For the first time, noble-metal-free nickel phosphide (Ni2P) was used as an excellent catalyst precursor for water oxidation catalysis. The lowest onset potential was observed at ∼1.54 V (vs. RHE) ...and a Tafel slope of 60 mV dec(-1) was obtained in alkaline solution (pH = 13.6).
Abstract
Metallic tungsten disulfide (WS
2
) monolayers have been demonstrated as promising electrocatalysts for hydrogen evolution reaction (HER) induced by the high intrinsic conductivity, however, ...the key challenges to maximize the catalytic activity are achieving the metallic WS
2
with high concentration and increasing the density of the active sites. In this work, single-atom-V catalysts (V SACs) substitutions in 1T-WS
2
monolayers (91% phase purity) are fabricated to significantly enhance the HER performance via a one-step chemical vapor deposition strategy. Atomic-resolution scanning transmission electron microscopy (STEM) imaging together with Raman spectroscopy confirm the atomic dispersion of V species on the 1T-WS
2
monolayers instead of energetically favorable 2H-WS
2
monolayers. The growth mechanism of V SACs@1T-WS
2
monolayers is experimentally and theoretically demonstrated. Density functional theory (DFT) calculations demonstrate that the activated V-atom sites play vital important role in enhancing the HER activity. In this work, it opens a novel path to directly synthesize atomically dispersed single-metal catalysts on metastable materials as efficient and robust electrocatalysts.
The production of hydrogen through water splitting via electrolysis/photocatalysis seems a promising and appealing pathway for clean energy conversion and storage. Herein we report for the first time ...that a series of water-soluble copper complexes can be used as catalyst precursors to generate the copper-based bifunctional catalyst composite for both hydrogen production and water oxidation reactions. Under an applied cathodic potential, a thin catalyst film was grown on a fluorine-doped tin oxide (FTO) electrode, accompanied by the production of a large amount of hydrogen gas bubbles. Scanning electron microscopy shows the presence of nanoparticulate material on the FTO. Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results indicated that the materials consist of amorphous cuprous oxide mixed copper hydroxide (H2–CuCat), which can catalyze water reduction in a copper-free aqueous solution (pH = 9.2) under a low overpotential. Remarkably, under an applied anodic potential, the material can also efficiently catalyze water oxidation to evolve oxygen. The present robust, bifunctional, switchable, and noble-metal-free catalytic material has potential applications in solar water-splitting devices.
Six cobalt and manganese corrole complexes were synthesized and examined as single-site catalysts for water splitting. The simple cobalt corrole Co(tpfc)(py)2 (1, tpfc = ...5,10,15-tris(pentafluorophenyl)corrole, py = pyridine) catalyzed both water oxidation and proton reduction efficiently. By coating complex 1 onto indium tin oxide (ITO) electrodes, the turnover frequency for electrocatalytic water oxidation was 0.20 s(−1) at 1.4 V (vs. Ag/AgCl, pH = 7), and it was 1010 s(−1) for proton reduction at −1.0 V (vs. Ag/AgCl, pH = 0.5). The stability of 1 for catalytic oxygen evolution and hydrogen production was evaluated by electrochemical, UV-vis and mass measurements, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), which confirmed that 1 was the real molecular catalyst. Titration and UV-vis experiments showed that the pyridine group on Co dissociated at the beginning of catalysis, which was critical to subsequent activation of water. A proton-coupled electron transfer process was involved based on the pH dependence of the water oxidation reaction catalyzed by 1. As for manganese corroles 2–6, although their oxidizing powers were comparable to that of 1, they were not as stable as 1 and underwent decomposition at the electrode. Density functional theory (DFT) calculations indicated that water oxidation by 1 was feasible through a proposed catalytic cycle. The formation of an O–O bond was suggested to be the rate-determining step, and the calculated activation barrier of 18.1 kcal mol(−1) was in good agreement with that obtained from experiments.
