Electrodeposition of cobalt-sulfide nanosheets film as an efficient electrocatalyst for oxygen evolution reaction

A Review of Transition Metal Boride, Carbide, Pnictide, and Chalcogenide Water Oxidation Electrocatalysts

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of "catalytically active sites/species/phases" in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

Skeleton-coated CoCu-Based bimetal hollow nanoprisms as High-Performance electrocatalysts for oxygen evolution reaction

CoSx materials with high catalytic activity are considered as promising HER electrocatalysts, but their inherent low electrical conductivity and easy loss of active sites have greatly limited their applications in OER electrocatalysis. Herein, we present a convenient method to synthesize Co-Cu hollow nanoprisms after wrapping and calcining with trithiocyanuric acid (C3H3N3S3) (denoted N-Co-Cu-S-x HNs). The results showed that Cu doping modified the charge density of Co center, leading to the enhancement of the intrinsic activity of the Co3S4 active center, meanwhile wrapping trithiocyanuric acid on the surfaces and calcinating to form N-containing C skeleton as a flexible substrate to encapsulate the catalysts, which effectively protected the active sites inside the catalysts. Notably, the OER catalyst that was optimized by adjusting the metal ratio and controlling the trithiocyanuric acid incorporation exhibited a low overpotential of 306 mV under a current density of 10 mA cm-2 and showed a superior durability of more than 27 h. This work may provide some insights into the preparation of oxygen evolution reaction catalysts with excellent performance through doping transition metals and protecting the internal active sites strategies.

In Situ Synthesis and Microfabrication of High Entropy Alloy and Oxide Compounds by Femtosecond Laser Direct Writing under Ambient Conditions

Synthesis and coating of multi-metal oxides (MMOs) and alloys on conductive substrates are indispensable to electrochemical applications, yet demand multiple, resource-intensive, and time-consuming processes. Herein, an alternative approach to the synthesis and coating of alloys and MMOs by femtosecond laser direct writing (FsLDW) is reported. A solution-based precursor ink is deposited and dried on the substrate and illuminated by a femtosecond laser. During the illumination, dried precursor ink is transformed to MMO/alloys and is simultaneously bonded to the substrate. The formulation of the alloy and MMO precursor ink for laser processing is universally applicable to a large family of oxides and alloys. The process is conducted at room temperature and in an open atmosphere. To demonstrate, a large family of 57 MMOs and alloys are synthesized from a group of 13 elements. As a proof of concept, Ni_0.24 Co_0.23 Cu_0.24 Fe_0.15 Cr_0.14 high entropy alloy synthesized on stainless-steel foil by FsLDW is used for the oxygen evolution reaction, which achieves a current density of 10 mA cm^-2 at a significantly low overpotential of 213 mV. Further, FsLDW can also achieve microfabrication of alloys/MMO with feature sizes down to 20 µm.

Flowery ln2MnSe4 Novel Electrocatalyst Developed via Anion Exchange Strategy for Efficient Water Splitting

Oxygen and hydrogen generated by water electrolysis may be utilized as a clean chemical fuel with high gravimetric energy density and energy conversion efficiency. The hydrogen fuel will be the alternative to traditional fossil fuels in the future, which are near to exhaustion and cause pollution. In the present study, flowery-shaped In₂MnSe₄ nanoelectrocatalyst is fabricated by anion exchange reaction directly grown on nickel foam (NF) in 1.0 M KOH medium for oxygen evolution reaction (OER). The physiochemical and electrical characterization techniques are used to investigate the chemical structure, morphology, and electrical properties of the In₂MnSe₄ material. The electrochemical result indicates that synthesized material exhibits a smaller value of Tafel slope (86 mV/dec), lower overpotential (259 mV), and high stability for 37 h with small deterioration in the current density for a long time. Hence, the fabricated material responds with an extraordinary performance for the OER process and for many other applications in the future.

