Strong Electronic Interaction of Amorphous Fe2O3 Nanosheets with Single‐Atom Pt toward Enhanced Carbon Monoxide Oxidation

Platinum‐based catalysts are critical to several chemical processes, but their efficiency is not satisfying enough in some cases, because only the surface active‐site atoms participate in the reaction. Henceforth, catalysts with single‐atom dispersions are highly desirable to maximize their mass efficiency, but fabricating these structures using a controllable method is still challenging. Most previous studies have focused on crystalline materials. However, amorphous materials may have enhanced performance due to their distorted and isotropic nature with numerous defects. Here reported is the facile synthesis of an atomically dispersed catalyst that consists of single Pt atoms and amorphous Fe₂O₃ nanosheets. Rational control can regulate the morphology from single atom clusters to sub‐nanoparticles. Density functional theory calculations show the synergistic effect resulted from the strong binding and stabilization of single Pt atoms with the strong metal‐support interaction between the in situ locally anchored Pt atoms and Fe₂O₃ lead to a weak CO adsorption. Moreover, the distorted amorphous Fe₂O₃ with O vacancies is beneficial for the activation of O₂, which further facilitates CO oxidation on nearby Pt sites or interface sites between Pt and Fe₂O₃, resulting in the extremely high performance for CO oxidation of the atomic catalyst.     

Stabilization of Single Metal Atoms on Graphitic Carbon Nitride

Graphitic carbon nitride (g‐C₃N₄) exhibits unique properties as a support for single‐atom heterogeneous catalysts (SAHCs). Understanding how the synthesis method, carrier properties, and metal identity impact the isolation of metal centers is essential to guide their design. This study compares the effectiveness of direct and postsynthetic routes to prepare SAHCs by incorporating palladium, silver, iridium, platinum, or gold in g‐C₃N₄ of distinct morphology (bulk, mesoporous and exfoliated). The speciation (single atoms, dimers, clusters, or nanoparticles), distribution, and oxidation state of the supported metals are characterized by multiple techniques including extensive use of aberration‐corrected electron microscopy. SAHCs are most readily attained via direct approaches applying copolymerizable metal precursors and employing high surface area carriers. In contrast, although post‐synthetic routes enable improved control over the metal loading, nanoparticle formation is more prevalent. Comparison of the carrier morphologies also points toward the involvement of defects in stabilizing single atoms. The distinct metal dispersions are rationalized by density functional theory and kinetic Monte Carlo simulations, highlighting the interplay between the adsorption energetics and diffusion kinetics. Evaluation in the continuous three‐phase semihydrogenation of 1‐hexyne identifies controlling the metal–carrier interaction and exposing the metal sites at the surface layer as key challenges in designing efficient SAHCs.     

A Pt–Fe Carbon Nitride Nano‐electrocatalyst for Polymer Electrolyte Membrane Fuel Cells and Direct‐Methanol Fuel Cells: Synthesis,Characterization, and Electrochemical Studies

This report describes the preparation of a new nano‐electrocatalyst for applications in polymer electrolyte fuel cells operating with H₂ and methanol. The nano‐electrocatalyst, having the composition K_0.12[Pt₁Fe_1.6C₅₅N_0.12], consists of a distribution of Pt and Fe bimetallic clusters supported on carbon nitride nanoparticles. This material was synthesized by thermal treatment of a zeolitic inorganic–organic polymer electrolyte‐like (Z‐IOPE) precursor, prepared by reacting H₂PtCl₆ and K₃Fe(CN)₆ in the presence of sucrose, as organic binder, in a water solution. This reaction allows the desired material to be prepared by means of a sol→gel process followed by a gel→plastic transition. The morphology and surface properties of K_0.12[Pt₁Fe_1.6C₅₅N_0.12] were studied via scanning and high‐resolution transmission electron microscopies and X‐ray photoelectron spectroscopy. Far‐infrared, mid‐infrared, and micro‐Raman‐laser spectroscopies, as well as X‐ray diffraction studies, together with detailed compositional data reveal the structural information and describe the interactions characterizing the mass activity of the K_0.12[Pt₁Fe_1.6C₅₅N_0.12] system. This material has structural and morphological features that are very different to those usually found in commercially available electrocatalysts for application in H₂ polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). K_0.12[Pt₁Fe_1.6C₅₅N_0.12] consists of active bimetallic catalytic sites supported on a mixture of α and graphitic carbon nitride‐like nanoparticles. The studies performed by cyclic voltammetry with the thin‐film rotating‐disk electrode indicate that the performance of K_0.12[Pt₁Fe_1.6C₅₅N_0.12] and of the EC‐20 reference material is a) equal to –255 and –216 A g^–1 Pt, respectively, in the oxygen‐reduction reaction at 0.75 V; and b) equal to 967 and 533 A g^–1 Pt, respectively, in the hydrogen‐oxidation reaction at potentials lower than 0.2 V. The activation potential of K_0.12[Pt₁Fe_1.6C₅₅N_0.12] is about 15 mV higher than that of the EC‐20 reference. In conclusion, the proposed synthesis route is general and promising for the development of new, improved nano‐electrocatalysts for low‐temperature fuel cells such as PEMFCs and DMFCs.     

