Nickel-Based Transition Metal Nitride Electrocatalysts for the Oxygen Evolution Reaction

Recent progress in metal oxide-based electrode materials for safe and sustainable variants of supercapacitors

A significant amount of energy can be produced using renewable energy sources; however, storing massive amounts of energy poses a substantial obstacle to energy production. Economic crisis has led to rapid developments in electrochemical (EC) energy storage devices (EESDs), especially rechargeable batteries, fuel cells, and supercapacitors (SCs), which are effective for energy storage systems. Researchers have lately suggested that among the various EESDs, the SC is an effective alternate for energy storage due to the presence of the following characteristics: SCs offer high-power density (PD), improvable energy density (ED), fast charging/discharging, and good cyclic stability. This review highlighted and analyzed the concepts of supercapacitors and types of supercapacitors on the basis of electrode materials, highlighted the several feasible synthesis processes for preparation of metal oxide (MO) nanoparticles, and discussed the morphological effects of MOs on the electrochemical performance of the devices. In this review, we primarily focus on pseudo-capacitors for SCs, which mainly contain MOs and their composite materials, and also highlight their future possibilities as a useful application of MO-based materials in supercapacitors. The novelty of MO's electrode materials is primarily due to the presence of synergistic effects in the hybrid materials, rich redox activity, excellent conductivity, and chemical stability, making them excellent for SC applications.

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.

Effect of Synthetic Methodology on the Physicochemical Attributes and Electrocatalytic Activity of NiAl-LDHs for the Oxygen Evolution Reaction

Layered double hydroxides (LDHs) are promising materials for oxygen evolution reactions (OERs), a key component of water splitting to produce hydrogen and oxygen via water electrolysis. However, the performance of LDHs can be limited by their low surface area and poor accessibility of active sites. In this work, we synthesized highly exfoliated 2D NiAl-LDHs by aqueous miscible solvent treatment method (AMOST) and compared its electrocatalytic efficiency with its analogue synthesised via slow urea hydrolysis. We demonstrate that the exfoliated 2D LDHs prepared by AMOST method have a higher surface area and more active sites than the crystalline LDHs obtained through urea hydrolysis, resulting in a superior OER activity and efficiency. The exfoliated 2D LDHs required a lower overpotential of 280 mV to reach a current density of 50 mA cm-2 and it also outperformed IrO2 , a benchmark OER catalyst, in terms of overpotential and stability. We demonstrate that the physicochemical properties of nanosheets derived from NIAl-LDH-based materials are strongly influenced by the synthetic methodology, which affects the exfoliation degree, surface area and active site density. These factors are crucial for improving the OER catalytic performance of these materials, as shown by our results.

Nanoflower-like FeVNi3S2-xas efficient electrocatalyst for alkaline oxygen evolution reaction

The development of low cost efficient catalysts for oxygen evolution reaction (OER) is still a obstacle to realize the commercialization of electrocatalytic water splitting. Herein, interface engineering and heteroatom doping is adopted to synthesize iron and vanadium doped nickel sulfide on nickel foam via hydrothermal method followed by hydrogen treatment to create sulfur defects. The optimized nanoflower-like FeVNi3S2-x/NF is an efficient OER electrocatalyst that outperforms many of the reported transition metals catalysts. Benefiting from abundant sulfur defects and the synergistic effect of heteroatom doping, FeVNi3S2-x/NF exhibits an ultralow overpotential of 230 mV to reach a current density of 100 mA cm-2, a rapid reaction kinetics with a small Tafel slope of 46.6 mV dec-1, and a stable long-term durability in 1 M KOH. Experimental results and characterizations confirm that sulfur vacancies together with the synergistic effect from multiple heteroatom doping can effectively regulate the electronic structure, resulting in increased electrical conductivity and electrochemically active surface area, thus enhancing OER performance. Furthermore,in situRaman spectroscopy reveals that, the reconstitution amorphous nickel oxyhydroxide (NiOOH) on the catalyst surface is responsible for catalyzing the OER reaction. This work represents a promising methodology to synthesize low-cost and highly active OER electrocatalysts.