Template free-synthesis of cobalt-iron chalcogenides [Co0.8Fe0.2L2, L = S, Se] and their robust bifunctional electrocatalysis for the water splitting reaction and Cr(vi) reduction

The ease of production of materials and showing multiple applications are appealing in this modern era of advanced technology. This paper reports the synthesis of a pair of novel cobalt-iron chalcogenides [Co0.8Fe0.2S2 and Co0.8Fe0.2Se2] with enhanced electro catalytic activities. These ternary metal chalcogenides were synthesized by a one-step template-free approach via a hexamethyldisilazane (HMDS)-assisted synthetic method. Transient photocurrent (TPC) studies and electrochemical impedance spectra (EIS) of these materials showed free electron mobility. Their bifunctional activities were verified in both the electrochemical oxygen evolution reaction (OER) and in the electrochemical reduction of toxic inorganic heavy metal ions [Cr(vi)] in polluted water. The materials showed robust catalytic ability in the oxygen evolution reaction with minimum possible over potential (345 and 350 mV @ η10) as determined by linear sweep voltammetry and the lower Tafel values (52.4 and 84.5 mV dec-1) for Co0.8Fe0.2Se2 and Co0.8Fe0.2S2 respectively. Surprisingly, both the materials also showed an excellent activity towards electrochemical Cr(vi) reduction to Cr(iii). Besides the maximum current achieved for Co0.8Fe0.2S2, a minimum value for the Limit of detection (LOD) was obtained for Co0.8Fe0.2S2 (0.159 μg L-1) compared to Co0.8Fe0.2Se2 (0.196 μg L-1). We tested the durability of catalysts, the critical factor for the prolonged use of catalysts, through the recyclability measurements of these materials as catalysts. Both the catalysts presented outstanding durability and balanced electro catalytic activities for up to 1500 CV cycles, and chronoamperometry studies also confirmed exceptional stability. The enhanced catalytic activities of these materials are ascribed to the free electron movement, evidenced by the increased TPC measured and EIS. Therefore, the template-free synthesis of these electro catalysts containing non-noble metal illustrates the practical approach to develop such types of catalysts for multiple functions.

Integrated Bifunctional Electrodes Based on Amorphous Co-Ni-S Nanoflake Arrays with Atomic Dispersity of Active Sites for Overall Water Splitting

Fabrication of amorphous electrocatalysts without noble metals for cost-effective full water splitting is highly desired but remains a substantial challenge. In the present work, we report a facile strategy for exploring integrated bifunctional electrocatalysts based on amorphous cobalt/nickel sulfide nanoflake arrays self-supported on carbon cloth, by tailoring competitive coordination of metal ions between glucose and 2-aminoterephthalic acid. Ultrahigh dispersion of binary metal active sites with balanced atomic distribution enables the optimization of catalytic properties for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in an alkaline solution. The obtained catalyst exhibits remarkably enhanced OER and HER activities as compared with its oxide counterpart and analogues with different Co/Ni ratios. It requires overpotentials of 296 and 192 mV to deliver a current density of 10 mA cm^-2 for the OER and HER, respectively; it retains 96.6 and 96.9% activity after 32 h of OER and 36 h of HER tests at 10 mA cm^-2, respectively. As directly used an anode and a cathode in an alkaline electrolyzer, a low cell voltage of 1.60 V could endow a water splitting current of 10 mA cm^-2, outperforming the benchmark RuO₂ and Pt/C-based electrolyzer at 1.72 V@10 mA cm^-2. The current synthetic strategy may provide more opportunities for the design and direct synthesis of amorphous catalysts for overall water splitting and beyond.

A novel monoclinic metal oxide catalyst for oxygen evolution reaction in alkaline media

The main bottleneck of electrolytic water for hydrogen production in alkaline media is the oxygen evolution reaction (OER) involving four-electron transfer. Designing highly efficient OER catalysts is attractive to accelerate...

Research Progress of Oxygen Evolution Reaction Catalysts for Electrochemical Water Splitting

The development of a low-cost and high-efficiency oxygen evolution reaction (OER) catalyst is essential to meet the future industrial demand for hydrogen production by electrochemical water splitting. Given the limited reserves of noble metals and many competitive applications in environmental protection, new energy, and chemical industries, many studies have focused on exploring new and efficient non-noble metal catalytic systems, improving the understanding of the OER mechanism of non-noble metal surfaces, and designing electrocatalysts with higher activity than traditional noble metals. This Review summarizes the research progress of anode OER catalysts for hydrogen production by electrochemical water splitting in recent years, for noble metal and non-noble metal catalysts, where non-noble metal catalysts are highlighted. The categories are as follows: (1) Transition metal-based compounds, including transition metal-based oxides, transition metal-based layered hydroxides, and transition metal-based sulfides, phosphides, selenides, borides, carbides, and nitrides. Transition metal-based oxides can also be divided into perovskite, spinel, amorphous, rock-salt-type, and lithium oxides according to their different structures. (2) Carbonaceous materials and their composite materials with transition metals. (3) Transition metal-based metal-organic frameworks and their derivatives. Finally, the challenges and future development of the OER process of water splitting are discussed.

