Spin Polarization and Phase Transformation-Aided Efficient Overall Water Splitting Using Ni50Mn18Ga25Cu7 Ferromagnetic Shape Memory Heusler Alloy

We demonstrate experimentally that the combination of half-metallic property and shape memory features of the Ni50Mn18Ga25Cu7 (NMGC) alloy can synergistically catalyze both the oxygen and hydrogen evolution reactions, leading to excellent water splitting. NMGC, a copper-doped nickel-based ferromagnetic shape memory alloy, undergoes first-order martensite to austenite phase transition with temperature variations. The martensite phase of NMGC demonstrates remarkable efficiency for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). With a large current density of 414 ± 3.8 mA/cm2 at 2.9 V, an OER overpotential of only 220 ± 1.7 mV at 20 mA/cm2, and a HER overpotential of 282 ± 2.2 mV at -10 mA/cm2, NMGC (martensite) exhibits superior electrocatalytic performance compared to the austenite phase. Additionally, under a 5000 Oe external magnetic field, NMGC (martensite) shows a significant reduction of 52 mV in OER overpotential and 6 mV for HER, highlighting the promising role of spin and phase in enhancing the water-splitting kinetics.

Trimetallic FeNiCu Atomic Clusters Supported on Carbon Matrix: Highly Active Catalysts for C3H6-SCR of NO

C3H6-SCR denitrification technology faces catalyst deactivation problems and low catalytic performance at medium-low temperatures. This study utilized the intermetallic synergies to prepare atomic cluster catalysts (FeNiCu/NC) by anchoring Fe-Ni-Cu on a carbon matrix to enhance the C3H6-SCR performance at medium-low temperatures. The synergistic effect of the Fe-Ni-Cu is reflected in the differences in the physicochemical properties of the catalysts, which is proved by several characterization techniques. Results showed that the FeNiCu/NC catalyst had a larger surface area (541.4 m2/g) and there were no metal oxides on the surface of the catalyst but abundant defective sites that anchored Fe/Ni/Cu atoms through N atoms to form M-Nx active sites and atomic clusters. The hollow carbon morphology provides sufficient active sites for C3H6-SCR. The coordination environments of active sites were M-Nx-C, Fe2/FeCu2/FeNi2, Ni3/NiFe/NiCu2, and Cu4/CuFe2/CuNi2, where the synergistic action of trimetal leads to the presence of Fe-Ni-Cu-Nx-C. The synergistic action of the Fe-Ni-Cu significantly improved the C3H6-SCR performance at medium-low temperatures. The FeNiCu/NC exhibited an 81% NO conversion at 150 °C under 2% O2, 15% and 20% higher than FeNi/NC and FeCu/NC catalysts, respectively. Even at 4% O2, the FeNiCu/NC catalyst was active to remove 78% NO and achieve a 93% N2 selectivity at 150 °C and maintained a 100% NO conversion at 300-425 °C. The DRIFTS results demonstrated that NO and C3H6 could combine with active O at metal cluster, M-Nx, or defective oxygen sites to produce various intermediate species, wherein acetates and nitrates were the main active intermediates. Based on the DRIFTS results, a reaction pathway for C3H6-SCR over the FeNiCu/NC catalyst was proposed.

Carbon encapsulated nanoparticles: materials science and energy applications

The technological implementation of electrochemical energy conversion and storage necessitates the acquisition of high-performance electrocatalysts and electrodes. Carbon encapsulated nanoparticles have emerged as an exciting option owing to their unique advantages that strike a high-level activity-stability balance. Ever-growing attention to this unique type of material is partly attributed to the straightforward rationale of carbonizing ubiquitous organic species under energetic conditions. In addition, on-demand precursors pave the way for not only introducing dopants and surface functional groups into the carbon shell but also generating diverse metal-based nanoparticle cores. By controlling the synthetic parameters, both the carbon shell and the metallic core are facilely engineered in terms of structure, composition, and dimensions. Apart from multiple easy-to-understand superiorities, such as improved agglomeration, corrosion, oxidation, and pulverization resistance and charge conduction, afforded by the carbon encapsulation, potential core-shell synergistic interactions lead to the fine-tuning of the electronic structures of both components. These features collectively contribute to the emerging energy applications of these nanostructures as novel electrocatalysts and electrodes. Thus, a systematic and comprehensive review is urgently needed to summarize recent advancements and stimulate further efforts in this rapidly evolving research field.

N-Doped Carbon Modified (NixFe1-x)Se Supported on Vertical Graphene toward Efficient and Stable OER Performance

NiFe-based nanomaterials are extensively studied as one of the promising candidates for the oxygen evolution reaction (OER). However, their practical application is still largely impeded by the unsatisfied activity and poor durability caused by the severe leaching of active species. Herein, a rapid and facile combustion method is developed to synthesize the vertical graphene (VG) supported N-doped carbon modified (NixFe1-x)Se composites (NC@(NixFe1-x)Se/VG). The interconnected heterostructure of obtained materials plays a vital role in boosting the catalytic performance, offering rich active sites and convenient pathways for rapid electron and ion transport. The incorporation of Se into NiFe facilitates the formation of active species via in situ surface reconstruction. According to density functional theory (DFT) calculations, the in situ formation of a Ni0.75Fe0.25Se/Ni0.75Fe0.25OOH layer significantly enhances the catalytic activity of NC@(NixFe1-x)Se/VG. Furthermore, the surface-adsorbed selenoxide species contribute to the stabilization of the catalytic active phase and increase the overall stability. The obtained NC@(NixFe1-x)Se/VG exhibits a low overpotential of 220 mV at 20 mA cm-2 and long-term stability over 300 h. This work offers a novel perspective on the design and fabrication of OER electrocatalysts with high activity and stability.

Ce-4f as an electron-modulation reservoir weakening Fe-O bond to induce iron vacancies in CeFevNi hydroxide for enhancing oxygen evolution reaction

Designing novel rare-earth-transition metal composites is at the forefront of electrocatalyst research. However, the modulation of transition metal electronic structures by rare earths to induce vacancy defects and enhance electrochemical performance has rarely been reported. In this study, we systematically investigate the mechanism by which Ce-4f electron modulation weakens the Fe-O bond, thereby altering the electronic structure in CeFevNi hydroxide to improve oxygen evolution reaction (OER) performance. Theoretical calculations and experimental characterizations reveal that Ce-4f orbitals function as electron-modulation reservoirs, capable not only of retaining or donating electrons but also of influencing the material's electronic structure. Moreover, Ce-4f bands optimize the Fe lower Hubbard bands (LHB) and O-2p bands, leading to weakened Fe-O bonds and the formation of cationic vacancies. This change results in the upshift of the d-band center at the active sites, favoring the reaction energy barrier for oxygen intermediates in the OER process. The synthesized catalyst demonstrated an overpotential of 201 mV at 10 mA cm-2 and a lifetime exceeding 200 h at 100 mA cm-2 under alkaline conditions. This work offers a proof-of-concept for the application of the mechanism of rare earth-induced transition metal vacancy defects, providing a general guideline for the design and development of novel highly efficient catalysts.

