Triple Functions of Ni(OH)2 on the Surface of WN Nanowires Remarkably Promoting Electrocatalytic Activity in Full Water Splitting

In-situ revealed inhibition of W2C to excessive oxidation of CoOOH for high-efficiency alkaline overall water splitting

The design of low-cost, efficient, and stable multifunctional basic catalysts to replace the high-cost noble metal catalysts remains a challenge. In this work, we report a dual-component Co-W2C catalytic system which achieves excellent properties of hydrogen evolution reaction (HER, η10 = 63 mV), oxygen evolution reaction (OER, η10 = 259 mV) and overall water splitting (η10 = 1.53 V) by adjusting the interfacial electronic structure of the material. Further density functional theory (DFT) calculations indicate that the efficient electronic modulation at the W2C/Co interface leads to the generation of favorable hydroxyl and hydrogen species energetics on the hybrid surface. The results of the in-situ Raman spectra show that W2C can suppress the excessive oxidation of the active site during the OER process, and the existence of core-shell structure also protects the W2C substrate. The stable and efficient catalytic performance of Co-W2C is attributed to the common advantages of structural and interface manipulation.

Anchoring Ni(OH)2-CeOx Heterostructure on FeOOH-Modified Nickel-Mesh for Efficient Alkaline Water-Splitting Performance with Improved Stability under Quasi-Industrial Conditions

Developing low-cost and industrially viable electrode materials for efficient water-splitting performance and constructing intrinsically active materials with abundant active sites is still challenging. In this study, a self-supported porous network Ni(OH)2-CeOx heterostructure layer on a FeOOH-modified Ni-mesh (NiCe/Fe@NM) electrode is successfully prepared by a facile, scalable two-electrode electrodeposition strategy for overall alkaline water splitting. The optimized NiCe0.05/Fe@NM catalyst reaches a current density of 100 mA cm-2 at an overpotential of 163 and 262 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in 1.0 m KOH with excellent stability. Additionally, NiCe0.05/Fe@NM demonstrates exceptional HER performance in alkaline seawater, requiring only 148 mV overpotential at 100 mA cm-2. Under real water splitting conditions, NiCe0.05/Fe@NM requires only 1.701 V to achieve 100 mA cm-2 with robust stability over 1000 h in an alkaline medium. The remarkable water-splitting performance and stability of the NiCe0.05/Fe@NM catalyst result from a synergistic combination of factors, including well-optimized surface and electronic structures facilitated by an optimal Ce ratio, rapid reaction kinetics, a superhydrophilic/superaerophobic interface, and enhanced intrinsic catalytic activity. This study presents a simple two-electrode electrodeposition method for the scalable production of self-supported electrocatalysts, paving the way for their practical application in industrial water-splitting processes.

Heterointerface-Rich Ni3N/WO3 Hierarchical Nanoarrays for Efficient Glycerol Oxidation-Assisted Alkaline Hydrogen Evolution

Glycerol oxidation-assisted water electrolysis has emerged as a cost-effective way of co-producing green hydrogen and HCOOH. Still, preparing highly selective and stable nickel-based metal electrocatalysts remains a challenge. Herein, heterostructure Ni3N/WO3 nanosheet arrays of bifunctional catalysts with large specific surface areas loaded on nickel foam (denoted as Ni3N/WO3/NF) were synthesized. This catalyst was for glycerol oxidation reaction (GOR) and hydrogen evolution reaction (HER) with excellent catalytic performance, a voltage saving of 267 mV compared to oxygen evolution reaction (OER), and a HER overpotential of 104 mV at 100 mA cm-2. The cell voltage in the assembled GOR//HER hybrid electrolysis system reaches 100 mA cm-2 at 1.50 V, 296 mV lower than the potential required for overall water splitting. This work demonstrates that replacing GOR with OER using a cost-effective and highly active Ni-based bifunctional electrocatalyst can make hybrid water electrolysis an energy-efficient, sustainable, and green strategy for hydrogen production.

Treasure-bowl style bifunctional site in cerium-tungsten hetero-clusters for superior solar-driven hydrogen production

Electrochemical water splitting powered by renewable energy sources hold potential for clean hydrogen production. However, there is still persistent challenges such as low solar-to-hydrogen conversion efficiency and sluggish oxygen evolution reactions. Here, we address the poor kinetics by studying and strengthening the coupling between Ce and W, and concurrently establishing Ce-W bi-atomic clusters on P,N-doped carbon (WN/WC-CeO2-x@PNC) with a "treasure-bowl" style. The bifunctional active sites are established using a novel and effective self-sacrificial strategy involving in situ induced defect formation. In addition, by altering the coupling of the W(d)-N(p) and W(d)-Ce(f) orbitals in the WN/WC-CeO2-x supramolecular clusters, we are able to disrupt the linear relationship between the binding energies of reaction intermediates, a key to obtain high catalytic performance for transition metals. Through the confinement of the WN/WC-CeO2-x composite hetero-clusters within the sub-nanometre spaces of hollow nano-bowl-shaped carbon reactors, a stable and efficient hydrogen production via water electrolysis could be achieved. When assembled together with a solar GaAs triple junction solar cell, a solar-to-hydrogen conversion efficiency of 18.92% in alkaline media could be realized. We show that the key to establish noble metal free catalysts with high efficiency lies in the fine-tuning of the metal-metal interface, forming regions with near optimal adsorption energies for the reaction intermediates participating in water electrolysis.

