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The demand for innovative materials in energy storage and generation necessitates precise atomic-scale chemical control in nanomaterials. Double-transition metal (DTM) MXenes have expanded the chemical diversity of layered 2D materials, exhibiting unique physicochemical properties. However, the atomic ordering of DTMs and its impact on lithium storage performance require further investigation. Here, we report the synthesis of two-dimensional niobium–vanadium carbides (NbαV2-αCTx) by Lewis acid etching strategy, a previously unexplored class of DTM MXenes. By utilizing X-ray absorption fine structure (XAFS) spectra, we demonstrate that adjusting the Nb/V ratio enables tuning of the coordination number of Nb/V in NbαV2-αCTx. As a result, the resulting Nb1.4V0.6CTxwith enhanced local atomic ordering exhibited excellent rate performance and remarkable cycling stability. This study highlights the atomic-scale characterization of local structures using advanced X-ray spectroscopic techniques, expanding the diversity of the MXenes family.

The selective hydrogenation of carbon dioxide (CO2) to value-added chemicals, e.g., methanol, using green hydrogen retrieved from renewable resources is a promising approach for CO2emission reduction and carbon resource utilization. However, this process suffers from the competing side reaction of reverse water–gas shift (RWGS) and methanol decomposition, which often leads to a strong conversion-selectivity trade-off and thus a poor methanol yield. Here, we report that InOxcoating of PdCu bimetallic nanoparticles (NPs) to construct intimate InOx/Cu and InOx/PdIn dual interfaces enables the break of conversion-selectivity trade-off by achieving ∼80% methanol selectivity at ∼20% CO2conversion close to the thermodynamic limit, far superior to that of conventional metal catalysts with a single active metal/oxide interface. Comprehensive microscopic and spectroscopic characterization revealed that the InOx/PdIn interface favors the activation of CO2to formate, while the adjacent InOx/Cu interface readily converts formate intermediates to methoxy species in tandem, which thus cooperatively boosts methanol production. These findings of dual-interface synergies via oxide coating of bimetallic NPs open a new avenue to the design of active and selective catalysts for advanced catalysis.

With the advancement of modern science and technology, large scientific facilities are increasingly oriented toward demand and application, and can be used for basic research as well as serving multiple disciplines. Developing large scientific facilities and related analytical technologies enhances understanding of large scientific facilities and popularizes their application in research across multiple disciplines. The combination of light or neutron sources from large scientific facilities and advanced analytical technologies can be achieved for materials structure information, dynamics study of chemical reactions, high dissociation of biomolecules, 3D visualization of energy materials or biological samples, etc. We first introduce the progress of domestic large scientific facilities of synchrotron radiation (SR) and free electron lasers (FELs) with different wavelengths and neutron sources. We further discuss the comparison between Chinese and typical foreign facilities in X-ray radiation from X-ray tubes, synchrotrons, X-ray FELs, and neutron sources based on physical parameters of light and neutron sources. In addition, we focus on the technological progress and perspectives combined with advanced X-ray radiation and neutron sources of large scientific facilities in China, especially in the nanoscience fields of energy catalysis and biological science. We hope that this roadmap will provide references on technology and methods to experimental users, as well as prospects for future development of technologies based on large research infrastructure facilities. Comprehensive studies and guidelines for basic research to practical application in various disciplines can be made with the assistance of large scientific facilities.

MXene, with highly tunable and controllable surface terminations, is an emerging electrode material for electric double-layer (EDL) capacitors used in electrochemical energy storage. However, the influence of alterations in the electronic configuration of MXene induced by modifications in functional groups on EDL capacitance remains elusive. Thus, an implicit self-consistent electrolyte model is developed to investigate the EDL capacitance and structure of Mo2CTxMXene as a function of electronic configuration at an atomic scale. We reveal a strong correlation between the electronic configurations of metal Mo in Mo2CTxMXene and its EDL capacitance, with the dz2orbital of Mo perpendicular to the MXene surface playing a crucial role. The higher EDL capacitance and thinner EDL thickness primarily originate from a lower number of occupied electrons in the d orbitals (higher unoccupied d orbitals) and a larger d-band occupied center. Furthermore, this relationship can be further extended to the halogen termination of MXene. Notably, by manipulating the surface terminations, the electronic configurations (occupied and unoccupied orbitals) of Mo orbitals can be regulated, thus providing a facilitative way to control the EDL capacitance. The results show that the EDL capacitance depends not only on the electrode–electrolyte interfacial structure but also on the electronic configuration. These findings provide a solid foundation for regulating the structure and capacitance of the EDL of MXene from an electronic perspective, which could have significant implications for the development of advanced energy storage devices.

