Ternary NiCoFe Layered Double Hydroxide Nanosheets Synthesized by Cation Exchange Reaction for Oxygen Evolution Reaction

Improving the Oxygen Evolution Reaction Performance of Ternary Layered Double Hydroxides by Tuning All Three Cations' Electronic Structures

The pursuit of efficient and sustainable hydrogen production is essential in the fight against climate change. One important method for achieving this is the electrolysis of water, particularly through the oxygen evolution reaction (OER). Recent studies indicate that trimetallic layered double hydroxides (LDHs) can enhance OER performance compared to bimetallic LDHs. This improvement occurs because the third cation alters the electronic structures of the other two cations, thereby increasing the intermediates' binding energies and enhancing electrical conductivity. This study proposes an approach enabling the modulation of the electronic structures of all three cations involved in the synthesis of the trimetallic LDHs. It suggested intercalating sodium dodecyl sulfate (SDS) into the interlayer of the trimetallic NiFe-La-LDH. A successful intercalation of SDS has been confirmed through the XRD, FT-IR, EDS, and XPS. This has expanded the interlayer distance which was beneficial for the electrical conductivity. Furthermore, SDS generated sulphur, which modulated the electronic structures of all three cations enriching the active sites and improving electrical conductivity and OER performance compared to its counterparts. This approach is beneficial: 1. The interlayer can be further enlarged by using different doping ratios of SDS. 2. Sulphur can enrich the active sites and improve the OER performance.

Design and Fabrication of MoCuOx Bimetallic Oxide Electrodes for High-Performance Micro-Supercapacitor by Electro-Spark Machining

Transition metal oxides, distinguished by their high theoretical specific capacitance values, inexpensive cost, and low toxicity, have been extensively utilized as electrode materials for high-performance supercapacitors. Nevertheless, their conductivity is generally insufficient to facilitate rapid electron transport at high rates. Therefore, research on bimetallic oxide electrode materials has become a hot spot, especially in the field of micro-supercapacitors (MSC). Hence, this study presents the preparation of bimetallic oxide electrode materials via electro-spark machining (EM), which is efficient, convenient, green and non-polluting, as well as customizable. The fabricated copper-molybdenum bimetallic oxide (MoCuOx) device showed good electrochemical performance under the electrode system. It provided a high areal capacity of 50.2 mF cm-2 (scan rate: 2 mV s-1) with outstanding cycling retention of 94.9% even after 2000 cycles. This work opens a new window for fabricating bimetallic oxide materials in an efficient, environmental and customizable way for various electronics applications.

Multifunctional Design of Catalysts for Seawater Electrolysis for Hydrogen Production

Direct seawater electrolysis is a promising technology within the carbon-neutral energy framework, leveraging renewable resources such as solar, tidal, and wind energy to generate hydrogen and oxygen without competing with the demand for pure water. High-selectivity, high-efficiency, and corrosion-resistant multifunctional electrocatalysts are essential for practical applications, yet producing stable and efficient catalysts under harsh conditions remains a significant challenge. This review systematically summarizes recent advancements in advanced electrocatalysts for seawater splitting, focusing on their multifunctional designs for selectivity and chlorine corrosion resistance. We analyze the fundamental principles and mechanisms of seawater electrocatalytic reactions, discuss the challenges, and provide a detailed overview of the progress in nanostructures, alloys, multi-metallic systems, atomic dispersion, interface engineering, and functional modifications. Continuous research and innovation aim to develop efficient, eco-friendly seawater electrolysis systems, promoting hydrogen energy application, addressing efficiency and stability challenges, reducing costs, and achieving commercial viability.

