Biomineralization of Sulfate-Reducing Bacteria In Situ-Induced Preparation of Nano Fe2O3-Fe(Ni)S/C as High-Efficiency Oxygen Evolution Electrocatalyst

Transition metal-based catalysts possess high catalytic activity for oxygen evolution reaction (OER). However, the preparation of high-performance OER electrocatalysts using simple strategies with a low cost still faces a major challenge. Herein, this work presents an innovative, in situ-induced preparation of the Fe2O3, FeS, and NiS nanoparticles, supported on carbon blacks (CBs) (denoted as Fe2O3-Fe(Ni)S/C) as a high-efficiency oxygen evolution electrocatalyst by employing biomineralization. Biomineralization, a simple synthesis strategy, demonstrates a huge advantage in controlling the size of the Fe2O3 and Fe(Ni)S nanoparticles, as well as achieving uniform nanoparticle distribution on carbon blacks. It is found that the electrocatalyst Fe2O3-Fe(Ni)S/C-200 shows a good OER electrocatalytic activity with a small loading capacity, and it has a small overpotential and Tafel slope in 1 m KOH solution with values of 264 mV and 42 mV dec-1, respectively, at a current density of 10 mA cm-2. Additionally, it presents good electrochemical stability for over 24 h. The remarkable and robust electrocatalytic performance of Fe2O3-Fe(Ni)S/C-200 is attributed to the synergistic effect of Fe2O3, FeS, and doped-Ni species as well as its distinct 3D spherical structure. This approach indicates the promising applications of biomineralization for the bio-preparation of functional materials and energy conversion.

Fe,Ni-Based Metal-Organic Frameworks Embedded in Nanoporous Nitrogen-Doped Graphene as a Highly Efficient Electrocatalyst for the Oxygen Evolution Reaction

The quest for economically sustainable electrocatalysts to replace critical materials in anodes for the oxygen evolution reaction (OER) is a key goal in electrochemical conversion technologies, and, in this context, metal-organic frameworks (MOFs) offer great promise as alternative electroactive materials. In this study, a series of nanostructured electrocatalysts was successfully synthesized by growing tailored Ni-Fe-based MOFs on nitrogen-doped graphene, creating composite systems named MIL-NG-n. Their growth was tuned using a molecular modulator, revealing a non-trivial trend of the properties as a function of the modulator quantity. The most active material displayed an excellent OER performance characterized by a potential of 1.47 V (vs. RHE) to reach 10 mA cm-2, a low Tafel slope (42 mV dec-1), and a stability exceeding 18 h in 0.1 M KOH. This outstanding performance was attributed to the synergistic effect between the unique MOF architecture and N-doped graphene, enhancing the amount of active sites and the electron transfer. Compared to a simple mixture of MOFs and N-doped graphene or the deposition of Fe and Ni atoms on the N-doped graphene, these hybrid materials demonstrated a clearly superior OER performance.

Perspective into ion storage of pristine metal-organic frameworks in capacitive deionization

Metal-organic frameworks (MOFs), featuring tunable conductivity, tailored pore/structure and high surface area, have emerged as promising electrode nanomaterials for ion storage in capacitive deionization (CDI) and garnered tremendous attention in recent years. Despite the many advantages, the perspective from which MOFs should be designed and prepared for use as CDI electrode materials still faces various challenges that hinder their practical application. This summary proposes design principles for the pore size, pore environment, structure and dimensions of MOFs to precisely tailor the surface area, selectivity, conductivity, and Faradaic activity of electrode materials based on the ion storage mechanism in the CDI process. The account provides a new perspective to deepen the understanding of the fundamental issues of MOFs electrode materials to further meet the practical applications of CDI.

Ce Hydroxide-Interfaced NiFe Sulfide Electrocatalyst with Improved Performance for the Oxygen Evolution Reaction

The development of electrochemically inexpensive, durable, and active electrocatalysts for the oxygen evolution reaction (OER) is attracting considerable attention. The heterogeneous interfacing might regulate the electronic structure and further improve the electrochemical activity. Herein, a Ce(OH)3 nanoparticle-interfaced Fe-doped nickel sulfide (Ce(OH)3@Fe-Ni3S2) electrocatalyst was prepared to improve the OER performance. The fabricated electrocatalyst displayed excellent intrinsic activity and long-term stability in 1 M KOH for the OER. The catalyst shows an ultralow overpotential of 195 mV at a current density of 10 mA cm-2 and a Tafel slope of 52 mV dec-1, which are remarkably smaller than those of the control samples. This excellent electrocatalytic activity is attributed to the incorporation of Ce(OH)3 nanoparticles on the surface of the Fe-Ni3S2 nanosheet, which increases the electrochemical activity and enlarges the active surface area of the catalyst. In comparison to previous nonprecious OER electrocatalysts, the prepared Ce(OH)3@Fe-Ni3S2 exhibits greater electrocatalytic activity and longer durability, allowing for the selection of new electrocatalysts for practical applications.

