Growth of ultrathin nanosheets of nickel iron layered double hydroxide for the oxygen evolution reaction

Because of low cost and abundance, nickel-iron double layered hydroxide (NiFe LDH) is seen as a viable substitute for noble-metal-based electrodes for the oxygen evolution reaction (OER). Herein, we report the growth of NiFe LDH in the form of fine nanosheets in a single step using benzyl alcohol-mediated chemistry. The electrochemical studies clearly suggest that benzyl alcohol is capable of inducing effective chemical interaction between Ni and Fe in the NiFe LDH. The overpotential to produce benchmark 10 mA cm^?2 (η₁₀) for the NiFe LDH electrode is only ～270 mV_RHE, which is much smaller than those of benchmark IrO₂ (η₁₀ = 318 mV_RHE), nickel hydroxide (η₁₀ = 370 mV_RHE) and iron hydroxide (η₁₀ = 410 mV_RHE) for the OER. The difference of the overpotential requirement increases further with increasing current density, indicating faster kinetics of the OER at the catalytic interface of the NiFe LDH. Estimation of Tafel values verifies this notion – the Tafel slopes of NiFe LDH, Ni(OH)₂, and FeOOH are calculated to be 48.6, 55.8, and 59.3 mV dec^?1, respectively. At η = 270 mV, the turnover frequency (TOF) of the NiFe LDH is 0.48 s^?1, which is ～8 and ～11 folds higher than those of Ni(OH)₂ (0.059 s^?1) and FeOOH (0.042 s^?1). In addition to Tafel and TOF, the NiFe LDH electrode has favorable electrochemically active surface area and electrochemical impedance. The electrochemical stability of the NiFe LDH electrode is assessed by conducting potentiostatic measurements at η = 270 mV_RHE (～10 mA cm^?2) and at η = 355 mV_RHE (～30 mA cm^?2) for 24 h of continuous oxygen production.     

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.     

Facile construction of well-defined hierarchical NiFe2O4/NiFe layered double hydroxides with a built-in electric field for accelerating water splitting at the high current density

Interfacial charge redistribution induced by a strong built-in electric field can expertly optimize the adsorption energy of hydrogen and hydroxide for improving the catalytic activity. Herein, we develop a well-defined hierarchical NiFe₂O₄/NiFe layered double hydroxides (NFO/NiFe LDH) catalysts, exhibiting superior performance due to the strong interfacial electric field interaction between NiFe₂O₄ nanoparticle layers and NiFe LDH nanosheets. In 1 M KOH, NFO/NiFe LDH needs 251 mV and 130 to drive 50 and 10 mA cm^?2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Moreover, only 1.517 V cell voltage is needed to reach 10 mA cm^?2 towards overall water splitting. Notably, under simulated industrial electrolysis conditions, NFO/NiFe LDH only needs 289 mV to drive 1000 mA cm^?2. This work puts a deep insight into the role of the built-in electric field in transition metal-based catalysts for accelerating water splitting and scalable industrial electrolysis applications.     

NiFe LDH/Ti3C2Tx/nickel foam as a binder-free electrode with enhanced oxygen evolution reaction performance

In this work, NiFe LDH/Ti₃C₂T_x/Nickel foam (NF) was successfully prepared as a binder-free electrode by depositing NiFe layered double hydroxide (LDH) nanosheets on Ti₃C₂T_x/NF substrate through electrodeposition approach. The strong electrostatic interactions between the negatively charged surface of MXene and positively charged NF substrate enabled the direct growth of NiFe LDH nanosheets on Ti₃C₂T_x/NF substrate. As a result, the as-prepared NiFe LDH/Ti₃C₂T_x/NF electrode exhibited an excellent OER performance, fast catalytic reaction kinetics and good chemical stability. Its overpotential reached 200 mV at a current density of 10 mA cm^?2, and the cycling tests suggested a good cycling stability.     