Ultrafine Electrospun Cobalt-Molybdenum Bimetallic Nitride as a Durable Electrocatalyst for Hydrogen Evolution

Transition metal nitrides are promising electrocatalysts for hydrogen evolution reaction (HER) owing to their Pt-like electronic structure. However, the harsh nitriding conditions greatly limit their large-scale applications. Herein, ultrafine Co₃Mo₃N-Mo₂C (<1 nm)-decorated carbon nanofibers (Co₃Mo₃N-Mo₂C/CNFs) were prepared by electrostatic spinning followed by pyrolysis treatment, in which the MoCo-MOF simultaneously serves as the precursor and nitrogen source. The generated synergistic interactions between Mo₂C and Co₃Mo₃N significantly adjust the electronic structure of Mo₂C and afford a fast charge transfer, which endows the resultant hybrid with superior HER electrocatalytic performances. Specifically, the as-obtained Co₃Mo₃N-Mo₂C/CNF delivers a low overpotential of only 76 mV to achieve a current density of 10 mA cm^-2 and superior durability with no obvious degradation for 200 h in acidic media. This performance outperforms most of the transition metal-based electrocatalysts reported to date. This work paves a new way for the design of catalysts with ultrasmall size and high efficiency in energy conversion.

Synthesis of Ketjenblack Decorated Pillared Ni(Fe) Metal-Organic Frameworks as Precursor Electrocatalysts for Enhancing the Oxygen Evolution Reaction

Metal-organic frameworks (MOFs) have been investigated with regard to the oxygen evolution reaction (OER) due to their structure diversity, high specific surface area, adjustable pore size, and abundant active sites. However, the poor conductivity of most MOFs restricts this application. Herein, through a facile one-step solvothermal method, the Ni-based pillared metal-organic framework [Ni2(BDC)2DABCO] (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane), its bimetallic nickel-iron form [Ni(Fe)(BDC)2DABCO], and their modified Ketjenblack (mKB) composites were synthesized and tested toward OER in an alkaline medium (KOH 1 mol L-1). A synergistic effect of the bimetallic nickel-iron MOF and the conductive mKB additive enhanced the catalytic activity of the MOF/mKB composites. All MOF/mKB composite samples (7, 14, 22, and 34 wt.% mKB) indicated much higher OER performances than the MOFs and mKB alone. The Ni-MOF/mKB14 composite (14 wt.% of mKB) demonstrated an overpotential of 294 mV at a current density of 10 mA cm-2 and a Tafel slope of 32 mV dec-1, which is comparable with commercial RuO2, commonly used as a benchmark material for OER. The catalytic performance of Ni(Fe)MOF/mKB14 (0.57 wt.% Fe) was further improved to an overpotential of 279 mV at a current density of 10 mA cm-2. The low Tafel slope of 25 mV dec-1 as well as a low reaction resistance due to the electrochemical impedance spectroscopy (EIS) measurement confirmed the excellent OER performance of the Ni(Fe)MOF/mKB14 composite. For practical applications, the Ni(Fe)MOF/mKB14 electrocatalyst was impregnated into commercial nickel foam (NF), where overpotentials of 247 and 291 mV at current densities of 10 and 50 mA cm-2, respectively, were realized. The activity was maintained for 30 h at the applied current density of 50 mA cm-2. More importantly, this work adds to the fundamental understanding of the in situ transformation of Ni(Fe)DMOF into OER-active α/β-Ni(OH)2, β/γ-NiOOH, and FeOOH with residual porosity inherited from the MOF structure, as seen by powder X-ray diffractometry and N2 sorption analysis. Benefitting from the porosity structure of the MOF precursor, the nickel-iron catalysts outperformed the solely Ni-based catalysts due to their synergistic effects and exhibited superior catalytic activity and long-term stability in OER. In addition, by introducing mKB as a conductive carbon additive in the MOF structure, a homogeneous conductive network was constructed to improve the electronic conductivity of the MOF/mKB composites. The electrocatalytic system consisting of earth-abundant Ni and Fe metals only is attractive for the development of efficient, practical, and economical energy conversion materials for efficient OER activity.