In-situ construction of iron-modified nickel nanoparticles assisted by hexamethylenetetramine with the internal and external collaboration for highly selective electrocatalytic carbon dioxide reduction

Carbon dioxide (CO2) electroreduction provides a sustainable route for realizing carbon neutrality and energy supply. Up to now, challenges remain in employing abundant and inexpensive nickel materials as candidates for CO2 reduction due to their low activity and favorable hydrogen evolution. Here, the representative iron-modified nickel nanoparticles embedded in nitrogen-doped carbon (Ni1-Fe0.125-NC) with the porous botryoid morphology were successfully developed. Hexamethylenetetramine is used as nitrogen-doped carbon source. The collaboration of internal lattice expansion with electron effect and external confinement effect with size effect endows the significant enhancement in electrocatalytic CO2 reduction. The optimized Ni1-Fe0.125-NC exhibits broad potential ranges for continuous carbon monoxide (CO) production. A superb CO Faradaic efficiency (FECO) of 85.0 % realized at -1.1 V maintains a longtime durability over 35 h, which exceeds many state-of-the-art metal catalysts. Theoretical calculations further confirm that electron redistribution promotes the desorption of CO in the process for favorable CO production. This work opens a new avenue to design efficient nickel-based materials by considering the intrinsic structure and external confinement for CO2 reduction.

Polyoxometalate-incorporated NiFe-based oxyhydroxides for enhanced oxygen evolution reaction in alkaline media

NiFe-based oxyhydroxides are promising electrocatalysts for the oxygen evolution reaction (OER) in alkaline media, but further enhancing their OER performance remains a significant challenge. Herein, we in situ incorporated polyoxometalates into NiFe oxyhydroxides to form a homogeneous/heterogeneous hybrid material, which induces the electronic interaction between Ni, Fe and Mo sites, as revealed by a variety of characterization experiments and theoretical calculations. The resulting hybrid electrocatalyst delivers a low overpotential of 203 mV at 10 mA cm-2 and a TOF of 2.34 s-1 at 1.53 V in alkaline media. This work presents a critical step towards developing high-performance OER catalysts by constructing metal-POM hybrids.

General and Facile Synthesis of Co/CoO Nanoparticals Supported by Nitrogen-Doped Graphenic Networks as Efficient Oxygen Electrocatalyst for Zn-Air Batteries

Reasonable design of low-cost, high-efficiency and stable bifunctional oxygen electrocatalysts is of great significance to improve the reaction efficiency of Zn-air batteries, which is still a huge challenge. Here, we report a highly efficient bifunctional oxygen electrocatalyst with three-dimensional (3D) N-doped graphene network-supported cobalt and cobalt oxide nanoparticles (Co/CoO-NG), which can be in situ synthesized by inducing metal ions on metal plates via graphene oxide as an inducer. This 3D network structure and open active center show excellent bifunctional oxygen electrocatalytic activity under alkaline conditions, and can be used as an air electrode in rechargeable Zn-air batteries, with significantly better power density (244.28 mW cm-2) and stability (over 340 h) than commercial Pt/C+RuO2 mixtures. This work is conducive to advancing the practical application of graphene-based materials as air electrodes for rechargeable zinc-air batteries.

Electron regulation of CeO2 on CoP multi-shell hetero-junction micro-sphere towards highly efficient water oxidation

CeO2 has been identified as a significant cocatalyst to enhance the electrocatalytic activity of transition metal phosphides (TMPs). However, the electrocatalytic mechanism by which CeO2 enhances the catalytic activity of TMP remains unclear. In this study, we have successfully developed a unique CeO2-CoP-1-4 multishell microsphere heterostructure catalyst through a simple hydrothermal and calcination process. CeO2-CoP-1-4 exhibits great potential for electrocatalytic oxygen evolution reaction (OER), requiring only an overpotential of 254 mV to achieve a current density of 10 mA cm-2. Moreover, CeO2-CoP-1-4 demonstrates excellent operating durability lasting for 55 h. The presence of CeO2 as a cocatalyst can regulate the microsphere structure of CoP, the resulting multishell microsphere structure can shorten the mass transfer distance, and improve the utilization rate of the active site. Furthermore, in situ Raman and ex situ characterizations, and DFT theoretical calculation results reveal that CeO2 can effectively regulates the electronic structure of Co species, reduces the reaction free energy of rate-limiting step, thus increase the reaction kinetic. Overall, this study provides experimental and theoretical evidence to better comprehend the mechanism and structure evolution of CeO2 in enhancing the OER performance of CoP, offering a unique design inspiration for the development of efficient hollow heterojunction electrocatalysts.

Site-Selective Growth of fcc-2H-fcc Copper on Unconventional Phase Metal Nanomaterials for Highly Efficient Tandem CO2 Electroreduction

Copper (Cu) nanomaterials are a unique kind of electrocatalysts for high-value multi-carbon production in carbon dioxide reduction reaction (CO2RR), which holds enormous potential in attaining carbon neutrality. However, phase engineering of Cu nanomaterials remains challenging, especially for the construction of unconventional phase Cu-based asymmetric heteronanostructures. Here the site-selective growth of Cu on unusual phase gold (Au) nanorods, obtaining three kinds of heterophase fcc-2H-fcc Au-Cu heteronanostructures is reported. Significantly, the resultant fcc-2H-fcc Au-Cu Janus nanostructures (JNSs) break the symmetric growth mode of Cu on Au. In electrocatalytic CO2RR, the fcc-2H-fcc Au-Cu JNSs exhibit excellent performance in both H-type and flow cells, with Faradaic efficiencies of 55.5% and 84.3% for ethylene and multi-carbon products, respectively. In situ characterizations and theoretical calculations reveal the co-exposure of 2H-Au and 2H-Cu domains in Au-Cu JNSs diversifies the CO* adsorption configurations and promotes the CO* spillover and subsequent C-C coupling toward ethylene generation with reduced energy barriers.

Active Sites of Mixed-Metal Core-Shell Oxygen Evolution Reaction Catalysts: FeO4 Sites on Ni Cores or NiN4 Sites in C Shells?

