In Situ Growth of 3D NiFe LDH-POM Micro-Flowers on Nickel Foam for Overall Water Splitting

Polyoxometalate-derived electrocatalysts enabling progress in hydrogen evolution reactions

Platinum-based catalysts exhibit outstanding electrocatalytic performance in the hydrogen evolution reaction (HER). However, platinum-based catalysts face significant challenges due to their rarity and high cost. This paper endeavors to shed light on a promising alternative: polyoxometalate (POM)-based catalysts, which possess significant potential for the synthesis of non-noble metal-based catalysts for the HER. Utilizing POMs as raw materials to assemble POM-derived materials, including POM-derived crystalline materials, metal sulfides, phosphides, carbides, nitrides, and so on, has emerged as an effective approach for the synthesis of hydrogen evolution electrocatalysts. This approach offers advantages in both stability and electrocatalytic performance. This comprehensive review navigates through latest progress in the assembly strategy and HER performance of POM-based crystal materials, alongside discussion on transition metal compounds derived from POMs, such as carbides, phosphides, and sulfides. Besides, future developments in POM-derived electrocatalyst regulation of the electrochemical HER are prospected.

Unravelling the Bi-Functional Electrocatalytic Properties of {Mo72Fe30} Polyoxometalate Nanostructures for Overall Water Splitting Using Scanning Electrochemical Microscope and Electrochemical Gating Methods

This study reports the use of Keplerate-type {Mo72Fe30} polyoxometalate (POMs) nanostructures as a bi-functional-electrocatalyst for HER and OER in an alkaline medium with a lower overpotential (135 mV for HER and 264 mV for OER), and excellent electrochemical stability. The bi-functional catalytic properties of {Mo72Fe30} POM are studied using a scanning electrochemical microscope (SECM) via current mapping using substrate generation and tip collection mode. Furthermore, the bipolar nature of the {Mo72Fe30} POM nano-electrocatalysts is studied using the electrochemical gating via simultaneous monitoring of the electrochemical (cell) and electrical ({Mo72Fe30} POM) signals. Next, a prototype water electrolyzer fabricated using {Mo72Fe30} POM electrocatalysts showed they can drive 10 mA cm-2 with a low cell voltage of 1.62 V in lab-scale test conditions. Notably, the {Mo72Fe30} POM electrolyzers' performance assessment based on recommended conditions for industrial aspects shows that they require a very low overpotential of 1.89 V to drive 500 mA cm-2, highlighting their promising candidature toward clean-hydrogen production.

Tungstate Intercalated NiFe Layered Double Hydroxide Enables Long-Term Alkaline Seawater Oxidation

Renewable electricity-driven seawater splitting presents a green, effective, and promising strategy for building hydrogen (H2)-based energy systems (e.g., storing wind power as H2), especially in many coastal cities. The abundance of Cl- in seawater, however, will cause severe corrosion of anode catalyst during the seawater electrolysis, and thus affect the long-term stability of the catalyst. Herein, seawater oxidation performances of NiFe layered double hydroxides (LDH), a classic oxygen (O2) evolution material, can be boosted by employing tungstate (WO4 2-) as the intercalated guest. Notably, insertion of WO4 2- to LDH layers upgrades the reaction kinetics and selectivity, attaining higher current densities with ≈100% O2 generation efficiency in alkaline seawater. Moreover, after a 350 h test at 1000 mA cm-2, only trace active chlorine can be detected in the electrolyte. Additionally, O2 evolution follows lattice oxygen mechanism on NiFe LDH with intercalated WO4 2-.

