Efficient Photocatalytic Nitrogen Fixation over Cuδ+‐Modified Defective ZnAl‐Layered Double Hydroxide Nanosheets

The photocatalytic reduction of nitrogen (N₂) with water (H₂O) as the reducing agent holds great promise as a sustainable future technology for the synthesis of ammonia (NH₃). Herein, the effect of oxygen vacancies and electron‐rich Cu^δ+ on the performance of zinc‐aluminium layered double hydroxide (ZnAl‐LDH) nanosheet photocatalysts for N₂ reduction to NH₃ under UV–vis excitation is systematically explored. Results show that a 0.5%‐ZnAl‐LDH nanosheet photocatalyst (containing 0.5 mol% Cu by metal basis) affords a remarkable NH₃ production rate of 110 µmol g^?1 h^?1 and excellent stability in pure water. The X‐ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory calculations reveal that Cu addition imparts oxygen vacancies and coordinatively unsaturated Cu^δ+ (δ < 2) with electron‐rich property in the ZnAl‐LDH nanosheets, both of which readily contribute to efficient separation and transfer of photogenerated electrons and holes and promote N₂ adsorption, thereby both activating N₂ and facilitating its multielectrons reduction to NH₃.     

A Simple Synthetic Strategy toward Defect‐Rich Porous Monolayer NiFe‐Layered Double Hydroxide Nanosheets for Efficient Electrocatalytic Water Oxidation

In this work, porous monolayer nickel‐iron layered double hydroxide (PM‐LDH) nanosheets with a lateral size of ≈30 nm and a thickness of ≈0.8 nm are successfully synthesized by a facile one‐step strategy. Briefly, an aqueous solution containing Ni²⁺ and Fe³⁺ is added dropwise to an aqueous formamide solution at 80 °C and pH 10, with the PM‐LDH product formed within only 10 min. This fast synthetic strategy introduces an abundance of pores in the monolayer NiFe‐LDH nanosheets, resulting in PM‐LDH containing high concentration of oxygen and cation vacancies, as is confirmed by extended X‐ray absorption fine structure and electron spin resonance measurements. The oxygen and cation vacancies in PM‐LDH act synergistically to increase the electropositivity of the LDH nanosheets, while also enhancing H₂O adsorption and bonding strength of the OH* intermediate formed during water electrooxidation, endowing PM‐LDH with outstanding performance for the oxygen evolution reaction (OER). PM‐LDH offers a very low overpotential (230 mV) for OER at a current density of 10 mA cm^?2, with a Tafel slope of only 47 mV dec^?1, representing one of the best OER performance yet reported for a NiFe‐LDH system. The results encourage the wider utilization of porous monolayer LDH nanosheets in electrocatalysis, catalysis, and solar cells.     

Sub‐3 nm Ultrafine Monolayer Layered Double Hydroxide Nanosheets for Electrochemical Water Oxidation

This study reports the synthesis of ultrafine NiFe‐layered double hydroxide (NiFe‐LDH) nanosheets, possessing a size range between 1.5 and 3.0 nm with a thickness of 0.6 nm. Abundant metal and oxygen vacancies impart the ultrafine nanosheets with semi‐metallic character, and thus superior charge transfer properties and electrochemical water oxidation performance with overpotentials (η) of 254 mV relative to monolayer LDH nanosheets (η of 280 mV) or bulk LDH materials (η of 320 mV) at 10 mA cm^?2. These results are highly encouraging for the future application of ultrafine monolayer LDH nanosheets in electronics, solar cells, and catalysis.     