Water electrolysis for clean hydrogen production requires high-activity, high-stability, and low-cost catalysts for its particularly sluggish half-reaction, the oxygen evolution reaction (OER). Currently, the most promising of such catalysts working in alkaline conditions is a core-shell nanostructure, NiFe@NC, whose Fe-doped Ni (NiFe) nanoparticles are encapsulated and interconnected by N-doped graphitic carbon (NC) layers, but the exact OER mechanism of these catalysts is still unclear, and even the location of the OER active site, either on the core side or on the shell side, is still debated. Therefore, we herein derive a plausible active-site model for each side based on various experimental evidence and density functional theory calculations and then build OER free-energy diagrams on both sides to determine the active-site location. The core-side model is an FeO4-type (rather than NiO4-type) active site where an Fe atom sits on Ni oxide layers grown on top of the core surface during catalyst activation, whose facile dissolution provides an explanation for the activity loss of such catalysts directly exposed to the electrolyte. The shell-side model is a NiN4-type (rather than FeN4-type) active site where a Ni atom is intercalated into the porphyrin-like N4C site of the NC shell during catalyst synthesis. Their OER free-energy diagrams indicate that both sites require similar amounts of overpotentials, despite a complete shift in their potential-determining steps, i.e., the final O2 evolution from the oxophilic Fe on the core and the initial OH adsorption to the hydrophobic shell. We conclude that the major active sites are located on the core, but the NC shell not only protects the vulnerable FeO4 active sites on the core from the electrolyte but also provides independent active sites, owing to the N doping.

Amorphous conversion in pyrolytic symmetric trinuclear nickel clusters trigger trifunctional electrocatalysts

The pursuit of multifunctional electrocatalysts holds significant importance due to their comprehension of material chemistry. Amorphous materials are particularly appealing, yet they pose challenges in terms of rational design due to their structural disorder and thermal instability. Herein, we propose a strategy that entails the tandem (low-temperature/250-350 °C) pyrolysis of molecular clusters, enabling preservation of the local short-range structures of the precursor Schiff base nickel (Ni3[2(C21H24N3Ni1.5O6)]). The temperature-dependent residuals demonstrate exceptional activity and stability for at least three distinct electrocatalytic processes, including the oxygen evolution reaction (η10 = 197 mV), urea oxidation reaction (η10 = 1.339 V), and methanol oxidation reaction (1358 mA cm-2 at 0.56 V). Three distinct nickel atom motifs are discovered for three efficient electrocatalytic reactions (Ni1 and Ni1' are preferred for UOR/MOR, while Ni2 is preferred for OER). Our discoveries pave the way for the potential development of multifunctional electrocatalysts through disordered engineering in molecular clusters under tandem pyrolysis.

Mn-doped Sequentially Electrodeposited Co-based Oxygen Evolution Catalyst for Efficient Anion Exchange Membrane Water Electrolysis

Designing high-performance and durable oxygen evolution reaction (OER) catalysts is important for green hydrogen production through anion exchange membrane water electrolysis (AEMWE). Herein, a series of Mn-doped Co-based OER catalysts supported on FeOxHy (FCMx) are presented to enhance the OER activity. Mn doping effectively reduces the size of the Co oxide particles, thereby augmenting the active surface area. Moreover, Mn doping induces the creation of oxygen vacancies, leading to an efficient structural conversion during the OER, which is confirmed via in situ Raman spectroscopy. Under optimal conditions, the catalyst exhibits an overpotential of 234.4 mV at 10 mA cm-2 and a Tafel slope of 37.2 mV dec-1 under half-cell conditions. The AEMWE single-cell system demonstrates a current density of 1560 mA cm-2 at 1.8 V at 60 °C with a degradation rate of 0.4 mV h-1 for 500 h at 500 mA cm-2. Our development of a robust OER catalyst represents notable progress in the field of nonprecious-metal water electrolysis, marking a step toward cost-effective green hydrogen production.

Phase control of solid-solution RuIn nanoparticles and their catalytic properties

The properties of solids could be largely affected by their crystal structures. We achieved, for the first time, the phase control of solid-solution RuIn nanoparticles (NPs) from face-centred cubic (fcc) to hexagonal close-packed (hcp) crystal structures by hydrogen heat treatment. The effect of the crystal structure of RuIn alloy NPs on the catalytic performance in the hydrogen evolution reaction (HER) was also investigated. In the hcp RuIn NPs, enhanced HER catalytic performance was observed compared to the fcc RuIn NPs and monometallic Ru NPs. The intrinsic electronic structures of the NPs were investigated by valence-band X-ray photoelectron spectroscopy (VB-XPS). The d-band centre of hcp RuIn NPs obtained from VB-XPS was deeper than that of fcc RuIn NPs and monometallic Ru NPs, which is considered to enable the hcp RuIn NPs to exhibit enhanced HER catalytic performance.

FeNi supported on carbon sponge for efficient urea oxidation in direct urea fuel cell

The direct urea fuel cell (DUFC) is a power generation equipment with urea-rich wastewater or urine as fuel source. It has the unique ability to purify sewage while simultaneously generating electricity, making it a highly efficient and environmentally friendly option. In this paper, pomegranate seed-like Ni nano-blocks and Fe nanosheets were synthesized by electrodeposition and chemical reduction and attached to the carbonized melamine sponge matrix. The N-doped carbon sponge (NCS) provided a large number of polyhedral holes, which allowed for efficient gas escape through channels. The combination of Fe reduces the initial urea oxidation potential, reaction activation energy and reaction resistance. The synthesized FeNi supported on N-doped carbon sponge composite (FeNi@NCS) has a catalytic current density of 625 mA cm-2 and a Tafel slope of 42.51 mV dec-1 for urea electrooxidation reaction (UOR). Assembling the direct urine-hydrogen peroxide fuel cell (DUrHPFC) resulted in the highest performance output. The open circuit voltage (OCV) was 0.98 V, and the peak power density reached 9.61 mW cm-2. The results show that the prepared catalyst provides an opportunity to solve the problems that hinder the development of urea green cycle at present.