Recent Advances in Engineering of 2D Materials-Based Heterostructures for Electrochemical Energy Conversion

2D materials, such as graphene, transition metal dichalcogenides, black phosphorus, layered double hydroxides, and MXene, have exhibited broad application prospects in electrochemical energy conversion due to their unique structures and electronic properties. Recently, the engineering of heterostructures based on 2D materials, including 2D/0D, 2D/1D, 2D/2D, and 2D/3D, has shown the potential to produce synergistic and heterointerface effects, overcoming the inherent restrictions of 2D materials and thus elevating the electrocatalytic performance to the next level. In this review, recent studies are systematically summarized on heterostructures based on 2D materials for advanced electrochemical energy conversion, including water splitting, CO2 reduction reaction, N2 reduction reaction, etc. Additionally, preparation methods are introduced and novel properties of various types of heterostructures based on 2D materials are discussed. Furthermore, the reaction principles and intrinsic mechanisms behind the excellent performance of these heterostructures are evaluated. Finally, insights are provided into the challenges and perspectives regarding the future engineering of heterostructures based on 2D materials for further advancements in electrochemical energy conversion.

A Highly Efficient Electromagnetic Wave Absorption System with Graphene Embedded in Hybrid Perovskite

To cope with the explosive increase in electromagnetic radiation intensity caused by the widespread use of electronic information equipment, high-performance electromagnetic wave (EMW)-absorbing materials that can adapt to various frequency bands of EMW are also facing great demand. In this paper, CH3NH3PbI3/graphene (MG) high-performance EMW-absorbing materials were innovatively synthesized by taking organic-inorganic hybrid perovskite (OIHP) with high equilibrium holes, electron mobility, and accessible synthesis as the main body, graphene as the intergranular component, and adjusting the component ratio. When the component ratio was 16:1, the thickness of the absorber was 1.87 mm, and MG's effective EMW absorption width reached 6.04 GHz (11.96-18.00 GHz), achieving complete coverage of the Ku frequency band. As the main body of the composite, CH3NH3PbI3 played the role of the polarization density center, and the defects and vacancies in the crystal significantly increased the polarization loss intensity; graphene, as a typical two-dimensional material distributed in the crystal gap, built an efficient electron transfer channel, which significantly improved the electrical conductivity loss strength. This work effectively broadened the EMW absorption frequency band of OIHP and promoted the research process of new EMW-absorbing materials based on OIPH.

Three-dimensional graphene/metal-organic framework composites for electrochemical energy storage and conversion

Three-dimensional graphene (3DG)/metal-organic framework (MOF)-based composites have attracted more and more attention in the field of energy due to their unique hierarchical porous structure and properties. The combination of graphene with MOFs can not only effectively overcome the limitations of poor electrical conductivity and low stability of MOFs, but also prevent the aggregation and reaccumulation between graphene sheets. Moreover, 3DG/MOF composites can also be used as multifunctional precursors with adjustable structures and composition of derivatives, thus expanding their applications in the field of electrochemistry. This feature article elaborates the latest synthesis methods of 3DG/MOF composites and their derivatives, along with their applications in batteries, supercapacitors (SCs) and electrocatalysis. In addition, the current challenges and future prospects of 3DG/MOF-based composites are discussed.

Chemical Transformation Induced Core-Shell Ni2P@Fe2P Heterostructures toward Efficient Electrocatalytic Oxygen Evolution

The oxygen evolution reaction (OER) is a crucial reaction in water splitting, metal-air batteries, and other electrochemical conversion technologies. Rationally designed catalysts with rich active sites and high intrinsic activity have been considered as a hopeful strategy to address the sluggish kinetics for OER. However, constructing such active sites in non-noble catalysts still faces grand challenges. To this end, we fabricate a Ni₂P@Fe₂P core-shell structure with outperforming performance toward OER via chemical transformation of rationally designed Ni-MOF hybrid nanosheets. Specifically, the Ni-MOF nanosheets and their supported Fe-based nanomaterials were in situ transformed into porous Ni₂P@Fe₂P core-shell nanosheets composed of Ni₂P and Fe₂P nanodomains in homogenous dispersion via a phosphorization process. When employed as the OER electrocatalyst, the Ni₂P@Fe₂P core-shell nanosheets exhibits excellent OER performance, with a low overpotential of 238/247 mV to drive 50/100 mA cm^-2, a small Tafel slope of 32.91 mV dec^-1, as well as outstanding durability, which could be mainly ascribed to the strong electronic interaction between Ni₂P and Fe₂P nanodomains stabilizing more Ni and Fe atoms with higher valence. These high-valence metal sites promote the generation of high-active Ni/FeOOH to enhance OER activity.