Polyoxometalate-Structured Materials: Molecular Fundamentals and Electrocatalytic Roles in Energy Conversion

Polyoxometalates (POMs), a kind of molecular metal oxide cluster with unique physical-chemical properties, have made essential contributions to creating efficient and robust electrocatalysts in renewable energy systems. Due to the fundamental advantages of POMs, such as the diversity of molecular structures and large numbers of redox active sites, numerous efforts have been devoted to extending their application areas. Up to now, various strategies of assembling POM molecules into superstructures, supporting POMs on heterogeneous substrates, and POMs-derived metal compounds have been developed for synthesizing electrocatalysts. From a multidisciplinary perspective, the latest advances in creating POM-structured materials with a unique focus on their molecular fundamentals, electrocatalytic roles, and the recent breakthroughs of POMs and POM-derived electrocatalysts, are systematically summarized. Notably, this paper focuses on exposing the current states, essences, and mechanisms of how POM-structured materials influence their electrocatalytic activities and discloses the critical requirements for future developments. The future challenges, objectives, comparisons, and perspectives for creating POM-structured materials are also systematically discussed. It is anticipated that this review will offer a substantial impact on stimulating interdisciplinary efforts for the prosperities and widespread utilizations of POM-structured materials in electrocatalysis.

NiFe-layered double hydroxide/CoP2@MnP heterostructures of clustered flower nanowires on MXene-modified nickel foam for overall water-splitting

Exploiting efficient and economical electrocatalysts is indispensable to promoting the sluggish kinetics of overall water-splitting. Herein, we designed a phosphate reaction and two-step hydrothermal method to construct a 3D porous clustered flower-like heterogeneous structure of NiFe-layered double hydroxide (NiFe) and CoP2@MnP (CMP) grown in-situ on MXene-modified nickel foam (NF) substrate (denoted as NiFe/CMP/MX), with favorable kinetics. Density functional theory calculations (DFT) demonstrate that the self-driven transfer of heterojunction charges causes electron redistribution of the catalyst, and optimizes the electron transfer rate of the active site and the d-band center near the Fermi level, thereby reducing the adsorption energy of H and O reaction intermediates (H*, OH*, OOH*). As expected, the combination of CMP and NiFe with naturally conductive MXene forms a strong chemical and electron synergistic effect, which enables the synthesized NiFe/CMP/MX heterogeneous structure exhibits good activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with a low overpotential of 200 mV and 126 mV at 10 mA cm-2, respectively. Furthermore, the overpotential of 1.58 V is enough to drive a current density of 10 mA cm-2 in a two-electrode configuration, which is better than noble metals (RuO2(+)//Pt/C(-)) (1.68 V).

Defective blue titanium oxide induces high valence of NiFe-(oxy)hydroxides over heterogeneous interfaces towards high OER catalytic activity

Nickel-iron (oxy)hydroxides (NiFeOxHy) have been validated to speed up sluggish kinetics of the oxygen evolution reaction (OER) but still lack satisfactory substrates to support them. Here, non-stoichiometric blue titanium oxide (B-TiOx) was directly derived from Ti metal by alkaline anodization and used as a substrate for electrodeposition of amorphous NiFeOxHy (NiFe/B-TiOx). The performed X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations evidenced that there is a charge transfer between B-TiOx and NiFeOxHy, which gives rise to an elevated valence at the Ni sites (average oxidation state ∼ 2.37). The synthesized NiFe/B-TiOx delivers a current density of 10 mA cm-2 and 100 mA cm-2 at an overpotential of 227 mV and 268 mV, respectively, which are better than that of pure Ti and stainless steel. It also shows outstanding activity and stability under industrial conditions of 6 M KOH. The post-OER characterization studies revealed that the surface morphology and valence states have no significant change after 24 h of operation at 500 mA cm-2, and also can effectively inhibit the leaching of Fe. We illustrate that surface modification of Ti which has high corrosion resistance and mechanical strength, to generate strong interactions with NiFeOxHy is a simple and effective strategy to improve the OER activity and stability of non-precious metal electrodes.