In Situ Synthesis of Exfoliated Ni(OH)2 Nanosheets and AgNPs-Embedded Functionalized Polyindole-Based Trinary Hybrid Microspheres: A Z-Scheme Photocatalyst for the Sunlight-Driven Degradation of Organic Pollutants with Enhanced Antibacterial Efficacy

Advancing a facile one-pot synthetic approach for the fabrication of a hybrid heterojunction photocatalyst remains a significant challenge in research pursuits. Herein, a microsphere-like trinary hybrid nanocomposite has been synthesized (NH/PIn/MAA/Ag). It comprises exfoliated single- and a few-layered Ni(OH)2 (NH nanosheets), mercaptoacetate-functionalized polyindole (PIn/MAA), and Ag nanoparticles (AgNPs) through an in situ approach. The formation mechanism is based on the exfoliation of stacked Ni(OH)2 multilayers [i.e., Ni(OH)2 microflowers] and stabilization of NH nanosheets through host-guest formation of PIn/MAA, followed by the adsorption-reduction of Ag+ ions in a one-pot reaction at low temperature. Surface morphological analyses of hybrid nanocomposite microspheres have exhibited that highly dense Ni(OH)2 microflowers have been transformed into low-density layered forms (NH nanosheets) within the polymeric platform (PIn/MAA) with deposited AgNPs. An interfacial heterojunction has been developed between the components in the depletion region, leading to an improvement in photocatalytic efficiency through a synergistic effect over the components for charge separation and transfer through the heterojunction interface via solid-state mediator Ag-based Z-scheme charge transfer dynamics. The superior photocatalytic degradation of tetracycline (98.2%) by trinary hybrid microspheres can be attributed to the deteriorated recombination rate of electron-hole pairs with reduced charge transfer resistance of the heterojunction in the photocatalyst, as obvious from photoluminescence, electrochemical impedance spectroscopy, chronoamperometry, and time-resolved photoluminescence (TRPL) analyses. Moreover, the antibacterial properties of microspheres against Bacillus pumilus (Gram-positive) and Escherichia coli (Gram-negative) bacteria have validated their potential as promising materials for the overall purification of aquatic systems.

Nitrided Rhodium Nanoclusters with Optimized Water Bonding and Splitting Effects for pH-Universal H2-Production

The nitridation of noble metals-based catalysts to further enhance their hydrogen evolution reaction (HER) kinetics in neutral and alkaline conditions would be an effective strategy for developing high-performance wide pH HER catalysts. Herein, a facile molten urea method is employed to construct the nitrided Rh nanoclusters (RhxN) supported on N-doped carbon (RhxN-NC). The uniformly distributed RhxN clusters exhibited optimized water bonding and splitting effects, therefore resulting in excellent pH-universal HER performance. The optimized RhxN-NC catalyst only requires 8, 12, and 109 mV overpotentials to reach the current density of 10 mA cm-2 in 0.5 M H2SO4, 1.0 M KOH, and 1.0 M PBS electrolytes, respectively. The spectroscopic characterizations and theoretical calculation further confirm the vital role of Rh-N moieties in RhxN clusters in improving the transfer of electrons and facilitating the generation of H2. This work not only provides a suitable nitridation method for noble metal species in mild conditions but also makes a breakthrough in synthesizing noble metal nitrides-based electrocatalysts to achieve an exceptional wide-pH HER performance and other catalysis.

Wood-Derived Freestanding Carbon-Based Electrode with Hierarchical Structure for Industrial-Level Hydrogen Production

The sustainable and scalable fabrication of low-cost, efficient, and durable electrocatalysts that operate well at industrial-level current density is urgently needed for large-scale implementation of the water splitting to produce hydrogen. In this work, an integrated carbon electrode is constructed by encapsulating Ni nanoparticles within N-doped carbonized wood framework (Ni@NCW). Such integrated electrode with hierarchically porous structure facilitates mass transfer process for hydrogen evolution reaction (HER). Ni@NCW electrode can be employed directly as a robust electrocatalyst for HER, which affords the industrial-level current density of 1000 mA cm-2 at low overpotential of 401 mV. The freestanding binder-free electrode exhibits extraordinary stability for 100 h. An anion exchange membrane water electrolysis (AEMWE) electrolyzer assembled with such freestanding carbon electrode requires only a lower cell voltage of 2.43 V to achieve ampere-level current of 4.0 A for hydrogen production without significant performance degradation. These advantages reveal the great potential of this strategy in designing cost-effective freestanding electrode with monometallic, bimetallic, or trimetallic species based on abundant natural wood resources for water splitting.