Ruthenium and Iron Co-doped Molybdenum Carbide as a Stable Hydrogen Evolution Electrocatalyst in Harsh Electrolyte

Electrocatalytic water splitting is one of the most commercially valuable pathways of hydrogen production especially combined with renewable electricity; however, efficient and durable electrocatalysts are urgently needed to reduce electric energy consumption. Here, we reported a Ru and Fe co-doped Mo2 C on nitrogen doped carbon via a controllable two-step method, which can be used for efficient and enduring hydrogen evolution reaction. At 10, 100 and 200 mA cm-2 in acidic electrolyte, the resultant Ru-Fe/Mo2 C@NC delivered low overpotentials of 31, 78 and 103 mV, respectively, which are comparable to that of the commercial Pt/C (20 wt %). At an applied current density of 100 mA cm-2 , stable hydrogen production was conducted for 120 h without obvious degradation. In alkaline media, Ru-Fe/Mo2 C@NC can also deliver a current density of 100 mA cm-2 for more than 100 h. Furthermore, the Ru-Fe/Mo2 C@NC electrocatalyst was used as cathode in an anion exchange membrane water electrolyzer under industrial environments for robust hydrogen production. The characterization and electrochemical results prove the synergism effects between Ru, Fe dopants and Mo2 C for promoting hydrogen evolution activity. This work would pave a new avenue to fabricate low-cost, high-performance hydrogen evolution electrocatalysts for industrial water electrolyzers.

Optimizing Pt-Based Alloy Electrocatalysts for Improved Hydrogen Evolution Performance in Alkaline Electrolytes: A Comprehensive Review

The splitting of water through electrocatalysis offers a sustainable method for the production of hydrogen. In alkaline electrolytes, the lack of protons forces water dissociation to occur before the hydrogen evolution reaction (HER). While pure Pt is the gold standard electrocatalyst in acidic electrolytes, since the 5d orbital in Pt is nearly fully occupied, when it overlaps with the molecular orbital of water, it generates a Pauli repulsion. As a result, the formation of a Pt-H* bond in an alkaline environment is difficult, which slows the HER and negates the benefits of using a pure Pt catalyst. To overcome this limitation, Pt can be alloyed with transition metals, such as Fe, Co, and Ni. This approach has the potential not only to enhance the performance but also to increase the Pt dispersion and decrease its usage, thus overall improving the catalyst's cost-effectiveness. The excellent water adsorption and dissociation ability of transition metals contributes to the generation of a proton-rich local environment near the Pt-based alloy that promotes HER. Significant progress has been achieved in comprehending the alkaline HER mechanism through the manipulation of the structure and composition of electrocatalysts based on the Pt alloy. The objective of this review is to analyze and condense the latest developments in the production of Pt-based alloy electrocatalysts for alkaline HER. It focuses on the modified performance of Pt-based alloys and clarifies the design principles and catalytic mechanism of the catalysts from both an experimental and theoretical perspective. This review also highlights some of the difficulties encountered during the HER and the opportunities for increasing the HER performance. Finally, guidance for the development of more efficient Pt-based alloy electrocatalysts is provided.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Pyrolysis-catalysis upcycling of waste plastic using a multilayer stainless-steel catalyst toward a circular economy

Current un-sustainable plastic management is exacerbating plastic pollution, an urgent shift is thus needed to create a recycling society. Such recovering carbon (C) and hydrogen (H) from waste plastic has been considered as one practical route to achieve a circular economy. Here, we performed a simple pyrolysis-catalysis deconstruction of waste plastic via a monolithic multilayer stainless-steel mesh catalyst to produce multiwalled carbon nanotubes (MWCNTs) and H2, which are important carbon material and energy carrier to achieve sustainable development. Results revealed that the C and H recovery efficiencies were as high as 86% and 70%, respectively. The unique oxidation-reduction process and improvement of surface roughness led to efficient exposure of active sites, which increased MWCNTs by suppressing macromolecule hydrocarbons. The C recovery efficiency declined by only 5% after 10 cycles, proving the long-term employment of the catalyst. This catalyst can efficiently convert aromatics to MWCNTs by the vapor-solid-solid mechanism and demonstrate good universality in processing different kinds of waste plastics. The produced MWCNTs showed potential in applications of lithium-ion batteries and telecommunication. Owing to the economic profits and environmental benefits of the developed route, we highlighted its potential as a promising alternative to conventional incineration, simultaneously achieving the waste-to-resource strategy and circular economy.

Highly Durable and Efficient Seawater Electrolysis Enabled by Defective Graphene-Confined Nanoreactor

Direct seawater electrolysis is a promising technology for massive green hydrogen production but is limited by the lack of durable and efficient electrocatalysts toward the oxygen evolution reaction (OER). Herein, we develop a core-shell nanoreactor as a high-performance OER catalyst consisting of NiFe alloys encapsulated within defective graphene layers (NiFe@DG) by a facile microwave shocking strategy. This catalyst needs overpotentials of merely 218 and 276 mV in alkalized seawater to deliver current densities of 10 and 100 mA cm-2, respectively, and operates continuously for 2000 h with negligible activity decay (1.0%), making it one of the best OER catalysts reported to date. Detailed experimental and theoretical analyses reveal that the excellent durability of NiFe@DG originates from the formation of the built-in electric field triggered by the defective graphene coating against chloride ions at the electrode/electrolyte interface, thus protecting the active NiFe alloys at the core from dissolution and aggregation under harsh operation conditions. Further, a highly stable and efficient seawater electrolyzer is assembled with the NiFe@DG anode and the Pt/C cathode to demonstrate the practicability of the catalysts.

Lattice-Strain Engineering for Heterogenous Electrocatalytic Oxygen Evolution Reaction

The energy efficiency of metal-air batteries and water-splitting techniques is severely constrained by multiple electronic transfers in the heterogenous oxygen evolution reaction (OER), and the high overpotential induced by the sluggish kinetics has become an uppermost scientific challenge. Numerous attempts are devoted to enabling high activity, selectivity, and stability via tailoring the surface physicochemical properties of nanocatalysts. Lattice-strain engineering as a cutting-edge method for tuning the electronic and geometric configuration of metal sites plays a pivotal role in regulating the interaction of catalytic surfaces with adsorbate molecules. By defining the d-band center as a descriptor of the structure-activity relationship, the individual contribution of strain effects within state-of-the-art electrocatalysts can be systematically elucidated in the OER optimization mechanism. In this review, the fundamentals of the OER and the advancements of strain-catalysts are showcased and the innovative trigger strategies are enumerated, with particular emphasis on the feedback mechanism between the precise regulation of lattice-strain and optimal activity. Subsequently, the modulation of electrocatalysts with various attributes is categorized and the impediments encountered in the practicalization of strained effect are discussed, ending with an outlook on future research directions for this burgeoning field.