Recent Progress in Emerging Novel MXenes Based Materials and their Fascinating Sensing Applications

Early transition metals based 2D carbides, nitrides and carbonitrides nanomaterials are known as MXenes, a novel and extensive new class of 2D materials family. Since the first accidently synthesis based discovery of Ti₃ C₂ in 2011, more than 50 additional compositions have been experimentally reported, including at least eight distinct synthesis methods and also more than 100 stoichiometries are theoretically studied. Due to its distinctive surface chemistry, graphene like shape, metallic conductivity, high hydrophilicity, outstanding mechanical and thermal properties, redox capacity and affordable with mass-produced nature, this diverse MXenes are of tremendous scientific and technological significance. In this review, first we'll come across the MXene based nanomaterials possible synthesis methods, their advantages, limitations and future suggestions, new chemistry related to their selected properties and potential sensing applications, which will help us to explain why this family is growing very fast as compared to other 2D families. Secondly, problems that help to further improve commercialization of the MXene nanomaterials based sensors are examined, and many advances in the commercializing of the MXene nanomaterials based sensors are proposed. At the end, we'll go through the current challenges, limitations and future suggestions.

Evaluation of electrosynthesized reduced graphene oxide-Ni/Fe/Co-based (oxy)hydroxide catalysts towards the oxygen evolution reaction

In this work, the specific role of the addition of graphene oxide (GO) to state-of-the-art nickel-iron (NiFe) and cobalt-nickel-iron (CoNiFe) mixed oxides/hydroxides towards the oxygen evolution reaction (OER) is investigated. Morphology, structure, and OER catalytic activity of the catalysts with and without GO were studied. The catalysts were fabricated via a two-step electrodeposition. The first step included the deposition of GO flakes, which, in the second step, were reduced during the simultaneous deposition of NiFe or CoNiFe. As a result, NiFe-GO and CoNiFe-GO were fabricated without any additives directly on the nickel foam substrate. A significant improvement of the OER activity was observed after combining NiFe with GO (OER overpotential η(10 mA·cm^-2): 210 mV) compared to NiFe (η: 235 mV) and GO (η: 320 mV) alone. A different OER activity was observed for CoNiFe-GO. Here, the overall catalytic activity (η: 230 mV) increased compared to GO alone. However, it was reduced in comparison to CoNiFe (η: 224 mV). The latter was associated with the change in the morphology and structure of the catalysts. Further OER studies showed that each of the catalysts specifically influenced the process. The improvement in the OER by NiFe-GO results mainly from the structure of NiFe and the electroactive surface area of GO.

Magnetic Field-Assisted Construction and Enhancement of Electrocatalysts

Driven by the energy crisis and environmental pollution, developing sustainable clean energy is an effective strategy to realize carbon neutrality. Electrocatalytic reactions are crucial to sustainable energy conversion and storage technologies, and advanced electrocatalysts are required to improve the sluggish electrocatalytic reactions. The magnetic field, as a thermodynamic parameter independent of temperature and pressure, is vital in the construction of electrocatalysts and enhancement of electrocatalysis. In this Review, the recent progress of magnetic field-assisted construction of electrocatalysts and enhancement of electrocatalysis is comprehensively summarized. Originating from the structure-activity-performance relationship of electrocatalysts, the fundamentals of the magnetic field-induced construction of electrocatalysts, including the magnetocaloric effect, nucleation and growth, and phase regulation, have been illustrated. In addition, the magnetic effect on the electrocatalytic reaction, namely, the magnetothermal, magnetohydrodynamic and micro magnetohydrodynamic, Maxwell stress, Kelvin force, and spin selection effects, are discussed. Finally, the perspective and challenges for magnetic field-assisted construction of electrocatalysts and enhancement of electrocatalysis are proposed.

In Situ Anodic Oxidation Tuning of NiFeV Diselenide to the Core-Shell Heterojunction for Boosting Oxygen Evolution

Developing non-noble metal-based core-shell heterojunction electrocatalysts with high catalytic activity and long-lasting stability is crucial for the oxygen evolution reaction (OER). Here, we prepared novel core-shell Fe,V-NiSe₂@NiFe(OH)_x heterostructured nanoparticles on hydrophilic-treated carbon paper with high electronic transport and large surface area for accelerating the oxygen evolution rate via high-temperature selenization and electrochemical anodic oxidation procedures. Performance testing shows that Fe,V-NiSe₂@NiFe(OH)_x possesses the highest performance for OER compared to as-prepared diselenide core-derived heterojunctions, which only require an overpotential of 243 mV at 10 mA cm^-2 and a low Tafel slope of 91.6 mV decade^-1 under basic conditions. Furthermore, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) confirm the morphology and elementary stabilities of Fe,V-NiSe₂@NiFe(OH)_x after long-term chronopotentiometric testing. These advantages are largely because of the strong synergistic effect between the Fe,V-NiSe₂ core with high conductivity and the amorphous NiFe(OH)_x shell with enriched defects and vacancies. This study also presents a general approach to designing and synthesizing more active core-shell heterojunction electrocatalysts for OER.