Dyes and antibiotics as typical persistent organic pollutants (POPs) are widely present in the environment, but can hardly be removed completely by traditional water treatment methods. Here, we designed Bi4O5Br2/g-C3N4composite nanosheets for efficient photocatalytic removal of POPs in water. The Bi4O5Br2/g-C3N4composite with a heterojunction structure exhibited high adsorption and photocatalytic activity for removal of tetracycline (TC) and ciprofloxacin (CIP) with excellent cyclic stability, owing to its large specific surface area as well as enhanced charge separation and visible light utilization. Our characterization revealed that h+and ·OH are responsible for the photocatalytic degradation of TC and CIP. This work provides insights into the design of photocatalytic materials with synergy of adsorption and photocatalytic degradation, and offers a heterojunction construction strategy for addressing the increasingly severe environmental issues. The Bi4O5Br2/g-C3N4composite with a heterojunction structure was fabricated by a hydrothermal method. The Bi4O5Br2/g-C3N4composite exhibits high adsorption and photocatalytic activity for removal of tetracycline (TC) and ciprofloxacin (CIP) with excellent cyclic stability due to its large specific surface area as well as enhanced charge separation and visible light utilization.

Lewis acidic molten salt method is a promising synthesis strategy for achieving MXenes with controllable surface termination from numerous MAX materials. Understanding the phase evolution chemistry during etching and post-processing is highly desirable but remains a key challenge due to the lack of suitable in-situ characterizations and the complexity of the reaction process. Herein, we introduce an operando synchrotron radiation X-ray diffraction (SRXRD) technique to unveil the phase evolution process of Nb2GaC MAX under a molten-salt ambient, proposing a controllable synthesis to achieve optimal etching through precise temperature and time adjustment. Subsequently, the phase structure of Nb2CTxMXenes is successfully tailored from hexagonal to amorphous by time-dependent persulfate oxidation. The resulting amorphous Nb2CTxwith a well-patterned morphology and numerous chloride terminations exhibits highly improved specific capacity, rate capability, and long cycling for Li+storage with a Cl-containing surface protective film. Addressing the time-related phase evolution during the entire molten salt strategy provides new insights into achieving higher efficiency and controllability in preparing MXenes and shows great potential in high-performance energy storage systems based on MXenes.

Reactive metal–support interactions (RMSIs) induce the formation of bimetallic alloys and offer an effective way to tune the electronic and geometric properties of metal sites for advanced catalysis. However, RMSIs often require high-temperature reductions (>500 °C), which significantly limits the tuning of bimetallic compositional varieties. Here, we report that an atomically thick Ga2O3coating of Pd nanoparticles enables the initiation of RMSIs at a much lower temperature of ∼250 °C. State-of-the-art microscopic and in situspectroscopic studies disclose that low-temperature RMSIs initiate the formation of rarely reported Ga-rich PdGa alloy phases, distinct from the Pd2Ga phase formed in traditional Pd/Ga2O3catalysts after high-temperature reduction. In the CO2hydrogenation reaction, the Ga-rich alloy phases impressively boost the formation of methanol and dimethyl ether ∼5 times higher than that of Pd/Ga2O3. In situinfrared spectroscopy reveals that the Ga-rich phases greatly favor formate formation as well as its subsequent hydrogenation, thus leading to high productivity.

The surface of energy material is the direct place where energy storage and conversion reactions occur. Thus, the surface chemistry and the structure of the material under real reaction conditions are the key descriptors to clarify the reaction mechanism. However, such surfaces are usually immersed in gaseous or liquid environments under real reaction conditions, so it is not a simple task to identify the real physical and chemical properties of the interface under in situconditions. X-ray photoelectron spectroscopy (XPS), as a surface-sensitive technique, is one of the main techniques for studying complex composition and electronic structure of material surfaces. However, due to the limited mean free path of photoelectrons in gas, liquid and solid media, the traditional XPS is confined to vacuum conditions, which poses a significant obstacle for studying solid-gas and solid-liquid interfaces under in situconditions. With the introduction of differentially pumped analyzers and electrostatic lenses system, this limitation no longer restricts XPS only suitable for ultra-high vacuum conditions. With the active development of synchrotron radiation sources worldwide, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) offers advanced features combined with the benefits of synchrotron radiation sources. Compared to traditional X-ray source, synchrotron radiation sources have significantly higher photon flux and much smaller spot size, which enables more electrons to escape to the electron analyzer, therefore can effectively improve the signal-to-noise ratio and the maximum working pressure, and the continuous wavelength tunability of synchrotron radiation makes experimental measurements more flexible and provides more information on the surface reaction. Over the years, NAP-XPS has rapidly emerged as an influential tool for investigating various solid-gas and solid-liquid interfaces, reflecting the importance of understanding reaction mechanisms and structure-performance relationship of materials under conditions closer to practical reacting conditions, particularly in heterogeneous catalysis. Information at atomic scale can be delivered with surface and interface sensitivity by NAP-XPS in conjunction with several advanced spectroscopy and microscopy techniques. In this paper, we provide a concise overview of recent notable advancements in NAP-XPS to showcase the novel insights generated by research on solid-gas and solid-liquid interfaces in cutting-edge scientific fields. This demonstrates how the knowledge gained from NAP-XPS studies can contribute to a fundamental understanding of reaction mechanisms at a molecular level. Finally, we discuss new challenges and prospects to ensure a comprehensive understanding of this technique and, hopefully, inspire fresh ideas.