Rapid Formation of Epitaxial Oxygen Evolution Reaction Catalysts on Dendrites with High Catalytic Activity and Stability

Oxygen evolution reaction is an essential but kinetically sluggish step in many energy storage and conversion processes and therefore is in pursuit of highly efficient and stable catalysts. Although nanosized transition-metal-based oxides/hydroxides exhibit high catalytic activity toward the oxygen evolution reaction (OER), many of them suffer from low stability at an anode current density in industrial scale. Herein, by combining a rapid epitaxial formation method with dynamic bubble-templated electrodeposition, we successfully developed single crystalline NiFeCu oxide catalysts with a hierarchical porous structure. It was found that the structure can facilitate fast electron transportation for the catalysts and retard the diffusion of the O atoms to the inner metallic current collector. The hierarchical pores inherited from the hydrogen bubble templates built ideal channels for the massive and rapid release of oxygen bubbles. As a consequence, the NiFeCu oxides catalyzed the OER more efficiently and steadily than the commercial RuO2 catalyst at an anode current density in industrial scale (300 mA/cm2). This work, by resolving the durability concerns for nanosized oxides, offers a series of highly efficient and stable catalysts for OER and a structure building strategy to boost the catalytic activity and stability for nonconductive catalysts.

Photothermal-Magnetic Synergistic Effects in an Electrocatalyst for Efficient Water Splitting under Optical-Magnetic Fields

The slow oxygen evolution reaction (OER) limits water splitting, and external fields can help improve it. However, the effect of a single external field on the OER is limited and unsatisfactory. Furthermore, the mechanism by which external fields improve the OER is unclear, particularly in the presence of multiple fields. Herein, a strategy is proposed for enhancing the OER activity of a catalyst using the combined effect of an optical-magnetic field, and the mechanism of catalytic activity enhancement is studied. Under the optical-magnetic field, Co3 O4 reduces the resistance by increasing the catalyst temperature. Meanwhile, CoFe2 O4 further reduces the resistance via the negative magnetoresistance effect, thus decreasing the resistance from 16 to 7.0 Ω. Additionally, CoFe2 O4 acts as a spin polarizer, and electron polarization results in a parallel arrangement of oxygen atoms, which increases the kinetics of the OER under the magnetic field. Benefiting from the optical and magnetic response design, Co3 O4 /CoFe2 O4 @Ni foam requires an overpotential of 172.4 mV to reach a current density of 10 mA cm-2 under an optical-magnetic field, which is significantly higher than those of recently reported state-of-the-art transition-metal-based catalysts.

Interfacial Engineering of Copper-Nickel Selenide Nanodendrites for Enhanced Overall Water Splitting in Alkali Condition

Fabricating heterogeneous interfaces is an effective approach to improve the intrinsic activity of noble-metal-free catalysts for water splitting. Herein, 3D copper-nickel selenide (CuNi@NiSe) nanodendrites with abundant heterointerfaces are constructed by a precise multi-step wet chemistry method. Notably, CuNi@NiSe only needs 293 and 41 mV at 10 mA cm-2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Moreover, the assembled CuNi@NiSe system just requires 2.2 V at 1000 mA cm-2 in anion exchange membrane (AEM) electrolyzer, which is 2.0 times better than Pt/C//IrO2 . Mechanism studies reveal Cu defects on the Cu2-x Se surface boost the electron transfer between Cu atoms and Se atoms of Ni3 Se4 via Cu2-x Se/Ni3 Se4 interface, largely lowering the reaction barrier of rate-determining step for HER. Besides, the intrinsic activity of Ni atoms for in situ generated NiOOH is largely enhanced during OER because of the electron-modulating effect of Se atoms at Ni3 Se4 /NiOOH interface. The unique 3D structure also promotes the mass transfer during catalysis process. This work emphasizes the essential role of interfacial engineering for practical water splitting.

Multistage interfacial engineering of 3D carbonaceous Ni2P nanospheres/nanoflowers derived from Ni-BTC metal-organic frameworks for overall water splitting

The regulation of the multi-dimensional interface plays an important role in optimizing the electron transport and gas mass transfer during catalysis, which is conducive to promoting the electrocatalytic process. Herein, a self-supporting electrode has been developed with the multistage interface within 3D Ni₂P@C nanospheres/nanoflowers arrays derived from metal-organic frameworks (MOFs) as template skeletons and precursors. The constructed nanosphere interface protrudes outward to optimize the contact with the electrolyte while the nanoflower lamellar connection promotes rapid electron transfer and exposes more active sites, and accelerates the gas diffusion with the abundant interspace channels. According to theoretical calculation, the synergistic effect between Ni₂P and C is conducive to the optimal adsorption and desorption of H*, thus contributing to the improvement of catalytic kinetics. With the optimized growth times assembled onto nickel foam substrates, the Ni₂P@C-12 h requires overpotentials of only 69 mV and 205 mV to drive the current density of 10 mA cm^-2 towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. And it reveals an ultralow cell voltage of 1.55 V at 10 mA cm^-2 to achieve overall water splitting (OWS). In addition, the stability of the Ni₂P@C/NF electrocatalyst emerges as prominent long-term stability, which is attributed to the carbonaceous nanosphere anchors on the substrate to minimize the possibility of oxidation of the catalyst surface. This strategy of in situ growth of MOF-derived phosphates provides a general idea for interfacial engineering modification of OWS electrode materials.

