Modulating electronic and structural properties of NiCo- layered double hydroxide with iodine: As an efficient electro-catalyst for the oxygen evolution reaction

The development of an earth-abundant, highly active, long-lasting electro-catalyst for the oxygen evolution reaction (OER) with a novel and improved chemical composition and structure is basically needed since the oxygen evolution reaction is the primary reaction for splitting of water. In this article, we have adopted precipitation technique to create a 2D iodine doped Ni_0.5Co_0.5 layered double hydroxide (LDH) based electro-catalyst. Several techniques were used to characterize the structural and morphological properties of the electro-catalyst, including powder X-ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and BET analysis. Using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) in an alkaline environment, OER performance was evaluated. The iodine-doped Ni_0.5Co_0.5 LDH had exceptional OER performance and required 250 mV (vs RHE) less overpotential to drive geometric catalytic current density of 40 mA cm⁻² and lower Tafel slope (98 mVdec⁻¹) than its counterparts. Excellent OER activity was achieved by iodine-doped Ni_0.5Co_0.5 LDH due to the abundance of active sites, lower charge transfer resistance (R_ct), induced oxygen vacancies, and increased pore size to pore diameter ratio. Additionally, the iodine-doped Ni_0.5Co_0.5 LDH displayed strong long-term stability without degrading throughout the course of the prolonged time period. This case study of iodine doping to Ni_0.5Co_0.5 LDH illustrates a crucial technique for producing high-performance earth-abundant energy conversion electro-catalysts.     

NiFe layered double hydroxide nanosheet arrays for efficient oxygen evolution reaction in alkaline media

Exploring efficient oxygen evolution reaction (OER) catalysts synthesized from low-cost and earth-abundant elements are crucial to the progression of water splitting. In this paper, NiFe layered double hydroxide (LDH) nanosheets were grown on Ni foam (NF) through a straightforward hydrothermal method. The Fe doping effects were systematically investigated by controlling Ni/Fe ratios and Fe valence states, and the in-depth influence mechanisms were discussed. The results indicate that, through controlling structure morphology and enhancing Ni²⁺ oxidation, NiFe_III(1:1)-LDH displays the best and outstanding OER performance, with a low over potential of 382 mV at 50 mA cm^?2, a low Tafel slope of 31.1 mVdec^?1 and only 20 mV increase after 10 h continuous test at 50 mA cm^?2. To our knowledge, this is one of the best OER electrocatalysts in alkaline media to date. This work provides a facile and novel strategy for the fabrication of bimetallic LDH catalysts with desired structures and compositions.     

Defective layered double hydroxide formed by H2O2 treatment act as highly efficient electrocatalytic for oxygen evolution reaction

Electrocatalytic reaction is the important electrode reaction for many new generation electrochemistry energy and storage devices. However, the poor reaction kinetics of those electrode reaction severely restricts its application. Highly efficient electrocatalyst is essential to resolve the problem of commercial application of those electrochemistry energy and storage devices. Herein, by simple H₂O₂ treatment, the highly efficient CoFe-Layered Double Hydroxides (LDHs) electrocatalysts with multiple defects have been synthesized (noted as D-LDHs). The D-LDHs show a low overpotential of 283 mV at 10 mA cm⁻² and small Tafel slope of 39 mV dec⁻¹ for the oxygen evolution reaction (OER). The work offers a new strategy to create defects in LDHs as highly efficient electrocatalysts for OER.     

MoSe2 regulates Ce-doped NiFe layered double hydroxide for efficient oxygen evolution reaction: The increase of active sites

Oxygen evolution reaction (OER) is a common reaction in many sustainable energy conversion systems. However, it has become a bottleneck in the development of sustainable energy conversion systems because of its slow kinetics, especially in the common electrolytic water reaction. At present, although there are a lot of researches on OER's catalysts, it is still a great challenge. In this work, a new type of composite was prepared by simple co-precipitation method and Hydrothermal, which is composed of Ce-doped NiFe Layered Double Hydroxide (LDH) and MoSe₂. The electrochemical test results of OER show that the overpotential of 6.7%Ce–NiFe LDH@MoSe₂ is 221 mV at 10 mA/cm², which is better than that of NiFe LDH (409 mV). And it is better than most of the reported OER catalysts in literature, including precious metal catalysts. Simultaneously, 6.7%Ce–NiFe LDH@MoSe₂ also has smaller Tafel slope (35.8mV/dec), larger ESCA (6689 cm²), long-time stability and selectivity with 92.1% Faraday efficiency. The excellent OER performance of 6.7%Ce–NiFe LDH@MoSe₂ benefits from the increase of active and defective sites and the interface coordination between MoSe₂ and Ce–NiFe LDH.     