High‐Performance Electrocatalytic Conversion of N2 to NH3 Using Oxygen‐Vacancy‐Rich TiO2 In Situ Grown on Ti3C2Tx MXene

To achieve the energy‐effective ammonia (NH₃) production via the ambient‐condition electrochemical N₂ reduction reaction (NRR), it is vital to ingeniously design an efficient electrocatalyst assembling the features of abundant surface deficiency, good dispersibility, high conductivity, and large surface specific area (SSA) via a simple way. Inspired by the fact that the MXene contains thermodynamically metastable marginal transition metal atoms, the oxygen‐vacancy‐rich TiO₂ nanoparticles (NPs) in situ grown on the Ti₃C₂T_x nanosheets (TiO₂/Ti₃C₂T_x) are prepared via a one‐step ethanol‐thermal treatment of the Ti₃C₂T_x MXene. The oxygen vacancies act as the main active sites for the NH₃ synthesis. The highly conductive interior untreated Ti₃C₂T_x nanosheets could not only facilitate the electron transport but also avoid the self‐aggregation of the TiO₂ NPs. Meanwhile, the TiO₂ NPs generation could enhance the SSA of the Ti₃C₂T_x in return. Accordingly, the as‐prepared electrocatalyst exhibits an NH₃ yield of 32.17 µg h^?1 mg^?1_cat. at ?0.55 V versus reversible hydrogen electrode (RHE) and a remarkable Faradaic efficiency of 16.07% at ?0.45 V versus RHE in 0.1 m HCl, placing it as one of the most promising NRR electrocatalysts. Moreover, the density functional theory calculations confirm the lowest NRR energy barrier (0.40 eV) of TiO₂ (101)/Ti₃C₂T_x compared with Ti₃C₂T_x or TiO₂ (101) alone.     

Single‐Crystalline Ultrathin Co3O4 Nanosheets with Massive Vacancy Defects for Enhanced Electrocatalysis

The role of vacancy defects is demonstrated to be positive in various energy‐related processes. However, introducing vacancy defects into single‐crystalline nanostructures with given facets and studying their defect effect on electrocatalytic properties remains a great challenge. Here this study deliberately introduces oxygen defects into single‐crystalline ultrathin Co₃O₄ nanosheets with O‐terminated {111} facets by mild solvothermal reduction using ethylene glycol under alkaline condition. As‐prepared defect‐rich Co₃O₄ nanosheets show a low overpotential of 220 mV with a small Tafel slope of 49.1 mV dec^?1 for the oxygen evolution reaction (OER), which is among the best Co‐based OER catalysts to date and even more active than the state‐of‐the‐art IrO₂ catalyst. Such vacancy defects are formed by balancing with reducing environments under solvothermal conditions, but are surprisingly stable even after 1000 cycles of scanning under OER working conditions. Density functional theory plus U calculation attributes the enhanced performance to the oxygen vacancies and consequently exposed second‐layered Co metal sites, which leads to the lowered OER activation energy of 2.26 eV and improved electrical conductivity. This mild solvothermal reduction concept opens a new door for the understanding and future designing of advanced defect‐based electrocatalysts.     

Dramatically Enhanced Ambient Ammonia Electrosynthesis Performance by In‐Operando Created Li–S Interactions on MoS2 Electrocatalyst

The Haber‐Bosch process can be replaced by the ambient electrocatalytic N₂ reduction reaction (NRR) to produce NH₃ if suitable electrocatalysts can be developed. However, to develop high performance N₂ fixation electrocatalysts, a key issue to be resolved is to achieve efficient hydrogenation of N₂ without interference by the thermodynamically favored hydrogen evolution reaction (HER). Herein, in‐operando created strong Li–S interactions are reported to empower the S‐rich MoS₂ nanosheets with superior NRR catalytic activity and HER suppression ability. The Li⁺ interactions with S‐edge sites of MoS₂ can effectively suppress hydrogen evolution reaction by reducing H* adsorption free energy from 0.03 to 0.47 eV, facilitate N₂ adsorption by increasing N₂ adsorption free energy from –0.32 to –0.70 eV and enhance electrocatalytic N₂ reduction activity by decreasing the activation energy barrier of the reaction control step (*N₂ → *N₂H) from 0.84 to 0.42 eV. A NH₃ yield rate of 43.4 μg h^?1 mg^?1 MoS₂ with a faradaic efficiency (FE) of 9.81% can be achieved in presence of strong Li–S interactions, more than 8 and 18 times by the same electrocatalyst in the absence of Li–S interactions. This report opens a new way to design and develop catalysts and catalysis systems.     