Conductive N, S doped Copolymers as Stable Metal-Free Electrocatalysts for Water Splitting

Noble metals (Pt) and metal oxides (IrC and RuO2) are heavily utilized as benchmark electrocatalysts for alkaline water splitting; however, these materials possess several drawbacks including high cost, poor selectivity and stability, and high environmental impact. To address these issues, we synthesized a novel metal-free conducting polypyrrole-polythiophene (Ppy-Ptp) copolymer and a separate Ppy electrode material for water-splitting applications. The Ppy-Ptp and Ppy electrocatalysts exhibited remarkable activity in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The optimal Ppy-Ptp (1:3) formulation, when deposited on a conductive nickel foam (NF) substrate, exhibited an exceptional OER performance with a low overpotential of approximately 250 mV at 20 mAcm-2, thereby outperforming the benchmark IrC/NF electrocatalyst (290 mV, 20 mAcm-2). Additionally, a similarly prepared Ppy/NF electrocatalyst exhibited an extraordinary HER performance with an overpotential of approximately 72 mV at 10 mA cm-2. Furthermore, an alkaline anion-exchange membrane (AEM) electrolyzer incorporating Ppy-Ptp (1:3) and Ppy as the anode and cathode materials, respectively, displayed operating potentials of 1.55, 1.70, and 1.78 V at 10, 50, and 100 mA cm-2, which are lower than those observed in previously reported electrolyzers. This electrolyzer also exhibited considerable operational endurance over 50 h at 50 mA cm-2, over which a negligible decay of 0.02 V was observed. The novel polymer-based metal-free catalysts presented herein therefore exhibit considerable potential as alternative electrocatalytic materials for sustainable industrial-scale H2 synthesis.

Decorated Oxidation-resistive deficient Titanium oxide nanotube supported NiFe-nanosheets as high-efficiency electrocatalysts for overall water splitting

In this study, oxidation-resistive deficient TiO_2-x supported NiFe-based electrocatalysts were developed towards efficient and durable water splitting performance. The oxidation-resistive deficient TiO_2-x support with oxygen vacancies ensures good stability and electrical conductivity of the catalyst. The decorated NiFe and NiFeP nanosheets serve as efficient catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. In 1 M KOH, the NiFe@TiO_2-x and NiFeP@TiO_2-x electrodes show low overpotential for OER (300 mV) and HER (273 mV) at 100 mA cm^-2, respectively, and excellent stability performance in overall water splitting as well. In-situ Raman and theoretical analysis reveals that the in-situ formed Fe³⁺-doped NiOOH species are essential in catalyzing OER on NiFe@TiO_2-x, particularly the electron localization of surface Fe-O bonds offers lower energy barriers for OER elemental reactions and thus enhance its catalytic activity. This work provides an oxide-based catalyst support strategy for the development of stable and active overall water splitting catalysts, and advances the insights on catalytic origin of NiFe-based catalysts as well.

Construction of an Advanced NiFe-LDH/MoS2-Ni3S2/NF Heterostructure Catalyst toward Efficient Electrocatalytic Overall Water Splitting

Developing high-efficiency, low-cost, and earth-abundant electrocatalysts toward the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is highly desirable for boosting the energy efficiency of water splitting. Herein, we adopted an interfacial engineering strategy to enhance the overall water splitting (OWS) activity via constructing a bifunctional OER/HER electrocatalyst combining MoS₂-Ni₃S₂ with NiFe layered double hydroxide (NiFe-LDH) on a nickel foam substrate. The NiFe-LDH/MoS₂-Ni₃S₂/NF electrocatalyst delivers superior OER/HER activity and stability, such as low overpotentials (220 and 79 mV for OER and HER at current densities of 50 and 10 mA cm^-2, respectively) and a low Tafel slope. This excellent electrocatalytic performance mainly benefits from the electronic structure modulation and synergistic effects between NiFe-LDH and MoS₂-Ni₃S₂, which provides a high electrochemical activity area, more active sites, and strong electron interaction. Furthermore, the assembly of NiFe-LDH/MoS₂-Ni₃S₂/NF into a two-electrode system only requires an ultra-low cell voltage of 1.50 V at a current density of 10 mA cm^-2 and exhibits outstanding stability with a decay of current density of only 2.11% @50 mA cm^-2 after 50 h, which is far superior to numerous other reported transition metal NiFe-LDH and MoS₂-Ni₃S₂-based as well as RuO₂||Pt-C electrocatalysts. This research highlights the rational design of heterostructures to efficiently advance electrocatalysis for water splitting applications.