Graphene Architecture-Supported Porous Cobalt-Iron Fluoride Nanosheets for Promoting the Oxygen Evolution Reaction

The design of efficient oxygen evolution reaction (OER) electrocatalysts is of great significance for improving the energy efficiency of water electrolysis for hydrogen production. In this work, low-temperature fluorination and the introduction of a conductive substrate strategy greatly improve the OER performance in alkaline solutions. Cobalt-iron fluoride nanosheets supported on reduced graphene architectures are constructed by a one-step solvothermal method and further low-temperature fluorination treatment. The conductive graphene architectures can increase the conductivity of catalysts, and the transition metal ions act as electron acceptors to reduce the Fermi level of graphene, resulting in a low OER overpotential. The surface of the catalyst becomes porous and rough after fluorination, which can expose more active sites and improve the OER performance. Finally, the catalyst exhibits excellent catalytic performance in 1 M KOH, and the overpotential is 245 mV with a Tafel slope of 90 mV dec-1, which is better than the commercially available IrO2 catalyst. The good stability of the catalyst is confirmed with a chronoamperometry (CA) test and the change in surface chemistry is elucidated by comparing the XPS before and after the CA test. This work provides a new strategy to construct transition metal fluoride-based materials for boosted OER catalysts.

Corrosion-assisted in situ growth of NiCoFe-layered double hydroxides on Fe foam for sensitive non-enzymatic glucose detection

Because of their remarkable qualities including changeable chemical composition, good redox characteristics, and ease of manufacture, non-enzymatic glucose sensors based on metallic hydroxides have attracted much interest. However, enhancement of their peroxidase-like catalytic activity is challenging due to their poor substrate affinity and low electrical conductivity, affecting electron transfer. Herein, a three-dimensional hierarchical architecture of Ni/Co-decorated-Fe layered double hydroxide (NiCoFe-LDH) was straightforwardly constructed on Fe foam (FF) via a feasible corrosion strategy, and the non-enzymatic glucose sensing properties of the NiCoFe-LDH/FF electrode were investigated. In the linear detection range of 0.010-0.1 mM, the electrode exhibits an extreme sensitivity of 5717 μA mM-1 cm-2 with a low threshold for glucose determination of 2.61 μM (S/N = 3) and a short reaction time (∼2 s), which is ascribed to its specific intertwined nanosheet-like morphology with rich electron transfer passages that enhance conductivity and improve the accessibility to more active catalytic sites for glucose oxidation. Moreover, the electrode shows excellent selectivity, good stability, and promising practicality for glucose detection in actual serum samples. These results indicate that the feasible corrosion approach towards the simple synthesis of trimetallic layered double hydroxide electrodes results in improved affinity and stability, holding new prospects for achieving reliable, cost-efficient, and eco-friendly non-enzymatic glucose detection.

One-pot self-assembled bimetallic sulfide particle cluster-supported three-dimensional graphene aerogel as an efficient electrocatalyst for the oxygen evolution reaction

The preparation of an electrocatalyst for the oxygen evolution reaction (OER) with high catalytic activity, good long-term durability and rapid reaction kinetics through interface engineering is of great significance. Herein, we have developed a bimetallic sulfide particle cluster-supported three-dimensional graphene aerogel (FeNiS@GA), which serves as an efficient electrocatalyst for OER, by a one-step hydrothermal method. Profiting from the synergy of the FeNiS particle cluster with high capacitance and GA with its three-dimensional porous nanostructure, FeNiS@GA shows a high specific surface area, large pore volume, low contact resistance, and decreases the electron and ion transport routes. FeNiS@GA exhibits outstanding OER activity (when the current density is 50 mA cm-2, the overpotential is 341 mV), low Tafel slope (63.87 mV dec-1) and remarkable stability in alkaline solutions, outperforming FeNiS, NiS@GA, FeS@GA and RuO2. Due to its simple synthesis process and excellent electrocatalytic performance, FeNiS@GA shows great potential to replace noble metal-based catalysts in practical applications.

