Bifunctional Electrocatalyst For Overall Water Splitting Research Articles

Synthesis of Ni-doped 1T/2H MoS2 nanoparticles as an efficient and stable bifunctional electrocatalyst for overall water-splitting

In advancing hydrogen fuel production through water-splitting, we focus on the optimisation of 1T/2H phases of MoS2 nanoparticles to enrich the overall water-splitting performance which has garnered significant interest. We propose a straightforward hydrothermal method to develop a 1T/2H MoS2 catalyst by introducing Ni. Morphological and chemical investigations evidenced the generation of the metal/semiconductor MoS2 nanoparticles. Further, the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been demonstrated, and the optimised 1 m mol nickel-doped MoS2 catalyst (MSN-1) exhibits remarkable performance in both HER and OER, with a low overpotential of 117 and 250 mV respectively at a current density of 10 mA cm−2, and superior stability in alkaline medium (about 20 h). Additionally, it exhibits promising bifunctional activity with an overpotential of approximately 1.36 V at a current density of 10 mA cm−2, maintaining stability for 20 h in a 1.0 M KOH medium. These outcomes emphasise that MSN-1 has the potential as a practical bifunctional electrocatalyst with significant applications on the horizon.

In-situ construction of hexagonal-star-shaped MnCo2S4@MoS2 boosting overall water splitting performance at large-current-density: Compositional-electronic regulation, functions, and mechanisms

It remains to be challenging to develop bifunctional catalysts for overall water splitting (OWS) with high activity and durability at large current density. In an attempt to overcome this bottleneck, unique MnCo2S4 hexagonal stars covered with MoS2 nanosheets were in-situ grown on nickel foam (NF) to obtain MnCo2S4@MoS2/NF heterostructure with optimized composition and local electronic structure in this work. When employed as a bifunctional catalyst, it only needs low overpotentials of 208 and 332 mV in 6.0 M KOH to drive 1000 mA cm−2 with small Tafel slopes of 56.8 and 75.6 mV dec-1 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. In addition, MnCo2S4@MoS2/NF showed remarkable stability in simulated industrial conditions, operating stably for 50 h at 1000 mA cm−2 without any attenuation for HER/OER. Thus, the MnCo2S4@MoS2/NF can function as a bifunctional electrocatalyst for OWS, only requiring 1.795 V to afford 1000 mA cm−2 with splendid stability. The improved performance is ascribed to dual electric and compositional regulation, which endow MnCo2S4@MoS2/NF with rich active sites and heterointerfaces, thereby promoting electron transfer and boosting the reaction kinetic. Furthermore, density functional theory (DFT) calculations reveal that the construction of heterostructure can help regulate intrinsic electronic structure, resulting in accelerated reaction kinetics. This work provides a reasonable and meaningful method for boosting industrial green hydrogen production.

One-Step Hydrothermal Synthesis of Cobalt Sulfide/E-Waste Derived Activated Carbon Nanocomposite as a Bifunctional Electrocatalyst for Overall Water-Splitting

An electrocatalyst with high performance can enhance the hydrogen production for overall water-splitting. This study reports on the e-waste-derived activated carbon encapsulated cobalt sulfide (CoS2/AC) nanocomposite synthesized via a simple hydrothermal process for overall water-splitting application. The microstructural image of CoS2/AC showed the aggregated stacked nanosheets of activated carbon encapsulating the cobalt sulfide nanoparticles. The nanocomposite of CoS2/AC exhibited the overpotential of 240 mV at 10 mA cm−2 and a 34 mV dec−1 of Tafel slope value with extraordinary stability for OER. On the other hand, the nanocomposite exhibited the overpotential of 378 mV at 10 mA cm−2 with a Tafel slope of ∼134 mV dec−1 with splendid stability in 1 M KOH solution for HER. The enhanced electrical conductivity and electrochemically active surface area of the AC nanosheets and CoS2 nanoparticles in this nanocomposite account for its higher electrocatalytic activity. Thus, the hydrothermally synthesized CoS2/AC presents itself as a better bifunctional catalyst for overall water-splitting.