Pt–Cu Interaction Induced Construction of Single Pt Sites for Synchronous Electron Capture and Transfer in Photocatalysis

Single-atom photocatalysts have shown their fascinating strengths in enhancing charge transfer dynamics; however, rationally designing coordination sites by metal doping to stabilize isolated atoms is still challenging. Here, a one-unit-cell ZnIn₂S₄ (ZIS) nanosheet with abundant Cu dopants serving as the suitable support to achieve a single atom Pt catalyst (Pt₁/Cu–ZIS) is reported, and hence the metal single atom–metal dopant interaction at an atomic level is disclosed. Experimental results and density functional theory calculations highlight the unique stabilizing effect (Pt–Cu interaction) of single Pt atoms in Cu-doped ZIS, while apparent Pt clusters are observed in pristine ZIS. Specifically, Pt–Cu interaction provides an extra coordination site except three S sites on the surface, which induces a higher diffusion barrier and makes the single atom more stable on the surface. Apart from stabilizing Pt single atoms, Pt–Cu interaction also serves as the efficient channel to transfer electrons from Cu trap states to Pt active sites, thereby enhancing the charge separation and transfer efficiency. Remarkably, the Pt₁/Cu–ZIS exhibits a superb activity, giving a photocatalytic hydrogen evolution rate of 5.02 mmol g⁻¹ h⁻¹, nearly 49 times higher than that of pristine ZIS.     

Single‐Atom Catalysts for Electrocatalytic Applications

The recent advances in electrocatalysis for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), carbon dioxide reduction reaction (CO₂RR), and nitrogen reduction reaction (NRR) are thoroughly reviewed. This comprehensive review focuses on the single‐atom catalysts (SACs) including Sc, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Sn, W, Bi, Ru, Rh, Pd, Ag, Ir, Pt, and Au with single‐metal sites or dual‐metal sites. The recent development of single‐atom electrocatalysts with novel configurations and compositions is documented. The understanding of the process–structure–property relationships is highlighted. For the SACs, their electrocatalytic performance and stability in fuel cells, zinc–air batteries, electrolyzers, CO₂RR, and NRR are summarized. The challenges and perspectives in the emerging field of single‐atom electrocatalysis are discussed.     

Single‐Atom Fe‐Nx‐C as an Efficient Electrocatalyst for Zinc–Air Batteries

Highly efficient non‐noble metal electrocatalysts are vital for metal–air batteries and fuel cells. Herein, a noble‐metal–free single‐atom Fe‐N _x‐C electrocatalyst is synthesized by incorporating Fe‐Phen complexes into the nanocages in situ during the growth of ZIF‐8, followed by pyrolysis at 900 °C under inert atmosphere. Fe‐Phen species provide both Fe²⁺ and the organic ligand (Phen) simultaneously, which play significant roles in preparing single‐atom catalysts. The obtained Fe‐N_x‐C exhibits a half‐wave potential of 0.91 V for the oxygen reduction reaction, higher than that of commercial Pt/C (0.82 V). As a cathode catalyst for primary zinc–air batteries (ZABs), the battery shows excellent electrochemical performances in terms of the high open‐circuit voltage (OCV) of 1.51 V and a high power density of 96.4 mW cm^?2. The rechargeable ZAB with Fe‐N_x‐C catalyst and the alkaline electrolyte shows a remarkable cycling performance for 300 h with an initial round‐trip efficiency of 59.6%. Furthermore, the rechargeable all‐solid‐state ZABs with the Fe‐N_x‐C catalyst show high OCV of 1.49 V, long cycle life for 120 h, and foldability. The single‐atom Fe‐N_x‐C electrocatalyst may function as a promising catalyst for various metal–air batteries and fuel cells.     