A strategy for preparing high-efficiency and economical catalytic electrodes toward overall water splitting

Electrolyzing water technology to prepare high-purity hydrogen is currently an important field in energy development. However, the preparation of efficient, stable, and inexpensive hydrogen production technology from electrolyzed water is a major problem in hydrogen energy production. The key technology for hydrogen production from water electrolysis is to prepare highly efficient catalytic, stable and durable electrodes, which are used to reduce the overpotential of the hydrogen evolution reaction and the oxygen evolution reaction of electrolyzed water. The main strategies for preparing catalytic electrodes include: (i) choosing cheap, large specific surface area and stable base materials, (ii) modulating the intrinsic activity of the catalytic material through elemental doping and lattice changes, and (iii) adjusting the morphology and structure to increase the catalytic activity. Based on these findings, herein, we review the recent work in the field of hydrogen production by water electrolysis, introduce the preparation of catalytic electrodes based on nickel foam, carbon cloth and new flexible materials, and summarize the catalytic performance of metal oxides, phosphides, sulfides and nitrides in the hydrogen evolution and oxygen evolution reactions. Secondly, parameters such as the overpotential, Tafel slope, active site, turnover frequency, and stability are used as indicators to measure the performance of catalytic electrode materials. Finally, taking the material cost of the catalytic electrode as a reference, the successful preparations are comprehensively compared. The overall aim is to shed some light on the exploration of high-efficiency and economical electrodes in energy chemistry and also demonstrate that there is still room for discovering new combinations of electrodes including base materials, composition lattice changes and morphologies.

Electrocatalytic Oxygen Evolution by Hierarchically Structured Cobalt-Iron Composites

The development of scalable routes to highly active and efficient oxygen evolution reaction (OER) electrocatalysts based on earth-abundant materials is crucial for post-fossil fuel energy schemes. Here, we demonstrate how commercial copper foam electrodes can be functionalized for water oxidation using a facile electrodeposition process. The resulting composite electrode features hierarchically structured cobalt-iron-based catalyst particles, which offer channel-like structures for the transport of electrolyte and release of oxygen gas bubbles. We report high electrocatalytic OER performance as demonstrated by high current densities at low overpotentials (293 mV at j = 50 mA cm^-2) and long-term stability under technologically relevant alkaline conditions (>24 h in 1.0 M aqueous KOH).

Fibrous-Structured Freestanding Electrodes for Oxygen Electrocatalysis

Electrocatalysts used for oxygen reduction and oxygen evolution reactions are critical materials in many renewable-energy devices, such as rechargeable metal-air batteries, regenerative fuel cells, and water-splitting systems. Compared with conventional electrodes made from catalyst powders, oxygen electrodes with a freestanding architecture are highly desirable because of their binder-free fabrication and effective elimination of catalyst agglomeration. Among all freestanding electrode structures that have been investigated so far, fibrous materials exhibit many unique advantages, such as a wide range of available fibers, low material and material-processing costs, large specific surface area, highly porous structure, and simplicity of fiber functionalization. Recent advances in the use of fibrous structures for freestanding electrocatalytic oxygen electrodes are summarized, including electrospun nanofibers, bacterial cellulose, cellulose fibrous structures, carbon clothes/papers, metal nanowires, and metal meshes. After detailed discussion of common techniques for oxygen electrode evaluation, freestanding electrode fabrication, and their electrocatalytic performance, current challenges and future prospects are also presented for future development.

Earlier diagnoses of acute leukemia by a sandwich type of electrochemical aptasensor based on copper sulfide-graphene composite

Due to high affinity and specificity of aptamers, they are widely considered for construction of aptasensor to specific recognizing of analytes in biological complex matrix. So, in this work we design a high selective and sensitive aptasensor for leukemia cancer cells (CCRF-CEM) via superior catalytic effect of copper sulfide-graphene (CuS-GR) nanocomposite as label and Au-GR nanocomposite as sensing platform. The CuS-GR nano-composite (label component) is CuS nanoparticles that wrapping on graphene sheets. Its catalytic activity (CuS-GR) increases the current of sensor in parallel with adding of CCRF-CEM and provide sensitive detection of analytes. The detailed of signal amplification and effect on the aptasensor performance completely discussed. This sensor has a linear range of 50-1 × 10⁶ cell mL^-1, with a limit of detection of 18 cell mL^-1. Also, the developed aptasensor has a significance specificity, high sensitivity and accuracy. It was used for the identification of CCRF-CEM cells in blood samples.