Toward the Long-Term Stability of Cobalt Benzoate Confined Highly Dispersed PtCo Alloy Supported on a Nitrogen-Doped Carbon Nanosheet/Fe3C Nanoparticle Hybrid as a Multifunctional Catalyst for Zinc-Air Batteries

This work reports a new type of platinum-based heterostructural electrode catalyst that highly dispersed PtCo alloy nanoparticles (NPs) confined in cobalt benzoate (Co-BA) nanowires are supported on a nitrogen-doped ultra-thin carbon nanosheet/Fe₃C hybrid (PtCo@Co-BA-Fe₃C/NC) to show high electrochemical activity and long-term stability. One-dimensional Co-BA nanowires could alleviate the shedding and agglomeration of PtCo alloy NPs during the reaction so as to achieve satisfactory long-term durability. Moreover, the synergistic effect at the interface optimizes the surface electronic structure and prominently accelerates the electrochemical kinetics. The oxygen reduction reaction half-wave potential is 0.923 V, and the oxygen evolution reaction under the condition of 10 mA•cm^-2 is 1.48 V. Higher power density (263.12 mW•cm^-2), narrowed voltage gap (0.49 V), and specific capacity (808.5 mAh•g^-1) for PtCo@Co-BA-Fe₃C/NC in Zn-air batteries are achieved with long-term cycling measurements over 776 h, which is obviously better than the Pt/C + RuO₂ catalyst. The interfacial electronic interaction of PtCo@Co-BA-Fe₃C/NC is investigated, which can accelerate electron transfer from Fe to Pt. Density functional theory calculations also indicate that the interfacial potential regulates the binding energies of the intermediates to achieve the best performance.

Prussian blue analog-derived nickel iron phosphide-reduced graphene oxide hybrid as an efficient catalyst for overall water electrolysis

Efficient and bifunctional nonprecious catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are essential for the production of green hydrogen via water electrolysis. Transition metal (Ni, Co, Fe, etc.) phosphides are frequently documented HER catalysts, whereas their bimetallic oxides are efficient OER catalysts, thus enabling bifunctional catalysis for water electrolysis via proper operation. Herein, phosphide-reduced graphene oxide (rGO) hybrids were prepared from graphene oxide (GO)-incorporated bimetal Prussian blue analog (PBA) precursors. The hybrids could experience partial surface oxidation to create oxide layers with OER activities, and the hybrids also possessed considerable HER properties, therefore enabling bifunctional catalytic features for water electrolysis. The typical NiFeP-rGO hybrid demonstrated an overpotential of 250 mV at 10 mA cm^-2 and good durability for OER, as well as moderate HER catalytic features (overpotential of 165 mV at -10 mA cm^-2 and acceptable catalytic stability). Due to the bifunctional catalytic features, the NiFeP-rGO-based symmetric water electrolyzer demonstrated a moderate input voltage and high faradaic efficiency (FE) for O₂ and H₂ production. The current work provides a feasible way to prepare OER and HER bifunctional catalysts by facile phosphorization of PBA-associated precursors and spontaneous surface oxidation. Given the oxidation/reduction bifunctional catalytic behaviors, phosphide-rGO hybrid catalysts have great potential for widespread application in fields beyond water electrolysis, such as electrochemical pollution abatement, sensors, energy devices and organic syntheses.

Graphene-Encapsulated Bifunctional Catalysts with High Activity and Durability for Zn-Air Battery

Carbon-based electrocatalysts with both high activity and high stability are desirable for use in Zn-air batteries. However, the carbon corrosion reaction (CCR) is a critical obstacle in rechargeable Zn-air batteries. In this study, a cost-effective carbon-based novel material is reported with a high catalytic effect and good durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), prepared via a simple graphitization process. In situ growth of graphene is utilized in a 3D-metal-coordinated hydrogel by introducing a catalytic lattice of transition metal alloys. Due to the direct growth of few-layer graphene on the metal alloy decorated 3d-carbon network, greatly reduced CCR is observed in a repetitive OER test. As a result, an efficient bifunctional electrocatalytic performance is achieved with a low ΔE value of 0.63 V and good electrochemical durability for 83 h at a current density of 10 mA cm^-2 in an alkaline media. Moreover, graphene-encapsulated transition metal alloys on the nitrogen-doped carbon supporter exhibit an excellent catalytic effect and good durability in a Zn-air battery system. This study suggests a straightforward way to overcome the CCR of carbon-based materials for an electrochemical catalyst with wide application in energy conversion and energy storage devices.

Unconventional Phase Synergies with Doping Engineering Over Ni Electrocatalyst Featuring Regulated Electronic State for Accelerated Urea Oxidation

Exploring high-performing Ni-based electrocatalysts for the urea oxidation reaction (UOR) is crucial for developing urea-related energy technologies yet remains a daunting challenge. In this study, a synergistic anomalous hcp phase and heteroatom doping engineering over metallic Ni are found to enhance the UOR. A metal-organic framework-mediated approach is proposed to construct Ni nanoparticles (NPs) with designated crystal phase embedded in N-doped carbon (fcc-Ni/NC and hcp-Ni/NC). Significant crystal phase-dependent catalytic activity for the UOR is observed; hcp-Ni/NC, featuring unusual hcp phase, outperforms fcc-Ni/NC with conventional fcc phase. Moreover, incorporating foreign Mn species in hcp-Ni/NC can further dramatically promote UOR, making it among the best UOR catalysts reported to date. From experimental results and DFT calculations, the specific nanoarchitecture, involving an anomalous hcp phase together with Mn doping engineering, endows hcp-MnNi/NC with abundant exposed active sites, facile charge transfer, and more significantly, optimized electronic state, giving rise to enriched Ni³⁺ active species and oxygen vacancies on the catalyst surface during electrocatalysis. These features collectively contribute to the enhanced UOR activity. This work highlights a potent design strategy to develop advanced catalysts with regulated electronic state through synergistic crystal phase and doping engineering.

Metal-organic framework derived FeNi alloy nanoparticles embedded in N-doped porous carbon as high-performance bifunctional air-cathode catalysts for rechargeable zinc-air battery

Developing efficient and durable bifunctional air-cathode catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key efforts promoting the practical rechargeable zinc-air batteries (ZABs). In this paper, high-performance bifunctional air-cathode catalysts by a two-step strategy: atomically dispersed Ni on N-doped carbon is first derived from MOF to form uniformly dispersed NiNC, which are pyrolyzed together with Fe source at different high-temperatures to form FeNi@NC-T (T = 800, 900, and 1000 °C) catalysts. The as-synthesized non-noble metal FeNi@NC-900 catalyst exhibits a considerably small potential gap (ΔE) of 0.72 V between ORR and OER, which is as the same as commercial noble metal Pt/C + Ir black mixed catalyst. The performance of the ZABs using FeNi@NC-900 as the air-cathode catalyst displays a power density of 119 mW·cm^-2 and a specific capacity of 830.1 mAh·g^-1, which is superior to that of Pt/C + Ir black mixed catalyst. This work provides a guideline for designing alloy electrocatalysts with uniform size and nanoparticle distribution for metal-air batteries with bifunctional air-cathodes.