Infrared Light Emission Devices Based on Two-Dimensional Materials

Two-dimensional (2D) materials have garnered considerable attention due to their advantageous properties, including tunable bandgap, prominent carrier mobility, tunable response and absorption spectral band, and so forth. The above-mentioned properties ensure that 2D materials hold great promise for various high-performance infrared (IR) applications, such as night vision, remote sensing, surveillance, target acquisition, optical communication, etc. Thus, it is of great significance to acquire better insight into IR applications based on 2D materials. In this review, we summarize the recent progress of 2D materials in IR light emission device applications. First, we introduce the background and motivation of the review, then the 2D materials suitable for IR light emission are presented, followed by a comprehensive review of 2D-material-based spontaneous emission and laser applications. Finally, further development directions and challenges are summarized. We believe that milestone investigations of 2D-material-based IR light emission applications will emerge soon, which are beneficial for 2D-material-based nano-device commercialization.

Vanadium Nitride Supported on N-Doped Carbon as High-Performance ORR Catalysts for Zn–Air Batteries

It is desirable to prepare low-cost non-noble metal catalysts using a simple and efficient method. Herein, we display for the first time that nitrogen-doped hierarchical porous carbon-supported vanadium nitride (VN/NC/C-x) catalysts can be regulated by dicyandiamide (DCDA). The introduction of DCDA not only effectively controls the pore structure, but also plays an important role in adjusting oxygen vacancies and d-electrons. In addition, DCDA is not only a significant raw material for the N-doped carbon, but also a nitrogen source for the preparation of vanadium nitride. The VN/NC/C-3 catalyst was prepared after optimization of the preparation parameters, and the macro/micro structure demonstrates a superior ORR performance in alkaline media with a positive onset potential of 0.85 V and a half-wave potential of 0.75 V, the limiting current density is as high as 4.52 mA·cm−2, and the Tafel slope is only 75.54 mV·dec−1. The VN/NC/C-3-based Zn–air battery exhibits a highest peak power density (161.82 mW∙cm−2) and an excellent energy density (702.28 mAh·kgZn−1 and 861.51 Wh·kgZn−1). This work provides a valuable synthetic approach for the preparation of other transition metal nitride catalysts with a relative economic value and high performance.

Carbonate-Hydroxide Induced Metal-Organic Framework Transformation Strategy for Honeycomb-Like NiCoP Nanoplates to Drive Enhanced pH-Universal Hydrogen Evolution

Developing a low-cost, pH-universal electrocatalyst is desirable for electrochemical water splitting but remains a challenge. NiCoP is a promising non-noble hydrogen-evolving electrocatalyst due to its high intrinsic electrical conductivity, fast mass transfer effects, and tunable electronic structure. Nevertheless, its hydrogen evolution reaction (HER) activity in full pH-range has been rarely developed. Herein, a Ni-Co carbonate-hydroxide induced metal-organic framework transformation strategy is proposed to in situ grow porous, honeycomb-like NiCoP nanoplates on Ni foam for high-performance, pH-universal hydrogen evolution reaction. The resultant NiCoP catalyst exhibits a highly 2D nanoporous network in which 20-50 nm, well-crystalline nanoparticles are interconnected with each other closely, and delivers versatile HER electroactivity with η₁₀ of 98, 105, and 97 mV in 1 m KOH, 0.5 m H₂ SO₄ , and 1 m phosphate buffer solution electrolytes, respectively. This overpotential remarkably surpasses the one of commercial Pt/Cs in both neutral and alkaline media at a large current density (>100 mA cm^-2 ). The corresponding full water-splitting electrolyzer constructed from the 2D porous NiCoP cathode requires only a cell voltage of 1.43 V at 10 mA cm^-2 , superior to most recently reported electrocatalysts. This work may open up a new avenue on the rational design of nonprecious, pH-universal electrocatalyst.

