Quantitative analysis of lattice oxygen (Ao), strongly oxidative oxygen (Bo), surfactant oxygen (Co) and adsorbed water (Do) of LSC&MoSe2 and LSC obtained in Figure 24. Summary of the ratio of lattice oxygen (LO), strongly oxidative oxygen (OO ), surfactant oxygen (SO) and adsorbed water (AW) of LSC and LSC/K-MoSe2 obtained in Figure 46.
Introduction
Alkaline water electrolysis
- Research background
- Electrocatalysts
- HER electrocatalyst
- OER electrocatalyst
- Evolution mechanism
Alkaline HER electrocatalysts are mainly divided into noble metal-based and non-noble metal-based electrocatalysts. Although it has a lower HER activity compared to that of Pt, non-noble metal-based HER electrocatalysts have been reported to outperform Pt through various studies.
Transition metal dichalcogenides
- Synthesis of TMDs
- Catalyst for water electrolysis
- Limitation of single TMDs electrocatalyst for water electrolysis
Metallic TMDs, synthesized by chemical exfoliation, are actively used in water electrolysis catalysts due to their higher electrical conductivity than semiconducting TMDs. That is, even if the specific surface area can be improved through morphology engineering of TMDs, there is a limit to improving the performance of water electrolysis unless the number of active sites where the actual electrochemical reaction takes place does not increase.
Although they have emerged as candidates to replace noble metal water electrolysis catalysts, there are limitations. TMDs alone have poor hydrogen or oxygen adsorption/desorption kinetics compared to those of noble metal water electrolysis catalysts due to their limited electrical structure.
Facile Approach to Prepare HER electrode and to enhance dispersibility of TMDs in aqua
- Research background
- Results and Discussion
- Conclusion
- Experimental details
- References
The dispersibility of N-MoS2 is closely related to the Nafion surfactant concentration, which affects the Nafion cluster size in the solvent medium. Morphology and elemental analysis of MoS2 flakes were performed using SEM (S-4800, Hitach), AFM (DI-3100, Veeco) operating in pouring mode, and HRTEM (JEM-2100F, JEOL).
In-situ phase transition of TMDs in perovskite oxide/TMDs heterostructure and excellent
Research background
In-situ phase transition of TMDs in perovskite oxide/TMDs heterostructure and overall excellent water electrolysis. The Gibbs free energy of MoSe2 for hydrogen adsorption is close to zero and the hydrogen range is larger than other TMDs [24-26]. However, due to the low conductivity of MoSe2 in the internal 2H phase, complex structures based on MoSe2 such as MoSe2/carbon cloth [24], MoSe2/n+p-Si [27] and MoSe2/graphene [28,29] have generally been used to improve electrochemical properties.
Moreover, inducing the phase transition of metal (1T) from semiconductor (2H) in TMD is considered to improve the performance of TMDs-based composite electrochemical catalysts. However, the phase change process of TMDs is quite complicated and time-consuming, and inert environments are required due to highly reactive materials such as alkali metals [30, 31]. In our current work, we have devised a complex perovskite oxide TMD heterostructure consisting of MoSe2 (indicated MoSe2), La0.5Sr0.5CoO3–δ (indicated LSC only) and Ketjenblack carbon (indicated KB) as a dual-functional electrocatalyst for total water electrolysis.
Interestingly, an in-situ local phase transition of MoSe2 (2H- to 1T-MoSe2) is observed during the formation of LSC&MoSe2 due to the spontaneous migration of electrons from Co to Mo. In addition, the proposed electrode has excellent overall aqueous electrolysis stability over 1000 hours at a high current density of 100 mA cm-2, resulting in superior performance compared to Pt/C || IrO2 electrode.
Results and Discussion
Inset is the FFT image of the LSC. e) The XRD spectra of LSC, MoSe2 and LSC&MoSe2. The pore size of LSC&MoSe2 was investigated using the Barrett-Joyner-Halenda (BJH) method. Therefore, the enhanced OER activity of LSC&MoSe2 may be due to the higher Co3+/Co2+ ratio than LSC (Table 5).
Quantitative analysis of Co3+/Co2+ ratio in LSC&MoSe2 and LSC obtained the XPS result in Figure 23. SEM images before and after 1000 hours of general water splitting test of LSC&MoSe2. After the stability test, the chemical state of LSC&MoSe2 was further investigated through XPS analysis.
Quantitative analysis of Co3+/Co2+ ratio in LSC&MoSe2 obtained XPS result in Figure 33. Quantitative analysis of lattice oxygen (Ao), strong oxidative oxygen (Bo), surface active oxygen (Co) and adsorbed water (Do) of LSC&MoSe2 obtained in Figure 33 .
Conclusion
Experimental details
The total weight of the catalyst was kept at 500 mg, and each catalyst was dispersed in ethanol and ball milled at 400 rpm for 2 h using a Zr ball. The BET surface area and pore size of LSC&MoSe2 and LSC were investigated using a physical adsorption analyzer (ASAP 2420, Micromeritics Instruments) with N2 desorption/adsorption. LSC&MoSe2 and LSC used in TGA analysis were exposed to humid air for 24 hours to absorb moisture.