One-step achievement of Fe-doped and interfacial Ru nanoclusters co-engineered Ni(OH)2 electrocatalyst on Ni foam for promoted oxygen evolution reaction

The creation of inexpensive, high-performance catalysts to reduce the overpotential of the oxygen evolution reaction (OER) process is critical for the electrolysis of water for hydrogen production. Therefore, we applied a one-step hydrothermal method using cation exchange reaction (CER) to prepare Fe-doped and interfacial Ru nanoclusters co-engineered Ni(OH)₂ nanosheets directly grafted on Ni foam (Ru@Fe-Ni(OH)₂/NF) for OER process. Results of electrochemical tests reveal that Ru@Fe-Ni(OH)₂/NF has excellent OER activity, and its overpotential (η) is only 266.4 mV when the current density is 50 mA cm^-2 in 1 M KOH solution, even lower than that of commercial OER catalyst RuO₂ (355 mV). The Tafel slope also decreases from 133.8 mV dec^-1 for pristine Ni(OH)₂/NF material to 24.1 mV dec^-1 for Ru@Fe-Ni(OH)₂/NF, indicating the higher charge transfer rates and fastest kinetics for water oxidation. At an overpotential of 300 mV the optimal turnover frequency (TOF) of 0.062 s^-1 for Ru@Fe-Ni(OH)₂/NF is achieved compared to that of Ni(OH)₂/NF (0.014 s^-1, NN), demonstrating the fast reaction kinetics of the as-prepared electrocatcalyst. After 24 h stability test, the catalytic activity of Ru@Fe-Ni(OH)₂/NF was only attenuated by 2 %, showing excellent OER stability and durability. Our results show that we have successfully developed an efficient OER catalyst for green and efficient electrocatalytic hydrolysis to produce H₂ and O₂, providing a promising method for clean H₂ production.

Sea urchin-like amorphous MgNiCo mixed metal hydroxide nanoarrays for efficient overall water splitting under industrial electrolytic conditions

Exploring amorphous mixed transition metal hydroxide electrocatalysts with high performance and stability for overall water splitting is a difficult challenge under industrial electrolytic conditions. Herein, a sea urchin-like amorphous MgNiCo hydroxide (Mg_xNi_1-xCo-OH, 0 < x < 1), self-assembled from nanowire arrays, is synthesized by the hydrothermal process. The synergistic effect between Mg and Ni/Co adjusts their crystal structure and morphology, which can improve the inherent activity and provide more active sites. Benefiting from the favorable structural features, Mg_0.5Ni_0.5Co-OH exhibits superior electrocatalytic oxygen and hydrogen evolution reaction (OER and HER) activity with a low overpotential of 277 and 110 mV (10 mA cm^-2) in 1 M KOH at 25 °C. Furthermore, overpotentials of 239 and 197 mV are required to achieve a current density of 50 mA cm^-2 for the OER and HER under simulated industrial electrolysis conditions (5 M KOH at 65 °C). Notably, Mg_0.5Ni_0.5Co-OH remarkably accelerates water splitting with a low voltage of 1.938 and 1.699 V for 50 mA cm^-2 in 1 M KOH at 25 °C and 5 M KOH at 65 °C, respectively. This work presents a novel amorphous strategy to design and construct sea urchin-like mixed metal hydroxide bifunctional efficient electrocatalysts for industrial applications.

Surface Modified CoCrFeNiMo High Entropy Alloys for Oxygen Evolution Reaction in Alkaline Seawater

Electrolysis of seawater is a promising technique to desalinate seawater and produce high-purity hydrogen production for freshwater and renewable energy, respectively. For the application of seawater electrolysis technique on a large scale, simplicity of manufacture method, repeatability of catalyst products, and stable product quality is generally required in the industry. In this work, a facile, one-step, and metal salt-free fabrication method was developed for the seawater-oxygen-evolution-active catalysts composed of CoCrFeNiMo layered double hydroxide array self-supported on CoCrFeNiMo high entropy alloy substrate. The obtained catalysts show improved performance for oxygen evolution reaction in alkaline artificial seawater solution. The best-performing sample delivered the current densities of 10, 50, and 100 mA cm−2 at low overpotentials of 260.1, 294.3, and 308.4 mV, respectively. In addition, high stability is also achieved since no degradation was observed over the chronoamperometry test of 24 h at the overpotential corresponding to 100 mA cm−2. Furthermore, a failure mechanism OER activity of multi-element LDHs catalysts was put forward in order to enhance catalytic performance and design catalysts with long-term durability.