Hierarchical NiCo2S4@NiMoO4 nanotube arrays on nickel foam as an advanced bifunctional electrocatalyst for efficient overall water splitting

The development of efficient and robust electrocatalysts for overall water splitting (OWS) has a crucial effect on alleviating energy and environmental issues. Herein, an integrated electrode of hierarchical NiCo2S4 nanotube@NiMoO4 nanosheet arrays on nickel foam (NiCo2S4@NiMoO4/NF) is constructed via hydrothermal reaction. And the heterostructure can form the strong electron interaction and synergistic effect between NiCo2S4 and NiMoO4. Therefore, the NiCo2S4@NiMoO4/NF electrode exhibits prominent electrocatalytic performances with low overpotentials for oxygen and hydrogen evolution reaction (OER: 285 mV; HER: 197 mV) at the current density of 100 mA cm−2. Moreover, low potentials of 1.46, 1.63, and 1.75 V are needed to reach 10, 50, and 100 mA cm−2 and outstanding stability of 100 h is exhibited using NiCo2S4@NiMoO4/NF as a bifunctional electrocatalyst for OWS, which is superior over most of previously reported cobalt- and nickel-based electrocatalysts. These outstanding performances benefit from the unique hierarchical structure that combines the advantages of the nanosheet/nanotube and binder-free electrode, the specialty of NiCo2S4 and NiMoO4 in HER and OER, and the protective effect of the NiMoO4, which synergistically enhance the catalytic activity and stability of OWS.

Heterostructural CoFe2O4/CoO nanoparticles-embedded carbon nanotubes network for boosted overall water-splitting performance

Development of inexpensive and highly efficient bifunctional electrocatalysts for overall water-splitting is of great significance to produce sustainable hydrogen fuel from a renewable water source. Particularly, the sluggish oxygen evolution reaction kinetics limit the overall efficiency of water-splitting catalysis. Although, precious metal-based catalysts can reduce the energy barrier and drive the reaction at low overpotentials, their scarcity and high cost limit the commercialization. In order to address the aforementioned issues, we present a metal-organic framework (MOF)-derived CoFe2O4/CoO heterostructure-embedded carbon nanotubes (CNT)-network with exceptional water-splitting performance. Due to the collective advantages related to MOF-derived porous carbon with abundant oxygen-vacancies, CoFe2O4/CoO heterostructure-embedded CNT-networks with largely exposed catalytic sites, and their synergistic interactions, the hybrid catalyst (CoFe/C-650) delivers superior performance for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water-splitting: it requires a low overpotential of 246 mV (for OER) and 164 mV (for HER) at 10 mA/cm2 (ƞ10) with low Tafel slopes of 45.27 and 86.38 mV/dec, respectively. Interestingly, it requires an overpotential of 1.614 V (ƞ10) for full water-splitting catalysis, which is comparable to that of benchmark Pt/C (Cathode) and RuO2 (Anode) combination. This work presents a novel approach towards nanostructure design and facile production of transition metal-based oxide heterostructures to achieve the superior bifunctional activity.

Defect-Engineered 3D hierarchical NiMo3S4 nanoflowers as bifunctional electrocatalyst for overall water splitting

The design and construction of bifunctional electrocatalysts with high activity and durability is essential for overall water splitting. Herein, a unique 3D hierarchical NiMo3S4 nanoflowers with abundant defects and reactive sites were grown directly on carbon textiles (NiMo3S4/CTs) using a facile hydrothermal synthesis method. The defect-rich NiMo3S4 nanoflakes, prepared by doping Ni2+ in the lattice of Mo-S, displays extended d-spacing of (002) crystal plane, resulting in the electrocatalytic activity of hydrogen evolution and oxygen evolution reaction (HER and OER) was improved under alkaline conditions. The self-supported NiMo3S4/CTs electrode delivers a small overpotential of 149.5 mV for HER and 126.2 mV for OER at 10 mA cm−2, respectively. Based on detailed structure analysis and density functional theory (DFT) calculations, the excellent HER and OER activities can be attributed to the unique structure of the nanoflowers, where the metallic characteristics for Ni-doped Mo-S lead to the enhancement of intrinsic conductivity and the rich abundance of Ni3+ active sites. As a result, the NiMo3S4/CTs as efficient bifunctional electrocatalysts for overall water-splitting was performed in alkaline electrolyte, where the system required only 1.55, 1.66 and 1.76 V to deliver current densities of 10, 50 and 100 mA cm−2, respectively. This study provides a new method for improving the electrocatalysis properties of transition metal sulfides by metal-ion doping to generate more active defect sites, thus promoting the development of non-noble-metal electrocatalysts for overall water splitting.