Ce and MoS2 dual-doped cobalt aluminum layered double hydroxides for enhanced oxygen evolution reaction

Element doping has become an important means of designing and developing efficient and stable Oxygen Evolution Reaction (OER). In this work, a new type of CoAl LDH doped with Ce and MoS₂ was designed and prepared. The catalyst first prepared Ce-doped CoAl LDH (Ce–CoAl LDH) by co-precipitation and one-step hydrothermal method. Then, MoS₂ was introduced between Ce–CoAl LDH layers by hydrothermal method. The double doping of Ce and MoS₂ could significantly improve the electrocatalytic activity of CoAl LDH. At the current density of 10 mA/cm², the potential of 5% Ce–CoAl LDH@MoS₂ is 1.508 V, which is much lower than the 1.733 V of CoAl LDH. And the ECSA of 5% Ce-CoAL LDH@MoS₂ (23.4 mF/cm²) is nearly 8 times that of CoAl LDH (7.9 mF/cm²). Its excellent OER performance benefits from the increase of active sites and the enhancement of conductivity. This work provides a new research idea for doping design of effective OER electrocatalysts.     

Construction of Co(OH)F/Ni(OH)2@Fe(OH)3 core-shell heterojunction on nickel foam for efficient oxygen evolution

The sluggish anodic reaction (OER) kinetics hinder electrochemical water splitting at high energy densities, which can be solved by developing suitable catalysts. Herein, we report a novel Co(OH)F/Ni(OH)₂@Fe(OH)₃-D_x (D_x represents the hydrolysis time, X = 0.5, 1, 2 days) heterojunction grown on nickel foam, which was synthesized by the hydrolysis of Fe³⁺ on the Co(OH)F/Ni(OH)₂ surface at room temperature. Electrocatalytic oxygen evolution tests showed that the prepared Co(OH)F/Ni(OH)₂@Fe(OH)₃-D_x composites had better catalytic activity than pure Co(OH)F/Ni(OH)₂ in 1.0 M KOH, especially Co(OH)F/Ni(OH)₂@Fe(OH)₃-D₁. It only requires an ultra-low overpotential (η₁₀) of 270 mV, SEM and TEM showed that Co(OH)F/Ni(OH)₂@Fe(OH)₃-D₁ is a perfect all-encapsulated core-shell structure, which facilitates the exposure of active sites and electron transfer, and thus obviously improves oxygen evolution.     

Facile synthesis of nanometer-sized NiFe layered double hydroxide/nitrogen-doped graphite foam hybrids for enhanced electrocatalytic oxygen evolution reactions

We report a self-standing NiFe layered double hydroxide/nitrogen doped graphite foam (NiFe LDH/NGF) electrode for the oxygen evolution reaction (OER) prepared via a facile electrodeposition method. The electrode showed high electrocatalytic activity towards OER, exhibiting a low onset overpotential of 0.239 V and a small Tafel slope of 57.9 mV dec^?1 in basic electrolytes, as well as a good stability during the long-term cycling test. The outstanding electrocatalytic activity is mainly attributed to the synergy between the abundant catalytically active sites through good dispersion of NiFe LDH across NGF and fluent electron transport arising from NGF.     

Tailoring the activity of NiFe layered double hydroxide with CeCO3OH as highly efficient water oxidation electrocatalyst

Owing to the efficient modulation of the electronic structure of nanomaterials, rare earth elements introduction as promoters into nanomaterials has attracted great attention in oxygen evolution reaction (OER). This work demonstrates the cerium carbonate hydroxide (CeCO₃OH) in situ grown on nickel foam (NF) supported NiFe layered double hydroxide (LDH) as a novel promoter in OER process. The hybrid material (Ni_0.75Fe_0.15Ce_0.10/NF) possesses excellent performance for OER where the overpotentials at the current densities of 10 mA cm^?2 and 100 mA cm^?2 are 228 mV and 270 mV, respectively, along with the Tafel slope of 38.3 mV dec^?1. Such performance is comparable in activity to many state-of-the-art electrocatalysts. The enhanced performance in the NiFe LDH can be ascribed to the synergetic interaction between CeCO₃OH and NiFe LDH by utilizing the advantages of cerium and carbonate in OER. The novelty of our work is the exploration of CeCO₃OH as a promoter to enhance the OER performance, which expands the application of cerium-based compounds in energy storage and conversion.     