Soft Template-Based Synthesis of Mesoporous Phosphorus- and Boron-Codoped NiFe-Based Alloys for Efficient Oxygen Evolution Reaction

Controlling the morphology, composition, and crystalline phase of mesoporous nonnoble metal catalysts is essential for improving their performance. Herein, well-defined P- and B-codoped NiFe alloy mesoporous nanospheres (NiFeB-P MNs) with an adjustable Ni/Fe ratio and large mesopores (11 nm) are synthesized via soft-template-based chemical reduction and a subsequent phosphine-vapor-based phosphidation process. Earth-abundant NiFe-based materials are considered promising electrocatalysts for the oxygen evolution reaction (OER) because of their low cost and high intrinsic catalytic activity. The resulting NiFeB-P MNs exhibit a low OER overpotential of 252 mV at 10 mA cm^-2 , which is significantly smaller than that of B-doped NiFe MNs (274 mV) and commercial RuO₂ (269 mV) in alkaline electrolytes. Thus, this work highlights the practicality of designing mesoporous nonnoble metal structures and the importance of incorporating P in metallic-B-based alloys to modify their electronic structure for enhancing their intrinsic activity.

Surface-Induced Engineering: P-Induced Formation of Surface Bonding States Based on the ZIF Synthesis Strategy for Photocatalytic Hydrogen Evolution

The development of clean energy is one of the effective strategies to solve carbon peak and carbon neutrality. The severe recombination of photogenerated carriers is one of the fundamental reasons that hinder the development of photocatalysis. In this work, NiCo-MOF/ZIF was obtained by the "ZIF on MOF" strategy for the first time, and a stable bonding state of surface P(δ^-)-Co/Ni(δ⁺)-O(δ^-) was formed on the surface of the catalyst by a one-step oxidation-phosphorus doping strategy. The X-ray photoelectron spectroscopy technique proves that phosphorus doping forms a unique bonding state on the surface of CoO-NiO. The novel surface bonding state can effectively inhibit the recombination of photogenerated carriers and can increase the migration rate of photogenerated electrons, which accelerates the process of photocatalytic hydrogen evolution. Photocatalytic hydrogen evolution kinetics verifies that the formation of P(δ^-)-Co/Ni(δ⁺)-O(δ^-) bonding states can accelerate the process of photocatalytic hydrogen evolution, and the durability of the catalyst is verified by cycling experiments. This work provides a new strategy for catalyst synthesis, new horizons, and effective strategies for the surface design of catalysts and the development of photocatalytic hydrogen evolution.

Hollow Capsule NiCo2 NS Prepared by Self-Sacrificing Template Method for High-Efficiency Bifunctional Catalyst and Its Application in Zn-Air Battery

Exploring the application of high-efficiency bifunctional oxygen catalysts to rechargeable zinc-air batteries has been a research hotspot in recent years. We succeeded in obtaining NiCo₂ NS with a hollow capsule structure through the self-sacrificing template method, which has a larger specific surface area and can provide more active sites for electrocatalysis relative to his solid. The introduction of S can change the valence distribution of N and the electronic structure of the M-N bond, so that NiCo₂ NS exhibits excellent performance in the overpotential and stability of the oxygen reduction and oxygen evolution reactions. It shows an overpotential of 154 mV at 10 mA cm^-2 and a half-wave potential of 0.76 V. When used as a bi-functional catalyst in zinc-air batteries, it exhibits good stability within 400 h. The flexible battery assembled by NiCo₂ NS also shows excellent performance, and can be cycled stably for 20 h. The current maintains good stability when it is bent at different angles during the cycle.

Recent Advances in ZIF-Derived Atomic Metal-N-C Electrocatalysts for Oxygen Reduction Reaction: Synthetic Strategies, Active Centers, and Stabilities

Exploring highly active, stable electrocatalysts with earth-abundant metal centers for the oxygen reduction reaction (ORR) is essential for sustainable energy conversion. Due to the high cost and scarcity of platinum, it is a general trend to develop metal-N-C (M-N-C) electrocatalysts, especially those prepared from the zeolite imidazolate framework (ZIF) to replace/minimize usage of noble metals in ORR electrocatalysis for their amazingly high catalytic efficiency, great stability, and readily-tuned electronic structure. In this review, the most pivotal advances in mechanisms leading to declined catalytic performance, synthetic strategies, and design principles in engineering ZIF-derived M-N-C for efficient ORR catalysis, are presented. Notably, this review focuses on how to improve intrinsic ORR activity, such as M-N_x -C_y coordination structures, doping metal-free heteroatoms in M-N-C, dual/multi-metal sites, hydrogen passivation, and edge-hosted M-N_x . Meanwhile, how to increase active sites density, including formation of M-N complex, spatial confinement effects, and porous structure design, are discussed. Thereafter, challenges and future perspectives of M-N-C are also proposed. The authors believe this instructive review will provide experimental and theoretical guidance for designing future, highly active ORR electrocatalysts, and facilitate their applications in diverse ORR-related energy technologies.