Tuning the Electronic Structure of a Ni-Vacancy-Enriched AuNi Spherical Nanoalloy via Electrochemical Etching for Water Oxidation Studies in Alkaline and Neutral Media

Internal Ni-vacancy-enriched spherical AuNi nanoalloys (AuNi_1-2-T) have been prepared via a noble electrochemical etching method. AuNi_1.5-T showed the highest oxygen evolution reaction (OER) activity compared to bare AuNi_1.5, and it demands only 239 mV overpotential, which was 134 mV lesser than the overpotential required by commercial RuO₂ at 10 mA cm^-2 current density in a 1 M KOH solution (pH = 14). The calculated turnover frequency (TOF) value for AuNi_1.5-T (0.0229 s^-1) was 11.74 times higher than that of AuNi_1.5 (0.00195 s^-1). Also, the electrochemically activated AuNi_1.5-T showed superior neutral water oxidation activity by demanding only 335 mV overpotential with a TOF value of 0.000135 s^-1 in a 1 M Na₂SO₄ solution (pH = 7) at 10 mA cm^-2. The long-term stability studies (over 60 h) reveal the excellent robustness of an electrochemically treated alloy system. Density functional theory based electronic structure calculations showed that in the case of AuNi and AuNi_1.5, Au d, Au s, and Ni d orbitals have significant contributions, whereas in the Ni-vacant systems, the density of states is mainly governed by d orbitals of Au and Ni. Also, the Ni-vacant system possesses a work function value of 4.96 eV, which is lower than that of the pristine system (5.27 eV) and thereby favored OH^- binding with an optimum adsorption energy. This result is in reasonable agreement with the experimental outcome of an accelerated OER in a vacancy-enriched Ni-rich AuNi alloy system. Also, mechanistic analysis reveals that the creation of a Ni vacancy can effectively alter the overall mechanism of the OER and thereby facilitate the same with a lower applied energy.

A Fe-doped Co-oxide Electrocatalyst Synthesized Through Post-Modification Method Toward Advanced Water Oxidation

In the context of the ever-increasing energy crisis, electrocatalytic water splitting has attracted widespread attention as an effective means to provide clean energy. However, the oxygen evolution reaction (OER), which...

Nickel Boride/Boron Carbide Particles Embedded in Boron-Doped Phenolic Resin-Derived Carbon Coating on Nickel Foam for Oxygen Evolution Catalysis in Water and Seawater Splitting

Electrolysis of seawater can be a promising technology, but chloride ions in seawater can lead to adverse side reactions and the corrosion of electrodes. A new transition metal boride-based self-supported electrocatalyst was prepared for efficient seawater electrolysis by directly soaking nickel foam (NF) in a mixture of phenolic resin (PR) and boron carbide (B₄ C), followed by an 800 °C annealing. During PR carbonization process, the reaction of B₄ C and NF generated nickel boride (Ni_x B) with high catalytic activity, while PR-derived carbon coating was doped with boron atoms from B₄ C (B-C_PR ). The B-C_PR coating fixed Ni_x B/B₄ C particles in the frames and holes to improve the space utilization of NF. Meanwhile, the B-C_PR coating effectively protected the catalyst from the corrosion by seawater and facilitates the transport of electrons. The optimal Ni_x B/B₄ C/B-C_PR /NF required 1.50 and 1.58 V to deliver 100 and 500 mA cm^-2 , respectively, in alkaline natural seawater for the oxygen evolution reaction.

Strategies for Developing Transition Metal Phosphides in Electrochemical Water Splitting

Electrochemical water splitting involving hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a greatly promising technology to generate sustainable and renewable energy resources, which relies on the exploration regarding the design of electrocatalysts with high efficiency, high stability, and low cost. Transition metal phosphides (TMPs), as nonprecious metallic electrocatalysts, have been extensively investigated and proved to be high-efficient electrocatalysts in both HER and OER. In this minireview, a general overview of recent progress in developing high-performance TMP electrocatalysts for electrochemical water splitting has been presented. Design strategies including composition engineering by element doping, hybridization, and tuning the molar ratio, structure engineering by porous structures, nanoarray structures, and amorphous structures, and surface/interface engineering by tuning surface wetting states, facet control, and novel substrate are summarized. Key scientific problems and prospective research directions are also briefly discussed.