Boron, nitrogen co-doped biomass-derived carbon aerogel embedded nickel-cobalt-iron nanoparticles as a promising electrocatalyst for oxygen evolution reaction

The electrocatalytic performance of oxygen evolution reaction (OER) electrocatalysts is highly reliant on the activity of its catalytic active site, which may be augmented by raising the number of active sites. In this study, nanoscaled nickel-cobalt-iron (NiCoFe) alloy was embedded on conductive boron(B), nitrogen(N) co-doped/biomass-derived carbon aerogel as an OER electrocatalyst. The synthesized electrocatalysts were calcined under different temperatures and with variable dopants. The optimal electrocatalyst (BN/CA-NiCoFe-600) demonstrated a low overpotential of 321 mV (at current density of 10 mA cm^-2) and a minute Tafel slope of 42 mV dec^-1, which was even smaller than that of IrO₂ and RuO₂. Its mass activity and specific activity were calculated to be 201.7 A g^-1, and 34.1 cm^-2_ECSA, respectively. Furthermore, the electrocatalyst showed excellent stability and durability. This work provides an easy and practical synthetic strategy for acquiring very active and durable electrocatalysts for OER.

High catalytic performance of nano-flowered Mg-doped NiCo layered double hydroxides for the oxygen evolution reaction

Layered double hydroxides (LDHs) are one of the ideal functional materials for the oxygen evolution reaction (OER) because of their special configuration and good electrochemical activity.

ZIF-12/Fe-Cu LDH Composite as a High Performance Electrocatalyst for Water Oxidation

Layered double hydroxides (LDH) are being used as electrocatalysts for oxygen evolution reactions (OERs). However, low current densities limit their practical applications. Herein, we report a facile and economic synthesis of an iron-copper based LDH integrated with a cobalt-based metal-organic framework (ZIF-12) to form LDH-ZIF-12 composite (1) through a co-precipitation method. The as-synthesized composite 1 requires a low overpotential of 337 mV to achieve a catalytic current density of 10 mA cm-2 with a Tafel slope of 89 mV dec-1. Tafel analysis further demonstrates that 1 exhibits a slope of 89 mV dec-1 which is much lower than the slope of 284 mV dec-1 for LDH and 172 mV dec-1 for ZIF-12. The slope value of 1 is also lower than previously reported electrocatalysts, including Ni-Co LDH (113 mV dec-1) and Zn-Co LDH nanosheets (101 mV dec-1), under similar conditions. Controlled potential electrolysis and stability test experiments show the potential application of 1 as a heterogeneous electrocatalyst for water oxidation.

Advances in hydrogen production from electrocatalytic seawater splitting

As one of the most abundant resources on the Earth, seawater is not only a promising electrolyte for industrial hydrogen production through electrolysis, but also of great significance for the refining of edible salt. Despite the great potential for large-scale hydrogen production, the implementation of water electrolysis requires efficient and stable electrocatalysts that can maintain high activity for water splitting without chloride corrosion. Recent years have witnessed great achievements in the development of highly efficient electrocatalysts toward seawater splitting. Starting from the historical background to the most recent achievements, this review will provide insights into the current state, challenges, and future perspectives of hydrogen production through seawater electrolysis. In particular, the mechanisms of overall water splitting, key features of seawater electrolysis, noble-metal-free electrocatalysts for seawater electrolysis and the underlying mechanisms are also highlighted to provide guidance for fabricating more efficient electrocatalysts toward seawater splitting.

The importance of the iron valence state in NiCoFe nanosheet array catalysts for the oxygen evolution reaction

The catalytic performances of NiCoFe nanosheet array catalysts for the OER are strongly dependent on the valence state of iron cations in the precursors.