Facile synthesis of Co-Fe-B-P nanochains as an efficient bifunctional electrocatalyst for overall water-splitting.

Design of cost-effective bifunctional electrocatalysts for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is vital for developing hydrogen energy for the future. Herein, a cost-effective phosphorus-doped Co-Fe-B material with chain-like structure (denoted as Co1-Fe1-B-P) is reported as an efficient and novel bifunctional electrocatalyst for the OER and HER, and was produced via a facile water-bath synthesis and subsequent phosphorization. For the OER, the as-prepared Co1-Fe1-B-P nanochains require an extremely low overpotential of about 225 mV at 10 mA cm-2 and possess a small Tafel slope of 40 mV dec-1 in alkaline media. Impressively, the HER properties of Co1-Fe1-B-P nanochains are superior to those of P-free Co-Fe-B in terms of overpotential at 10 mA cm-2 (173 mV vs. 239 mV) and kinetic Tafel slope (96 mV dec-1vs. 105 mV dec-1). The synergetic effect between Co-Fe-B and doped-P is mainly responsible for the satisfactory bifunctional performance, while the one-dimensional (1D) chain-like structure endows Co1-Fe1-B-P with abundant catalytically active sites that enhance the atom utilization efficiency. Moreover, the developed Co1-Fe1-B-P nanochains can be simultaneously utilized as both the cathode and anode for overall water-splitting, which requires a cell voltage of only 1.68 V to deliver 10 mA cm-2. This work provides a feasible and promising protocol to realize metal borides as efficient electrocatalysts in energy-related applications.

NiO hollow microspheres as efficient bifunctional electrocatalysts for Overall Water-Splitting

Development of efficient, earth-abundant and low-cost electrocatalyst for effective water electrolysis is highly demanding for production of sustainable hydrogen energy. In this paper, we report the cost-effective synthetic protocol for porous NiO hollow spheres in large scale through a simple spray drying strategy, using aqueous nickel ammonium carbonate complex solution, followed by calcination. The synthesized NiO hollow spheres calcined at 300 °C (NiO-300) are porous, made of nanoparticles in size range of 10–16 nm with a size range of 2.5–4 μm and total surface area of 120 m2/g. The NiO-300 exhibited excellent bifunctional electrocatalytic water splitting characteristic, both OER, and HER, in basic solution. NiO-300 modified glassy carbon electrode showed superior water electrolysis kinetics and to achieve 10 mA cm−2 current density, it required 370 mV overpotential for OER and 424 mV overpotential for HER in 1 M KOH. It is also worked well with cost-effective plastic chip electrode. An assembled two-electrode system by pairing NiO modified plastic chip electrode as both anode and cathode in a 1.0 M KOH electrolyte for overall water splitting exhibit clear bubble formation at 1.6 V potential.

CoFe Layered Double Hydroxide Supported on Graphitic Carbon Nitrides: An Efficient and Durable Bifunctional Electrocatalyst for Oxygen Evolution and Hydrogen Evolution Reactions

Finding nonprecious metal based highly active and durable bifunctional electrocatalysts for overall water-splitting is essential for the development of various renewable energy storage and conversion technologies. Herein, we report the synthesis of cobalt iron layered double hydroxide (Co1−δFeδ LDH) and g-carbon nitride composite (Co1−δFeδ LDH/g-CNx) for alkaline water electrolysis. The thin Co1−δFeδ LDH nanosheets are successfully impregnated on graphitic carbon nitride surface by one pot co-precipitation method at ambient temperature. The optimal composite, Co0.4Fe0.6 LDH/g-CNx exhibited superior OER activity in 1 M KOH electrolyte with a small overpotential of 0.28 V for 10 mA cm–2, low Tafel slope of 29 mV/dec, 100% faradic efficiency, and high TOF of 0.25 s–1 which is superior to commercial (comm) IrO2. Furthermore, the Co0.4Fe0.6 LDH/g-CNx composite also exhibited remarkable HER activity in alkaline media and its HER activity is slightly lower than that of comm Pt/C at low overpotential but it outpe...

