Amorphous-Ni(OH)₂ on a Vertically Grown Lamellar Ag-Modified MoS_x Thin-Film Electrode with Surface Defects for Hydrogen Production in Alkaline Solutions

Abstract

A low-temperature radio-frequency-sputtered Ag-modified MoS x lamellar thin-film electrode with a home-made target was deposited on a carbon-cloth substrate and electrochemically modified with amorphous Ni­(OH)2. All the as-prepared thin-films’ properties were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and electrochemical measurements. Electrochemical measurements of a-Ni­(OH)2/Ag-modified MoS x lamellar thin films exhibited promising hydrogen evolution reaction properties in alkaline solutions. The linear sweep voltammetry and electrochemical impedance spectroscopy measurements indicated a relatively low Tafel slope of 95.3 mV/dec and a low electron-transfer resistivity of 12.26 Ω, respectively. The observed overpotentials were 0.12 and 0.26 V at 10 and 100 mA, respectively. Furthermore, cyclic voltammetry measurements revealed that the thin-film electrode had the highest double-layer capacity (C dl) of 11.3 mF/cm2, which also implied a highly active electrochemical surface area. Finally, the stability of a-Ni­(OH)2/Ag-modified MoS x thin films was examined with a constant current density of 10 mA/cm2 for 20 h. It was found that the non-stoichiometric MoS x played an essential role in the water-activation process due to the presence of sulfur-vacancy sites (VS 2+). During the electrochemical process, VS 2+ acts as an active site to pin water and weaken the OH–H bonding, in which the water-originated OH is further bonded with periodically terminated surface defect of Ni­(OH) x on the electrode. The defected Ni­(OH) x on the catalyst surface helps the dissociation of OH bonding in water adsorbed on Ag-MoS x to generate H* intermediates for further Heyrovsky steps. The low-cost thin-film electrode with a relatively low overpotential is promising for industrial applications based on the experimental data.

Epitaxial Electrocrystallization of Magnesium via Synergy of Magnesiophilic Interface, Lattice Matching, and Electrostatic Confinement

“…37,38,40 From the O 1s spectrum (Figure 4c), three peaks at 528.8, 531.2, and 533.5 eV are assigned to metal− oxygen bonds, hydroxyl, and chemisorbed water, respec-tively. 36,37,41 The adsorbed water peak further proves the existence of intercalated water of Ni(OH) 2 @CC, which agrees well with the XRD results.…”

“…Copper is less hydrophilic and To further disclose the electronic and structural changes during the initial discharge process of the Ni(OH) 2 @CC host, X-ray absorption near edge structure (XANES) was conducted after Mg plating for 30 min. In Figure 5c, both the Ni(OH) 2 @ CC and the discharged Ni(OH) 2 @CC samples show a strong peak at 8351.6 eV in the Ni K-edge spectrum in accordance 36,55,56 After Mg 0 is stripped, the binding energy of the O−M species cannot be restored to its pristine state and Mg-containing species are still detected (Figure S14). This indicates the incorporation of the intercalated Mg in the layered Ni(OH) 2 structure during the initial cycles.…”

“…As shown in Figure d (pictured middle and right), a typical copper current collector and graphite sheets show poor lattice misfits with (002) Mg (about 20.9% for Cu and 55.7% for graphite, respectively), which do not easily form a coherent or semicoherent interface with a Mg nucleus. To achieve better lattice matching, we shift to the popular 2D layered material Ni­(OH) 2 , which has been extensively exploited as electrode materials for alkaline batteries and supercapacitors. − Ni­(OH) 2 is of specific interest as a suitable candidate to epitaxially electrodeposit Mg because it shows a lower lattice geometrical misfit with Mg crystals of about 2.8% (Figure d, pictured left). In addition, the regulable interlayer gap prefers to accommodate Mg-ion intercalation due to its weak van der Waals interaction and the preintercalated water molecules in the lattice structure.…”

Crystalline‐Amorphous Interfaces Coupling of CoSe2/CoP with Optimized d‐Band Center and Boosted Electrocatalytic Hydrogen Evolution

“…In recent years, amorphous electrocatalysts have attracted immense research attention due to their superior hydrogen evolution reaction (HER) performance over their crystalline counterparts in many occasions. [ 1 ] The enhanced electrocatalytic activity of amorphous electrocatalysts can be mainly attributed to the following factors. Amorphous materials can achieve both surface and volume confined electrocatalysis, while crystalline materials can only undergo surface catalysis.…”

Electrospinning Preparation of N, P Dual-Doped Molybdenum Carbide/Porous Carbon Fibers with Highly Improved Electrocatalytic Activity for Hydrogen Evolution Reaction

“…Among various clean energies, hydrogen energy is considered the most promising one due to its advantages of high energy density, zero emission of pollutants, and renewability. − Among many hydrogen production methods, water electrolysis is the cleanest and sustainable method for the large-scale production of high-purity hydrogen. − However, high overpotentials of the two half reactions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have reduced the efficiency and increased the energy consumption of the whole water electrolysis. Therefore, highly efficient electrocatalysts are desired to increase kinetic rates of HER, OER, and energy efficiency of the whole water electrolysis. − Although precious metal (Pt, Pd, Ru, and Ir)-based catalysts are the-state-of-art ones, scarce storage and high cost have limited their application on a large scale. , Therefore, non-noble metal electrocatalysts with high efficiencies are desired to substitute the noble metal-based ones. , …”