Phase Evolution on the Hydrogen Adsorption Kinetics of NiFe-Based Heterogeneous Catalysts for Efficient Water Electrolysis

Transition metal layered double hydroxides, especially nickel-iron layered double hydroxide (NiFe-LDH) shows significant advancement as efficient oxygen evolution reaction (OER) electrocatalyst but also plays a momentous role as a precursor for NiFe-based hydrogen evolution reaction (HER) catalysts. Herein, a simple strategy for developing Ni-Fe-derivative electrocatalysts via phase evolution of NiFe-LDH under controllable annealing temperatures in an argon atmosphere is reported. The optimized catalyst annealed at 340 ^o C (denoted NiO/FeNi₃ ) exhibits superior HER properties with an ultralow overpotential of 16 mV@10 mA cm^-2 . Density functional theory simulation and in situ Raman analyses reveal that the excellent HER properties of the NiO/FeNi₃ can be attributed to the strong electronic interaction at the interface of the metallic FeNi₃ and semiconducting NiO, which optimizes the H₂ O and H adsorption energies for efficient HER and OER catalytic processes. This work will provide rational insights into the subsequent development of related HER electrocatalysts and other corresponding compounds via LDH-based precursors.

Interface strong-coupled 3D Mo-NiS@Ni-Fe LDH flower-cluster as exceptionally efficient electrocatalyst for water splitting in wide pH range

It is crucial to create a bifunctional catalyst with high efficiency and low cost for electrochemical water splitting under alkaline and neutral pH conditions. This study investigated the in-situ creation of ultrafine Mo-NiS and NiFe LDH nanosheets as an effective and stable electrocatalyst with a three-dimensional (3D) flower-cluster hierarchical structure (Mo-NiS@NiFe LDH). The strong interfacial connection between Mo-NiS and NiFe LDH enhances the formation of metal higher chemical states in the material, optimizes the electronic structure, increases OH^- adsorption capacity improves electron transfer/mass diffusion, and promotes O₂/H₂ gas release. As a result, at 10 mA cm^-2, Mo-NiS@NiFe LDH/NF demonstrates the outstanding bifunctional electrocatalytic activity of just 107 mV (HER, hydrogen evolution reaction) and 184 mV (hydrogen evolution reaction) (OER, oxygen evolution reaction). The catalytic performance is remarkably stable after 72 h of continuous operation in 1 M KOH at high current densities (300 mA cm^-2). More interestingly, in the overall water splitting system, the cell voltages for anode and cathode in both alkaline and neutral electrolytes for Mo-NiS@NiFe LDH/NF are only 1.54 V (alkaline) and 2.06 V (neutral) at 10 mA cm^-2. These results demonstrated that the bifunctional electrocatalyst design concept is a viable solution for water splitting in both alkaline and neutral systems.

Recent Progress of Natural Mineral Materials in Environmental Remediation

Organic contaminants, volatile organic compounds (VOCs), and heavy metals have posed long-term threats to the ecosystem and human health. Natural minerals have aroused widespread interest in the field of environmental remediation due to their unique characteristics such as rich resources, environmentally benign, and excellent photoelectric properties. This review briefly introduced the contributions of natural minerals such as sulfide minerals, oxide minerals, and oxysalt minerals in pollution control, which include organic pollution degradation, sterilization, air purification (NO VOCs oxidation), and heavy metal treatment by means of photocatalysis, Fenton catalysis, persulfate activation, and adsorption process. At last, the future challenges of natural mineral materials in pollution control are also outlooked.