Harnessing the Extracellular Electron Transfer Capability of Geobacter sulfurreducens for Ambient Synthesis of Stable Bifunctional Single-Atom Electrocatalyst for Water Splitting

Single-atom metal (SA-M) catalysts with high dispersion of active metal sites allow maximum atomic utilization. Conventional synthesis of SA-M catalysts involves high-temperature treatments, leading to low yield with a random distribution of atoms. Herein, a nature-based facile method to synthesize SA-M catalysts (M = Fe, Ir, Pt, Ru, Cu, or Pd) in a single step at ambient temperature, using the extracellular electron transfer capability of Geobacter sulfurreducens (GS), is presented. Interestingly, the SA-M is coordinated to three nitrogen atoms adopting an MN₃ on the surface of GS. Dry samples of SA-Ir@GS without further heat treatment show exceptionally high activity for oxygen evolution reaction when compared to benchmark IrO₂ catalyst and comparable hydrogen evolution reaction activity to commercial 10 wt% Pt/C. The SA-Ir@GS exhibits the best water-splitting performance compared to other SA-M@GS, showing a low applied potential of 1.65 V to achieve 10 mA cm⁻² in 1.0 M KOH with cycling over 5 h. The density functional calculations reveal that the large adsorption energy of H₂O and moderate adsorption energies of reactants and reaction intermediates for SA-Ir@GS favorably improve its activity. This synthesis method at room temperature provides a versatile platform for the preparation of SA-M catalysts for various applications by merely altering the metal precursors.     

The Quasi‐Pt‐Allotrope Catalyst: Hollow PtCo@single‐Atom Pt1 on Nitrogen‐Doped Carbon toward Superior Oxygen Reduction

Single‐atom Pt and bimetallic Pt₃Co are considered the most promising oxygen reduction reaction (ORR) catalysts, with a much lower price than pure Pt. The combination of single‐atom Pt and bimetallic Pt₃Co in a highly active nanomaterial, however, is challenging and vulnerable to agglomeration under realistic reaction conditions, leading to a rapid fall in the ORR. Here, a sustainable quasi‐Pt‐allotrope catalyst, composed of hollow Pt₃Co (H‐PtCo) alloy cores and N‐doped carbon anchoring single atom Pt shells (Pt₁N‐C), is constructed. This unique nanoarchitecture enables the inner and exterior spaces to be easily accessible, exposing an extra‐high active surface area and active sites for the penetration of both aqueous and organic electrolytes. Moreover, the novel Pt₁N‐C shells not only effectively protect the H‐PtCo cores from agglomeration but also increase the efficiency of the ORR in virtue of the isolated Pt atoms. Thus, the H‐PtCo@Pt₁N‐C catalyst exhibits stable ORR without any fade over a prolonged 10 000 cycle test at 0.9 V in HClO₄ solution. Furthermore, this material can offer efficient and stable ORR activities in various organic electrolytes, indicating its great potential for next‐generation lithium–air batteries as well.     

g‐C3N4 Loading Black Phosphorus Quantum Dot for Efficient and Stable Photocatalytic H2 Generation under Visible Light

Black phosphorus (BP) is an interesting two‐dimensional material with low‐cost and abundant metal‐free properties and is used as one cocatalyst for photocatalytic H₂ production. However, the BP quantum dot (BPQD) is not studied. Herein, for the first time, BPQD is introduced as a hole‐migration cocatalyst of layered g‐C₃N₄ for visible‐light‐driven photocatalytic hydrogen generation. A high‐vacuum stirring method is developed for BPQD loading without the dissociation of BP. The layered BPQD is coupled on the layered g‐C₃N₄ surface to form a heterojunction structure. The 7% BPQD–C₃N₄ samples show similar time‐resolved photoluminescence curves as 0.5% Pt–C₃N₄. The optimum hydrogen rates of the modified sample (7% BPQD–C₃N₄) are 190, 133, 90, and 10.4 µmol h^?1 under simulated sunlight, LED‐405, LED‐420, and LED‐550 nm irradiation, respectively, which are 3.5, 3.6, and 3 times larger than that of the pristine g‐C₃N₄. Such low‐cost layered system not only optimizes the optical, electrical, and texture properties of the hybrid materials for photocatalytic water splitting to generate hydrogen but also provides ideas for designing novel or easily oxidized candidates by incorporating different available materials with given carriers.     