The correction of the reversible hydrogen electrode (RHE) was experimentally determined at a scan rate of 1mV s-1 in H2-saturated 1M KOH, where platinum wires were used as working and counter electrodes, and Ag/AgCl were used as reference electrodes. All half-cell profiles were iR-compensated by measuring solution resistance (1 M KOH). Then, a supercell structure was created, and then half of the La atoms were replaced by Sr atoms, resulting in the stoichiometry of La0.5Sr0.5CoO3.
The unrelaxed CoO2 and (La, Sr)O terminal sheet energy, the total energy of the bulk unit cell, N is the formula unit of the sheet model, and A is the surface part. In the denominator, the acquisition of four factors takes place on the four split surfaces of the two ends.
Directional Construction of Vertical Nitrogen-Doped 1T-2H MoSe2/Graphene Shell/Core Nanoflake Arrays for Efficient Hydrogen Evolution Reaction. Charge-mediated semiconducting to metallic phase transition in molybdenum disulfide monolayer and hydrogen evolution reaction in new 1T' phase. Epitaxial growth of Ni(OH)2 nanoclusters on MoS2 nanosheets for enhanced alkaline hydrogen evolution reaction.
CoSe2/MoSe2 heterostructures with enriched water adsorption/dissociation sites for enhanced alkaline hydrogen evolution reaction. Integrated 3D MoSe2@ Ni0.85Se nanowire network with synergistic cooperation as highly efficient electrocatalysts for hydrogen evolution reaction in alkaline medium. Doped MoSe2 nanoflakes/3D metal oxide-Hydr (Oxy) Oxides hybrid catalysts for pH-universal electrochemical hydrogen evolution reaction.
Ni3S2/carbon nanotube nanocomposite as electrode material for hydrogen evolution reaction in alkaline electrolyte and enzyme-free glucose detection. Easily prepared dinickel phosphide (Ni2P) nanoparticles as an efficient and robust electrocatalyst for hydrogen evolution.
Multidirectional charge transfer in perovskite oxide and transition metal dichalcogenides
Research background
Summary of charge transfer resistance of LSC/K-MoSe2 with different weighting ratios obtained from Nyquist plots in Figure 41. This confirms that the electronic structure modulation of LSC/K-MoSe2 occurs by charge transfer between LSC and K-MoSe2. XPS analysis was performed to further elucidate the origin of the enhanced HER and OER performance of LSC/K-MoSe2.
Summary of the ratio of Co3+/Co2+ in LSC and LSC/K-MoSe2 obtained from Figure 45. Complementary charge transfer in LSC/K-MoSe2. a) Schematic of the atomic structure and difference in charge transfer effect for K-MoSe2 and LSC/K-MoSe2. The OER initiation potential decreases in the same decreasing order of LSC > IrO2 > LSC/K-MoSe2.
Complete aqueous electrolysis of LSC/K-MoSe2. a) Digital image of a full-cell water electrolysis system with LSC/K-MoSe2 couples. A summary of the relationship between lattice oxygen (LO), highly oxidizing oxygen (OO), surface active oxygen (SO) and adsorbed water (AW) of LSC/K-MoSe2 obtained in Figure 59. XPS analysis further shows the excellent chemical stability of LSC/K- MoSe2 (Figure 59 and Table 15, 16).
Operational stability of the LSC/K-MoSe2 couple measured at 100 mA cm–2 in 10 M KOH at room temperature.
Results and Discussion
Conclusion
We have developed a novel heterostructure-based electrocatalyst that exhibits excellent overall water electrolysis performance and stability. Modulated electronic structure of MoSe2 with high metallic purity and enhanced electrical conductivity enhanced the HER kinetics. Overall water electrolysis performance with LSC/K-MoSe2 pairs outperformed noble metal pairs, exhibiting a lower overpotential cell voltage at 10 and 100 mA cm-2 and excellent operational stability for 2,500 hours.
Experimental details
The increased affinity of LSC improved the OER performance over IrO2 by enhancing the adsorption capacity of oxygen-generating intermediates on the catalyst surface. The crystallographic information of the catalyst was analyzed through high-power XRD (D/MAX2500V/PC, Rigaku) at 40 kV and 200 mA at a scanning speed of 1°. TGA analysis was performed to investigate the surface adsorption capacity of the catalyst at a ramp temperature rate of 10 °C min-1 using a thermogravimetric analyzer (Q500, TA).
The surface area and pore size of the catalyst were evaluated using the N2 desorption/adsorption isotherm of the catalyst using a physical adsorption analyzer (ASAP 2420). The optical properties of the catalyst were collected using a UV-Vis-NIR spectrometer (Cary 5000, Agilent). To measure the double layer capacitance (Cdl), the potential window of the cyclic voltage flow diagram was spread at different scan rates of 20-160 mVs-1 in a non-Faraday region of 0.03 to 0.33 V (vs. RHE).
The results of the Chronopotentiometry stability test of total water electrolysis at a current density of 100 mA cm-2 were obtained using electrochemical workstations (ZIVE BP2C, Wonatech Co., Ltd.). Second, the free energy of the HER reaction was calculated until the residual force component was within 5 10−3 eV/Å using the equation 𝐺𝐻= 𝐸(𝐻) + 0.24 𝑒𝑉.
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