Heterogeneous layered multiple transition metal composite electrocatalysts with controlled composition for hydrogen production

The exploration of highly efficient and low-cost bifunctional electrocatalyst is essential for overall water splitting, especially for industrial application under alkaline conditions. Herein, we propose a controllable structural engineering strategy of constructing heterogeneous layered electrocatalyst with wetting surface for hydrogen evolution reaction and oxygen evolution reaction. Heterogeneous layered NiFe LDH (layered double hydroxide)/CoFeP/NF (Ni foam) with superhydrophilic surfaces is successfully fabricated by successive electrodeposition, phosphorization and solvothermal method. The NiFe LDH/CoFeP/NF for hydrogen evolution achieves a low overpotential of 198 mV at 50 mA cm^?2 in 1.0 M KOH. An overpotential of 269 mV is required at 50 mA cm^?2 for oxygen evolution. Meanwhile, the practical utilization of NiFe LDH/CoFeP/NF as bifunctional electrocatalysts for overall water splitting yields 1.73 V at 50 mA cm^?2 in the two-electrode cell. Moreover, NiFe LDH/CoFeP/NF can retain over 50 h without an obvious degradation at 10 mA cm^?2. The satisfactory operating stability and high activity of NiFe LDH/CoFeP/NF in alkaline solution can be attributed to the heterogeneous layered structure and excellent hydrophilic surface. The study provides a strategy to engineering heterogeneous layered structures with wetting surface for excellent electrocatalytic activities toward overall water splitting.     

One-step hydrothermal synthesized 3D P–MoO3/FeCo LDH heterostructure electrocatalysts on Ni foam for high-efficiency oxygen evolution electrocatalysis

Low-cost yet high-efficiency oxygen evolution reaction (OER) catalysts have attracted ardent attention to speed up the development of water electrolysis. Recent researches have shown that layered double hydroxides (LDH) are promising candidates towards OER, but further improvement is still highly demanded for its large-scale practical application in water splitting. Herein, we report a 3D P-doped MoO₃/FeCo LDH/NF (P–MoO₃/FeCo LDH/NF) ultrathin nanosheet heterostructure electrocatalyst with an extremely low overpotentials of 225 mV for delivering a current density of 10 mA cm^?2 for OER and a great durability for at least 80 h by a simple one-step hydrothermal method. Extraordinarily, the P–MoO₃/FeCo LDH catalyst achieves a high current density of 300 mA cm^?2 and even 350 mA cm^?2 at an extremely low overpotential of 297 mV and 302 mV, respectively, which is crucial for the water electrolysis industry. The remarkable performance may be attributed to that the heterostructure between P–MoO₃ and FeCo LDH not only optimizes electronic structure, thus inducing electron transfer from P–MoO₃ to FeCo LDH and then realizing fast electron transfer rates, but also produces more catalytic active sites. Moreover, the synergetic effect between MoO₃ and FeCo LDH also plays an essential role for enhancing the catalytic performances. This work explores the effect of phosphomolybdic acid on the structure, composition and performances of FeCo LDH catalysts, and also provides a simple and cost-effective way to prepare high-efficiency and low-cost layered double hydroxide electrocatalysts for OER.     

Constructing microstructures in nickel-iron layered double hydroxide electrocatalysts by cobalt doping for efficient overall water splitting