Graphene Layers‐Wrapped Fe/Fe5C2 Nanoparticles Supported on N‐doped Graphene Nanosheets for Highly Efficient Oxygen Reduction

Synthesis of highly efficient nonprecious metal electrocatalysts for the oxygen reduction reaction (ORR) superior to platinum (Pt) is still a big challenge. Herein, a new highly active ORR electrocatalyst is reported based on graphene layers‐wrapped Fe/Fe₅C₂ nanoparticles supported on N‐doped graphene nanosheets (GL‐Fe/Fe₅C₂/NG) through simply annealing a mixture of bulk graphitic carbon nitride (g‐C₃N₄) and ferrocene. An interesting exfoliation–denitrogen mechanism underlying the conversion of bulk g‐C₃N₄ into N‐doped graphene nanosheets is revealed. Owing to the high graphitic degree, optimum N‐doping level and sufficient active sites from the graphene layers‐wrapped Fe/Fe₅C₂ nanoparticles, the as‐prepared GL‐Fe/Fe₅C₂/NG electrocatalyst obtained at 800 °C exhibits outstanding ORR activity with a 20 mV more positive half‐wave potential than the commercial Pt/C catalyst in 0.1 m KOH solution and a comparable onset potential of 0.98 V. This makes GL‐Fe/Fe₅C₂/NG an outstanding electrocatalyst for ORR in alkaline solution.     

Enhancing Catalytic Activity of Titanium Oxide in Lithium–Sulfur Batteries by Band Engineering

The altering of electronic states of metal oxides offers a promising opportunity to realize high‐efficiency surface catalysis, which play a key role in regulating polysulfides (PS) redox in lithium–sulfur (Li–S) batteries. However, little effort has been devoted to understanding the relationship between the electronic state of metal oxides and a catalyst's properties in Li–S cells. Herein, defect‐rich heterojunction electrocatalysts composed of ultrathin TiO_2‐x nanosheets and carbon nanotubes (CNTs) for Li–S batteries are reported. Theoretical simulations indicate that oxygen vacancies and heterojunction can enhance electronic conductivity and chemical adsorption. Spectroscopy and electrochemical techniques further indicate that the rich surface vacancies in TiO_2‐x nanosheets result in highly activated trapping sites for LiPS and lower energy barriers for fast Li ion mobility. Meanwhile, the redistribution of electrons at the heterojunction interfaces realizes accelerated surface electron exchange. Coupled with a polyacrylate terpolymer (LA132) binder, the CNT@TiO_2‐x–S electrodes exhibit a long cycle life of more than 300 cycles at 1 C and a high area capacity of 5.4 mAh cm^?2. This work offers a new perspective on understanding catalyst design in energy storage devices through band engineering.     

Tailoring of Metal Boride Morphology via Anion for Efficient Water Oxidation

The metal‐metalloid materials have received a massive interest as oxygen‐evolving catalysts due to their ability for charge transfer between different elements and modified electronic structures lowering the kinetic energy barriers of the electrochemical processes. Herein, a facile and systematic preparation of metal borides by chemical reduction is reported, with morphologies ranging from nanoparticles to nanosheets which is driven by a careful selection of metal salts solution. The iron doping in cobalt boride nanosheets is found to be an effective approach to further tune the water oxidation activity. The as‐prepared catalyst exhibited superior oxygen evolution performance in 1.0 m KOH as the optimized ternary CoFe boride needs an overpotential of 265 mV to achieve a current density of 10 mA cm^?2 at a mass loading of 0.3 mg cm^?2.     