Revealing the Crystal Phase-Activity Relationship on NiRu Alloy Nanoparticles Encapsulated in N-Doped Carbon towards Efficient Hydrogen Evolution Reaction

Adjusting the crystal phase of a metal alloy is an important method to optimize catalytic performance. However, detailed understanding about the phase-property relationship for the hydrogen evolution reaction (HER) is still limited. In this work, the crystal phase-activity relationship of NiRu nanoparticles is studied employing N-doped carbon shell coated NiRu nanoparticles with different phase contents. It is found that the NiRu@NC (mix) with both face-centred cubic (fcc) and thermodynamically unstable hexagonal close-packed (hcp) phase NiRu give the best HER performance. Further activity studies demonstrate that hcp NiRu has better HER performance, and NiRu@NC (mix) with rich (∼70 %) hcp phase presented outstanding performance with an overpotential of only 27 mV @ 10 mA ⋅ cm^-2 . The high HER activity of NiRu@NC (mix) is attributed to the formation of hcp phase. This finding indicates that the regulation of crystal structure can provide a new strategy for optimizing HER activity.

Unique amorphous/crystalline heterophase coupling for an efficient oxygen evolution reaction

Designing amorphous/crystalline heterophase catalysts is still in the initial stage, and the study of amorphous/crystalline heterophase and carbon-free catalysts has not yet been realized. Herein, we report a unique amorphous/crystalline heterophase catalyst consisting of NiFe alloy nanoparticles (NPs) supported on Ti₄O₇ (NiFe/Ti₄O₇) for the first time, which is achieved by a heterophase supporting strategy of dual heat treatment. Surprisingly, the amorphous/crystalline heterophase is flexibly composed of amorphous and crystalline phases of alloy NPs and Ti₄O₇. The heterophase coupling endows the catalyst with a low overpotential (256 mV at 10 mA cm^-2), a small Tafel slope (47 mV dec^-1) and excellent endurance stability (over 100 h) in 1 M KOH electrolyte, which already outperforms commercial RuO₂ (338 mV and 113 mV dec^-1) and exceeds most reported representative carbon-based and titanium-based non-precious metal catalysts. The density functional theory (DFT) calculations and experimental results reveal that the unique amorphous/crystalline heterophase coupling in NiFe/Ti₄O₇ results in electron transfer between the alloy NPs and Ti₄O₇, allowing more catalytically active sites and faster interfacial electron transfer dynamics. This work provides insights into the synthesis of amorphous/crystalline heterophase catalysts and can be generalized to the heterophase coupling of other transition metal-based electrocatalysts.

Mastering the D-Band Center of Iron-Series Metal-Based Electrocatalysts for Enhanced Electrocatalytic Water Splitting

The development of non-noble metal-based electrocatalysts with high performance for hydrogen evolution reaction and oxygen evolution reaction is highly desirable in advancing electrocatalytic water-splitting technology but proves to be challenging. One promising way to improve the catalytic activity is to tailor the d-band center. This approach can facilitate the adsorption of intermediates and promote the formation of active species on surfaces. This review summarizes the role and development of the d-band center of materials based on iron-series metals used in electrocatalytic water splitting. It mainly focuses on the influence of the change in the d-band centers of different composites of iron-based materials on the performance of electrocatalysis. First, the iron-series compounds that are commonly used in electrocatalytic water splitting are summarized. Then, the main factors affecting the electrocatalytic performances of these materials are described. Furthermore, the relationships among the above factors and the d-band centers of materials based on iron-series metals and the d-band center theory are introduced. Finally, conclusions and perspectives on remaining challenges and future directions are given. Such information can be helpful for adjusting the active centers of catalysts and improving electrochemical efficiencies in future works.

Bismuth-nickel bimetal nanosheets with a porous structure for efficient hydrogen production in neutral and alkaline media

Active and durable electrocatalysts are very important for efficient and economically sustainable hydrogen generation via electrocatalytic water splitting. A bismuth-nickel (Bi-Ni) bimetal nanosheet with a mesoporous structure was prepared via a self-template electrochemical in situ process. The Bi-Ni catalyst required overpotentials of 56 mV and 183 mV at 10 mA cm^-2 for the hydrogen evolution reaction (HER), which were close to that of commercial Pt/C in 1.0 M KOH and 1.0 M PBS (pH 7.0), respectively. The electrocatalyst maintained a steady current density during 20 h electrolysis in 1.0 M KOH and 1.0 M PBS (pH 7.0). Density functional theory (DFT) indicated that the alloying effect could induce charge transfer from the Bi atom to Ni atom and thus modulate the d-band centre of Bi-Ni nanosheets, which could efficiently accelerate H* conversion and H₂ desorption at the Ni active site. This promotes the HER kinetics. By adopting the Bi_84.8Ni_15.2 alloy as the cathode to establish a full-cell (IrO₂∥Bi_84.8Ni_15.2) for water splitting in 1.0 M KOH, the required cell voltage was 1.53 V to drive 10 mA cm^-2, which was lower than that of the IrO₂∥Pt/C electrolyzer (1.64 V@10 mA cm^-2).

Tuning Electronic Structure and Composition of FeNi Nanoalloys for Enhanced Oxygen Evolution Electrocatalysis via a General Synthesis Strategy

Developing low-cost and efficient oxygen evolution electrocatalysts is key to decarbonization. A facile, surfactant-free, and gram-level biomass-assisted fast heating and cooling synthesis method is reported for synthesizing a series of carbon-encapsulated dense and uniform FeNi nanoalloys with a single-phase face-centered-cubic solid-solution crystalline structure and an average particle size of sub-5 nm. This method also enables precise control of both size and composition. Electrochemical measurements show that among Fe_x Ni_{(1- x )} nanoalloys, Fe_0.5 Ni_0.5 has the best performance. Density functional theory calculations support the experimental findings and reveal that the optimally positioned d-band center of O-covered Fe_0.5 Ni_0.5 renders a half-filled antibonding state, resulting in moderate binding energies of key reaction intermediates. By increasing the total metal content from 25 to 60 wt%, the 60% Fe_0.5 Ni_0.5 /40% C shows an extraordinarily low overpotential of 219 mV at 10 mA cm^-2 with a small Tafel slope of 23.2 mV dec^-1 for the oxygen evolution reaction, which are much lower than most other FeNi-based electrocatalysts and even the state-of-the-art RuO₂ . It also shows robust durability in an alkaline environment for at least 50 h. The gram-level fast heating and cooling synthesis method is extendable to a wide range of binary, ternary, quaternary nanoalloys, as well as quinary and denary high-entropy-alloy nanoparticles.