NiFe Layered Double Hydroxide/FeOOH Heterostructure Nanosheets as an Efficient and Durable Bifunctional Electrocatalyst for Overall Seawater Splitting

Electrolysis of seawater can not only desalinate seawater but also produce high-purity hydrogen. Nevertheless, the presence of chloride ions in seawater will cause electrode corrosion and also undergo a chlorine oxidation reaction (ClOR) that competes with the oxygen evolution reaction (OER). Therefore, highly efficient and long-term stable electrocatalysts are needed in this field. In this work, an advanced bifunctional electrocatalyst based on NiFe layered double hydroxide (LDH)/FeOOH heterostructure nanosheets (NiFe LDH/FeOOH) was synthesized on nickel-iron foam (INF) via a simple electrodeposition method. The NiFe LDH/FeOOH electrode demonstrates excellent electrocatalytic activity and stability, which results from the strong interaction between FeOOH and NiFe LDH. Furthermore, ex situ X-ray photoelectron spectroscopy (XPS) and in situ Raman spectroscopy revealed the catalytic process and also demonstrated that the NiFe LDH/FeOOH heterostructure could facilitate the formation of active NiOOH species in the reaction. The obtained NiFe LDH/FeOOH catalyst displays low overpotentials of 181.8 mV at 10 mA·cm^-2 for hydrogen evolution reaction (HER) and 286.2 mV at 100 mA·cm^-2 for OER in the 1.0 M KOH + 0.5 M NaCl electrolyte. Furthermore, it also exhibits a low voltage of 1.55 V to achieve the current density of 10 mA·cm^-2 and works steadily for 105 h at 100 mA·cm^-2 for overall alkaline simulated seawater splitting. This work will afford a valid strategy for designing a non-noble metal catalyst for seawater splitting.

Biogenesis and Application of Nickel Nanoparticles: A Review

Biogenic synthesis of Nanoparticles (NPs) is attractive due to their ecological benefits and cheap, rapid, and sustainable nature. Among them, Nickel Oxide NPs (NiO-NPs) are acquired for their varied catalytic and clinical applications, as they have antibacterial, antifungal, cytotoxic, anticancer, antioxidant, remediation, and enzyme inhibition properties. Though several chemical-dependent methods were applied for the fabrication of nanoparticles, due to their substantial disadvantages, mainly toxicity and higher cost synthesis methods, the more secure, greener, eco-friendly, cost-effective, and synthetic methods are in demand. Greener approaches can take away the arduousness and complications of physicochemical methods. The present review is aimed at displaying the recent advancement related to the catalytic activity, antimicrobial activity, cytotoxicity, and antioxidant application of green synthesized Nickle. In this study, nickle oxide nanoparticles have been highlighted along with their sustainable synthesis options.

Optimization of Ni-Co-Fe-Based Catalysts for Oxygen Evolution Reaction by Surface and Relaxation Phenomena Analysis

Trimetallic double hydroxide NiFeCo-OH is prepared by coprecipitation, from which three different catalysts are fabricated by different heat treatments, all at 350 °C maximum temperature. Among the prepared catalysts, the one prepared at a heating and cooling rate of 2 °C min^-1 in N₂ atmosphere (designated NiFeCo-N₂ -2 °C) displays the best catalytic properties after stability testing, exhibiting a high current density (9.06 mA cm^-2 at 320 mV), low Tafel slope (72.9 mV dec^-1 ), good stability (over 20 h), high turnover frequency (0.304 s^-1 ), and high mass activity (46.52 A g^-1 at 320 mV). Stability tests reveal that the hydroxide phase is less suitable for long-term use than catalysts with an oxide phase. Two causes are identified for the loss of stability in the hydroxide phase: a) Modeling of the distribution function of relaxation times (DFRT) reveals the increase in resistance contributed by various relaxation processes; b) density functional theory (DFT) surface energy calculations reveal that the higher surface energy of the hydroxide-phase catalyst impairs the stability. These findings represent a new strategy to optimize catalysts for water splitting.