A partial sulfidation approach that significantly enhance the activity of FeCo layered double hydroxide for oxygen evolution reaction

We report a partial sulfidation approach that effectively boosts the OER activity of FeCo-layered double hydroxides (LDH). It is found that the mild sulfurized FeCo-LDH nanosheets using Na₂S converted a portion of their surface metal-hydroxide bonds to metal-sulfur (-hydrosulfide) bonds without significantly altering their crystal structure. The sulfidation degree is controlled by Na₂S concentration for obtaining a moderately surface electronic configurations. Benefits from the regulated electronic configurations, the sulfurized FeCo-LDH nanosheets only require an overpotential of 281 mV to produce oxygen at 10 mA cm⁻² and their Tafel slope is 51.8 mV dec⁻¹, which are both lower than the 348 mV and 72.7 mV dec⁻¹ of pristine FeCo-LDH nanosheets. The sulfurized catalysts have sustained 12 h of operation without notable activity loss. This work can provide new insights into understanding the roles of metal-sulfur bonds for OER and offer an attractive strategy to design low cost but efficient OER catalysts.     

One-step synthesis of atomic Ru doped ultra-thin Co(OH)2 nanosheets for oxygen evolution reaction in different pH values

Herein, atomic Ru doped ultra-thin Co(OH)₂ nanosheet arrays are firstly synthesized by a one-step electrochemical deposition method. Importantly, the obtained electrocatalyst can display excellent activity for oxygen evolution reaction, which only needs 305 mV at 50 mA cm^?2 in 1 M KOH and 261 mV at 10 mA cm^?2 in 0.1 M KOH. Further mechanism studies disclose that the doping of Ru could reduce the thickness of nanosheets and contribute to the generation of active Co³⁺ sites by donating electrons from Co to Ru atoms via the Co–O–Ru bonds. This work paves a simple method to fabricate Co based nanosheet catalyst, which may be extended to the preparation of other highly active electrocatalysts.     

Intercalation and elimination of carbonate ions of NiCo layered double hydroxide for enhanced oxygen evolution catalysis

The developments of inexpensive and efficient oxygen evolution reaction (OER) electrocatalysts without noble metals are very critical for energy conversion and storage systems. In this work, a series of NiCo-layered double hydroxide (NiCo-LDH) and NiCo oxides using co-precipitation and thermal treatment method have been successfully synthesized. Structural characterizations have been investigated by X-ray powder diffraction (XRD), Field emission scanning electron microscope (FE-SEM) equipped with energy-dispersive X-ray mapping technology (EDS), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy respectively (XPS). By intercalating and eliminating CO₃³⁻ anions in the layers of bulk NiCo-layered double hydroxide (NiCo-LDH), the as-present catalyst (NiCo–CH) exhibit remarkable advantages for OER performance, including porous nanostructures, high surface area, high content of Ni³⁺ and Co²⁺ on the surface and abundant active sites. With these favorable features, NiCo–CH shows a much better OER performance than that of other catalysts and commercial Pt/C, which has a low onset potential (1.51 V), a low overpotential (343 mV at 10mA/cm⁻²) and a small Tafel slope (66mV/dec⁻¹). Our work presents an effective strategy to controllably design and synthesize NiCo-LDH electrocatalysts with optimizable OER performances.     

Self-construction of pea-like Cu/Cu2S Mott-Schottky electrocatalyst for the oxygen evolution reaction

The speed of the oxygen evolution reaction seriously affects the hydrogen production efficiency of water electrolysis. Hence it is crucial to develop efficient and durable OER electrocatalysts. Construction of heterojunction catalysts is also one of the strategies to develop efficient catalysts. In this paper, a pea-like Cu/Cu₂S–C3 Mott?Schottky electrocatalyst was self-constructed by vapor deposition, while CF (copper foam) was used as substrate material and copper source, and thiourea was served as sulfur source. The built-in electric field is formed at the metal-semiconductor interface, which endows it with promising electrocatalytic performance. As the working electrode, the overpotentials of Cu/Cu₂S–C3 required to reach the current density of 10 and 50 mA cm^?2 were about 170 and 335 mV. The impact of the Mott-Schottky structure on the catalyst was also reflected in stability. The i-t tests of the sample Cu/Cu₂S–C3 were carried out under 10 and 60 mA cm^?2 and performed well.     