Reversed Spillover Effect Activated by Pt Atom Dimers Boosts Alkaline Hydrogen Evolution Reaction

The hydrogen spillover effect has garnered considerable attention as a promising avenue to enhance the activity of the hydrogen evolution reaction (HER) in metal-support compound materials. Herein, Pt atom dimers on the NiOOH support are successfully synthesized with a reversed hydrogen spillover effect, demonstrating much better alkaline HER activity than Pt single atoms and Pt clusters. Atomic and electronic structure characterizations unequivocally verify the anchoring of Pt atom dimers on NiOOH through Pt─O bonds, thus obtaining a reversed and enhanced hydrogen spillover effect. Theoretical and experimental results indicate that NiOOH exhibits pronounced water dissociation capability, while the Pt atom dimers, in comparison to Pt single atoms and Pt clusters, demonstrate superior hydrogen desorption ability. The reversed spillover with Pt atom dimers leads to remarkable HER activity in alkaline solutions, as evidenced by an ultra-small overpotential of 13 mV at 10 mA cm⁻². These findings not only provide insights into the potential use of atom dimers for HER, but also shed light on reversed spillover in designing high-performance catalysts.     

Activating Basal Planes of NiPS3 for Hydrogen Evolution by Nonmetal Heteroatom Doping

NiPS₃, one of the most promising catalysts among transition metal trichalcogenidophosphates (MTPs) in hydrogen evolution reaction (HER) electrocatalysis, is still inhibited by its unsatisfactory activity originating from its semiconducting nature and inert basal plane. Here, it is proposed, for the first time, to engineer the basal surface activity of NiPS₃ by nonmetal heteroatom doping, and predict that the degree to which the valance band of NiPS₃ is filled dominates not only the electrical conductivity of the catalyst, but also the strength of hydrogen adsorption at its surface. Direct experimental evidence is offered that in all the single nonmetal doping samples, C‐doped NiPS₃ exhibits the optimum activity owing to its moderate filled state of valance band and that C, N codoping even shows Pt‐like activity with an ultralow overpotential of 53.2 mV to afford 10 mA cm^?2 current density and a high exchange current density of 0.7 mA cm^?2 in 1 m KOH. The findings that less valance electrons of dopants than substitutional atoms are of pivotal importance for improving HER activity of NiPS₃ catalyst pave the way for readily designing novel MTPs of ever high performance to replace the incumbent Pt‐based catalysts.     

Atomic‐Scale Insights into the Low‐Temperature Oxidation of Methanol over a Single‐Atom Pt1‐Co3O4 Catalyst

Heterogeneous catalysts with single‐atom active sites offer a means of expanding the industrial application of noble metal catalysts. Herein, an atomically dispersed Pt₁‐Co₃O₄ catalyst is presented, which exhibits an exceptionally high efficiency for the total oxidation of methanol. Experimental and theoretical investigations indicate that this catalyst consists of Pt sites with a large proportion of occupied high electronic states. These sites possess a strong affinity for inactive Co²⁺ sites and anchor over the surface of (111) crystal plane, which increases the metal–support interaction of the Pt₁‐Co₃O₄ material and accelerates the rate of oxygen vacancies regeneration. In turn, this is determined to promote the coadsorption of the probe methanol molecule and O₂. Density functional theory calculations confirm that the electron transfer over the oxygen vacancies reduces both the methanol adsorption energy and activation barriers for methanol oxidation, which is proposed to significantly enhance the dissociation of the C? H bond in the methanol decomposition reaction. This investigation serves as a solid foundation for characterizing and understanding single‐atom catalysts for heterogeneous oxidation reactions.     

Unique P?Co?N Surface Bonding States Constructed on g‐C3N4 Nanosheets for Drastically Enhanced Photocatalytic Activity of H2 Evolution

Developing high‐efficiency and low‐cost photocatalysts by avoiding expensive noble metals, yet remarkably improving H₂ evolution performance, is a great challenge. Noble‐metal‐free catalysts containing Co(Fe)? N? C moieties have been widely reported in recent years for electrochemical oxygen reduction reaction and have also gained noticeable interest for organic transformation. However, to date, no prior studies are available in the literature about the activity of N‐coordinated metal centers for photocatalytic H₂ evolution. Herein, a new photocatalyst containing g‐C₃N₄ decorated with CoP nanodots constructed from low‐cost precursors is reported. It is for the first time revealed that the unique P(δ^?)? Co(δ⁺)? N(δ^?) surface bonding states lead to much superior H₂ evolution activity (96.2 µmol h^?1) compared to noble metal (Pt)‐decorated g‐C₃N₄ photocatalyst (32.3 µmol h^?1). The quantum efficiency of 12.4% at 420 nm is also much higher than the record values (≈2%) of other transition metal cocatalysts‐loaded g‐C₃N₄. It is believed that this work marks an important step toward developing high‐performance and low‐cost photocatalytic materials for H₂ evolution.     