Superlative photoelectrochemical properties of 3D MgCr-LDH nanoparticles influencing towards photoinduced water splitting reactions

In the present work, we report the synthesis of single system three-dimensional (3D) open porous structure of MgCr-LDH nanoparticles in a substrate-free path by using one-step formamide assisted hydrothermal reaction followed by visible light irradiation for significant photoelectrochemical (PEC) properties that manifest towards photocatalytic H₂ and O₂ production. The as-prepared nanostructured materials were characterized by various physico-chemical characterization techniques. Moreover, this unique synthetic approach produces 3D open porous network structure of MgCr-LDH nanoparticles, which were formed by stacking of numerous 2D nanosheets, for effective light harvestation, easy electronic channelization and unveil superlative PEC properties, including high current density (6.9 mA/cm²), small Tafel slope of 82 mV/decade, smallest arc of the Nyquist plot (59.1 Ω cm⁻²) and photostability of 6000 s for boosting water splitting activity. In addition, such perfectly self-stacked 2D nanosheets in 3D MgCr-LDH possess more surface active defect sites as enriched 50% oxygen vacancy resulting a good contact surface within the structure for effective light absorption along with easy electron and hole separation, which facilitates the adsorption of protons and intermediate for water oxidation. Additionally, the Cr³⁺ as dopant pull up the electrons from water oxidation intermediates, thereby displaying superior photocatalytic H₂ and O₂ production activity of 1315 μmol/h and 579 μmol/h, respectively. Therefore, the open 3D morphological aspects of MgCr-LDH nanoparticles with porous network structure and high surface area possess more surface defect sites for electron channelization and identified as distinct novel features of this kind of materials for triggering significant PEC properties, along with robustly enhance the photocatalytic water splitting performances.

Construction of Integrated Electrodes with Transport Highways for Pure-Water-Fed Anion Exchange Membrane Water Electrolysis

The design of high-performance and durable electrodes for the oxygen evolution reaction (OER) is crucial for pure-water-fed anion exchange membrane water electrolysis (AEMWE). In this study, an integrated electrode with vertically aligned ionomer-incorporated nickel-iron layered double hydroxide nanosheet arrays, used on one side of the liquid/gas diffusion layer, is fabricated for the OER. Transport highways in the fabricated integrated electrode, significantly improve the transport of liquid/gas, hydroxide ions, and electron in the anode, resulting in a high current density of 1900 mA cm^-2 at 1.90 V in pure-water-fed AEMWE. Specifically, three-electrode and single-cell measurement results indicate that an anion-exchange ionomer can increase the local OH^- concentration on the integrated electrodes surface and facilitate the OER for pure-water-fed AEMWE. This study highlights a new approach to fabricating and understanding electrode architecture with enhanced performance and durability for pure-water-fed AEMWE.

Boosting alkaline water splitting and the urea electrolysis kinetic process of a Co3O4 nanosheet by electronic structure modulation of F, P co-doping

Designing non-precious metal electrocatalysts for accelerated electron transfer and richer active site exposure is necessary and challenging to achieve the versatility of electrocatalysts. In this research, a self-grown nanosheet array electrocatalyst on nickel foam with high structural stability is first rationally designed through suitable anionic doping. The combined experimental and theoretical calculations reveal that the F-P-Co₃O₄/NF material optimizes the adsorption energy of hydrogen/water through electron coupling, and its nanosheet structure provides abundant active sites, accelerating the mass and electron transfer in the reaction process. It is worth noting that the as-developed F-P-Co₃O₄/NF materials exhibit outstanding catalytic activity for overpotentials of 192 and 110 mV at a current density of 10 mA cm^-2 for the oxygen evolution reaction and the hydrogen evolution reaction in 1 M KOH, respectively. More notably, an assembled F-P-Co₃O₄/NF//F-P-Co₃O₄/NF alkaline electrolytic cell requires only an ultra-low cell voltage of 1.53 V to achieve a current density of 10 mA cm^-2, which is one of the best activities reported so far. Furthermore, F-P-Co₃O₄/NF also shows excellent performance for urea electrolysis. Theoretical calculations show that the superior activity of the F-P-Co₃O₄/NF catalyst is attributed to the optimal electron configuration and the lower Gibbs free energy of hydrogen adsorption due to co-doping of P and F. The work provides an alternative solution for the preparation of electrocatalysts with high structural stability, high catalytic activity and multifunction for alkaline water splitting and urea electrolysis.