Highly dispersed secondary building unit-stabilized binary metal center on a hierarchical porous carbon matrix for enhanced oxygen evolution reaction

Restricting the aggregation and rationally adjusting the electronic structure of binary metal centers in metal-organic framework (MOF) precursors are important for optimizing their performance as electrocatalysts for the oxygen evolution reaction (OER) and achieving low overpotential and high stability in such applications. Herein, we demonstrate the possibility of enhancing the electrochemical activity of MOF-derived binary metal center catalysts by controlling the form of the Fe species. The introduction of Fe-SBU (iron 2,5-dihydroxyterephthalic acid) into ZIF-67 is found to induce a distinct confinement effect and this can be exploited to improve the electroconductivity of binary metal center catalysts, and therefore, to reduce the OER reaction barrier (OOH* → O*). When applied as an OER catalyst in 1 M KOH solution, the Fe-SBU@Co-Matrix catalyst exhibits a low overpotential of 249 mV to reach a current density of 10 mA cm^-2 and high stability for over 40 h. This work describes the secondary growth treatment of MOF-derived porous carbons to promote their application as catalysts in energy conversion reactions.

Recent advances of noble-metal-free bifunctional oxygen reduction and evolution electrocatalysts

Bifunctional oxygen reduction and evolution constitute the core processes for sustainable energy storage. The advances on noble-metal-free bifunctional oxygen electrocatalysts are reviewed.

Ni(ii) dithiolate anion composites with two-dimensional materials for electrochemical oxygen evolution reactions (OERs)

A redox active anionic nickel dithiolate complex was synthesized and its composites with GO, rGO and GN were prepared and used as electrocatalyts in the OER.

RuN2 Monolayer: A Highly Efficient Electrocatalyst for Oxygen Reduction Reaction

The transition metal-based nitride (TMN) holds great promise as catalysts with high efficiency for energy-related technologies. Herein, on the basis of global structure search and density functional theory calculations, a novel two-dimensional (2D) TMN was identified: RuN₂ monolayer with tetracoordinated Ru atoms and isolated N═N dimers, which is revealed to possess high thermal, dynamic, and chemical stabilities as well as metallic nature, thus providing great feasibility for its practical application in electrochemical reactions. Remarkably, we found that the predicted RuN₂ monolayer exhibits superior catalytic performance for the oxygen reduction reaction (ORR) with a rather high limiting potential (0.99 V) and an overwhelming four-electron reduction pathway selectivity. Thus, our results suggested the robust applicability of RuN₂ monolayer as a novel non-Pt catalyst due to its excellent catalytic efficiency and outstanding selectivity for ORR, which not only proposes a new member to the hypercoordinate 2D TMN with novel properties, but also provides a feasible strategy to further develop novel TMN-based nanomaterials for electrocatalytic energy conversion.

Favorable Amorphous-Crystalline Iron Oxyhydroxide Phase Boundaries for Boosted Alkaline Water Oxidation

Interface engineering has proven an effective strategy for designing high-performance water-oxidation catalysts. Interface construction combining the respective advantages of amorphous and crystalline phases, especially embedding amorphous phases in crystalline lattices, has been the focus of intensive research. This study concerns the construction of an amorphous-crystalline FeOOH phase boundary (a-c-FeOOH) by structural evolution of iron oxyhydroxide-isolated Fe(OH)₃ precursors from one-step hydrothermal synthesis. a-c-FeOOH demonstrates superb electrocatalytic activity for the oxygen evolution reaction (OER) with overpotential of 330 mV to drive a current density of 300 mA cm^-2 in 1.0 m KOH, which is among the best OER catalysts and much better than the pristine amorphous or crystalline FeOOH alone. Density functional theory calculations reveal that the high-density a-c phase boundaries play a critical role in determining high OER activity.

Recent Progress, Challenges, and Prospects in Two-Dimensional Photo-Catalyst Materials and Environmental Remediation

The successful photo-catalyst library gives significant information on feature that affects photo-catalytic performance and proposes new materials. Competency is considerably significant to form multi-functional photo-catalysts with flexible characteristics. Since recently, two-dimensional materials (2DMs) gained much attention from researchers, due to their unique thickness-dependent uses, mainly for photo-catalytic, outstanding chemical and physical properties. Photo-catalytic water splitting and hydrogen (H2) evolution by plentiful compounds as electron (e-) donors is estimated to participate in constructing clean method for solar H2-formation. Heterogeneous photo-catalysis received much research attention caused by their applications to tackle numerous energy and environmental issues. This broad review explains progress regarding 2DMs, significance in structure, and catalytic results. We will discuss in detail current progresses of approaches for adjusting 2DMs-based photo-catalysts to assess their photo-activity including doping, hetero-structure scheme, and functional formation assembly. Suggested plans, e.g., doping and sensitization of semiconducting 2DMs, increasing electrical conductance, improving catalytic active sites, strengthening interface coupling in semiconductors (SCs) 2DMs, forming nano-structures, building multi-junction nano-composites, increasing photo-stability of SCs, and using combined results of adapted approaches, are summed up. Hence, to further improve 2DMs photo-catalyst properties, hetero-structure design-based 2DMs' photo-catalyst basic mechanism is also reviewed.