Bi‐Based Metal‐Organic Framework Derived Leafy Bismuth Nanosheets for Carbon Dioxide Electroreduction

Electroreduction of carbon dioxide (CO₂) into high‐value and readily collectable liquid products is vital but remains a substantial challenge due to the lack of highly efficient and robust electrocatalysts. Herein, Bi‐based metal‐organic framework (CAU‐17) derived leafy bismuth nanosheets with a hybrid Bi/Bi? O interface (Bi NSs) is developed, which enables CO₂ reduction to formic acid (HCOOH) with high activity, selectivity, and stability. Specially, the flow cell configuration is employed to eliminate the diffusion effect of CO₂ molecules and simultaneously achieve considerable current density (200 mA cm^?2) for industrial application. The faradaic efficiency for transforming CO₂ to HCOOH can achieve over 85 or 90% in 1 m KHCO₃ or KOH for at least 10 h despite a current density that exceeds 200 mA cm^?2, outperforming most of the reported CO₂ electroreduction catalysts. The hybrid Bi/Bi? O surface of leafy bismuth nanosheets boosts the adsorption of CO₂ and protects the surface structure of the as‐prepared leafy bismuth nanosheets, which benefits its activity and stability for CO₂ electroreduction. This work shows that modifying electrocatalysts by surface oxygen groups is a promising pathway to regulate the activity and stability for selective CO₂ reduction to HCOOH.     

Defect‐Engineered Ultrathin δ‐MnO2 Nanosheet Arrays as Bifunctional Electrodes for Efficient Overall Water Splitting

Recently, defect engineering has been used to intruduce half‐metallicity into selected semiconductors, thereby significantly enhancing their electrical conductivity and catalytic/electrocatalytic performance. Taking inspiration from this, we developed a novel bifunctional electrode consisting of two monolayer thick manganese dioxide (δ‐MnO₂) nanosheet arrays on a nickel foam, using a novel in‐situ method. The bifunctional electrode exposes numerous active sites for electrocatalytic rections and displays excellent electrical conductivity, resulting in strong performance for both HER and OER. Based on detailed structure analysis and density functional theory (DFT) calculations, the remarkably OER and HER activity of the bifunctional electrode can be attributed to the ultrathin δ‐MnO₂ nanosheets containing abundant oxygen vacancies lead to the formation od Mn³⁺ active sites, which give rise to half‐metallicity properties and strong H₂O adsorption. This synthetic strategy introduced here represents a new method for the development of non‐precious metal Mn‐based electrocatalysts for eddicient energy conversion.     

MnMoO4 Electrocatalysts for Superior Long‐Life and High‐Rate Lithium‐Oxygen Batteries

Lithium‐oxygen batteries represent a significant scientific challenge for high‐rate and long‐term cycling using oxygen electrodes that contain efficient electrocatalysts. The mixed transition metal oxide catalysts provide the most efficient catalytic activity for partial heterogeneous surface cations with oxygen vacancies as the active phase. They include multiple oxidation states and oxygen vacancies. Here, using a combination of transmission electron microscopy, differential electrochemical mass spectrometry, X‐ray photoelectron spectroscopy, and electrochemical properties to probe the surface of the MnMoO₄ nanowires, it is shown that the intrinsic MnMoO₄ oxygen vacancies on the oxygen electrode are an effective strategy to achieve a high reversibility and high efficiency for lithium‐oxygen (Li‐O₂) batteries. The modified MnMoO₄ nanowires exhibit a highly stable capacity at a fixed capacity of 5000 mA h g_sp^?1 (calculated weight of Super P carbon black) during 50 cycles, a high‐rate capability at a current rate of 3000 mA g_sp^?1 during 70 cycles, and a long‐term reversible capacity during 188 cycles at a fixed capacity of 1000 mA h g_sp^?1. It is demonstrated that this strategy for creating mixed transition metal oxides (e.g., MnMoO₄) may pave the way for the new structural design of electrocatalysts for Li‐O₂ batteries.     