Unique PCoN Surface Bonding States Constructed on g‐C3N4 Nanosheets for Drastically Enhanced Photocatalytic Activity of H2 Evolution

Developing high‐efficiency and low‐cost photocatalysts by avoiding expensive noble metals, yet remarkably improving H₂ evolution performance, is a great challenge. Noble‐metal‐free catalysts containing Co(Fe)?N?C moieties have been widely reported in recent years for electrochemical oxygen reduction reaction and have also gained noticeable interest for organic transformation. However, to date, no prior studies are available in the literature about the activity of N‐coordinated metal centers for photocatalytic H₂ evolution. Herein, a new photocatalyst containing g‐C₃N₄ decorated with CoP nanodots constructed from low‐cost precursors is reported. It is for the first time revealed that the unique P(δ^?)?Co(δ⁺)?N(δ^?) surface bonding states lead to much superior H₂ evolution activity (96.2 µmol h^?1) compared to noble metal (Pt)‐decorated g‐C₃N₄ photocatalyst (32.3 µmol h^?1). The quantum efficiency of 12.4% at 420 nm is also much higher than the record values (≈2%) of other transition metal cocatalysts‐loaded g‐C₃N₄. It is believed that this work marks an important step toward developing high‐performance and low‐cost photocatalytic materials for H₂ evolution.     

Optoelectronic Properties of Quasi‐Linear,Self‐Assembled Platinum Complexes: Pt–Pt Distance Dependence

Charge‐carrier mobilities of various self‐assembled platinum complexes were measured by time‐resolved microwave conductivity techniques in the temperature range –80 to +100 °C. Eight compounds were investigated in the present study, including the original Magnus' green salt ([Pt(NH₃)₄][PtCl₄]) and derivatives with the general structure [Pt(NH₂R)₄][PtCl₄], where R denotes an alkyl side chain. In one instance, the chlorines were substituted with bromines. For these complexes, which all consist of a linear backbone of platinum atoms with Pt–Pt distances, d, varying from 3.1 to ≥ 3.6 Å, a strong, inverse correlation was found between d and the one‐dimensional charge‐carrier mobility, Σμ_1D. The highest value of Σμ_1D at room temperature was observed for R = (S)‐3,7‐dimethyloctyl (dmoc) with Σμ_1D ≥ 0.06 cm² V^–1 s^–1. Almost all materials exhibited a charge‐carrier mobility that was relatively independent of the temperature over the range studied. One exceptional compound (R = (R)‐2‐ethylhexyl) showed a pronounced negative temperature dependence of the charge‐carrier mobility; upon decreasing the temperature from +100 °C to –80 °C the charge‐carrier mobility increased by a factor of about ten.     

Laser Assisted Solution Synthesis of High Performance Graphene Supported Electrocatalysts

Simple, yet versatile, methods to functionalize graphene flakes with metal (oxide) nanoparticles are in demand, particularly for the development of advanced catalysts. Herein, based on light‐induced electrochemistry, a laser‐assisted, continuous, solution route for the simultaneous reduction and modification of graphene oxide with catalytic nanoparticles is reported. Electrochemical graphene oxide (EGO) is used as starting material and electron–hole pair source due to its low degree of oxidation, which imparts structural integrity and an ability to withstand photodegradation. Simply illuminating a solution stream containing EGO and metal salt (e.g., H₂PtCl₆ or RuCl₃) with a 248 nm wavelength laser produces reduced EGO (rEGO, oxygen content 4.0 at%) flakes, decorated with Pt (≈2.0 nm) or RuO₂ (≈2.8 nm) nanoparticles. The RuO₂–rEGO flakes exhibit superior catalytic activity for the oxygen evolution reaction, requiring a small overpotential of 225 mV to reach a current density of 10 mA cm^?2. The Pt–rEGO flakes (10.2 wt% of Pt) show enhanced mass activity for the hydrogen evolution reaction, and similar performance for oxygen reduction reaction compared to a commercial 20 wt% Pt/C catalyst. This simple production method is also used to deposit PtPd alloy and MnO_x nanoparticles on rEGO, demonstrating its versatility in synthesizing functional nanoparticle‐modified graphene materials.     