Ultrasonication construction of the nano-petal NiCoFe-layered double hydroxide: An excellent water oxidation electrocatalyst

Unlike other preparation methods of NiCoFe-layered double hydroxides, the present study provides a facile ultrasound method for synthesis of the nano-petal NiCoFe-layered double hydroxide (LDH) prepared under intensification frequency of 40 kHz and ultrasonic power of 305 W. The effect of time reaction on the morphology of NiCoFe-LDH was investigated using the Field Emission-Scanning Electron Microscopy images. The results show that time reaction can affect the morphology and it also showed that the optimal time for synthesis of nano-petal NiCoFe-LDH was 60 min. Then, the effect of nano-petal NiCoFe-LDH on oxygen evaluation reaction activity was studied and compared with NiCoFe-LDH-c nano paricles. Also, in order to study the effect of Co²⁺ of nano-petal NiCoFe-LDH at water oxidation, the activity of NiFe-LDH synthesized in the same conditions was investigated. The results show that nano-petal NiCoFe-LDH has low onset potential (0.46 V vs. SCE), overpotential (~227 mV) and Tafel slope (234 mV per decade) in comparison with other NiCoFe-LDH nanoparticles (synthesis using co-precipitation method and ultrasonication method within 30 and 120 min), and NiFe-LDH. Based on the obtained results, the nano-petal NiCoFe-LDH can be as a suitable electrocatalyst with good stability for water oxidation reaction in the present 0.1 M KOH media.

Holey Assembly of Two-Dimensional Iron-Doped Nickel-Cobalt Layered Double Hydroxide Nanosheets for Energy Conversion Application

Layered double hydroxides (LDHs) containing first-row transition metals such as Fe, Co, and Ni have attracted significant interest for electrocatalysis owing to their abundance and excellent performance for the oxygen evolution reaction (OER) in alkaline media. Herein, the assembly of holey iron-doped nickel-cobalt layered double hydroxide (NiCo-LDH) nanosheets ('holey nanosheets') is demonstrated by employing uniform Ni-Co glycerate spheres as self-templates. Iron doping was found to increase the rate of hydrolysis of Ni-Co glycerate spheres and induce the formation of a holey interconnected sheet-like structure with small pores (1-10 nm) and a high specific surface area (279 m²  g^-1 ). The optimum Fe-doped NiCo-LDH OER catalyst showed a low overpotential of 285 mV at a current density of 10 mA cm^-2 and a low Tafel slope of 62 mV dec^-1 . The enhanced OER activity was attributed to (i) the high specific surface area of the holey nanosheets, which increases the number of active sites, and (ii) the improved kinetics and enhanced ion transport arising from the iron doping and synergistic effects.

Flexible Active-Site Engineering of Monometallic Co-Layered Double Hydroxides for Achieving High-Performance Bifunctional Electrocatalyst toward Oxygen Evolution and H2O2 Reduction

It is highly desirable but challenging to develop a facile and scalable strategy to synthesize efficient bifunctional electrocatalysts for oxygen evolution and H₂O₂ reduction by engineering the active site of monometallic-layered double hydroxides (LDHs). Herein, we developed a convenient, efficient, and scalable method for the construction of monometallic Co-LDHs with tunable Coⁿ⁺ (n = 2, 3) concentration by a one-pot solvothermal reaction in a short time (e.g., 2 and 4 h) using only cobalt nitrate and hexamine as raw materials. The catalytic performance of Co-LDHs was mainly determined by the Coⁿ⁺ (n = 2, 3) concentration, which could be simply regulated by tuning the solvothermal time. Combining the joint merits of three-dimensional flowerlike architecture (abundant accessible active sites and a fast electron/mass transport), Co-LDHs-4 with abundant Co³⁺ species exhibited an excellent electrocatalytic activity for oxygen evolution reaction in terms of a low overpotential at 10 mA cm^-2 (η₁₀ = 241 mV) and long-term durability for 70 h at 100 mA cm^-2, better than the state-of-the-art IrO₂ and most of the reported analogues. Besides, Co-LDHs-2 enriched in Co²⁺ displayed a superior electrochemical activity for H₂O₂ detection with a broad linear range (0.002-20 mM), a low detection limit (0.002 mM), and a high response sensitivity (272.02 μA mM^-1 cm^-2). Therefore, this work opens a new horizon for the rational development of a highly active electrocatalyst with tunable concentrations of active components.