3D structured Mo-doped Ni3S2 nanosheets as efficient dual-electrocatalyst for overall water splitting

Searching for a cost-effective, high efficient and stable bifunctional electrocatalyst for overall water-splitting is critical to renewable energy systems. In this study, three-dimensional (3D) curved nanosheets of Mo-doped Ni3S2 grown on nickel foam were successfully synthesized via a one-step hydrothermal process. The hydrogen-evolution reaction (HER) and the oxygen-evolution reaction (OER) in alkaline environment of this 3D catalyst are investigated in detail. The results show that it possesses lower overpotential, high current densities and small Tafel slopes both in OER and HER. For HER, the catalysts show excellent electrochemical performance, demonstrating a low over-potential of 212 mV at 10 mA cm−2 with a large decrease of 127 mV compared to the undoped Ni3S2. And it also shows a lower overpotential of 260 mV at 10 mA cm−2 which decreases 30 mV for OER. In addition, it is only need 1.67 V for the overall water splitting at 10 mA cm−2 which is 70 mV. It found that the Mo element would change the morphology of Ni3S2 and induce much more active sites for HER and OER. The as-prepared Mo-doped Ni3S2 bi-functional electrocatalyst could act as the promising electrode materials for water splitting.

Novel CoP Hollow Prisms as Bifunctional Electrocatalysts for Hydrogen Evolution Reaction in Acid media and Overall Water-splitting in Basic media

Cobalt phosphide (CoP) with hollow prisms nanostructure has been successfully synthesized via a facile two-step micro-assisted method. Firstly, uniform Co3(CH3COO)5(OH) cubes are prepared by microwave method. Then as-prepared Co3(CH3COO)5(OH) cubes as precursors have been conducted by phosphorization at low temperature. Novel CoP hollow prisms with 1μm length, 500nm width and 500nm height have been synthesized. The obtained CoP hollow prisms can be used as both an efficient electrocatalyst for HER in acid media (0.5M H2SO4 solution) and a remarkable bifunctional electrocatalyst for overall water-splitting in alkaline media (1.0M KOH solution) which might be attributed to their high surface area, porosity and good distribution. The OER mechanisms of CoP in alkaline solution have been investigated through XPS and SEM Mapping, which demonstrate that the amorphous oxygen-containing nanostructure on the surface of CoP may be the real catalytic active species. In addition, phosphidation of uniform cobalt salt hydrates precursor with specific structure at low temperature is a newfangled and effective strategy to synthesis bifunctional electrocatalyst CoP.

Inside Cover: Hierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water‐Splitting (Angew. Chem. Int. Ed. 21/2016)

Inside Cover: Hierarchical NiCo₂O₄ Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water‐Splitting (Angew. Chem. Int. Ed. 21/2016)

Highly Efficient and Robust Nickel Phosphides as Bifunctional Electrocatalysts for Overall Water-Splitting.

To search for the efficient non-noble metal based and/or earth-abundant electrocatalysts for overall water-splitting is critical to promote the clean-energy technologies for hydrogen economy. Herein, we report nickel phosphide (NixPy) catalysts with the controllable phases as the efficient bifunctional catalysts for water electrolysis. The phases of NixPy were determined by the temperatures of the solid-phase reaction between the ultrathin Ni(OH)2 plates and NaH2PO2·H2O. The NixPy with the richest Ni5P4 phase synthesized at 325 °C (NixPy-325) delivered efficient and robust catalytic performance for hydrogen evolution reaction (HER) in the electrolytes with a wide pH range. The NixPy-325 catalysts also exhibited a remarkable performance for oxygen evolution reaction (OER) in a strong alkaline electrolyte (1.0 M KOH) due to the formation of surface NiOOH species. Furthermore, the bifunctional NixPy-325 catalysts enabled a highly performed overall water-splitting with ∼100% Faradaic efficiency in 1.0 M KOH electrolyte, in which a low applied external potential of 1.57 V led to a stabilized catalytic current density of 10 mA/cm(2) over 60 h.