Magneto-Electrodeposition of 3D Cross-Linked NiCo-LDH for Flexible High-Performance Supercapacitors

Layered double hydroxides (LDHs) with outstanding redox activity on flexible current collectors can serve as ideal cathode materials for flexible hybrid supercapacitors in wearable energy storage devices. Electrodeposition is a facile, time-saving, and economical technique to fabricate LDHs. The limited loading mass induced by insufficient mass transport and finite exposure of active sites, however, greatly hinders the improvement of areal capacity. Herein, magneto-electrodeposition (MED) under high magnetic fields up to 9 T is developed to fabricate NiCo-LDH on flexible carbon cloth (CC) as well as Ti₃ C₂ T_x functionalized CC. Owing to the magneto-hydrodynamic effect induced by magnetic-electric field coupling, the loading mass and exposure of active sites are significantly increased. Moreover, a 3D cross-linked nest-like microstructure is constructed. The MED-derived NiCo-LDH delivers an ultrahigh areal capacity of 3.12 C cm^-2 at 1 mA cm^-2 and as-fabricated flexible hybrid supercapacitors show an excellent energy density with an outstanding cycling stability. This work provides a novel route to improve electrochemical performances of layered materials through MED technique.

Engineering Bimodal Oxygen Vacancies and Pt to Boost the Activity Toward Water Dissociation

Water dissociation is the rate-limiting step of several energy-related reactions due to the high energy barrier required for breaking the oxygen-hydrogen bond. In this work, a bimodal oxygen vacancy (V_O ) catalysis strategy is adopted to boost the efficient water dissociation on Pt nanoparticles. The single facet-exposed TiO₂ surface and NiO_x nanocluster possess two modes of V_O different from each other. In ammonia borane hydrolysis, the highest catalytic activity among Pt-based materials is achieved with the turnover frequency of 618 min^-1 under alkaline-free conditions at 298 K. Theoretical simulation and characterization analyses reveal that the bimodal V_O significantly promotes the water dissociation in two ways. First, an ensemble-inducing effect of Pt and V_O in TiO₂ drives the activation of water molecules. Second, an electron promoter effect induced by the electron transfer from V_O in NiO_x to Pt further enhances the ability of Pt to dissociate water and ammonia borane. This insight into bimodal V_O catalysis establishes a new avenue to rationally design heterogeneous catalytic materials in the energy chemistry field.

Self-assembly of bimetallic polyoxometalates and dicyandiamide to form Co/WC@NC for efficient electrochemical hydrogen generation

Graphene carbon-coated and N-doped WC and cobalt (Co) nanoparticles (Co/WC@NC) were synthesized via a one-step straightforward high-temperature calcination. The resultant Co/WC@NC manifests excellent hydrogen evolution activity.

In situ ball-milling gram-scale preparation of polyoxoniobate-intercalated MgAl-layered double hydroxides for selective aldol and Michael addition cascade reactions

A facile one-step ball-milling strategy to prepare gram-scale Mg3Al-LDH-Nb6 has been demonstrated and the thus-obtained catalyst exhibited efficient selective catalytic activities in the synthesis of biologically active organic molecules in water.

Polyoxometalate-based metal–organic complexes and their derivatives as electrocatalysts for energy conversion in aqueous systems

The research progress on polyoxometalate-based metal–organic complexes and their derivatives as electrocatalysts in sustainable and clean energy conversion applications in aqueous systems is summarized.