Three-Dimensional Porous Nitrogen-Doped Carbon Nanosheet with Embedded NixCo3-xS4 Nanocrystals for Advanced Lithium-Sulfur Batteries

The shuttle effect of lithium polysulfides (Li₂S_n) in electrolyte and the low conductivity of sulfur are the two key hindrances of lithium sulfur (Li-S) batteries. In order to address the two issues, we propose a three-dimensional porous nitrogen-doped carbon nanosheet with embedded Ni_xCo_3-xS₄ nanocrystals derived from metal-organic frameworks for the durable-cathode host material in Li-S batteries. Experiments and density functional theory simulations show that the large porosity, robust N-doped carbon framework, and evenly embedded Ni_xCo_3-xS₄ nanocrystals with high polarity act as strong "traps" for the immobilization of Li₂S_n, which leads to an effective suppressing of the shuttle effect and promotes efficient utilization of sulfur. The Ni_xCo_3-xS₄/N-doped carbon hybrid material exhibits a high reversible capacity of 1122 mAh g^-1 at a current density of 0.5 C after 100 cycles. Even at high areal sulfur loadings of 10 and 12 mg cm^-2, the hybrid cathode materials can maintain good areal capacities of 7.2 and 7.6 mAh cm^-2 after 100 cycles. The present study sheds light on the principles of the anchoring behaviors of Li₂S_n species on bimetallic sulfide hybrid materials and reveals an attractive route to design the highly desirable cathode materials for Li-S batteries.

Recent Advances in Self-Supported Layered Double Hydroxides for Oxygen Evolution Reaction

Electrochemical water splitting driven by clean and sustainable energy sources to produce hydrogen is an efficient and environmentally friendly energy conversion technology. Water splitting involves hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), in which OER is the limiting factor and has attracted extensive research interest in the past few years. Conventional noble-metal-based OER electrocatalysts like IrO₂ and RuO₂ suffer from the limitations of high cost and scarce availability. Developing innovative alternative nonnoble metal electrocatalysts with high catalytic activity and long-term durability to boost the OER process remains a significant challenge. Among all of the candidates for OER catalysis, self-supported layered double hydroxides (LDHs) have emerged as one of the most promising types of electrocatalysts due to their unique layered structures and high electrocatalytic activity. In this review, we summarize the recent progress on self-supported LDHs and highlight their electrochemical catalytic performance. Specifically, synthesis methods, structural and compositional parameters, and influential factors for optimizing OER performance are discussed in detail. Finally, the remaining challenges facing the development of self-supported LDHs are discussed and perspectives on their potential for use in industrial hydrogen production through water splitting are provided to suggest future research directions.

Loading FeOOH on Ni(OH)2 hollow nanorods to obtain a three-dimensional sandwich catalyst with strong electron interactions for an efficient oxygen evolution reaction

Sustainable production of hydrogen by water splitting requires the exploration of highly efficient electrocatalysts from abundant non-precious metals on Earth. Ni(OH)2 hollow nanorod arrays were obtained on Ni foam by simple alkali etching, and FeOOH was electrodeposited on the walls of hollow nanorods to construct FeOOH@Ni(OH)2 sandwich hollow nanorod arrays, which help overcome the drawbacks of the poor conductivity and poor stability of FeOOH and boost the catalytic performance of the oxygen evolution reaction (OER) in comparison with the individual components. A fully contacted three-dimensional nanorod array structure provides many exposed catalytically active sites and promotes charge transfer during the electrochemical OER process. The presence of FeOOH can promote the formation of a more conductive catalytically active component, NiOOH, which improves the catalytic performance of Ni(OH)2. The electronic interaction and synergistic catalysis between nickel and iron enhances the electrochemical performance of the catalyst significantly. The optimized FeOOH@Ni(OH)2 sandwich hollow nanorod arrays show an outstanding OER activity with a small overpotential of 245 mV at 50 mA cm-2 and a low Tafel slope of 45 mV dec-1. The catalyst can maintain a substantially constant voltage over 40 h in 1.0 M KOH solution. Our work provides a new strategy to prepare Ni-Fe bimetallic materials as OER electrocatalysts.