Interstitial Hydrogen Atom to Boost Intrinsic Catalytic Activity of Tungsten Oxide for Hydrogen Evolution Reaction

Tungsten oxide (WO₃ ) is an appealing electrocatalyst for the hydrogen evolution reaction (HER) owing to its cost-effectiveness and structural adjustability. However, the WO₃ electrocatalyst displays undesirable intrinsic activity for the HER, which originates from the strong hydrogen adsorption energy. Herein, for effective defect engineering, a hydrogen atom inserted into the interstitial lattice site of tungsten oxide (H_0.23 WO₃ ) is proposed to enhance the catalytic activity by adjusting the surface electronic structure and weakening the hydrogen adsorption energy. Experimentally, the H_0.23 WO₃ electrocatalyst is successfully prepared on reduced graphene oxide. It exhibits significantly improved electrocatalytic activity for HER, with a low overpotential of 33 mV to drive a current density of 10 mA cm^-2 and ultra-long catalytic stability at high-throughput hydrogen output (200 000 s, 90 mA cm^-2 ) in acidic media. Theoretically, density functional theory calculations indicate that strong interactions between interstitial hydrogen and lattice oxygen lower the electron density distributions of the d-orbitals of the active tungsten (W) centers to weaken the adsorption of hydrogen intermediates on W-sites, thereby sufficiently promoting fast desorption from the catalyst surface. This work enriches defect engineering to modulate the electron structure and provides a new pathway for the rational design of efficient catalysts for HER.

Magnetic Heating Amorphous NiFe Hydroxide Nanosheets Encapsulated Ni Nanoparticles@Wood Carbon to Boost Oxygen Evolution Reaction Activity

The oxygen evolution reaction (OER) has significant effects on the water-splitting process and rechargeable metal-air batteries; however, the sluggish reaction kinetics caused by the four-electron transfer process for transition metal catalysts hinder large-scale commercialization in highly efficient electrochemical energy conversion devices. Herein, a magnetic heating-assisted enhancement design for low-cost carbonized wood with high OER activity is proposed, in which Ni nanoparticles are encapsulated in amorphous NiFe hydroxide nanosheets (a-NiFe@Ni-CW) via direct calcination and electroplating. The introduction of amorphous NiFe hydroxide nanosheets optimizes the electronic structure of a-NiFe@Ni-CW, accelerating electron transfer and reducing the energy barrier in the OER. More importantly, the Ni nanoparticles located on carbonized wood can function as magnetic heating centers under the effect of an alternating current (AC) magnetic field, further promoting the adsorption of reaction intermediates. Consequently, a-NiFe@Ni-CW demonstrated an overpotential of 268 mV at 100 mA cm^-2 for the OER under an AC magnetic field, which is superior to that of most reported transition metal catalysts. Starting with sustainable and abundant wood, this work provides a reference for highly effective and low-cost electrocatalyst design with the assistance of a magnetic field.

Tunable d-band center of a NiFeMo alloy with enlarged lattice strain enhancing the intrinsic catalytic activity for overall water-splitting

Developing efficient bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) under alkaline conditions is prospective for reducing energy consumption during water electrolysis. In this work, we successfully synthesized nanocluster structure composites composed of NiFeMo alloys with controllable lattice strain by the electrodeposition method at room temperature. The unique structure of NiFeMo/SSM (stainless steel mesh) facilitates the exposure of abundant active sites and promotes mass transfer and gas exportation. The NiFeMo/SSM electrode exhibits a low overpotential of 86 mV at 10 mA cm^-2 for the HER and 318 mV at 50 mA cm^-2 for the OER, and the assembled device reveals a low voltage of 1.764 V at 50 mA cm^-2. Moreover, both the experimental results and theoretical calculations reveal that the dual doping of Mo and Fe can induce the tunable lattice strain of nickel, which in turn changes the d-band center and electronic interaction of the catalytically active site, and finally enhances the HER and OER catalytic activity. This work may provide more options for the design and preparation of bifunctional catalysts based on non-noble metals.

Efficient removal of bromate from contaminated water using electrochemical membrane filtration with metal heteroatom interface

Efficient utilization of atomic hydrogen (H*) is of great importance for achieving efficient bromate reduction using electrochemical technologies. Herein, an electrochemical membrane with metal heteroatom interface of Ru and Ni was developed to enhance the utilization efficiency of H* via the membrane filtration process. The RuNi membrane demonstrated 91.3% of bromate removal at 5 mA cm^-2 under the flow-through operation (40 L m^-2 h^-1). Cyclic voltammetry (CV) curves and electron spin resonance (ESR) spectra elucidated that the bromate reduction was mainly attributed to H* -mediated reduction rather than the direct electron transfer between bromate and RuNi active layer. The quenching experiments revealed a significant contribution of adsorbed H* to the bromate removal during the membrane filtration. Based on X-ray photoelectron spectrometry and X-ray diffraction analyses, we found that the resultant Ru⁰Ni⁰ structure on the electrochemical membrane could facilitate the generation of H* during the bromate reduction reaction. Besides, the higher pH might suppress the formation of H* and increase the energy barrier for breaking the Br-O bond, resulting in dramatic increase of energy consumption for removing bromate. Our work highlights the potential of utilizing H* in electrochemical membrane for removing bromate in water treatment and remediation.