NiMnO3 Anchored on Reduced Graphene Oxide Nanosheets: A New High-Performance Microwave Absorbing Material

With the increasing influence of electromagnetic radiation on precision instruments and organisms, there is an urgent need for research on lightweight and high-strength electromagnetic wave absorbing materials. This study has probed into a new composite absorbing material based on reduced graphene oxide (rGO)-NiMnO₃, where the like-core-shell NiMnO₃ is anchored on the rGO nanosheets to significantly improve the electromagnetic wave dissipation ability of the composite material using the inter-component dipole polarization and interface polarization. At the same time, NiMnO₃ can effectively adjust the impedance matching ratio of rGO so that electromagnetic waves can effectively enter the absorbing material. At a thickness of 3.73 mm, the maximum absorption strength of rGO-NiMnO₃ reaches −61.4 dB at 6.6 GHz; at a thickness of 2.5 mm, the adequate absorption bandwidth is 10.04–18.00 GHz, achieving a full coverage for the Ku band. As a new option for preparing lightweight and broadband electromagnetic wave absorbing materials, rGO-NiMnO₃ is an ideal material for electromagnetic wave protection.

Mixed Metal Fe2Ni MIL-88B Metal-Organic Frameworks Decorated on Reduced Graphene Oxide as a Robust and Highly Efficient Electrocatalyst for Alkaline Water Oxidation

The development of cost-effective and efficient oxygen evolution reaction (OER) catalysts has found increasing popularity due to the sluggish kinetics of OER, which has hampered the H₂ production by H₂O electrolysis. In this study, Fe₂Ni MIL-88 (denoted FeNi) was composited by reduced graphene oxide (rGO, denoted R). Owing to the high porosity and abundant active sites of bimetallic MOF, proper conductivity of rGO, and the synergistic impact of Ni and Fe, the optimal composite (R@FeNi (1:1)) offered remarkable OER activity in alkaline environments. The obtained composite was employed in the OER, which led to a low overpotential of 264 mV at a current density of 10 mA cm^-2 with a Tafel slope of 62 mV dec^-1. Also, the bimetallic Fe₂Ni MIL-88 nanorods grown on rGO led to a reduction in the onset potential of the OER. These findings exceeded the results of standard IrO₂-based catalysts; they are also comparable or even better than the previously reported MOF-based catalysts.

Synthesis of Highly Active Carbon-encapsulated Ni2P Catalysts by One-step Pyrolysis–phosphidation for Hydrodeoxygenation of Phenolic Compounds

Hydrodeoxygenation (HDO) of phenolic compounds is a promising technology to convert biomass materials to value-added chemicals and fuels. However, the development of highly efficient catalysts remains a great challenge. In...

Interface Engineering of CoP3/Ni2P for Boosting the Wide pH Range Water-Splitting Activity

Developing electrocatalysts with low price, high energy efficiency, and universal pH value for hydrogen/oxygen evolution reaction (HER and OER) is very important for the wide application of electrochemical water splitting in hydrogen production. The results of density functional theory show that the interface region of CoP3/Ni2P heterostructures can significantly boost all of the catalytic performances. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were used to confirm the abundant structural defects and the corresponding adjustment of the electronic state, thus ameliorating the activation energy, conductivity, and active area of the catalyst. Benefiting from these, CoP3/Ni2P heterostructures exhibit superior performance of both HER and OER in a wide pH range. CoP3/Ni2P can also be used for water splitting (1.557 V at 10 mA cm-2) more than 40 h, superior to benchmark pairs of Pt/C and RuO2 on Ni foam.

Ni2P nanocrystals embedded Ni-MOF nanosheets supported on nickel foam as bifunctional electrocatalyst for urea electrolysis

It’s highly desired but challenging to synthesize self-supporting nanohybrid made of conductive nanoparticles with metal organic framework (MOF) materials for the application in the electrochemical field. In this work, we report the preparation of Ni₂P embedded Ni-MOF nanosheets supported on nickel foam through partial phosphidation (Ni₂P@Ni-MOF/NF). The self-supporting Ni₂P@Ni-MOF/NF was directly tested as electrode for urea electrolysis. When served as anode for urea oxidation reaction (UOR), it only demands 1.41 V (vs RHE) to deliver a current of 100 mA cm⁻². And the overpotential of Ni₂P@Ni-MOF/NF to reach 10 mA cm⁻² for hydrogen evolution reaction HER was only 66 mV, remarkably lower than Ni₂P/NF (133 mV). The exceptional electrochemical performance was attributed to the unique structure of Ni₂P@Ni-MOF and the well exposed surface of Ni₂P. Furthermore, the Ni₂P@Ni-MOF/NF demonstrated outstanding longevity for both HER and UOR. The electrolyzer constructed with Ni₂P@Ni-MOF/NF as bifunctional electrode can attain a current density of 100 mA cm⁻² at a cell voltage as low as 1.65 V. Our work provides new insights for prepare MOF based nanohydrid for electrochemical application.