Recent advances in transition metal based compound catalysts for water splitting from the perspective of crystal engineering

A review of the recent progress on the transition metal based catalysts for water splitting with emphasis on crystal engineering.

3D amorphous NiFe LDH nanosheets electrodeposited on in situ grown NiCoP@NC on nickel foam for remarkably enhanced OER electrocatalytic performance

NiFe LDH (layered double hydroxide) is currently attracting increasing attention as a type of promising electrocatalyst for oxygen evolution reaction (OERs); however, the biggest obstacle to its large-scale practical application is its poor conductivity and limited active sites. Herein, we report a three-dimensional NiFe LDH with high conductivity and dense active sites, where amorphous NiFe LDH nanosheets are directly electrodeposited on the surface of a hierarchical porous NiCoP@NC derived from the calcination and phosphorization of metal-organic frameworks (ZIF-67) in situ grown on nickel foam. Based on the 3D porous structure, abundant exposed active sites, fast electron and mass transfer rates and strong synergetic effects between NiCoP@NC and NiFe LDH, the resultant NiFe LDH/NiCoP@NC/NF catalysts exhibited significantly enhanced OER catalytic performances compared with NiFe LDH on nickel foam and most of the reported NiFe LDH-based catalysts: a low overpotential of 210 mV for yielding a current density of 10 mA cm-2, an extremely small Tafel slope (35 mV dec-1) and excellent durability. For overall water splitting, with NiFe LDH/NiCoP@NC/NF as the anode and NiCoP@NC/NF as the cathode, the assembled two-electrode system only required 1.54 V to obtain a stable current density of 10 mA cm-2 in 1 M KOH for at least 40 h. This research provided a simple and facile way to develop non-noble-metal oxygen evolution catalysts for replacing high-cost noble metal catalysts.

Recent advances in ternary layered double hydroxide electrocatalysts for the oxygen evolution reaction

The recent advances in ternary layered double hydroxide electrocatalysts, including the strategies used for the design, synthesis, and evaluation of their performance for oxygen evolution reaction are reviewed in this account.

Fluoridated Iron-Nickel Layered Double Hydroxide for Enhanced Performance in the Oxygen Evolution Reaction

Layered double hydroxides (LDHs) are very promising but still far from satisfactory for catalyzing the electrochemical oxygen evolution reaction (OER) in water electrolysis. Herein, it was found that the catalytic performance of iron-nickel LDHs for OER can be largely boosted by a facile and controllable fluoridation approach at low temperatures. Temperature dependence of the crystal structure and surface chemical state was observed for the simple fluoridation of the iron-nickel LDH. However, no significant surface roughness and electrochemical active surface area increases were found, which was probably owing to the structure change from nanosheets to nanorods. Significant improvements in the performance, including the catalytic activity, stability, efficiency, and kinetics, were found compared with the pristine iron-nickel LDH. Specifically, iron-nickel fluoride obtained at 250 °C afforded the lowest overpotential of 225 mV (no iR correction) to drive 10 mA cm^-2 loaded on an inert glassy carbon electrode with a small Tafel slope of 79 mV dec^-1 , outperforming the noble-metal IrO₂ catalyst and most of the similar Fe-Ni based catalysts. The performance improvement could be mainly attributed to the phase-structure transfer from metal-O bonding in the FeNi-LDHs to metal-F bonding after fluoridation, which means it is easier to form the real active sites of Fe-doped high-valence Ni-(oxy)hydroxide over the iron-nickel fluoride surface.