1D@2D Hierarchical Structures of Co(OH)x Nanosheets on NiMoOx Nanorods Can Mediate Alkaline Hydrogen Evolution with Industry-Level Current Density and Stability

Developing efficient electrocatalysts at ampere-scale current densities is of paramount importance to advance industrial applications of alkaline water electrolysis. Herein, a hierarchical nanostructured electrocatalyst with two-dimensional Co(OH)_x nanosheets grown on one-dimensional NiMoO_x nanorods over three-dimensional porous Ni foam substrate is designed. The resulting catalyst delivers ultrahigh hydrogen evolution reaction (HER) activity in the alkaline solution, which only requires overpotentials of 185 and 332 mV to achieve the current densities of -500 and -1000 mA cm^-2 in 1.0 m KOH, respectively, and shows robust stability at -1000 mA cm^-2 for 11 days. The unique 1D @ 2D hierarchical structures with abundant hetero-interfaces can not only expose sufficient active sites but also boost alkaline HER kinetics with fast water dissociation ability. This present work may pave a new insight to design efficient electrocatalysts with hierarchical structures for alkaline HER with industry-level current density and stability.

Tungsten-Based Nanocatalysts: Research Progress and Future Prospects

The high price of noble metal resources limits its commercial application and stimulates the potential for developing new catalysts that can replace noble metal catalysts. Tungsten-based catalysts have become the most important substitutes for noble metal catalysts because of their rich resources, friendly environment, rich valence and better adsorption enthalpy. However, some challenges still hinder the development of tungsten-based catalysts, such as limited catalytic activity, instability, difficult recovery, and so on. At present, the focus of tungsten-based catalyst research is to develop a satisfactory material with high catalytic performance, excellent stability and green environmental protection, mainly including tungsten atomic catalysts, tungsten metal nanocatalysts, tungsten-based compound nanocatalysts, and so on. In this work, we first present the research status of these tungsten-based catalysts with different sizes, existing forms, and chemical compositions, and further provide a basis for future perspectives on tungsten-based catalysts.

Controllable Synthesis of Ultrathin Defect-Rich LDH Nanoarrays Coupled with MOF-Derived Co-NC Microarrays for Efficient Overall Water Splitting

Water electrolysis has attracted immense research interest, nevertheless the lack of low-cost but efficient bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions greatly hinders its commercial applications. Herein, the controllable synthesis of ultrathin defect-rich layered double hydroxide (LDH) nanoarrays assembled on metal-organic framework (MOF)-derived Co-NC microarrays for boosting overall water splitting is reported. The Co-NC microarrays can not only provide abundant nucleation sites to produce a large number of LDH nuclei for favoring the growth of ultrathin LDHs, but also help to inhibit their tendency to aggregate. Impressively, five types of ultrathin bimetallic LDH nanoarrays can be electrodeposited on the Co-NC microarrays, forming desirable nanoarray-on-macroarray architectures, which show high uniformity with thicknesses from 1.5 to 1.9 nm. As expected, the electrocatalytic performance is significantly enhanced by exploiting the respective advantages of Co-NC microarrays and ultrathin LDH nanoarrays as well as the potential synergies between them. Especially, the optimal Co-NC@Ni₂ Fe-LDH as both cathode and anode can afford the lowest cell voltage of 1.55 V at 10 mA cm^-2 , making it one of the best earth-abundant bifunctional electrocatalysts for water electrolysis. This study provides new insights into the rational design of highly-active and low-cost electrocatalysts and facilitates their promising applications in the fields of energy storage and conversion.

Defect engineering tuning electron structure of biphasic tungsten-based chalcogenide heterostructure improves its catalytic activity for hydrogen evolution and triiodide reduction

The design and exploration of high-efficiency and low-cost electrode catalysts are of great significance to the development of novel energy conversion technologies. In this work, metal and nonmetal heteroatoms co-doped biphasic tungsten-based chalcogenide heterostructured catalyst (Co-WS₂/P-WO_2.9) with rich defects is successfully synthesized by a vulcanization technique. The electrocatalytic performance of WS₂/WO₃ in the hydrogen evolution reaction (HER) and triiodide reduction reaction is significantly enhanced by modifying and optimizing its electronic structure through a defect engineering strategy. As an electrocatalyst for HER, the optimized Co-WS₂/P-WO_2.9 exhibits a low overpotential at 10 mA cm^-2 of 146 and 120 mV with small Tafel slopes of 86 and 74 mV dec^-1 in alkaline and acidic electrolyte, respectively. In addition, a Co-WS₂/P-WO_2.9 assembled solar cell yields a short circuit current density of 15.85 mA cm^-2, an open-circuit voltage of 0.74 V, a fill factor of 0.66, and a competitive power conversion efficiency (7.83%), which is comparable or higher than conventional Pt-based solar cell (16.02 mA cm^-2, 0.70 V, 0.63, 7.14%). The formation of a heterostructure in Co-WS₂/P-WO_2.9 leads to the presence of a built-in electric field in the interfacial region between Co-WS₂ and P-WO_2.9, which leads to an increased open-circuit voltage from 0.70 V for Pt to 0.74 V for Co-WS₂/P-WO_2.9. This work can provide a technical support for developing high-performance heterostructured catalysts, which open up a way for improving catalytic performance of heterostructured catalysts in the field of electrocatalysis.