Facile electrodeposited amorphous Co–Mo–Fe electrocatalysts for oxygen evolution reaction

A new type of superior activity and highly cost-effective amorphous electrocatalyst Co–Mo–Fe on nickel foam (NF) supports is prepared by facile one-step rapid electrodeposition. The amorphous electrocatalyst Co–Mo–Fe/NF shows excellent oxygen evolution reaction (OER) performance, with a small overpotential of 218 mV at 10 mA cm^?2 current density in 1 M KOH. It only needs overpotential of 252 mV at 50 mA cm^?2 current density in 1 M KOH, and the Tafel slope is 45 mV dec^?1. The results show that the doping of Fe significantly improves the oxygen evolution capacity of the Co–Mo–Fe system. The synergistic effect of the three metals and the doping of the third metal iron make the oxygen evolution active sites of the whole system increase significantly. This provides a feasible direction for the oxygen evolution reaction of cobalt transition metal.     

Accelerated oxygen evolution kinetics on NiFeAl-layered double hydroxide electrocatalysts with defect sites prepared by electrodeposition

NiFe layered double hydroxides (LDHs) is considered to be one of the LDHs electrocatalyst materials with the best electrocatalytic oxygen evolution properties. However, its poor conductivity and inherently poor electrocatalytic activity are considered to be the limiting factors inhibiting the electrocatalytic properties for oxygen evolution reaction (OER). The amorphous NiFeAl-LDHs electrocatalysts were prepared by electrodeposition with nickel foam as the support, and the D-NiFeAl-LDHs electrocatalyst with defect sites was then obtained by alkali etching. The mechanism of catalysts with defect sites in OER was analyzed. The ingenious defects can selectively accelerate the adsorption of OH⁻, thus enhancing the electrochemical activity. The D-NiFeAl-LDHs electrocatalyst had higher OER electrocatalytic activity than NiFe-LDHs electrocatalyst: its accelerated OER kinetics were mainly due to the introduction of iron and nickel defects in NiFeAl-LDHs nanosheets, which effectively adjusted the surface electronic structure and improved OER electrocatalytic performance. There was only a low overpotential of 262 mV with the current density of 10 mA cm⁻², and the Tafel slope was as low as 41.67 mV dec⁻¹. The OER electrocatalytic performance of D-NiFeAl-LDHs was even better than those of most of the reported NiFe-LDHs electrocatalysts.     

Enhanced oxygen evolution reaction activity of NiFe layered double hydroxide on nickel foam- reduced graphene oxide interfaces

Herein, we prepared a novel nickel iron-layered double hydroxide/reduced graphene oxide/nickel foam (NiFe-LDH/RGO/NF) electrodes by two step electrodeposition processes for oxygen evolution reaction (OER). The modification of NF by RGO increased the interface conductivity and electrochemical active surface areas (ECSA) of the electrode. The NiFe-LDH/RGO/NF electrode has shown higher catalytic activity with a lower overpotential of 150 mV at the current density of 10 mA cm⁻². The NiFe-LDH/RGO/NF electrode has also shown a small Tafel slope of 35 mV per decade due to the synergy effect between the larger ECSA and the conductive RGO interface. Furthermore, the electrodes exhibits almost 10 h stability under a general current density of 10 mA cm⁻².     

Electrodeposition of NiFe layered double hydroxide on Ni3S2 nanosheets for efficient electrocatalytic water oxidation

The oxygen evolution reaction (OER) plays a vital role in various energy conversion applications. Up to now, the highly efficient OER catalysts are mostly based on noble metals, such as Ir- and Ru-based catalysts. Thus, it is extremely urgent to explore the non-precious electrocatalysts with great OER performance. Herein, a simple electrodeposition combined with hydrothermal method is applied to synthesize a non-precious OER catalyst with a three-dimensional (3D) core-shell like structure and excellent OER performance. In our work, NiFe layered double hydroxide (LDH) was electrodeposited on Ni₃S₂ nanosheets on nickel foam (NF), which exhibits a better performance compared with RuO₂, and a low overpotential of 200 mV is needed to reach the current density of 10 mA/cm² in 1 M KOH. Notably, the Ni₃S₂/NiFe LDH only need an overpotential of 273 mV to reach the current density of 200 mA/cm².     