Metal‐Free 2D/2D Heterojunction of Graphitic Carbon Nitride/Graphdiyne for Improving the Hole Mobility of Graphitic Carbon Nitride

The design and synthesis of efficient metal‐free photoelectrocatalysts for water splitting are of great significance, as nonmetal elements are generally earth abundant and environment friendly. As a typical metal‐free semiconductor, g‐C3N4 has received much attention in the field of photocatalytic water splitting. However, the poor photoinduced hole mobility of g‐C₃N₄ restrains its catalytic performance. Herein, for the first time, graphdiyne (GDY) is used to interact with g‐C₃N₄ to construct a metal‐free 2D/2D heterojunction of g‐C₃N₄/GDY as an efficient photoelectrocatalyst for water splitting. The g‐C₃N₄/GDY photocathode exhibits enhanced photocarriers separation due to excellent hole transfer nature of graphdiyne and the structure of 2D/2D heterojunction of g‐C₃N₄/GDY, realizing a sevenfold increase in electron life time (610 μs) compared to that of g‐C₃N₄ (88 μs), and a threefold increase in photocurrent density (?98 μA cm^?2) compared to that of g‐C₃N₄ photocathode (?32 μA cm^?2) at a potential of 0 V versus normal hydrogen electrode (NHE) in neutral aqueous solution. The photoelectrocatalytic performance can be further improved by fabricating Pt@g‐C₃N₄/GDY, which displays an photocurrent of ?133 μA cm^?2 at a potential of 0 V versus NHE in neutral aqueous solution. This work provides a new strategy for the design of efficient metal‐free photoelectrocatalysts for water splitting.     

Atomically Dispersed Fe‐Nx/C Electrocatalyst Boosts Oxygen Catalysis via a New Metal‐Organic Polymer Supramolecule Strategy

The development of high‐performance oxygen reduction reaction (ORR) catalysts derived from non‐Pt group metals (non‐PGMs) is urgent for the wide applications of proton exchange membrane fuel cells (PEMFCs). In this work, a facile and cost‐efficient supramolecular route is developed for making non‐PGM ORR catalyst with atomically dispersed Fe‐N_x/C sites through pyrolyzing the metal‐organic polymer coordinative hydrogel formed between Fe³⁺ and α‐L‐guluronate blocks of sodium alginate (SA). High‐angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) and X‐ray absorption spectroscopy (XAS) verify that Fe atoms achieve atomic‐level dispersion on the obtained SA‐Fe‐N nanosheets and a possible fourfold coordination with N atoms. The best‐performing SA‐Fe‐N catalyst exhibits excellent ORR activity with half‐wave potential (E_1/2) of 0.812 and 0.910 V versus the reversible hydrogen electrode (RHE) in 0.5 m H₂SO₄ and 0.1 m KOH, respectively, along with respectable durability. Such performance surpasses that of most reported non‐PGM ORR catalysts. Density functional theory calculations suggest that the relieved passivation effect of OH* on Fe‐N₄/C structure leads to its superior ORR activity to Pt/C in alkaline solution. The work demonstrates a novel strategy for developing high‐performance non‐PGM ORR electrocatalysts with atomically dispersed and stable M‐N_x coordination sites in both acidic and alkaline media.     