The development of Ni–Fe layered double hydroxide (NiFe LDH) catalysts for overall water splitting (OWS) is urgently required. NiFe LDHs are promising catalysts for the oxygen evolution reaction (OER). However, their hydrogen evolution reaction (HER) performance is restricted by slow kinetics. The construction of multiple types of active sites to simultaneously optimise the OER and HER performance is significant for OWS using NiFe LDHs. Hence, a Co-doped NiFe LDH electrocatalyst with dislocations and stacking faults was designed to modulate the electronic structure and generate multiple types of activity sites. The Co_0.03-NiFe_0.97 LDH catalyst only required overpotentials of 280 (50 mA cm⁻², OER) and 170 mV (10 mA cm⁻², HER). However, it reached a current density of 50 mA cm⁻² at 1.53 V during OWS. Co_0.03-NiFe_0.97 LDHs could be stabilised for 140 h at 1.52 V. Furthermore, Co_0.03-NiFe_0.97 LDHs exhibited a higher electrocatalytic activity than commercial Raney nickel and Pt/C||IrO₂ under industrial conditions. The significant specific surface area, high conductivity, and unique microstructures are the major factors contributing to the excellent OWS performance. This study suggests an efficient strategy for introducing microstructures to fabricate catalysts with high activity for application in OWS.     

Superhydrophilic 3D peony flower-like Mo-doped Ni2S3@NiFe LDH heterostructure electrocatalyst for accelerating water splitting

Constructing highly efficient nonprecious electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential to improve the efficiency of overall water splitting, but still remains lots of obstacles. Herein, a novel 3D peony flower-like electrocatalyst was synthesized by employing Mo–Ni₂S₃/NF nanorod arrays as scaffolds to in situ growth ultrathin NiFe LDH nanosheets (Mo-Ni₂S₃@NiFe LDH). As expected, the novel peony flower-like Mo–Ni₂S₃@NiFe LDH displays superior electrocatalytic activity and stability for both OER and HER in alkaline media. Low overpotentials of only 228 mV and 109 mV are required to achieve the current densities of 50 mA cm^?2 and 10 mA cm^?2 for OER and HER, respectively. Additionally, the material remarkably accelerates water splitting with a low voltage of 1.54 V at 10 mA cm^?2, which outperforms most transition metal electrodes. The outstanding electrocatalytic activity benefits from the following these features: 3D peony flower-like structure with rough surface provides more accessible active sites; superhydrophilic surfaces lead to the tight affinity between electrode with electrolyte; metallic Ni substrate and highly conductive Mo–Ni₂S₃ nanorods scaffold together with offer fast electron transfer; the nanorod arrays and porous Ni foam accelerate gas bubble release and ions transmission; the strong interfacial effect between Mo-doped Ni₃S₂ and NiFe LDH shortens transport pathway, which are benefit for electrocatalytic performance enhancement. This work paves a new avenue for construction and fabrication the 3D porous structure to boost the intrinsic catalytic activities for energy conversion and storage applications.     

Microwave-assisted growth of spherical core-shell NiFe LDH@CuxO nanostructures for electrocatalytic water oxidation reaction

The high energy demand for electrochemical water splitting arises from sluggish oxygen evolution reaction (OER) kinetics. In this regard, Layered double hydroxide (LDH) has been introduced as an outstanding catalyst for the OER due to its exceptional physiochemical and 2D infrastructure properties. Herein, we report the design and synthesiss of core-shell nanostructured electrocatalyst by rationally decorating vertically oriented NiFe LDH ultrathin nanosheets on Cu_xO support (NiFe LDH@Cu_xO) via microwave-assisted hydrothermal reaction. For OER, the NiFe LDH@Cu_xO core-shell nanostructured catalyst demonstrated promising electrocatalytic performance, requiring only 1.43 V onset potential and 270 mV overpotential at 10 mA cm^?2. The NiFe LDH@Cu_xO also outperformed pristine NiFe LDH and iridium oxide (IrO₂) in terms of electrocatalytic activity, durability, and Faradaic efficiency. The fabricated NiFe-LDH@Cu_xO electrocatalyst with outer shell NiFe-LDH ultrathin nanosheets provides numerous exposed active sites, benefits electrolyte diffusion and oxygen gas releasing and also reduces the interfacial charge transfer resistance to enhance OER activity. Furthermore, exclusive core-shell 3D infra-structure effectively prevents NiFe-LDH nanosheets agglomeration and restacking, enhancing electrochemical stability.     