A size tunable bimetallic nickel-zinc nitride as a multi-functional co-catalyst on nitrogen doped titania boosts solar energy conversion

To enable high-efficiency solar energy conversion, rational design and preparation of low cost and stable semiconductor photocatalysts with associated co-catalysts are desirable. However preparation of efficient catalytic systems remains a challenge. Here, N-doped TiO2/ternary nickel-zinc nitride (N-TiO2-Ni3ZnN) nanocomposites have been shown to be a multi-functional catalyst for photocatalytic reactions. The particle size of Ni3ZnN can be readily tuned using N-TiO2 nanospheres as the active support. Due to its high conductivity and Pt-like properties, Ni3ZnN promotes charge separation and transfer, as well as reaction kinetics. The material shows co-catalytic performance relevant for multiple reactions, demonstrating its multifunctionality. Density functional theory (DFT) based calculations confirm the intrinsic metallic properties of Ni3ZnN. N-TiO2-Ni3ZnN exhibits evidently improved photocatalytic performances as compared to N-TiO2 under visible light irradiation.

An amorphous carbon nitride/NiO/CoN-based composite: a highly efficient nonprecious electrode for supercapacitors and the oxygen evolution reaction

Due to their features of low cost, good corrosion resistance and environmental friendliness, transition metal oxides/nitrides are among the most promising materials for energy storage and conversion. Meanwhile, graphitic carbon nitride is a non-metallic polymer that has been widely used in the environmental and energy conversion fields due to its abundant precursor species and simple process of synthesis. In this study, an amorphous carbon nitride/NiO/CoN-based composite (Ni-Co-CN) is in situ fabricated via simple one-step pyrolysis; it displays high capacitive performance and efficient electrocatalytic capability for the oxygen evolution reaction (OER). Specifically, the optimized Ni-Co-CN electrode shows an ultra-high areal specific capacitance of 18.8 F cm-2 at 2 mA cm-2 in 3 M KOH electrolyte, and it retains 91.4% of its areal specific capacitance even after 10 000 cycles of CV scans. Upon being used as an electrocatalyst in the OER process, the overpotential of Ni-Co-CN can reach 195 mV versus a reference hydrogen electrode (RHE) at 10 mA cm-2, which is far lower than those of most reported Ni/Co-based catalysts. Additionally, the potential loss of Ni-Co-CN electrode is less than 1% after a long-term durability test over 60 h. The experimental results integrated with density functional theoretical calculations reveal that the excellent performance of the Ni-Co-CN self-supported electrode can be ascribed to the fast redox reduction of multi-valent transition metal ions, abundant surface defects and plentiful nano-scaled porous structures. This work provides a promising strategy for exploring methods to combine economic Ni/Co-based compounds with carbon-based materials to obtain low-cost yet efficient electrode materials for electrochemical energy storage and conversion.

Laser-Ablation-Produced Cobalt Nickel Phosphate with High-Valence Nickel Ions as an Active Catalyst for the Oxygen Evolution Reaction

Cost-effective, highly efficient and stable non-noble metal-based catalysts for the oxygen evolution reaction (OER) are very crucial for energy storage and conversion. Here, an amorphous cobalt nickel phosphate (CoNiPO₄ ), containing a considerable amount of high-valence Ni³⁺ species as an efficient electrocatalyst for OER in alkaline solution, is reported. The catalyst was converted from Co-doped Ni₂ P through pulsed laser ablation in liquid (PLAL) and exhibits a large specific surface area of 162.5 m²  g^-1 and a low overpotential of 238 mV at 10 mA cm^-2 with a Tafel slope of 46 mV dec^-1 , which is much lower than those of commercial RuO₂ and IrO₂ . This work demonstrates that PLAL is a powerful technology for generating amorphous CoNiPO₄ with high-valence Ni³⁺ , thus paving a new way towards highly effective OER catalysts.