Low‐Overpotential Electrocatalytic Water Splitting with Noble‐Metal‐Free Nanoparticles Supported in a sp3 N‐Rich Flexible COF

Covalent organic frameworks (COFs) are crystalline organic polymers with tunable structures. Here, a COF is prepared using building units with highly flexible tetrahedral sp³ nitrogens. This flexibility gives rise to structural changes which generate mesopores capable of confining very small (<2 nm sized) non‐noble‐metal‐based nanoparticles (NPs). This nanocomposite shows exceptional activity toward the oxygen‐evolution reaction from alkaline water with an overpotential of 258 mV at a current density of 10 mA cm^?2. The overpotential observed in the COF‐nanoparticle system is the best in class, and is close to the current record of ≈200 mV for any noble‐metal‐free electrocatalytic water splitting system—the Fe–Co–Ni metal‐oxide‐film system. Also, it possesses outstanding kinetics (Tafel slope of 38.9 mV dec^?1) for the reaction. The COF is able to stabilize such small‐sized NP in the absence of any capping agent because of the COF–Ni(OH)₂ interactions arising from the N‐rich backbone of the COF. Density‐functional‐theory modeling of the interaction between the hexagonal Ni(OH)₂ nanosheets and the COF shows that in the most favorable configuration the Ni(OH)₂ nanosheets are sandwiched between the sp³ nitrogens of the adjacent COF layers and this can be crucial to maximizing their synergistic interactions.     

Operando Oxygen Vacancies for Enhanced Activity and Stability toward Nitrogen Photofixation

Photocatalysts with oxygen vacancies (OVs) have exhibited exciting activity in N₂ photofixation due to their superiority in capture and activation of N₂. However, the surface OVs are easily oxidized by seizing the oxygen atoms from water or oxygen during the catalytic reaction. Here, it is reported that the grain boundaries (GBs) in nanoporous WO₃ induce plenty of operando OVs under light irradiation to significantly boost catalytic activity toward N₂ photofixation. Impressively, nanoporous WO₃ with abundant GBs (WO₃‐600) exhibit an ammonia production rate of 230 µmol g_cat.^?1 h^?1 without any sacrificial agents at room temperature, 17 times higher than that for WO₃ nanoparticles without GBs. Moreover, WO₃‐600 also manifests remarkable stability by maintaining nearly ≈100% catalytic activity after ten successive reaction rounds. Further mechanistic studies reveal that both OVs and GBs regulate the band structures of WO₃ nanocrystals, as well as favor the delivery of photogenerated electrons to adsorbed N₂ by enhancing W–O covalency. More importantly, plenty of operando OVs induced by GBs generate during catalytic reaction, directly contributing to the excellent catalytic performance for WO₃‐600. This work opens a novel avenue to developing efficient photocatalysts by construction of operando OVs.     

Layered Double Hydroxide Nanostructured Photocatalysts for Renewable Energy Production

An enormous research effort is currently being directed towards the development of efficient visible‐light‐driven photocatalysts for renewable energy applications including water splitting, CO₂ reduction and alcohol photoreforming. Layered double hydroxide (LDH)‐based photocatalysts have emerged as one of the most promising candidates to replace TiO₂‐based photocatalysts for these reactions_, owing to their unique layered structure, compositional flexibility, controllable particle size, low manufacturing cost and ease of synthesis. By introducing defects into LDH materials through the control of their size to the nanoscale, the atomic structure, surface defect concentration, and electronic and optical characteristics of LDH materials can be strategically engineered for particular applications. Furthermore, through the use of advanced characterization techniques such as X‐ray absorption fine structure, positron annihilation spectrometry, X‐ray photoelectron spectroscopy, electron spin resonance, density‐functional theory calculations, and photocatalytic tests, structure‐activity relationships can be established and used in the rational design of high‐performance LDH‐based photocatalysts for efficient solar energy capture. LDHs thus represent a versatile platform for semiconductor photocatalyst development with application potential across the energy sector.     