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.     

Amorphous FeOOH decorated hierarchy capillary-liked CoAl LDH catalysts for efficient oxygen evolution reaction

Electrocatalytic water splitting is a promising route for the generation of clean hydrogen. However, the anodic oxygen evolution reaction (OER) suffers greatly from low reaction kinetics and thereby hampers the energy efficiency of alkaline water electrolysers. In recent years, tremendous efforts have been dedicated to the pursuit of highly efficient, low cost and stable electrocatalysts for oxygen evolution reaction. Herein, an amorphous FeOOH roughened capillary-liked CoAl layered double hydroxide (LDH) catalyst grown on nickel foam (denoted as FeOOH–CoAl LDH/NF) was reported for OER electrolysis. The developed FeOOH–CoAl LDH/NF electrode shows excellent OER activity with overpotentials of 228 mV and 250 mV to deliver a current density of 50 mA cm^?2 and 100 mA cm^?2 in 1.0 M KOH solution, respectively, ranking it one of the most promising OER catalysts based on transition-metal-based LDH. This is owed to the formed capillary-liked hierarchy structure with high-porosity as well as the strong electronic interaction between FeOOH and CoAl LDH. The developed morphological engineering approach to build hierarchal porous structures together with facile amorphous FeOOH modification may be extended to other layered double hydroxide catalyst for enhanced OER activities.     

Facile construction of heterostructural Ni3(NO3)2(OH)4/CeO2 bifunctional catalysts for boosted overall water splitting

Interface engineering has aroused vitally widespread concern since it could be an effective strategy for exploring high-performance and low-cost water oxidation electrocatalysts. Herein, we report a hetero-structured Ni₃(NO₃)₂(OH)₄/CeO₂/NF (NNO/CeO₂/NF) electrode, exhibiting superior performance owning to the NO₃^? anion substitution for the OH^? in nickel hydroxide to form Ni₃(NO₃)₂(OH)₄, together with its interface synergy with ceria. In alkaline solution, the NNO/CeO₂/NF electrocatalyst could catalyze the OER with an overpotential of 330 mV to approach 50 mA cm^?2. Also, it needs only an overpotential of 120 mV to reach 10 mA cm^?2 for HER. Additionally, when a standard two-electrode water electrolyzer is fabricated by employing NNO/CeO₂/NF as both the cathode and anode, it can generate 10 mA cm^?2 at 1.64 V and operate steadily without performance degradation after 25 h. This research provides a novel perspective for reasonable design of advanced catalytic materials with improvements in the field of electrocatalysis.     

Vertical Nickel–Iron layered double hydroxide nanosheets grown on hills-like nickel framework for efficient water oxidation and splitting

Herein, the vertical thin nickel–iron layered double hydroxide nanosheets grown on the hills-like nickel framework (NiFe LDH/Ni@NF) are employed for the oxygen evolution reaction (OER), securing at the low overpotentials of 197 and 270 mV to obtain the current densities of 20 and 100 mA cm⁻², respectively, with a Tafel slope of 73.34 mV dec⁻¹. The electrodeposited nickel film induces the NiFe LDH nanosheets grow vertically and thinly. As well, the nickel abundant interfaces and inner space makes this catalyst effective for OER. It was further served as the OER electrode in a water splitting system coupled the Pt/C cathode, and a cell voltage was at 1.52 and 1.67 V to achieve the current density of 10 mA cm⁻² and 50 mA cm⁻². In addition, the water electrolyzer can suffer a long time of 24 h at 50 mA cm⁻², showing the feasibility in a practical unbiased alkaline water splitting system.     