Constructing 3D hierarchical MOFs nanospheres for oxygen evolution from high-throughput calculations

In order to realize outstanding electrochemical performance in oxygen evolution reactions (OER), it is important to construct 3D hierarchical nanospheres consisting of 2D bimetal metal-organic framework (MOF) nanosheets. Based on high-throughput density-functional theory (DFT) calculations, we chose Ni and V as central ions and prepared Ni-V bimetal MOFs nanospheres (NiV-MNs) assembled from ultrathin 2D MOFs nanosheets through a simple one-step solvothermal method. So far, V-based ultrathin 2D MOFs have been firstly reported. Gradient experiments demonstrated that NiV-MNs shows the best catalytic activity when the amount of Ni is equal to that of V (denoted as Ni₁V₁-MNs). The Ni₁V₁-MNs can deliver a high current density of 50 mA·cm^-2 at a low over-potential of 370 mV in alkaline condition even after 10000 s continuous catalytic testing. Coincidentally, the DFT calculations further confirmed that the ΔG of Ni₁V₁-MNs is much lower compared with Ni₁V₂-MNs and Ni₂V₁-MNs. Based upon the experimental results and DFT calculations, we propose that the better performance of Ni₁V₁-MNs should be attributed to the grater intrinsic activity of Ni and the coupling effect between Ni and V, as they are crucial for tuning the electrochemical activity.

Metal-Organic Frameworks and Metal-Organic Gels for Oxygen Electrocatalysis: Structural and Compositional Considerations

Increasing demand for sustainable and clean energy is calling for the next-generation energy conversion and storage technologies such as fuel cells, water electrolyzers, CO₂ /N₂ reduction electrolyzers, metal-air batteries, etc. All these electrochemical processes involve oxygen electrocatalysis. Boosting the intrinsic activity and the active-site density through rational design of metal-organic frameworks (MOFs) and metal-organic gels (MOGs) as precursors represents a new approach toward improving oxygen electrocatalysis efficiency. MOFs/MOGs afford a broad selection of combinations between metal nodes and organic linkers and are known to produce electrocatalysts with high surface areas, variable porosity, and excellent activity after pyrolysis. Some recent studies on MOFs/MOGs for oxygen electrocatalysis and their new perspectives in synthesis, characterization, and performance are discussed. New insights on the structural and compositional design in MOF/MOG-derived oxygen electrocatalysts are summarized. Critical challenges and future research directions are also outlined.

Recent Advances in Multimetal and Doped Transition-Metal Phosphides for the Hydrogen Evolution Reaction at Different pH values

Hydrogen is a fuel with a potentially zero-carbon footprint viewed as a viable alternative to fossil fuels. It can be produced in a large scale via electrochemical water splitting using electricity derived from renewable sources, but this would require highly active, inexpensive, and stable hydrogen evolution reaction (HER) catalysts to replace the Pt benchmark. Transition-metal phosphides (TMPs) are potential Pt replacements owing to their generally high activity as well as versatility as HER catalysts for different pH media. This review summarizes the recent progress in the development of TMP HER electrocatalysts, focusing on the strategies that have been recently explored to tune the activity in acidic, neutral, and basic media. These strategies are the doping of TMPs with metal and nonmetal elements, fabrication of multimetallic phosphide phases, and construction of multicomponent heterostructures comprising TMPs and another component such as a different TMP or a metal oxide/hydroxide. The synthetic methods utilized to design the catalysts are also presented. Finally, the challenges still remaining and future research directions are discussed.

A Complementary Co-Ni Phosphide/Bimetallic Alloy-Interspersed N-Doped Graphene Electrocatalyst for Overall Alkaline Water Splitting

Echinops-like bimetallic CoNiP-CoNi alloy is synthesized from a metal-organic framework (MOF) and serves as an efficient catalyst for the oxygen evolution reaction (OER), with a low overpotential of 300 mV in 1 M KOH at 10 mA cm^-2 (η₁₀ ). The cooperative effect of Ni and Co metal, as well as the interfacial properties of the integrated semiconducting phosphide/metallic alloy and electronic conductivity of the MOF-derived carbon regulate the performance of the catalyst. Moreover, the bimetallic CoNiP/CoNi alloy catalyst is interspersed with N-doped graphene, forming a triad catalyst that demonstrates superior activity towards the hydrogen evolution reaction (η₁₀ =150 mV) and excellent durability, owing to interfacial effects of the triad catalyst, large electrochemical active surface area, and enhanced conductivity from N-doped graphene. The stability of the carbon-containing catalyst during OER (oxidation) is altered by the high reactivity of heteroatom dopant. The assembled CoNiP/CoNi/N-RGO||CoNiP/CoNi water electrolyzer delivers a reasonable cell potential of 1.76 V at 10 mA cm^-2 . The synthesized bimetallic CoNiP/CoNi alloy-based triad catalyst thus demonstrates excellent electrocatalytic activity and high durability suitable for efficient alkaline water splitting.