Electrodeposited Sulfur and CoxS Electrocatalyst on Buckypaper as High-Performance Cathode for Li-S Batteries

Lithium-sulfur batteries (LSBs) are considered as the next generation of advanced rechargeable batteries because of their high energy density. In this study, sulfur and Co_xS electrocatalyst are deposited on carbon nanotube buckypaper (S/Co_xS/BP) by a facile electrodeposition method and are used as a binder-free high-performance cathode for LSBs. Elemental sulfur is deposited on buckypaper by electrooxidation of a polysulfide solution (~ S₆^2-). This approach substantially increased the current and time efficiency of sulfur electrochemical deposition on conductive material for LSBs. S/Co_xS/BP cathode could deliver an initial discharge capacity as high as 1650 mAh g^-1 at 0.1 C, which is close to the theoretical capacity of sulfur. At current rate of 0.5 C, the S/Co_xS/BP has a capacity of 1420 mAh g^-1 at the first cycle and 715 mAh g^-1 after 500 cycles with a fading rate of 0.099% per cycle. The high capacity of S/Co_xS/BP is attributed to both the homogeneous dispersion of nanosized sulfur within BP and the presence of Co_xS catalyst. The sodium dodecyl sulfate (SDS) pretreatment of BP renders it polarity to bind polysulfides and thus facilitates the good dispersibility of nanosized sulfur within BP. Co_xS catalyst accelerates the kinetics of polysulfide conversion and reduces the presence of polysulfide in the cathode, which suppresses the polysulfide diffusion to anode, i.e., the shuttle effect. The mitigation of the active material loss improves not only the capacity but also the cyclability of S/Co_xS/BP.

Amorphous Ni–Fe–Se hollow nanospheres electrodeposited on nickel foam as a highly active and bifunctional catalyst for alkaline water splitting

The electrodeposition of amorphous Ni–Fe–Se hollow nanospheres as a highly efficient bifunctional catalyst for the sustainable production of hydrogen.

Improving catalysis for electrochemical water splitting using a phosphosulphide surface

A yolk–shell-structured porous phosphosulphide catalyst exhibits superior activities towards the hydrogen and oxygen evolution reactions in water splitting in an alkaline electrolyte.

In situ confined vertical growth of a 1D-CuCo2S4 nanoarray on Ni foam covered by a 3D-PANI mesh layer to form a self-supporting hierarchical structure for high-efficiency oxygen evolution catalysis

Inspired by the patchwork of artificial turf, where planting in a smaller area can result in a more uniform lawn that grows in one direction, here, we defined the growth position and orientation of a CuCo₂S₄ nanoarray for the first time by electroplating a PANI mesh layer onto a Ni foam to obtain a self-supporting hierarchical electrode material. The nitrogen species derived from the PANI building blocks act as bridging sites to bind with metal ions, which provides a strong coupling effect for the in situ growth of CuCo₂S₄. At the same time, the mesh structure of PANI divides the growable location into smaller blocks. Compared with a mesh plane with uniformly distributed nitrogen sites, only a small portion of the nitrogen sites are located on the narrow-width fence structure, which may make it difficult for CuCo₂S₄ to grow onto the fence structure, thereby limiting the self-growth space and confining CuCo₂S₄. The uniformly distributed growth sites direct CuCo₂S₄ to grow perpendicular to the plane while limiting their growth size. The excellent structural features further enhance the electrochemical oxygen evolution activity, and the oxygen evolution overpotential at a current density of 100 mA cm^-2 is only 291 mV, which is superior to that of the currently known cobalt-copper-based catalyst materials. In addition, the stable structure provides excellent electrode cyclic stability. The preparation of hierarchical self-supporting cobalt-copper bimetallic sulfide nanoarrays provided a reference direction for other transition metal catalytic materials and provided a basis for industrial applications.

Optimization of iron-doped Ni3S2 nanosheets by disorder engineering for oxygen evolution reaction

Nowadays, disorder engineering of catalytic materials has attracted significant attention because it can increase catalytic active sites and thus enhance their catalytic activity for electrocatalytic reactions. However, it is extremely important to uncover the relationship between disorder engineering and catalytic activity. Particularly, deep exploration of the relationship is very important for fabricating excellent highly active catalysts for oxygen evolution reaction (OER), which is one of the promising technologies in energy transition. In this study, we prepared Fe-doped Ni3S2 materials and simultaneously controlled the disorder degree by regulating the ion concentration to improve the activity for OER. By investigating the as-prepared catalysts with various disorder degrees for OER, we also explored the relationship between the disordered structure and OER catalytic performance. In particular, the optimized electrocatalyst with an appropriate disorder degree showed excellent activity and stability. We hope that this study provides a feasible direction to fabricate and optimize transition metal chalcogenide (TMC) electrocatalysts as efficient and stable electrocatalysts for OER.