A tin porphyrin axially-coordinated two-dimensional covalent organic polymer for efficient hydrogen evolution

Herein, we demonstrate a facile strategy for constructing an efficient and stable hydrogen evolution reaction (HER) catalyst, i.e. a tin porphyrin axially-coordinated 2D covalent organic polymer (SnTPPCOP). SnTPPCOP exhibits promising HER activity with a low overpotential of 147 mV at 10 mA cm^-2 due to its unique structural properties, ranking among the best records reported recently.

Copper dendrite stabilized NiFe(OH)x electrocatalyst for durable alkaline hydrogen evolution over 1000 h

Durable Cu/NiFe(OH)_x electrocatalyst was designed for hydrogen evolution reaction in alkaline media. The in situ generated Cu nanodendrites protect the NiFe(OH)_x from being hydrogenated, giving it a > 1000 h lifetime for high-performance water splitting (1.51 V, 10 mA cm^-2 in 1 M KOH) when coupled with a NiFe-layered double hydroxide anode.

Dual-doping in the bulk and the surface to ameliorate the hematite anode for photoelectrochemical water oxidation

Aiming at the drawbacks of hematite like poor conductivity and tardy oxidation kinetics, herein, we utilized dual dopants in the bulk and surface to ameliorate the situation. Specifically, doping optimal amount of Zr⁴⁺ in the hematite (Zr:Fe₂O₃) enhances the conductivity of hematite due to the higher charge carrier density. Further, F:FeOOH could form p-n heterojunction in bulk where a potential barrier is built up that repels electrons but prompts holes transferring to F:FeOOH for water oxidation. What's more, the high electronegative of F^- would withdraw electron from the Fe site in FeOOH, and the enhanced positive electricity of Fe³⁺ is beneficial for adsorption of OH^- as well as enhance the conductivity of FeOOH to expedite holes transfer. As a result, the composite photoanode (F:FeOOH/Zr:Fe₂O₃) shows a 3.25-times enhanced photocurrent density comparing with α-Fe₂O₃. The special designation employs ultrathin F:FeOOH to act as both p-type semiconductor and efficient co-catalyst, avoiding redundant layer that would extend the migration distance of holes. On the top of that, the dual modification approach provides an extensive prospect for the further application of hematite.

Unveiling the advantages of an ultrathin N-doped carbon shell on self-supported tungsten phosphide nanowire arrays for the hydrogen evolution reaction experimentally and theoretically

Packaging electrocatalysts with carbon shells offers an opportunity to develop stable and effective hydrogen evolution reaction (HER) materials. Here, an ultrathin N-doped carbon-coated self-supported WP nanowire array (WP@NC NA) hybrid has been synthesized. Owing to the encapsulation of the ultrathin N-doped carbon shell on the WP surface, the as-prepared WP@NC NA hybrid exhibits enhanced physicochemical stability, more active sites, and superior conductivity compared with WP NA without carbon coating. Besides, density functional theory calculations demonstrate that the carbon shell can optimize the hydrogen adsorption step in the acidic HER, and simultaneously facilitate water physical adsorption, water dissociation, and hydroxyl group desorption steps during the alkaline HER. These findings demonstrate the intrinsic mechanism of how a carbon shell promotes the acidic and alkaline HER kinetics, and provide scientific guidance for the packaging design of promising carbon-encapsulating self-supported electrocatalysts.

Metal nitride-based nanostructures for electrochemical and photocatalytic hydrogen production

The over-dependence on fossil fuels is one of the critical issues to be addressed for combating greenhouse gas emissions. Hydrogen, one of the promising alternatives to fossil fuels, is renewable, carbon-free, and non-polluting gas. The complete utilization of hydrogen in every sector ranging from small to large scale could hugely benefit in mitigating climate change. One of the key aspects of the hydrogen sector is its production via cost-effective and safe ways. Electrolysis and photocatalysis are well-known processes for hydrogen production and their efficiency relies on electrocatalysts, which are generally noble metals. The usage of noble metals as catalysts makes these processes costly and their scarcity is also a limiting factor. Metal nitrides and their porous counterparts have drawn considerable attention from researchers due to their good promise for hydrogen production. Their properties such as active metal centres, nitrogen functionalities, and porous features such as surface area, pore-volume, and tunable pore size could play an important role in electrochemical and photocatalytic hydrogen production. This review focuses on the recent developments in metal nitrides from their synthesis methods point of view. Much attention is given to the emergence of new synthesis techniques, methods, and processes of synthesizing the metal nitride nanostructures. The applications of electrochemical and photocatalytic hydrogen production are summarized. Overall, this review will provide useful information to researchers working in the field of metal nitrides and their application for hydrogen production.