Facet and d-band center engineering of CuNi nanocrystals for efficient nitrate electroreduction to ammonia

Electrocatalytic nitrate reduction offers a sustainable route to ammonia synthesis and wastewater treatment. However, the nitrate-to-ammonia conversion remains inefficient due to the sluggish kinetics and diverse side reactions. Herein, well-faceted CuNi nanocrystals with Ni-rich surfaces and favorable d-band centres were synthesized with the assistance of γ-cyclodextrin via a solvothermal process. When used as catalysts for nitrate electroreduction, they delivered an ammonia yield of 1.374 mmol h^-1 mg^-1 (0.5496 mmol h^-1 cm^-2) at -0.3 V with the faradaic efficiency and selectivity reaching 94.5% and 65.0%, respectively, surpassing pure Cu or Ni nanocrystals and most reported catalysts. Such excellent performances originated from the optimal geometric and electronic structures and special element distribution, which optimized the adsorption behaviors and accelerated the reaction kinetics. A NO₃^--NO₂^--NH₃ pathway was proposed with the chemical process following the initial electron transfer process as the rate-determining step. This work sheds light on the design of efficient catalysts to achieve carbon neutrality through simultaneous geometric and electronic structure modulation.

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

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

Bio-derived FeNi alloy confined in N-doped carbon nanosheets as efficient air electrodes for Zn-air battery

It is imperative to design and manufacture electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for popularization of rechargeable Zn-air batteries. Herein, FeNi alloy confined in N-doped carbon nanosheets (FeNi@NCSs) was harvested via a facile complexation-pyrolysis strategy from the mixture of guanine and metal chlorides. After strictly exploring the pyrolysis temperature and metal types, the resulted FeNi@NCSs showed greatly improved performances on both the ORR (onset potential of 0.93 V and half-wave potential of 0.84 V) and OER (overpotential of 318 mV at 10 mA cm^-2 and 379 mV at 100 mA cm^-2). Further, the FeNi@NCSs based Zn-air battery exhibited a higher open circuit voltage (1.496 V), a larger power density (128.8 mW cm^-2), and prominent durability (360 cycles, 120 h). This study provides an appealing approach to utilize biomass for synthesis of low-cost and high-efficiency electrocatalysts in energy associated systems.

Nickel-iron nanoparticles encapsulated in carbon nanotubes prepared from waste plastics for low-temperature solid oxide fuel cells

Low-temperature solid oxide fuel cells (LT-SOFCs) are a promising next-generation fuel cell due to their low cost and rapid start-up, posing a significant challenge to electrode materials with high electrocatalytic activity. Herein, we reported the bimetallic nanoparticles encapsulated in carbon nanotubes (NiFe@CNTs) prepared by carefully controlling catalytic pyrolysis of waste plastics. Results showed that plenty of multi-walled CNTs with outer diameters (14.38 ± 3.84 nm) were observed due to the smallest crystalline size of Ni-Fe alloy nanoparticles. SOFCs with such NiFe@CNTs blended in anode exhibited remarkable performances, reaching a maximum power density of 885 mW cm⁻² at 500°C. This could be attributed to the well-dispersed alloy nanoparticles and high graphitization degree of NiFe@CNTs to improve HOR activity. Our strategy could upcycle waste plastics to produce nanocomposites and demonstrate a high-performance LT-SOFCs system, addressing the challenges of sustainable waste management and guaranteeing global energy safety simultaneously.

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The M@CNTs from the waste plastics were utilized as anode additive of LT-SOFCs

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The effects of active metal species on the quality of nanocomposite were studied

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Maximum power density of 885 mW cm⁻² at 500°C was obtained with NiFe@CNTs

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The excellent performances of SOFCs could be attributed to the improved HOR activity

Supramolecular Gel-Derived Highly Efficient Bifunctional Catalysts for Omnidirectionally Stretchable Zn-Air Batteries with Extreme Environmental Adaptability

Most existing stretchable batteries can generally only be stretched uniaxially and suffer from poor mechanical and electrochemical robustness to withstand extreme mechanical and environmental challenges. A highly efficient bifunctional electrocatalyst is herein developed via the unique self-templated conversion of a guanosine-based supramolecular hydrogel and presents a fully integrated design strategy to successfully fabricate an omnidirectionally stretchable and extremely environment-adaptable Zn-air battery (ZAB) through the synergistic engineering of active materials and device architecture. The electrocatalyst demonstrates a very low reversible overpotential of only 0.68 V for oxygen reduction/evolution reactions (ORR/OER). This ZAB exhibits superior omnidirectional stretchability with a full-cell areal strain of >1000% and excellent durability, withstanding more than 10 000 stretching cycles. Promisingly, without any additional pre-treatment, the ZAB exhibits outstanding ultra-low temperature tolerance (down to -60 °C) and superior waterproofness, withstanding continuous water rinsing (>5 h) and immersion (>3 h). The present work offers a promising strategy for the design of omnidirectionally stretchable and high-performance energy storage devices for future on-skin wearable applications.

Size Effects of Electrocatalysts: More Than a Variation of Surface Area

The efficiency of electrocatalytic reactions has been continuously improved in recent years due to the great effort in the development of electrocatalysts. A popular strategy is engineering the size of electrocatalysts for better electrochemical performance and lower cost. Nanosized electrocatalysts with high specific surface area have been widely used in state-of-the-art electrochemical devices such as fuel cells. From an engineering aspect, nanosizing electrocatalysts increases the surface area of the electrode and improves the electrode/device performance. Beyond an engineering scope, this perspective highlights the size effects of certain scientific fundamentals in electrocatalytic reactions. The paper summarizes the representative examples in studying the size effects of electrocatalysts and sheds light on the change of intrinsic properties of electrocatalysts caused by the size variation. The size effects of electrocatalysts should be investigated in terms of both engineering and fundamental aspects; that is, the observed activity change is more than a result of surface area variation, and it is interesting to investigate the link between the intrinsic activity and the properties of the catalysts.