Controlled phase evolution from Cu0.33Co0.67S2 to Cu3Co6S8 hexagonal nanosheets as oxygen evolution reaction catalysts

Developing cheap and efficient transition metal-based catalysts for the oxygen evolution reaction (OER) plays the key role in large-scale implementation of hydrogen production.

Self-Interconnected Porous Networks of NiCo Disulfide as Efficient Bifunctional Electrocatalysts for Overall Water Splitting

Electrochemical splitting of water has been viewed as a highly efficient technique to produce clean hydrogen and oxygen energy. However, designing inexpensive multifunctional electrocatalysts with high performance is a great challenge. Here, a unique three-dimensional catalyst of self-interconnected porous Ni-Co disulfide networks grown on carbon cloth [(Ni_0.33Co_0.67)S₂ nanowires (NWs)/CC] was prepared by a facile hydrothermal method coupled with further low-temperature sulfuration strategy. As a bifunctional electrocatalyst, (Ni_0.33Co_0.67)S₂ NWs/CC exhibits a remarkable activity to catalyze both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). To drive a current density of 100 mA cm^-2, (Ni_0.33Co_0.67)S₂ NWs/CC needs the overpotentials of 156 mV in 0.5 M H₂SO₄ solution and 334 mV in 1.0 M KOH solution for HER, respectively. Moreover, when used as a catalyst of OER, (Ni_0.33Co_0.67)S₂ NWs/CC needs an overpotential of 295 mV to produce a current density of 100 mA cm^-2. The excellent electrochemical properties are mainly attributed to the synergetic catalysis of a Ni-Co-based bimetallic disulfide, the porous network structure, and the high conduction of CC. Moreover, the two-electrode alkaline water-splitting system constructed by (Ni_0.33Co_0.67)S₂ NWs/CC only needs a low cell voltage of 1.57 V to approach 10 mA cm^-2. This work offers more new insights for the design and preparation of the non-noble metal catalysts based on transition metal sulfides with excellent electrocatalytic performance in overall water splitting.

Cobalt Sulfide/Nickel Sulfide Heterostructure Directly Grown on Nickel Foam: An Efficient and Durable Electrocatalyst for Overall Water Splitting Application

Fabrication of high-performance noble-metal-free bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water is a promising strategy toward future carbon-neutral economy. Herein, a one-pot hydrothermal synthesis of cobalt sulfide/nickel sulfide heterostructure supported by nickel foam (CoS _x/Ni₃S₂@NF) was performed. The Ni foam acted as the three-dimensional conducting substrate as well as the source of nickel for Ni₃S₂. The formation of CoS _x/Ni₃S₂@NF was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The formation of CoS _x/Ni₃S₂@NF facilitated easy charge transport and showed synergistic electrocatalytic effect toward HER, OER, and overall water splitting in alkaline medium. Remarkably, CoS _x/Ni₃S₂@NF showed catalytic activity comparable with that of benchmarking electrocatalysts Pt/C and RuO₂. For CoS _x/Ni₃S₂@NF, overpotentials of 204 and 280 mV were required to achieve current densities of 10 and 20 mA cm^-2 for HER and OER, respectively, in 1.0 M KOH solution. A two-electrode system was formulated for overall water splitting reaction, which showed current densities of 10 and 50 mA cm^-2 at 1.572 and 1.684 V, respectively. The prepared catalyst exhibited excellent durability in HER and OER catalyzing conditions and also in overall water splitting operation. Therefore, CoS _x/Ni₃S₂@NF could be a promising noble-metal-free electrocatalyst for overall water splitting application.