Mesh‐on‐Mesh Graphitic‐C3N4@Graphene for Highly Efficient Hydrogen Evolution

Mesoporous materials have attracted considerable interest due to their huge surface areas and numerous active sites that can be effectively exploited in catalysis. Here, 2D mesoporous graphitic‐C₃N₄ nanolayers are rationally assembled on 2D mesoporous graphene sheets (g‐CN@G MMs) by in situ selective growth. Benefiting from an abundance of exposed edges and rich defects, fast electron transport, and a multipathway of charge and mass transport from a continuous interconnected mesh network, the mesh‐on‐mesh g‐CN@G MMs hybrid exhibits higher catalytic hydrogen evolution activity and stronger durability than most of the reported nonmetal catalysts and some metal‐based catalysts.     

Accelerating CO2 Electroreduction to CO Over Pd Single‐Atom Catalyst

The electrochemical conversion of carbon dioxide (CO₂) into value‐added chemicals is regarded as one of the promising routes to mitigate CO₂ emission. A nitrogen‐doped carbon‐supported palladium (Pd) single‐atom catalyst that can catalyze CO₂ into CO with far higher mass activity than its Pd nanoparticle counterpart, for example, 373.0 and 28.5 mA mg^?1_Pd, respectively, at ?0.8 V versus reversible hydrogen electrode, is reported. A combination of in situ X‐ray characterization and density functional theory (DFT) calculation reveals that the Pd? N₄ site is the most likely active center for CO production without the formation of palladium hydride (PdH), which is essential for typical Pd nanoparticle catalysts. Furthermore, the well‐dispersed Pd? N₄ single‐atom site facilitates the stabilization of the adsorbed CO₂ intermediate, thereby enhancing electrocatalytic CO₂ reduction capability at low overpotentials. This work provides important insights into the structure‐activity relationship for single‐atom based electrocatalysts.     

Tuning the Catalytic Preference of Ruthenium Catalysts for Nitrogen Reduction by Atomic Dispersion

Developing cost‐effective, high‐performance nitrogen reduction reaction (NRR) electrocatalysts is required for the production of green and low‐cost ammonia under ambient conditions. Here, a strategy is proposed to adjust the reaction preference of noble metals by tuning the size and local chemical environment of the active sites. This proof‐of‐concept model is realized by single ruthenium atoms distributed in a matrix of graphitic carbon nitride (Ru SAs/g‐C₃N₄). This model is compared, in terms of the NRR activity, to bulk Ru. The as‐synthesized Ru SAs/g‐C₃N₄ exhibits excellent catalytic activity and selectivity with an NH₃ yield rate of 23.0 µg mg_cat^?1 h^?1 and a Faradaic efficiency as high as 8.3% at a low overpotential (0.05 V vs the reversible hydrogen electrode), which is far better than that of the bulk Ru counterpart. Moreover, the Ru SAs/g‐C₃N₄ displays a high stability during five recycling tests and a 12 h potentiostatic test. Density functional theory calculations reveal that compared to bulk Ru surfaces, Ru SAs/g‐C₃N₄ has more facile reaction thermodynamics, and the enhanced NRR performance of Ru SAs/g‐C₃N₄ originates from a tuning of the d‐electron energies from that of the bulk to a single‐atom, causing an up‐shift of the d‐band center toward the Fermi level.     

Reversible Hydrogen Storage by a Li–Al–N–H Complex

Stepwise solid‐state reaction between LiNH₂ and LiAlH₄ at a molar ratio of 2:1 is investigated in this paper. It is observed that approximately four H atoms are evolved from a mixture of LiNH₂–LiAlH₄ (2:1) after mechanical ball milling. The transformation of tetrahedral [AlH₄]^– in LiAlH₄ to the octahedral [AlH₆]^3– in Li₃AlH₆ is observed after ball milling LiAlH₄ with LiNH₂. Al–N bonding is identified by using solid‐state ²⁷Al nuclear magnetic resonance (NMR) measurements. The NMR data, together with the results of X‐ray diffraction and Fourier transform IR measurements, indicate that a Li–Al–N–H intermediate with the chemical composition of Li₃AlN₂H₄ forms after ball milling. Heating the post‐milled sample to 500 °C results in the liberation of an additional four H atoms and the formation of Li₃AlN₂. More than 5 wt % hydrogen can be reversibly stored by Li₃AlN₂. The hydrogenated sample contains LiNH₂, LiH, and AlN. The role of AlN in the reversible hydrogen storage over Li–Al–N–H is discussed.