissolved in ethylene carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC) at a volume ratio 1:1:1. The electrochemical cells were assembled in a high-purity argon atmosphere (<1 ppm of O₂ and H₂O). The electrode activities were performed at various current rate (1 C is defined as 148.0 mAh·g⁻¹) and voltage range from 3.0 to 4.5 V (vs. Li⁺/Li) by using Land CT2001A system (Wuhan Jinnuo Electronics). The cyclic voltammogram (CV) measurements at a scan rate of 0.05 mV·s⁻¹ and the electrochemical impedance spectroscopy (EIS) tests in the frequency range of 0.1 Hz to 100 kHz were performed on an electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.).

CR2016 coin-type cells were assembled in a glove box under an inert atmosphere without water and oxygen to test the electrode performance. Polypropylene films were used as separators (the thickness of the separator was 25 µm) between the working and counter electrode (lithium wafer) in the electrolyte. An amount of 1 M LiPF₆ dissolved in the solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was used as the electrolyte (1:1, v:v). The electrode was made by applying a coating slurry of the above active materials, conductive carbon black, and PVDF binder (7:2:1, w:w:w) to the copper foil (the mass loading of the electrode was about 1.2 mg·cm⁻²), which was then dried under vacuum conditions at 120 °C for 14 h. Finally, the copper foil was cut into wafers with uniform size of 9 μm. Galvanostatic cycling measurements were conducted using a CT2001A battery tester (Wuhan LAND Electronic Co. Ltd., Wuhan, China) at specific voltage windows. Electrochemical impedance spectroscopy characteristics and cyclic voltammogram (CV) were obtained by using an electrochemical workstation (Shanghai Chenhua Instrument Co. Ltd., Shanghai, China) with a fixed voltage range and scan rate.

The electrode was prepared by mixing 80 wt% of SSAC or HSGC, 10 wt% of the conductive agent (Super-P), and 10 wt% of polymer binder (CMC : SBR = 1 : 1) uniformly into a slurry, and applied it on the copper foil with thickness of 300 μm, and then dried in a vacuum oven at 100 °C for 12 hours. We assembled the CR2032 coin-type cells in a glove box filled with Ar atmosphere, using K metal as the counter electrode, glass fiber membrane as the separator, and 0.8 M KPF6 in EC and DEC (1 : 1, v/v) for the electrolyte. Galvanostatic charge and discharge tests was performed on the land battery test system (LAND 2001 CT, China), including cycle tests and rate tests. The cyclic voltammetry (CV) tests were carried out on the Chenhua electrochemical workstation (CHI760E, China), the scanning speed is 0.1 mV s⁻¹. In the galvanostatic intermittent titration technique tests (GITT), each single GITT titration was charged or discharged at a current density of 50 mA g⁻¹ for 15 minutes, followed by a 30 minutes' relaxation. All electrochemical tests were carried out at room temperature, and the voltage range of the potassium ion battery was 2.0–0.01 V versus K/K⁺.

The photoeletrochemical characterization was carried out on an electrochemical workstation (Chenhua Instrument Co., Ltd., Shanghai, China) in a conventional three-electrode configuration, with Pt as the counter electrode and Ag/AgCl as the reference electrode. A 0.2 mol/L Na₂SO₄ aqueous solution was used as an electrolyte. A 500 W Xe lamp served as the light source. The working electrodes were prepared as follows: 10 mg of as-prepared photocatalyst was dispersed in 1 mL ethanol solution, and 50 μL of Nafion ethanol solution was added to form a uniform suspension by ultrasound for 30 min. Next, 150 μL of suspension was coated on the surface of ITO glass and dried at room temperature for photoeletrochemical measurement. The reaction was conducted in a nitrogen stream. Transient photocurrent response was measured at 0.5 V with the irradiation/dark interval of 20 s. Electrochemical impedance spectroscopy (EIS) was measured at an AC voltage magnitude of 5 mV with a frequency range of 10⁵ to 10⁻² Hz, with the initial potential of 0 V.

The electrochemical workstation (Chenhua, Shanghai, China) was used in the electrochemical experiment. The three-electrodes system was used in the electrochemical experiment. The working electrode was a Zn-Mn-Mg alloy sample with an exposed surface area of 1 cm², the reference electrode was a saturated calomel electrode, the auxiliary electrode was a platinum electrode. The corrosion behavior of the MAO coating in Hank’s solution was studied by electrochemical impedance spectroscopy (EIS) and the Tafel curve. The potential scanning rate was at the rate of 10 mV/s, and the constant frequency was set at 1000 Hz. The test solution was Hank’s solution with a pH of 7.2–7.4 at 37 °C.