In Situ Formation of Co9S8 Quantum Dots in MOF‐Derived Ternary Metal Layered Double Hydroxide Nanoarrays for High‐Performance Hybrid Supercapacitors

Layered double hydroxides (LDHs) are promising cathode materials for supercapacitors because of the enhanced flow efficiency of ions in the interlayers. However, the limited active sites and monotonous metal species further hinder the improvement of the capacity performance. Herein, cobalt sulfide quantum dots (Co₉S₈‐QDs) are effectively created and embedded within the interlayer of metal‐organic‐frameworks‐derived ternary metal LDH nanosheets based on in situ selective vulcanization of Co on carbon fibers. The hybrid CF@NiCoZn‐LDH/Co₉S₈‐QD retains the lamellar structure of the ternary metal LDH very well, inheriting low transfer impedance of interlayer ions. Significantly, the selectively generated Co₉S₈‐QDs expose more abundant active sites, effectively improving the electrochemical properties, such as capacitive performance, electronic conductivity, and cycling stability. Due to the synergistic relationship, the hybrid material delivers an ultrahigh electrochemical capacity of 350.6 mAh g^?1 (2504 F g^?1) at 1 A g^?1. Furthermore, hybrid supercapacitors fabricated with CF@NiCoZn‐LDH/Co₉S₈‐QD and carbon nanosheets modified by single‐walled carbon nanotubes display an outstanding energy density of 56.4 Wh kg^?1 at a power density of 875 W kg^?1, with an excellent capacity retention of 95.3% after 8000 charge–discharge cycles. Therefore, constructing hybrid electrode materials by in situ‐created QDs in multimetallic LDHs is promising.     

Atomic‐Level Reactive Sites for Semiconductor‐Based Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction is an effective means to generate renewable energy. It involves redox reactions, reduction of CO₂ and oxidation of water, that leads to the production of solar fuel. Significant research effort has therefore been made to develop inexpensive and practically sustainable semiconductor‐based photocatalysts. The exploration of atomic‐level active sites on the surface of semiconductors can result in an improved understanding of the mechanism of CO₂ photoreduction. This can be applied to the design and synthesis of efficient photocatalysts. In this review, atomic‐level reactive sites are classified into four types: vacancies, single atoms, surface functional groups, and frustrated Lewis pairs (FLPs). These different photocatalytic reactive sites are shown to have varied affinity to reactants, intermediates, and products. This changes pathways for CO₂ reduction and significantly impacts catalytic activity and selectivity. The design of a photocatalyst from an atomic‐level perspective can therefore be used to maximize atomic utilization efficiency and lead to a high selectivity. The prospects for fabrication of effective photocatalysts based on an in‐depth understanding are highlighted.     

Highly Efficient and Durable Pd Hydride Nanocubes Embedded in 2D Amorphous NiB Nanosheets for Oxygen Reduction Reaction

A highly efficient and durable electrocatalyst of Pd hydride nanocubes encapsulated within 2D amorphous Ni‐B nanosheets is reported. The PdH_0.43 nanocubes are first synthesized via a simple N ,N ‐dimethylformamide thermal treatment. The as‐synthesized PdH_0.43 nanocubes are then encapsulated in 2D amorphous NiB nanosheets by NaBH₄ reduction in the presence of nickel species. During the NaBH₄ treatment, the PdH_0.43 can be further transformed into PdH_0.706 due to the presence of endogenous H₂. Electrochemical studies demonstrate that the degree of hydride of Pd nanocubes (PdH_x ) plays an important role in the enhancement of their oxygen reduction reaction (ORR) activity. With increasing x value, both the activity and stability increase significantly. At 0.90 V versus reversible hydrogen electrode, the ORR activity of PdH_0.706 @Ni‐B reaches 1.05 A mg_Pd^?1, which is nearly five times higher than that of the state‐of‐the‐art Pt catalysts. Accelerated durability tests show that even after 10 000 potential cycles, there is negligible shift in their half‐wave potential and no shape and structure change occurs, indicating the incorporation of amorphous 2D Ni‐B nanosheets can greatly improve their stability without compromising their activity. The present study illustrates the importance of high degree of hydride and presence of amorphous Ni‐B nanosheets on the enhancement of ORR activity for Pd‐based electrocatalyst.