Quench-Induced Surface Engineering Boosts Alkaline Freshwater and Seawater Oxygen Evolution Reaction of Porous NiCo2 O4 Nanowires

The electrochemical oxygen evolution reaction (OER) by efficient catalysts is a crucial step for the conversion of renewable energy into hydrogen fuel, in which surface/near-surface engineering has been recognized as an effective strategy for enhancing the intrinsic activities of the OER electrocatalysts. Herein, a facile quenching approach is demonstrated that can simultaneously enable the required surface metal doping and vacancy generation in reconfiguring the desired surface of the NiCo₂ O₄ catalyst, giving rise to greatly enhanced OER activities in both alkaline freshwater and seawater electrolytes. As a result, the quenched-engineered NiCo₂ O₄ nanowire electrode achieves a current density of 10 mA cm^-2 at a low overpotential of 258 mV in 1 m KOH electrolyte, showing the remarkable catalytic performance towards OER. More impressively, the same electrode also displays extraordinary activity in an alkaline seawater environment and only needs 293 mV to reach 10 mA cm^-2 . Density functional theory (DFT) calculations reveal the strong electronic synergies among the metal cations in the quench-derived catalyst, where the metal doping regulates the electronic structure, thereby yielding near-optimal adsorption energies for OER intermediates and giving rise to superior activity. This study provides a new quenching method to obtain high-performance transition metal oxide catalysts for freshwater/seawater electrocatalysis.

Densely vertical-grown NiFe hydroxide nanosheets on a 3D nickel skeleton as a dendrite-free lithium anode

Densely vertical-grown NiFe hydroxide nanosheets on a nickel foam (DVS-NFOH@NF) were designed and synthesized for a dendrite-free lithium anode. As a result, the Li dendrite was significantly suppressed. The invented Li anode presented a uniform morphology and great cycle performance in a symmetric cell.

Ru doping induces the construction of a unique core-shell microflower self-supporting electrocatalyst for highly efficient overall water splitting

Since the large reaction energy barrier caused by multi-step electron transfer processes of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) gravely restricts the practical application of electrocatalytic water splitting, it is urgent to develop a dual-functional electrocatalyst which can effectively reduce the reaction energy barrier and actually speed up the reaction. Herein, the Ru species are doped into the complex of magnetite and FeNi-layered double hydroxide by a one-step oil bath method, and a self-supporting binder-free bifunctional electrocatalyst was synthesized on the surface of iron foam (named Ru-Fe₃O₄@FeNi-LDH/IF). The unique 3D core-shell microflower structure of Ru-Fe₃O₄@FeNi-LDH/IF, the combination of active ingredient and conductive substrate, together with the doping of Ru may immensely provide a large number of active sites, adjust the electronic structure, accelerate electron transfer, and thus greatly improve the electrocatalytic activity and durability. It is worth mentioning that when Ru-Fe₃O₄@FeNi-LDH/IF is used as the anode and cathode for overall water splitting, only 1.52 V battery voltage can generate a current density of 10 mA cm^-2, and also maintain a prominent stability for at least 36 hours. This work provides a feasible strategy for heteroatom-doping LDH as a bifunctional electrocatalyst.

Zr-doped CoFe-layered double hydroxides for highly efficient seawater electrolysis

Efficient generation of hydrogen from electrocatalytic water-splitting is of great importance to realize the hydrogen economy. In that field, designing efficient and bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is critical for water splitting. With the increasing demands for bifunctional catalysts, a universal strategy in favor of these catalytic processes is particularly important. Herein, a variety of Zr-doped layered double hydroxide (LDH) with low-crystalline grown on nickel foam (NF) is designed to promote the bifunctional activities of electrocatalysts. It is found that the doping of Zr⁴⁺ into CoFe-LDH/NF can tune the electronic structure and also expose abundant catalytic active sites to enhance the electrocatalytic activities. In 1 M KOH, the as-prepared CoFeZr/NF exhibits superior OER and HER activities with low overpotentials of 233 and 159 mV at 10 mA cm^-2. When tested in alkaline simulated seawater electrolyte, CoFeZr/NF also shows high catalytic activities with almost no attenuation when compared with that in 1.0 M KOH. This work will provide a new way for the development of seawater electrolysis for large-scale hydrogen production.