Origin of the electrocatalytic oxygen evolution activity of nickel phosphides: in-situ electrochemical oxidation and Cr doping to achieve high performance

Zinc-air batteries (ZnABs) with high theoretical capacity and environmental benignity are the most promising candidates for next-generation electronics. However, their large-scale applications are greatly hindered due to the lack of high-efficient and cost-effective electrocatalysts. Transition metal phosphides (TMPs) have been reported as promising electrocatalysts. Notably, (Ni_1-xCr_x)₂P (0 ≤ x ≤ 0.15) is an unstable electrocatalyst, which undergoes in-situ electrochemical oxidation during the initial oxygen evolution reaction (OER) and even in the activation cycles, and is eventually converted to Cr-NiOOH serving as the actual OER active sites with high efficiency. Density functional theory (DFT) simulations and experimental results elucidate that the OER performance could be significantly promoted by the synergistic effect of surface engineering and electronic modulations by Cr doping and in-situ phase transformation. The constructed rechargeable ZnABs could stably cycle for more than 208 h at 5 mA cm^-2, while the voltage degradation is negligible. Furthermore, the developed catalytic materials could be assembled into flexible and all-solid-state ZnABs to power wearable electronics with high performance.

Nitrogen-doped carbon encapsulated zinc vanadate polyhedron engineered from a metal-organic framework as a stable anode for alkali ion batteries

In this work, we fabricated vanadium/zinc metal-organic frameworks (V/Zn-MOFs) derived from self-assembled metal organic frameworks, to further disperse ultrasmall Zn₂VO₄ nanoparticles and encapsulate them in a nitrogen-doped nanocarbon network (ZVO/NC) under in situ pyrolysis. When employed as an anode for lithium-ion batteries, ZVO/NC delivers a high reversible capacity (807 mAh g^-1 at 0.5 A g^-1) and excellent rate performance (372 mAh g^-1 at 8.0 A g^-1). Meanwhile, when used in sodium-ion batteries, it exhibits long-term cycling stability (7000 cycles with 145 mAh g^-1 at 2.0 A g^-1). Additionally, when employed in potassium-ion batteries, it also shows outstanding electrochemical performance with reversible capacities of 264 mAh g^-1 at 0.1 A g^-1 and 140 mAh g^-1 at 0.5 A g^-1 for 1000 cycles. The mechanism by which the pseudocapacitive behaviour of ZVO/NC enhances battery performance under a suitable electrolyte was probed, which offers useful enlightenment for the potential development of anodes of alkali-ion batteries. The performance of Zn₂VO₄ as an anode for SIBs/PIBs was investigated for the first time. This work provides a new horizon in the design ZVO/NC as a promising anode material owing to the intrinsically synergic effects of mixed metal species and the multiple valence states of V.

Bimetallic oxygen electrocatalyst derived from metallocenes doped MOFs

Herein, metallocens (ferrocene, ruthenocene and cobaltocene) werein situhybridized with two dimensional metal-organic frameworks (MOFs) via an improved inter-diffusion approach. The metallocens@MOFs hybrids were direct carbonized and transformed to Fe(Ru,Co)-Co@C composites. These bimetallic electrocatalysts show remarkable oxygen evolution reaction (OER) activity by taking advantage of the synergetic effect between the binary metals. Among of them, the obtained Fe-Co@C exhibits lower overpotential (320 mV at 10 mA cm^-2) and satisfactory stability toward OER. The study presents a novel and facile strategy to synthesize low-cost bimetallic catalyst, showing great promise in electrocatalysis of oxygen.

Ultra-small Fe3O4 nanodots encapsulated in layered carbon nanosheets with fast kinetics for lithium/potassium-ion battery anodes

Iron oxides are regarded as promising anodes for both lithium-ion batteries (LIBs) and potassium-ion batteries (KIBs) due to their high theoretical capacity, abundant reserves, and low cost, but they are also facing great challenges due to the sluggish reaction kinetics, low electronic conductivity, huge volume change, and unstable electrode interphases. Moreover, iron oxides are normally prepared at high temperature, forming large particles because of Ostwald ripening, and exhibiting low electronic/ionic conductivity and unfavorable mechanical stability. To address those issues, herein, we have synthesized ultra-small Fe₃O₄ nanodots encapsulated in layered carbon nanosheets (Fe₃O₄@LCS), using the coordination interaction between catechol and Fe³⁺, demonstrating fast reaction kinetics, high capacity, and typical capacitive-controlled electrochemical behaviors. Such Fe₃O₄@LCS nanocomposites were derived from coordination compounds with layered structures via van der Waals's force. Fe₃O₄@LCS-500 (annealed at 500 °C) nanocomposites have displayed attractive features of ultra-small particle size (∼5 nm), high surface area, mesoporous and layered feature. When used as anodes, Fe₃O₄@LCS-500 nanocomposites delivered exceptional electrochemical performances of high reversible capacity, excellent cycle stability and rate performance for both LIBs and KIBs. Such exceptional performances are highly associated with features of Fe₃O₄@LCS-500 nanocomposites in shortening Li/K ion diffusion length, fast reaction kinetics, high electronic/ionic conductivity, and robust electrode interphase stability.

Ultra-small Fe₃O₄ nanodots encapsulated in layered carbon nanosheet nanocomposites were synthesized, showing fast reaction kinetics, high conductivity, and robust stability.