Synergistic mechanism of Ni(OH)2/NiMoS heterostructure electrocatalyst with crystalline/amorphous interfaces for efficient hydrogen evolution over all pH ranges

Designing and fabricating efficient electrocatalysts is a practical step toward the commercial application of the efficient hydrogen evolution reaction (HER) over all pH ranges. Herein, novel Ti@Ni(OH)₂-NiMoS heterostructure with interface between crystalline Ni(OH)₂ and amorphous NiMoS was rationally designed and fabricated on Ti mesh (denoted as Ti@Ni(OH)₂-NiMoS). Acid etching and calcination experiments helped in accurate elucidation of the synergistic mechanism as well as the vital role on crystalline Ni(OH)₂ and amorphous NiMoS. In acidic solutions, the HER performance of Ti@Ni(OH)₂-NiMoS was mainly attributed to the amorphous NiMoS. In neutral, alkaline, and natural seawater solutions, the HER performance was mainly determined by the synergistic interface behaviors between the Ni(OH)₂ and NiMoS. The crystalline Ni(OH)₂ accelerated water dissociation kinetics, while the amorphous NiMoS provided abundant active sites and allowed for fast electron transfer rates. To deliver current densities of 10 mA·cm^-2 in acidic, neutral, alkaline, and natural seawater solutions, the Ti@Ni(OH)₂-NiMoS required overpotentials of 138, 198, 180 and 371 mV, respectively. This paper provides general guidelines for designing efficient electrocatalyst with crystalline/amorphous interfaces for efficient hydrogen evolution over all-pH ranges.

Ni3N/Co4N nanosheet heterojunction electrocatalyst for hydrogen evolution reaction in alkaline fresh water/simulated seawater

The Ni3N/Co4N nanosheet heterojunction exhibits higher HER activity in alkaline fresh water and simulated seawater.

Synergistic effect between 1D Co3S4/MoS2 heterostructures to boost the performance for alkaline overall water splitting

Reasonably designing and constructing the hetero-bimetal sulfides with high performance for oxygen/hydrogen evolution reaction (O/HER) in the alkaline electrolyte are promising but still challenging. Herein, the 1D Co3S4/MoS2 bimetallic sulfide...

Rapid Surface Reconstruction of Amorphous Co(OH)2 /WOx with Rich Oxygen Vacancies to Promote Oxygen Evolution

Herein, a transition metal dissolution-oxygen vacancy strategy, based on dissolution of highly oxidized transition metal species in alkaline electrolyte, was suggested to construct a high-performance amorphous Co(OH)₂ /WO_x (a-CoW) catalyst for the oxygen evolution reaction (OER). The surface reconstruction of a-CoW and its evolution were described by regulating oxygen vacancies. With continuous dissolution of W species, oxygen vacancies on the surface were generated rapidly, the surface reconstruction was promoted, and the OER performance was improved significantly. During the surface reconstruction, W species also played a role in electronic modulation for Co. Due to its rapid surface reconstruction, a-CoW exhibited excellent OER performance in alkaline electrolyte with an overpotential of 208 mV at 10 mA cm^-2 and had long-term stability for at least 120 h. This work shows that the transition metal dissolution-oxygen vacancy strategy is effective for preparation of high-performance catalysts.

Ce-Doped Ni-S nanosheets on Ni foam supported NiMoO4 micropillars: fast electrodeposition, improved electrocatalytic activity and ultralong durability for the oxygen evolution reaction in various electrolytes

Developing active, durable, and inexpensive electrocatalysts for the oxygen evolution reaction (OER) is drawing increased interest. Here, a mild hydrothermal-electrodeposition two-step route is designed for the preparation of Ce-doped Ni-S@NiMoO₄ micropillar composites on nickel foam (CeNiS@NiMoO₄/NF). The as-constructed CeNiS@NiMoO₄/NF electrode shows an ultralow overpotential, fast kinetics, superb intrinsic activity and excellent long-term stability for the OER. In 1 M KOH solution, 187 mV overpotential is required to deliver a current density of 10 mA cm^-2 with a Tafel slope of 35.28 mV dec^-1, and in a saline-alkaline solution of 1 M KOH and 0.5 M NaCl, only 260 mV overpotential is needed to reach 100 mA cm^-2, demonstrating its excellent OER performance. The above outstanding electrocatalytic activity is attributed to the influence of CeNiS nanosheets on the surface microstructure of NiMoO₄ micropillars, which not only improves the conductivity of the catalyst, but also increases the surface area, as well as accelerates the escape of gases produced. Compared with other non-precious metal OER electrocatalysts, the as-prepared CeNiS@NiMoO₄/NF presents stronger or close electrocatalytic activity and better durability, which provides a new electrocatalyst selection in practical applications.