Co–NiFe layered double hydroxide nanosheets as an efficient electrocatalyst for the electrochemical evolution of oxygen

The development of non-precious metal catalysts for the electrochemical oxygen evolution reaction (OER) is especially important for the water electrolysis process. Herein, a two-dimensional (2D) ultrathin hybrid Co–NiFe layered double hydroxide (LDH) is synthesized via a facile hydrothermal method. In 1.0 M KOH electrolyte, Co–NiFe LDH exhibits remarkable activities for OER. At the current density of 10 mA cm⁻², it only needs an overpotential of 278 mV, which is ca. 50 mV and 20 mV lower than those for NiFe LDH (328 mV) and RuO₂ catalysts (298 mV), respectively. In addition, Co–NiFe LDH also shows impressive long-term stability for OER. Besides the stable morphology and crystal structure, the potential is always kept at 1.50 V and shows almost no attenuation during the 20 h of durability test. Changes in the electronic structure of LDH due to introduction of Co ions, as well as the large specific surface area facilitate the mass/electron transfer and the oxygen bubbles release, and thus lead to the enhanced catalytic properties for OER. This work can be informative not only for understanding the role of physical and electronic structures on OER but also for designing high-performance non-precious metal OER electrocatalysts.     

Defective layered NiFe double hydroxides anchored on self-supported CoNi-nitrogen doped carbon nanotube composite as advanced electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) is an essential process during electrochemical water-splitting. Due to its sluggish kinetics, low cost and highly efficient catalyst is invariably desired to decrease its overpotential for large-scale application. However, the overpotential of most advanced OER electrocatalysts is still more than 200 mV at the current density of 10 mA cm^?2. In this work, we constructed active layered NiFe double hydroxides with cation defects on self-supported three-dimensional (3D) CoNi nitrogen-doped carbon nanotube composite substrate as integrated OER catalyst. Strikingly, electrochemical measurements showed that the optimized sample exhibited outstanding OER activity with low overpotentials of 178 and 268 mV at the current densities of 10 and 100 mA cm^?2 in alkaline environment, alongside a good durability. The excellent OER performance was ascribed to the strongly synergistic effect of intrinsically active NiFe double hydroxide layers with abundant cation vacancies and 3D carbon nanotube composite substrate with good conductivity and various functional moieties, thus facilitating the electrocatalytic kinetic.     

A nano-spherical structure Ni3S2/Ni(OH)2 electrocatalyst prepared by one-step fast electrodeposition for efficient and durable water splitting

Developing non-noble metal catalysts with excellent electrocatalytic performance and stability is of great significance to hydrogen production by water electrolysis, but there are still problems of low activity, complex preparation and high cost. Herein, we fabricated a novel Ni₃S₂/Ni(OH)₂ dual-functional electrocatalyst by a one-step fast electrodeposition on nickel foam (NF). While maintaining the electrocatalytic performance of Ni₃S₂, the existence of heterostructure and Ni(OH)₂ co-catalyst function greatly improves the overall water splitting performance of Ni₃S₂/Ni(OH)₂–NF. Hence, It shows a low overpotential of 66 mV at 10 mA cm^?2 for HER and 249 mV at 20 mA cm^?2 for OER. The dual-functional electrocatalyst needs only 1.58 V at 20 mA cm^?2 when assembled two-electrode electrolytic cell. Impressively, the electrocatalyst also shows outstanding catalytic stability for about 800 h when 20 and 50 mA cm^?2 constant current was applied, respectively which demonstrates a potential electrocatalyst for overall water splitting.     

Spatially confined growth of ultrathin NiFe layered double hydroxide nanosheets within carbon nanofibers network for highly efficient water oxidation