A novel FeS–NiS hybrid nanoarray: an efficient and durable electrocatalyst for alkaline water oxidation

A novel FeS–NiS/TM nanosheet array was developed for alkaline OER; this catalyst only requires an overpotential of 260 mV to afford a current density of 10 mA cm⁻² in 1.0 M KOH.

Impact of cation redox chemistry on continuous hydrothermal synthesis of 2D-Ni(Co/Fe) hydroxides

We challenge the transition from brucite-like to hydrotalcite-like phases for NiCo and NiFe hydroxides via continuous hydrothermal flow synthesis.

Recent Progress on Nickel-Based Oxide/(Oxy)Hydroxide Electrocatalysts for the Oxygen Evolution Reaction

Developing clean and sustainable energies as alternatives to fossil fuels is in strong demand within modern society. The oxygen evolution reaction (OER) is the efficiency-limiting process in plenty of key renewable energy systems, such as electrochemical water splitting and rechargeable metal-air batteries. In this regard, ongoing efforts have been devoted to seeking high-performance electrocatalysts for enhanced energy conversion efficiency. Apart from traditional precious-metal-based catalysts, nickel-based compounds are the most promising earth-abundant OER catalysts, attracting ever-increasing interest due to high activity and stability. In this review, the recent progress on nickel-based oxide and (oxy)hydroxide composites for water oxidation catalysis in terms of materials design/synthesis and electrochemical performance is summarized. Some underlying mechanisms to profoundly understand the catalytic active sites are also highlighted. In addition, the future research trends and perspectives on the development of Ni-based OER electrocatalysts are discussed.

3D-2D heterostructure of PdRu/NiZn oxyphosphides with improved durability for electrocatalytic methanol and ethanol oxidation

The rational design and engineering of bimetallic Pd-based nanocatalysts with both high activity and durability are of paramount significance for the practical applications of fuel cells. Herein, a new class of well-defined 2D NiZn oxyphosphide nanosheets (NiZnP NSs) have been successfully engineered to support unique 3D PdRu nanoflowers (PdRu NFs) via a facile strategy. Such nanohybrids with abundant surface active areas and modified electronic structure exhibit a great enhancement in electrocatalytic activity for the methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR), whose mass/specific activities are 1739.5 mA mg-1/4.5 mA cm-2 and 4719.8 mA mg-1/12.3 mA cm-2, which are 8.3/9.0 and 8.3/9.5 times higher than those of commercial Pd/C catalysts, respectively. More interestingly, with the remarkable promotional effect of NiZnP NSs, such 3D-2D PdRu/NiZn oxyphosphide nanohybrids can even retain 72.4% and 70.1% of initial catalytic activity toward MOR and EOR for 1000 potential cycles with negligible morphological or compositional variations. The successful construction of this new class of electrocatalysts opens up a new way for designing 3D-2D nanohybrids with high performance for electrochemical reactions and beyond.

Phosphorus-doped cobalt-iron oxyhydroxide with untrafine nanosheet structure enable efficient oxygen evolution electrocatalysis

Although explosive progresses have been achieved in the field of water splitting, the design and development of stable and inexpensive electrocatalysts for oxygen evolution remain a formidable challenge. Herein, the cost-efficient two dimensional (2D) phosphorus-doped CoFe oxyhydroxide nanosheets (denoted as CoFeP NSs) are successfully engineered and showing exceptional oxygen evolution reaction (OER) activity and chemical stability in 1 M KOH solution. This unique 2D nanosheet structure facilitates the mass transfer and electron transport, resulting in the remarkable OER activity that delivers a current density of 10 mA cm^-2 at a low overpotential of 305 mV with an ultra-small Tafel slope 49.6 mV/dec. More significantly, the doped P also plays a vital role in modulating the surface active sites, leading to the substantial enhancement of electrocatalytic performances. Our study provides a facile one-pot method for the successful fabrication of 2D P-doped CoFe NSs which display superior electrocatalytic performance, shedding great promise for environment and energy-related fields.