Constructing urchin-like Ni3S2@Ni3B on Ni plate as a highly efficient bifunctional electrocatalyst for water splitting reaction

Developing efficient and promising non-noble catalysts that can promote both the HER and OER in the same electrolyte is vital. Currently, these reported bifunctional catalysts show only moderate electrocatalytic water-splitting performance, which is much lower than expected. In addition, most of these promising nonprecious electrocatalysts work well only at small current densities (e.g. 10 mA cm^-1), but at large current densities their stability and activity are far from satisfactory for practical applications. Herein, we have successfully constructed an urchin-like Ni₃S₂@Ni₃B heterostructure electrocatalyst on Ni plates. The resulting material exhibits great catalytic activities for both the HER and OER, even at large current densities, reaching a current density of 1000 mA cm^-l at relatively low applied overpotentials of 517 and 632 mV, respectively. The excellent catalytic performance of Ni₃S₂@Ni₃B/NP is found to benefit from the effective integration of the unique surface structure and the interface electronic structure.

Hierarchical FeO(OH)-CoCeV (Oxy)hydroxide as a Water Cleavage Promoter

The search for a bifunctional electrocatalyst having water cleavage promoting ability along with the operational stability to efficiently generate oxygen and hydrogen could lead to robust systems for applications. These fundamental ideas can be achieved by designing the morphology, tuning the electronic structure, and using dopants in their higher oxidation states. Herein, we have fabricated a binder-free FeO(OH)-CoCeV-layered triple hydroxide (LTH) bifunctional catalyst by a two-step hydrothermal method, in which the nanograin-shaped FeO(OH) coupled with CoCeV-LTH nanoflakes provides more electrocatalytically active sites and enhances the charge-transfer kinetics for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The composition-optimized electrocatalyst (FeO(OH)-Co_0.5Ce_0.05V_0.15-LTH) acts as an efficient water cleavage composite by virtue of its favorable oxidation states leading to cyclic redox couples, which yields an overpotential of 53 mV for HER and 227 mV for OER to drive 10 mA/cm² current density in 1 M KOH with a corresponding Tafel slope of 70 mV/dec for HER and 52 mV/dec for OER. Furthermore, for the overall water splitting reaction, the heterostructure FeO(OH)-Co_0.5Ce_0.05V_0.15-LTH acts as a dual-functional electrocatalyst, which requires a cell voltage of 1.52 V versus RHE to drive 10 mA/cm² current density.

Synergistic Interfacial and Doping Engineering of Heterostructured NiCo(OH)x-CoyW as an Efficient Alkaline Hydrogen Evolution Electrocatalyst

To achieve high efficiency of water electrolysis to produce hydrogen (H₂), developing non-noble metal-based catalysts with considerable performance have been considered as a crucial strategy, which is correlated with both the interphase properties and multi-metal synergistic effects. Herein, as a proof of concept, a delicate NiCo(OH)_x-Co_yW catalyst with a bush-like heterostructure was realized via gas-template-assisted electrodeposition, followed by an electrochemical etching-growth process, which ensured a high active area and fast gas release kinetics for a superior hydrogen evolution reaction, with an overpotential of 21 and 139 mV at 10 and 500 mA cm^-2, respectively. Physical and electrochemical analyses demonstrated that the synergistic effect of the NiCo(OH)_x/Co_yW heterogeneous interface resulted in favorable electron redistribution and faster electron transfer efficiency. The amorphous NiCo(OH)_x strengthened the water dissociation step, and metal phase of CoW provided sufficient sites for moderate H immediate adsorption/H₂ desorption. In addition, NiCo(OH)_x-Co_yW exhibited desirable urea oxidation reaction activity for matching H₂ generation with a low voltage of 1.51 V at 50 mA cm^-2. More importantly, the synthesis and testing of the NiCo(OH)_x-Co_yW catalyst in this study were all solar-powered, suggesting a promising environmentally friendly process for practical applications.

Vanadium Substitution Steering Reaction Kinetics Acceleration for Ni3N Nanosheets Endows Exceptionally Energy-Saving Hydrogen Evolution Coupled with Hydrazine Oxidation

Designing highly active transition-metal-based electrocatalysts for energy-saving electrochemical hydrogen evolution coupled with hydrazine oxidation possesses more economic prospects. However, the lack of bifunctional electrocatalysts and the absence of intrinsic structure-property relationship research consisting of adsorption configurations and dehydrogenation behavior of N₂H₄ molecules still hinder the development. Now, a V-doped Ni₃N nanosheet self-supported on Ni foam (V-Ni₃N NS) is reported, which presents excellent bifunctional electrocatalytic performance toward both hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER). The resultant V-Ni₃N NS achieves an ultralow working potential of 2 mV and a small overpotential of 70 mV at 10 mA cm^-2 in alkaline solution for HzOR and HER, respectively. Density functional theory calculations reveal that the vanadium substitution could effectively modulate the electronic structure of Ni₃N, therefore facilitating the adsorption/desorption behavior of H* for HER, as well as boosting the dehydrogenation kinetics for HzOR.