The rational design of catalysts with low cost, high efficient and robust stability toward oxygen evolution reaction (OER) is greatly desired but remains a formidable challenge. In this work, a one-pot, spatially confined strategy was reported to fabricate ultrathin NiFe layered double hydroxide (NiFe-LDH) nanosheets interconnected by ultrafine, strong carbon nanofibers (CNFs) network. The as-fabricated NiFe-LDH/CNFs catalyst exhibits enhanced OER catalytic activity in terms of low overpotential of 230 mV to obtain an OER current density of 10 mA cm^?2 and very small Tafel slope of 34 mV dec^?1, outperforming pure NiFe-LDH nanosheets assembly, commercial RuO₂, and most non-noble metal catalysts ever reported. It also delivers an excellent structural and electrocatalytic stability upon the long-term OER operation at a large current of 30 mA cm^?2 for 40 h. Furthermore, the cell assembled by using NiFe-LDH/CNFs and commercial Pt/C as anode (+) and cathode (?) ((+)NiFe-LDH/CNFs||Pt/C(?)) only requires a potential of 1.50 V to deliver the water splitting current of 10 mA cm^?2, 130 mV lower than that of (+)RuO₂||Pt/C(?) couple, demonstrating great potential for applications in cost-efficient water splitting devices.     

Electroless deposition synthesis of composite catalysts Ni-Fe-P-WO3/NF with superior oxygen evolution performance

The proper construction of high efficiency, low-cost, earth-abundant oxygen evolution reaction (OER) catalyst is essential for hydrogen formation by water splitting. A novel electrocatalyst with highly active OER performance was manufactured by a simple electroless deposition method of Ni-Fe-P-WO₃ on nickel foam (NF). Benefiting from outstanding mass transfer capability of Ni-Fe-P-WO₃/NF heterogeneous structure, abundance of active sites in the amorphous architecture and etc., the Ni-Fe-P-WO₃/NF shows extremely superb electrocatalytic properties compare to noble metal catalyst IrO₂/NF for OER, which needs an overpotential of only 218 mV in 1.0 M KOH solution to achieve the current density of 10 mA cm^?2. It also has remarkable OER activity at high current density that only needs 298 mV to attain 100 mA cm^?2 current density. Moreover, the Ni-Fe-P-WO₃/NF has low Tafel slope of 42 mV dec^?1. This study offers a novel approach to the production of OER multiphase electrocatalysts from oxides and alloys.     

Core-shell nanoarray structured La doped Cu(OH)2@NiCo layered double hydroxide for oxygen evolution reaction

Efficient hydrogen production via water splitting is significant because of the zero-carbon emission property. Developing low-cost and highly efficient electrocatalysts for the oxygen evolution reaction (OER), a key half-reaction of water splitting, is critical. Herein, we designed Cu(OH)₂@NiCo layered double hydroxide core-shell nanoarray supported on copper foam (CF) with different La doping amount (abbreviated as Cu(OH)₂@NiCoLa LDH/CF) via the facile electrodeposition method. Owing to the synergistic effect between La and NiCo LDH by electronic structure tuning, Cu(OH)₂@NiCoLa LDH/CF shows excellent OER performance with the lowest overpotential of 254 mV to drive the current density of 10 mA cm^?2 and outstanding long-term durability for 24 h. The idea of doping rare-earth metal into non-noble NiCo-based LDHs core-shell nanoarray structure in this work can inspire the design of other efficient electrocatalysts.     

Synthesis of high crystalline nickel‐iron hydrotalcite‐like compound as an efficient electrocatalyst for oxygen evolution reaction

The nickel‐iron hydroxide‐like catalyst for oxygen evolution reaction (OER) is prepared by an improved coprecipitation method. The crystallization degree of hydrotalcite‐like compound is high, and the lamellar structure is homogeneous with no agglomeration, which helps to build efficient mass‐transfer layer channel of OH^? ions. The NiFe layered double hydroxide (LDH)/carbon nanotubes (CNTs) electrode shows good performance and stability for OER. The potential of NiFe LDH/CNTs electrode is only 0.592 V (vs HgO/Hg) at 200 mA·cm^?2 in 6 mol·L^?1 potassium hydroxide (KOH) electrolyte, which shows excellent catalytic activity for OER. The NiFe LDH/CNTs electrode works continuously for 620 hours at 200 mA·cm^?2, with the groove voltage only rises 0.1 V.