Cobalt-Doped Goethite-Type Iron Oxyhydroxide (α-FeOOH) for Highly Efficient Oxygen Evolution Catalysis

It is an urgent challenge to develop low-cost and high-performance catalysts for the oxygen evolution reaction (OER). We synthesized nanoparticulate electrocatalysts consisting of cobalt-doped goethite-type iron oxyhydroxide (α-FeOOH) with controlled Co/Fe ratios [Co _x Fe_1-x OOH (x ≤ 0.20)] based on our own wet process. A Co_0.20Fe_0.80OOH-coated glassy carbon electrode generated a current density (j) of 10 mA cm^-2 at an overpotential (η) as small as 383 mV (1.61 V vs the reversible hydrogen electrode) in an alkaline electrolyte, with a small Tafel slope of 40 mV dec^-1 and excellent durability, whereas pure α-FeOOH required η = 580 mV to reach the same current density. This can be ascribed to the effect of Co doping, which resulted in an increase in electrochemically active surface area and a decrease in charge-transfer resistance. The content of cobalt, a scarce resource, in the catalyst is much smaller than those in most of the other Fe-based catalysts reported so far. Thus, this study will provide a new strategy of designing cost-effective and high-performance catalysts for the OER in alkaline solution.

Facile, Room Temperature, Electroless Deposited (Fe1-x, Mnx )OOH Nanosheets as Advanced Catalysts: The Role of Mn Incorporation

Herein, bimetallic iron (Fe)-manganese (Mn) oxyhydroxide ((Fe_1-x, Mn_x )OOH, FeMnOOH) nanosheets on fluorine-doped tin oxide conducting substrates and on semiconductor photoanodes are synthesized by a facile, room temperature, electroless deposition method as catalysts for both electrochemical and photo-electrochemical (PEC) water splitting, respectively. Surprisingly, Mn-doped FeOOH can significantly modulate the nanosheet morphology to increase the active surface area, boost more active sites, and augment the intrinsic activity by tuning the electronic structure of FeOOH. Due to the 2D nanosheet architecture, the optimized FeMnOOH exhibits superior electrochemical activity and outstanding durability for the oxygen evolution reaction with a low overpotential of 246 mV at 10 mA cm^-2 and 414 mV at 100 mA cm^-2 , and long-term stability for 40 h without decay, which is comparable to the best electrocatalysts for water oxidation reported in the literature. By integrating with semiconductor photoanodes (such as α-Fe₂ O₃ nanorod (NR) arrays), bimetallic FeMnOOH catalysts achieve solar-driven water splitting with a significantly enhanced PEC performance (3.36 mA cm^-2 at 1.23 V vs reversible hydrogen electrode (RHE)) with outstanding long-term stability (≈8 h) compared to that of the bare Fe₂ O₃ NR (0.92 mA cm^-2 at 1.23 V vs RHE).

Carbon Cloth Supported Nano-Mg(OH)2 for the Enrichment and Recovery of Rare Earth Element Eu(III) From Aqueous Solution

Nano-Mg(OH)₂ is attracting great attention as adsorbent for pre-concentration and recovery of rare earth elements (REEs) from low-concentration solution, due to its superior removal efficiency for REEs and environmental friendliness. However, the nanoparticles also cause some severe problems during application, including aggregation, blockage in fixed-bed column, as well as the difficulties in separation and reuse. Herein, in order to avoid the mentioned problems, a carbon cloth (CC) supported nano-Mg(OH)₂ (nano-Mg(OH)₂@CC) was synthesized by electrodeposition. The X-ray diffraction and scanning electron microscopy analysis demonstrated that the interlaced nano-sheet of Mg(OH)₂ grew firmly and uniformly on the surface of carbon cloth fibers. Batch adsorption experiments of Eu(III) indicated that the nano-Mg(OH)₂@CC composite maintained the excellent adsorption performance of nano-Mg(OH)₂ toward Eu(III). After adsorption, the Eu containing composite was calcined under nitrogen atmosphere. The content of Eu₂O₃ in the calcined material was as high as 99.66%. Fixed-bed column experiments indicated that no blockage for Mg(OH)₂@CC composite was observed during the treatment, while the complete blockage of occurred to nano-Mg(OH)₂ at an effluent volume of 240 mL. Moreover, the removal efficiency of Mg(OH)₂@CC was still higher than 90% until 4,200 mL of effluent volume. This work provides a promising method for feasible application of nanoadsorbents in fixed-bed process to recycle low-concentration REEs from wastewater.

Construction of a hierarchical NiFe layered double hydroxide with a 3D mesoporous structure as an advanced electrocatalyst for water oxidation

A facile and cost-effective one-step hydrothermal method is used to synthesize NiFe LDH microclusters with a 3D hierarchically mesoporous architecture. This superior electrocatalyst can achieve a current density of 10 mA cm⁻² with an ultralow overpotential of 211 mV toward the oxygen evolution reaction.