Highly Durable and Efficient Ni-FeOx/FeNi3 Electrocatalysts Synthesized by a Facile In Situ Combustion-Based Method for Overall Water Splitting with Large Current Densities

Ni-/Fe-based materials are promising electrocatalysts for the oxygen evolution reaction (OER) but usually are not suitable for the hydrogen evolution reaction (HER). Herein, a durable and bifunctional catalyst consisting of Ni-FeO_x and FeNi₃ is prepared on nickel foam (Ni-FeO_x/FeNi₃/NF) by in situ solution combustion and subsequent calcination to accomplish efficient alkaline water splitting. Density functional theory (DFT) calculation shows that the high HER activity is attributed to the strong electronic coupling effects between FeO_x and FeNi₃ in the Janus nanoparticles by modulating ΔG_H* and electronic states. Consequently, small overpotentials (η) of 71 and 272 mV in HER and 269 and 405 mV in OER yield current densities (j) of 50 and 1000 mA cm^-2, respectively. The catalyst shows outstanding stability for 280 and 200 h in HER and OER at a j of ∼50 mA cm^-2. Also, the robustness and mechanical stability of the electrode at an elevated j of ∼500 mA cm^-2 are excellent. Moreover, Ni-FeO_x/FeNi₃/NF shows excellent water splitting activities as a bifunctional catalyst as exemplified by j of 50 and 500 mA cm^-2 at cell voltages of 1.58 and 1.80 V, respectively. The Ni-FeO_x/FeNi₃/NF structure synthesized by the novel, simple, and scalable strategy has large potential in commercial water electrolysis, and the in situ combustion method holds great promise in the fabrication of thin-film electrodes for different applications.

Hexagonal Single-Crystal CoS Nanosheets: Controllable Synthesis and Tunable Oxygen Evolution Performance

Cobalt-based sulfides with variable valence states and unique physical and chemical properties have shown great potential as oxygen evolution reaction (OER) catalysts for electrochemical water-splitting reactions. However, poor morphological characteristics and a small specific surface area limit its further application. Here, hexagonal single-crystal two-dimensional (2D) CoS nanosheets with different thicknesses are successfully prepared by an atmospheric-pressure chemical vapor deposition method. Because of the advantages of the 2D structure, more exposed catalytic active sites, better reactant adsorption ability, accelerated electron transfer, and enhanced electrical conductivities can be achieved from the thinnest 5 nm CoS nanosheets (CoS-5), significantly improving OER performance. The electrochemical tests manifest that CoS-5 show an overpotential of 290 mV at 10 mA cm^-2 and a Tafel slope of 65.6 mV dec^-1 in the OER in an alkaline solution, superior to those for other thicknesses of CoS, bulk CoS, and RuO₂. For the mechanistic investigation, the lowest charge transfer resistance (R_ct) and the highest double-layer capacitance (C_dl) were obtained for CoS-5, demonstrating the faster OER kinetics and the larger active area. Density functional theory calculations further reveal the enhanced density of states around the Fermi level and higher H₂O molecule adsorption energy for thinner CoS nanosheets, promoting its intrinsic catalytic activity. Moreover, the two-electrode system with CoS-5 as the anode and Pt/C as the cathode requires only 1.56 V to attain 10 mA cm^-2 in the overall water-splitting reaction. We believe that this study will provide a fresh view for thickness-dependent catalytic performance and offers a new material for the study of electronic and energy devices.

Optimized nano-metal particles filled into carbon nanohorns to achieve high N-doping amount and high porosity for enhanced oxygen evolution reaction

Nano-metal-filled N-doped carbon materials have been actively verified as promising alternatives for precious-metal catalysts in the oxygen evolution reaction (OER). Herein, Ni/Fe/Cu-filled N-doped carbon nanohorns (CNHs) are synthesized via a positive pressure assisted arc discharge method using a Ni/Fe/Cu rod charged in an anode hole in a N2 and Ar mixture. We first found that the amount of N atom doping can be controlled by the types of nano-metal particles encapsulated by CNHs. The content of N atoms on CNHs uniquely depended on the initial Ni wires inserted into the anode graphite; increasing the number of Ni wires induced the enrichment of N atoms until 3.56 at%, whereas the content of N atoms for Cu- and Fe-filled CNHs is against the results; loading Cu and Fe nanoparticles decreases the N-doping amount. And the morphologies and N-configurations can be changed by the types of metal nanoparticles. Furthermore, the OER performance of Ni-filled CNHs is much superior to that of Cu- and Fe-filled CNHs, which can be significantly enhanced by the tip opening structure, and the increase in Ni loading amount and the N atom content.

Amorphous-Amorphous Coupling Enhancing the Oxygen Evolution Reaction Activity and Stability of the NiFe-Based Catalyst

Efficient and stable electrocatalytic water splitting plays a critical role in energy storage and conversion but is strongly restricted by the low activity and stability of catalysts associated with the complicated oxygen evolution reaction (OER). This work provides a strategy to fabricate an advanced NiFe-based catalyst to steadily speed up the OER based on a strong amorphous-amorphous coupling effect generated through amorphous CuS that induces the formation of amorphous NiFe layered double hydroxide (LDH) nanosheets (A-NiFe NS/CuS). The presence of the strong coupling effect not only modifies the electronic structure of catalytic sites to accelerate the reaction kinetics but also enhances the binding between the catalyst and substrate to strengthen the durability. In comparison to well-grown core-shell crystalline NiFe LDH on CuO, the as-synthesized amorphous A-NiFe NS/CuS gives a low overpotential of 240 mV to achieve 100 mA cm^-2 and shows robust stability under 100 h of operation at the same current density. Therefore, amorphous-amorphous coupling between catalyst-substrate by elaborate and rational engineering yields an opportunity to design efficient and robust NiFe-based OER catalysts.

Iron phosphonate for highly efficient capture of U(VI) from acidic solution

In this study, a novel, high surface area iron phosphonate (IP) for highly efficient adsorption of uranyl ion in acidic medium was described. The as-prepared IP was amorphous with its specific surface area and total pore volume as high as 268 m²/g and 1.04 cm³/g, respectively. Particularly, the as-prepared IP with ferrous ions and oxygen, nitrogen-bearing functional groups prove excellent U(VI) adsorption capacity (154.6 mg/g) as compared to that of amorphous FePO₄ (67.3 mg/g) and Fe₃(PO₄)₂(H₂O)₈ (33.8 mg/g). Surprising, the saturation adsorption capacity could achieve up to 353.9 mg/g. Besides, the IP also had a fast adsorption rate for attaining adsorption equilibrium within 20 min, and followed pseudo-second-order kinetic and Freundlich models. Moreover, both the Dubinin-Radushkevich isotherm adsorption model and the value of enthalpy indicated a chemisorption process. Otherwise, the Na⁺-independent U(VI) adsorption on IP and the adsorption-desorption isotherm studies revealed that inner-layer surface complexation is the control step for U(VI) adsorption process, and the adsorbent featured an irreversible adsorption process. The structure and functional groups of the adsorbent remained unchanged after capture of U(VI). Further, X-ray photoelectron spectra (XPS) analysis demonstrated that the capture mechanism of U(VI) on IP from acidic aqueous solution was due to not only redox reaction, but also ascribed to the coordinated chemical adsorption.