Deep-Breathing Honeycomb-like Co-Nx-C Nanopolyhedron Bifunctional Oxygen Electrocatalysts for Rechargeable Zn-Air Batteries

Metal organic framework (MOF) derivatives have been extensively used as bifunctional oxygen electrocatalysts. However, the utilization of active sites is still not satisfactory owing to the sluggish mass transport within their narrow pore channels. Herein, interconnected macroporous channels were constructed inside MOFs-derived Co-N_x-C electrocatalyst to unblock the mass transfer barrier. The as-synthesized electrocatalyst exhibits a honeycomb-like morphology with highly exposed Co-N_x-C active sites on carbon frame. Owing to the interconnected ordered macropores throughout the electrocatalyst, these active sites can smoothly “exhale/inhale” reactants and products, enhancing the accessibility of active sites and the reaction kinetics. As a result, the honeycomb-like Co-N_x-C displayed a potential difference of 0.773 V between the oxygen evolution reaction potential at 10 mA cm⁻² and the oxygen reduction reaction half-wave potential, much lower than that of bulk-Co-N_x-C (0.842 V). The rational modification on porosity makes such honeycomb-like MOF derivative an excellent bifunctional oxygen electrocatalyst in rechargeable Zn-air batteries.

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A deep-breathing oxygen electrocatalyst with highly dispersed active sites was built

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Sculpturing ordered macropores in MOF derivatives enables fast mass transport

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The honeycomb-like Co-N_x-C nanopolyhedron worked well in rechargeable Zn-air battery

Robust Carbon-Stabilization of Few-Layer Black Phosphorus for Superior Oxygen Evolution Reaction

Few-layer exfoliated black phosphorus (Ex-BP) has attracted tremendous attention owing to its promising applications, including in electrocatalysis. However, it remains a challenge to directly use few-layer Ex-BP as oxygen-involved electrocatalyst because it is quite difficult to restrain structural degradation caused by spontaneous oxidation and keep it stable. Here, a robust carbon-stabilization strategy has been implemented to prepare carbon-coated Ex-BP/N-doped graphene nanosheet (Ex-BP/NGS@C) nanostructures at room temperature, which exhibit superior oxygen evolution reaction (OER) activity under alkaline conditions. Specifically, the as-synthesized Ex-BP/NGS@C hybrid presents a low overpotential of 257 mV at a current density of 10 mA cm−2 with a small Tafel slope of 52 mV dec−1 and shows high durability after long-term testing.

Gradient phosphorus-doping engineering and superficial amorphous reconstruction in NiFe2O4 nanoarrays to enhance the oxygen evolution electrocatalysis

A better solid-liquid-gas three-phase boundary is vital for low energy cost oxygen evolution reaction (OER), making the designed regulation of interfacial atmosphere necessary. Herein, we find that the OER electrocatalysis can be dramatically improved by synergistically forming disordered electronic structures and superficial amorphous layers, as superficial oxyhydroxide, phosphorus-doped NiFe2O4 nanoarrays on nitrogen-doped carbon nanofibers (OP-NiFe2O4/NCNFs). Unveiled by the depth-profiling analysis from the X-ray photoelectron spectroscopy, the contents of phosphorous doping in the OP-NiFe2O4 nanoarrays change dynamically from outside to inside due to its in situ superficial reconstruction into the oxyhydroxide layer, thereby accelerating electron transfer between heterogeneous phases. As revealed by density functional theory calculations, this amorphous oxyhydroxide layer and dynamically varied phosphorous content would positively shift the d-band center of the NiFe2O4-related compounds, leading to lower adsorption energy towards water molecule. Thus, the OP-NiFe2O4/NCNF electrocatalyst displays a low overpotential of 260 mV at a current density of 10 mA cm-2 and a small Tafel slope of 44.8 mV dec-1 in an alkaline medium.

Nickel iron phosphide ultrathin nanosheets anchored on nitrogen-doped carbon nanoflake arrays as a bifunctional catalyst for efficient overall water splitting

Development of high-efficiency and Earth-abundant bifunctional catalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is desirable to realize an efficient overall water splitting process. In this work, a highly active and durable bifunctional catalyst of coral-like nickel iron phosphide ultrathin nanosheets anchored on nitrogen-doped carbon nanoflake arrays on carbon cloth (CC-NC-NiFeP) was fabricated by using metal organic framework (MOF) derived nitrogen-doped carbon nanoflake arrays as catalyst supports. Combined with the electronic structure regulation by bimetallic phosphides and using three dimensional nitrogen-doped carbon nanoflakes as supports that provide a large specific surface area as well as fast charge/mass transport, the as-prepared CC-NC-NiFeP yields excellent bifunctional electrocatalytic activity in both the HER and OER in an alkaline medium with an overpotential of 94 mV and 145 mV to reach a current density of 10 mA cm^-2, respectively. Meanwhile, the CC-NC-NiFeP can behave as both a cathode and anode simultaneously for overall water splitting, achieving a low cell voltage of 1.54 V to reach a current density of 10 mA cm^-2, which outperforms that of most of the non-precious metal based catalysts.