Transition metal-based compounds generally undergo dynamic surface changes to form active metal (oxy)hydroxides during the oxygen evolution reaction (OER). However, due to the core-shell structure formed by insufficient surface reconstruction and the complexity of the dynamic evolution process, understanding the origin of the catalytic performance derived from the pre-catalyst itself is a great challenge. Herein, we first reveal that a transcriptional relationship of local coordination between the pre-catalyst and the in-situgenerated active species by regulating the lattice strain during phosphating with the aid of the nonequilibrium diffusion Kirkendall effect. The combination of electrochemical, ex-situX-ray absorption fine structure spectroscopy (XAFS) and in-situsynchrotron radiation Fourier transform infrared spectroscopy (SR-FTIR) characterizations uncover that the variation trend of the first shell Co–O bond length in the active species is inherited from the Co–P bond length in the pre-catalyst and the shortened optimal distance of the second shell dual-Co sites is strongly correlated with the inherent OER activity. Thereby, a relation mapping to modify the coordination structure of the active species via the lattice strain of the pre-catalysts is established. This work not only provides a strategy to regulate OER performance via the lattice strain, but also sheds light on the role of the structural and compositional evolution of catalysts in activity during electrocatalytic reactions.

An efficient catalytic system for nitrogen (N2) photofixation generally consists of light-harvesting units, active sites, and an electron-transfer bridge. In order to track photogenerated electron flow between different functional units, it is highly desired to develop in situcharacterization techniques with element-specific capability, surface sensitivity, and detection of unoccupied states. In this work, we developed in situsynchrotron radiation soft X-ray absorption spectroscopy (in situsXAS) to probe the variation of electronic structure for a reaction system during N2photoreduction. Nickel single-atom and ceria nanoparticle comodified reduced graphene oxide (CeO2/Ni-G) was designed as a model catalyst. In situsXAS directly reveals the dynamic interfacial charge transfer of photogenerated electrons under illumination and the consequent charge accumulation at the catalytic active sites for N2activation. This work provides a powerful tool to monitor the electronic structure evolution of active sites under reaction conditions for photocatalysis and beyond.

Interface engineering of zinc metal anodes is a promising remedy to relieve their inferior stability caused by dendrite growth and side reactions. Nevertheless, the low affinity and additional weight of the protective coating remain obstacles to their further implementation. Here, aroused by DFT simulation, self-assembled monolayers (SAMs) are selectively constructed to enhance the stability of zinc metal anodes in dilute aqueous electrolytes. It is found that the monolayer thiol molecules relatively prefer to selectively graft onto the unstable zinc crystal facets through strong Zn–S chemical interactions to engineer a covalent interface, enabling the uniform deposition of Zn2+onto (002) crystal facets. Therefore, dendrite-free anodes with suppressed side reactions can be achieved, proven by in situ optical visualization and differential electrochemical mass spectrometry (DEMS). In particular, the thiol endows the symmetric cells with a 4000 h ultrastable plating/stripping at a specific current density of 1.0 mA cm–2, much superior to those of bare zinc anodes. Additionally, the full battery of modified anodes enables stable cycling of 87.2% capacity retention after 3300 cycles. By selectively capping unstable crystal facets with inert molecules, this work provides a promising design strategy at the molecular level for stable metal anodes.

The coordinated configuration of atomic platinum (Pt) has always been identified as an active site with high intrinsic activity for hydrogen evolution reaction (HER). Herein, we purposely synthesize single vacancies in a carbon matrix (defective graphene) that can trap atomic Pt to form the Pt–C3configuration, which gives exceptionally high reactivity for HER in both acidic and alkaline solutions. The intrinsic activity of Pt–C3site is valued with a turnover frequency (TOF) of 26.41 s–1and mass activity of 26.05 A g–1at 100 mV, respectively, which are both nearly 18 times higher than those of commercial 20 wt % Pt/C. It is revealed that the optimal coordination Pt–C3has a stronger electron-capture ability and lower Gibbs free energy difference (ΔG), resulting in promoting the reduction of adsorbed H+and the acceleration of H2desorption, thus exhibiting the extraordinary HER activity. This work provides a new insight on the unique coordinated configuration of dispersive atomic Pt in defective C matrix for superior HER performance.