Three-dimensional Co3O4@NiCo2O4 nanoarrays with different morphologies as electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction is one of the key factors restricting the whole process of electrolysis of water. In this paper, hydrothermal and calcination method are used to in situ grow Co₃O₄@NiCo₂O₄ on nickel foam (NF). The formation of Co₃O₄@NiCo₂O₄ nanostructures depends on the different hydrothermal time, which further results in the different growth mechanism of Co₃O₄@NiCo₂O₄ nanostructures. The result shows that Co₃O₄@NiCo₂O₄-8h, as a catalytic material, could play a synergistic role to largely accelerate the electron transfer process and could be efficiently and persistently used in oxygen evolution reaction. The oxygen evolution reaction activity of Co₃O₄@NiCo₂O₄-8h material is significantly improved compared with Co₃O₄, Co₃O₄@NiCo₂O₄-6h and Co₃O₄@NiCo₂O₄-10 h. When the current density is 50 mA cm⁻², the overpotential is only 290 mV for Co₃O₄@NiCo₂O₄-8h material. The enhanced activity Co₃O₄@NiCo₂O₄-8h is attributed to more active site exposure, rapid charge transfer and synergistic catalysis of Co₃O₄ and NiCo₂O₄. This work provides a new idea for the development of efficient, stable and environmentally friendly hybrid catalysts.     

Ni/Ce co-doping δ-MnO2 nanosheets with oxygen vacancy for enhanced electrocatalytic oxygen evolution reaction

The design and manufacture of strongly engaged, low-cost, and resilient oxygen evolution reaction (OER) electrocatalysts is the most challenging task in electrochemical hydrolysis. Herein, Ce and Ni co-doped MnO₂ (NiCe/MnO₂) nanosheets (NSs) with oxygen vacancy (V_O) and abundant active sites have been prepared in one step employing a defect strategy. The co-doping of Ce/Ni on the one hand reduced the catalyst particle size and increased the specific surface area, which promoted the exposure of more active sites. On the other hand, heteroatom doping altered the species the crystalline surface, stimulating the formation of Vo and thus activating the catalyst performance simultaneously. The OER performance of NiCe/MnO₂ NSs was significantly enhanced over the pure δ-MnO₂, with an overpotential of 170 mV (10 mA cm^?2), which was verified by density functional theory. This work shows a straightforward and practical method for making non-precious metal electrocatalysts with high electrochemical hydrolysis performance.     

Core-shell Ni3Fe-based nanocomposites for the oxygen evolution reaction

To deal with energy and environmental issues, it is necessary to exploit efficient and stable electrocatalysts for the generation of clean hydrogen. Herein, we describe the synthesis of bimetallic Fe/Ni alloy encapsulated by amorphous carbon shells via a facile annealing strategy for electrocatalytic oxygen evolution reaction (OER). The ferric nickel tartrate annealed at 800 °C (Ni₃Fe₁O_x@C-800) exhibits a low OER overpotential of 264 mV at 10 mA cm^?2 and good stability in alkaline media. Compared with monometallic counterpart, bimetallic Ni₃Fe-based nanocomposites show lower OER barrier (ca. 324 kJ mol^?1) due to a cooperation mechanism between Ni and Fe sites in promoting electrocatalytic water oxidation. Compared with those annealed at other temperatures, the enhanced OER performance of Ni₃Fe₁O_x@C-800 can be ascribed to the large electrochemical surface area for exposing more active sites, smaller charge transfer, and better intrinsic activity of Ni₃Fe-based sites.     

Core-shell structure Co–Ni@Fe–Cu doped MOF–GR composites for water splitting

What is essential to solving energy scarcity problems is that develop the high activity, durable and non-noble metal-based dual-functional electrocatalysts for hydrogen evolution reactions (HER) and oxygen evolution reactions (OER). In this work, a series of core-shell structure M@Fe–Cu-GR nanocubes (NCs) are prepared. In the prepared process, the bimetallic FeCu prussian blue analogues (PBA) is used as precursor, transition metals ions Co²⁺ and Ni²⁺ are introduced into the FeCu-PBA using the exchange of potassium ions with other metal ions, and then the FeCu-PBA are successfully loaded on the graphene oxide (GO) employed the attraction of opposite charges between polydiallyldimethylammonium chloride (PDDA) and GO. Electrochemical tests show that the Tafel slope of Co–Ni@Fe–Cu–GR NCs for HER and OER are 60 and 82 mV dec^?1, respectively, and Co–Ni@Fe–Cu–GR NCs shows excellent performance in long-term stability test.