An Efficient Cobalt Phosphide Electrocatalyst Derived from Cobalt Phosphonate Complex for All-pH Hydrogen Evolution Reaction and Overall Water Splitting in Alkaline Solution

The development of low-cost and highly efficient electrocatalysts via an eco-friendly synthetic method is of great significance for future renewable energy storage and conversion systems. Herein, cobalt phosphides confined in porous P-doped carbon materials (Co-P@PC) are fabricated by calcinating the cobalt-phosphonate complex formed between 1-hydroxyethylidenediphosphonic acid and Co(NO₃ )₂ in alkaline solution. The P-containing ligand in the complex acts as the carbon source as well as in situ phosphorizing agent for the formation of cobalt phosphides and doping P element into carbon material upon calcination. The Co-P@PC exhibits high activity for all-pH hydrogen evolution reaction (overpotentials of 72, 85, and 76 mV in acidic, neutral, and alkaline solutions at the current density of 10 mA cm^-2 ) and oxygen evolution reaction in alkaline solution (an overpotential of 280 mV at the current density of 10 mA cm^-2 ). The alkaline electrolyzer assembled from the Co-P@PC electrodes delivers the current density of 10 mA cm^-2 at the voltage of 1.60 V with a durability of 60 h. The excellent activity and long-term stability of the Co-P@PC derives from the synergistic effect between the active cobalt phosphides and the porous P-doped carbon matrix.

0D/2D spatial structure of CdxZn1−xS/Ni-MOF-74 for efficient photocatalytic hydrogen evolution

A novel zero-dimensional/two-dimensional Cd_xZn_1−xS/Ni-MOF-74 (CZS/NMF) heterojunction was rationally constructed via a simple hydrothermal and physical mixing method.

Confined carburization-engineered synthesis of ultrathin nickel oxide/nickel heterostructured nanosheets for enhanced oxygen evolution reaction

Low-cost and highly effective transition metal oxides are being widely researched as one of the most promising electrocatalysts for the oxygen evolution reaction (OER). However, traditional transition metal oxides suffer from sluggish reaction kinetics due to their intrinsically poor electronic conductivity. Herein, we demonstrate a facile polydopamine-assisted carburization strategy for the confined synthesis of novel NiOx/Ni ultrathin heterostructured nanosheets. Benefiting from the large exposed surface area and fast charge transfer, the obtained ultrathin NiOx/Ni heterostructured nanosheets exhibit an overpotential of 358 mV at a current density of 10 mA cm-2 and a small Tafel slope of 51 mV dec-1, outperforming other reported representative nickel oxide based materials and commercial Ir/C catalysts. In addition, a sustainable and efficient overall water-splitting electrolyzer integrated ultrathin NiOx/Ni nanosheets with commercial Pt/C can be effectively and stably driven by solar cells.

Phosphorus Incorporation into Co9 S8 Nanocages for Highly Efficient Oxygen Evolution Catalysis

The improvement of activity of electrocatalysts lies in the increment of the density of active sites or the enhancement of intrinsic activity of each active site. A common strategy to realize dual active sites is the use of bimetal compound catalysts, where each metal atom contributes one active site. In this work, a new concept is presented to realize dual active sites with tunable electron densities in monometal compound catalysts. Dual Co²⁺ tetrahedral (Co²⁺ (T_d )) and Co³⁺ octahedral (Co³⁺ (O_h )) coordination active sites are developed and adjustable electron densities on the Co²⁺ (T_d ) and Co³⁺ (O_h ) are further achieved by phosphorus incorporation (P-Co₉ S₈ ). The experimental results and density functional theory calculations show that the nonmetal P doping can systematically modulate charge density of Co²⁺ (T_d ) and Co³⁺ (O_h ) in P-Co₉ S₈ and simultaneously improve the electrical conductivity of Co₉ S₈ , which substantially enhances oxygen evolution reaction performance of P-Co₉ S₈ .

Nickel Nitride Particles Supported on 2D Activated Graphene-Black Phosphorus Heterostructure: An Efficient Electrocatalyst for the Oxygen Evolution Reaction

Hydrogen is regarded as the most promising green clean energy in the 21st century. Developing the highly efficient and low-cost electrocatalysts for oxygen evolution reaction (OER) is of great concern for the hydrogen industry. In the water electrolyzed reaction, the overpotential and the kinetics are the main hurdles for OER. Therefore, an efficient and durable oxygen evolution reaction electrocatalyst is required. In this study, an activated graphene (AG)-black phosphorus (BP) nanosheets hybrid is fabricated for supporting Ni₃ N particles (Ni₃ N/BP-AG) in the application of OER. The Ni₃ N particles are combined with the BP-AG heterostructure via facile mechanical ball milling under argon protection. The synthesized Ni₃ N/BP-AG shows excellent catalytic performance toward the OER, demanding the overpotential of 233 mV for a current density of 10 mA cm^-2 with a Tafel slope of 42 mV dec^-1 . The Ni₃ N/BP-AG catalysts also show remarkable stability with a retention rate of the current density of about 86.4% after measuring for 10 000 s in potentiostatic mode.