The design and preparation of highly active catalysts for the hydrogen evolution reaction (HER) is very important for water splitting. Herein, we report a highly active HER catalyst, which is ...synthesized by loading nanostructured nickel phosphide (Ni 2 P) on three-dimensional few-layer graphene/nickel foam (G@NF). G@NF was successfully prepared by a chemical vapor deposition process in the presence of methane at high temperature. Compared with nickel phosphide, G@NF, as well as commercial platinum, the Ni 2 P–G@NF catalyst exhibited very high activity in electrocatalytic H 2 production from water (∼7 mV overpotential in alkaline solutions, pH ∼ 14; and ∼30 mV overpotential in acidic solutions, pH ∼ 0). The high catalytic activity of Ni 2 P–G@NF is attributed to the excellent performance of Ni 2 P, the large 3D framework which facilitates proton accessibility and electron transfer, and the high surface area.
Memristive devices have been extensively demonstrated for applications in nonvolatile memory, computer logic, and biological synapses. Precise control of the conducting paths associated with the ...resistance switching in memristive devices is critical for optimizing their performances including ON/OFF ratios. Here, gate tunability and multidirectional switching can be implemented in memristors for modulating the conducting paths using hexagonal α‐In2Se3, a semiconducting van der Waals ferroelectric material. The planar memristor based on in‐plane (IP) polarization of α‐In2Se3 exhibits a pronounced switchable photocurrent, as well as gate tunability of the channel conductance, ferroelectric polarization, and resistance‐switching ratio. The integration of vertical α‐In2Se3 memristors based on out‐of‐plane (OOP) polarization is demonstrated with a device density of 7.1 × 109 in.−2 and a resistance‐switching ratio of well over 103. A multidirectionally operated α‐In2Se3 memristor is also proposed, enabling the control of the OOP (or IP) resistance state directly by an IP (or OOP) programming pulse, which has not been achieved in other reported memristors. The remarkable behavior and diverse functionalities of these ferroelectric α‐In2Se3 memristors suggest opportunities for future logic circuits and complex neuromorphic computing.
Gate‐tunable and multidirection‐switchable memristive phenomena in a van der Waals ferroelectric α‐In2Se3 are demonstrated. The planar memristor exhibits a pronounced switchable photocurrent, as well as gate tunability of the channel conductance, ferroelectric polarization, and resistance‐switching ratio. A multidirectionally operated α‐In2Se3 memristor is also proposed, enabling the control of the out‐of‐plane (OOP) (or in‐plane (IP)) resistance state directly by an IP (or OOP) programming pulse.
In this present paper, cobalt oxide (CoOx) is studied as an effective cocatalyst in a photocatalytic hydrogen production system. CoOx-loaded titanium dioxide/cadmium sulfide (TiO2/CdS) semiconductor ...composites were prepared by a simple solvothermal method and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and X-ray photoelectron spectroscopy (XPS). Photocatalytic hydrogen production was studied using the as-synthesized photocatalysts in aqueous solution containing sodium sulfide (Na2S)/sodium sulfite (Na2SO3) as hole scavengers under visible light irradiation (λ > 400 nm). The optimal cobalt content in CoOx-loaded TiO2/CdS composite is determined to be 2.1 wt% and the corresponding rate of hydrogen evolution is 660 μmol g−1 h−1, which is about 7 times higher than TiO2/CdS and CdS photocatalysts under the same condition. Visible light-driven photocurrents of the semiconductor composites were further measured on a photoelectrochemical electrode, revealing that the photocorrosion of CdS can be prevented due to the presence of TiO2–CoOx.
Cobalt oxide (CoOx) is studied as an effective cocatalyst for photocatalytic hydrogen production on TiO2/CdS semiconductor heterojunction, which exhibits the rate of hydrogen evolution as high as 660 μmol g−1 h−1. Display omitted
•Cobalt oxide (CoOx) as cocatalyst on TiO2/CdS for photocatalytic H2 production.•Improved visible light-driven H2 production from water at room temperature.•Cobalt oxide is earth-abundant materials for catalytic reactions.•CoOx-loaded TiO2/CdS composite shows good photocatalytic activity and stability.
Hydrogen is essential to many industrial processes and could play an important role as an ideal clean energy carrier for future energy supply. Herein, we report for the first time the growth of ...crystalline Cu3P phosphide nanosheets on conductive nickel foam (Cu3P@NF) for electrocatalytic and visible light-driven overall water splitting. Our results show that the Cu3P@NF electrode can be used as an efficient Janus catalyst for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). For OER catalysis, a current density of 10 mA/cm2 requires an overpotential of only ∼320 mV and the slope of the Tafel plot is as low as 54 mV/dec in 1.0 M KOH. For HER catalysis, the overpotential is only ∼105 mV to achieve a catalytic current density of 10 mA cm–2. Moreover, overall water splitting can be achieved in a water electrolyzer based on the Cu3P@NF electrode, which showed a catalytic current density of 10 mA/cm2 under an applied voltage of ∼1.67 V. The same current density can also be obtained using a silicon solar cell under ∼1.70 V for both the HER and the OER. This new Janus Cu3P@NF electrode is made of inexpensive and nonprecious metal-based materials, which opens new possibilities based on copper to exploit overall water splitting for hydrogen production. To the best of our knowledge, such high performance of a copper-based water oxidation and overall water splitting catalyst has not been reported to date.
Cobaloximes are usually used as molecular hydrogen evolution reaction (HER) catalysts. Herein we report for the first time the use of molecular cobaloximes as catalyst precursors for water oxidation ...when anodic potentials were applied. Highly active thin catalyst films were deposited at +1.5 V and +1.1 V (vs. Ag/AgCl) in 0.1 M borate buffer solution at pH = 9.2 containing 1 mM cobaloximes. Four catalyst films (CoOx-1-CoOx-4) were synthesized from four different cobaloximes. The current densities of CoOx-1 were up to ~5.5 mA cm(-2) and ~2.6 mA cm(-2) when the applied potentials were +1.5 V and +1.1 V, respectively, which were higher than the current densities of CoOx-2, CoOx-3 and CoOx-4 under the same conditions. Scanning electron microscopy (SEM) images reveal that the nanometer-sized particles of CoOx-1 possibly contribute to its high activity while the other three catalysts have micrometer-sized amorphous materials on the surface of FTO. X-ray photoelectron spectroscopy (XPS) data displayed the valence state of the cobalt element as Co(ii) or Co(iii) oxide species. The morphological stability of the CoOx-1 catalyst was further studied using SEM.
Herein we report for the first time to use multi-walled carbon nanotubes (MWCNTs) supported porous nickel oxide (NiOx) as non-precious electrocatalysts for oxidation of water at low overpotentials. ...The nickel oxide catalyst was facilely electrodeposited on MWCNTs in a 0.1 M KBi buffered solution at pH 9.2 containing 0.1 mM Ni2+ with an applied anodic potential. The current density of bulk electrolysis is 2.2 mA/cm2 at +1.1 V (vs Ag/AgCl) using NiOx-MWCNTs as the working electrode at pH 9.2, which is much higher than that in a system containing no MWCNTs. Tafel plot indicates that the present NiOx-MWCNTs catalyst requires the overpotential of only 200 mV to catalyze the water oxidation reaction at pH 9.2. The Faradaic efficiency of >95% has been achieved at +1.1 V. The highly porous character of the NiOx catalyst materials were further studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray analysis (EDX).
Highly porous NiOx was facilely electrodeposited on multi-walled carbon nanotubes for catalytic water oxidation at low overpotentials under the weak basic condition. Display omitted
•Noble metal-free nickel oxide (NiOx) for efficient water oxidation.•Carbon nanotubes supported NiOx improves catalytic current density.•NiOx is facilely electrodeposited with porous, honeycomb-like structure.•High Faradaic efficiency.•Low overpotentials for water oxidation.
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