Atomically dispersed metal catalysts maximize atom efficiency and display unique catalytic properties compared with regular metal nanoparticles. However, achieving high reactivity while preserving high stability at appreciable loadings remains challenging. Here we solve the challenge by synergizing metal–support interactions and spatial confinement, which enables the fabrication of highly loaded atomic nickel (3.1 wt%) along with dense atomic copper grippers (8.1 wt%) on a graphitic carbon nitride support. For the semi-hydrogenation of acetylene in excess ethylene, the fabricated catalyst shows extraordinary catalytic performance in terms of activity, selectivity and stability—far superior to supported atomic nickel alone in the absence of a synergizing effect. Comprehensive characterization and theoretical calculations reveal that the active nickel site confined in two stable hydroxylated copper grippers dynamically changes by breaking the interfacial nickel–support bonds on reactant adsorption and making these bonds on product desorption. Such a dynamic effect confers high catalytic performance, providing an avenue to rationally design efficient, stable and highly loaded, yet atomically dispersed, catalysts.

A series of Eu3+doped Y2O3nanophosphors have been synthesized via an ultra-fast ultrasonic-microwave method followed by thermal annealing. The emission of Y2O3:Eu3+nanophosphors depends tremendously on the concentration of Eu3+ions and maximum emission intensity is achieved at 612 nm (red luminescence) with a doping concentration of 3 mol%. Moreover, the Y2O3:Eu3+nanophosphors in this work have much higher photoluminescence lifetime (1.570 ms) and quantum efficiency (80.88%) than that synthesized by other methods. The results of chromaticity coordinates indicate that the Y2O3:Eu3+as red-emitting phosphor is promising candidate for white light-emitting diodes (LEDs).

Single-atom catalysts not only maximize metal atom efficiency, they also display properties that are considerably different to their more conventional nanoparticle equivalents, making them a promising family of materials to investigate. Herein we developed a general host–guest strategy to fabricate various metal single-atom catalysts on nitrogen-doped carbon (M1/CN, M = Pt, Ir, Pd, Ru, Mo, Ga, Cu, Ni, Mn). The iridium variant Ir1/CN electrocatalyses the formic acid oxidation reaction with a mass activity of 12.9 AmgIr−1whereas an Ir/C nanoparticle catalyst is almost inert (~4.8 × 10−3AmgIr−1). The activity of Ir1/CN is also 16 and 19 times greater than those of Pd/C and Pt/C, respectively. Furthermore, Ir1/CN displays high tolerance to CO poisoning. First-principle density functional theory reveals that the properties of Ir1/CN stem from the spatial isolation of iridium sites and from the modified electronic structure of iridium with respect to a conventional nanoparticle catalyst.

The controllable synthesis of stable single-metal site catalysts with an expected coordination environment for high catalytic activity and selectivity is still challenging. Here, we propose a cation-exchange strategy for precise production of an edge-rich sulfur (S) and nitrogen (N) dual-decorated single-metal (M) site catalysts (M = Cu, Pt, Pd, etc.) library. Our strategy relies on the anionic frameworks of sulfides and N-rich polymer shell to generate abundant S and N defects during high-temperature annealing, further facilitating the stabilization of exchanged metal species with atomic dispersion and excellent accessibility. This process was traced by in situ transmission electron microscopy, during which no metal aggregates were observed. Both experiments and theoretical results reveal the precisely obtained S, N dual-decorated Cu sites exhibit a high activity and low reaction energy barrier in catalytic hydroxylation of benzene at room temperature. These findings provide a route to controllably produce stable single-metal site catalysts and an engineering approach for regulating the central metal to improve catalytic performance.

This review summarizes the strategies of cation intercalated MXenes, their achievements on energy storage systems, as well as the synchrotron-based X-ray absorption spectroscopic characterizations in recent years.

The efficient electrochemical hydrogen evolution reaction (HER) plays a key role in accelerating sustainable H2production from water electrolysis, but its large-scale applications are hindered by the high cost of the state-of-the-art Pt catalyst. In this work, submonolayer Pt was controllably deposited on an intermetallic Pd3Pb nanoplate (AL-Pt/Pd3Pb). The atomic efficiency and electronic structure of the active surface Pt layer were largely optimized, greatly enhancing the acidic HER. AL-Pt/Pd3Pb exhibits an outstanding HER activity with an overpotential of only 13.8 mV at 10 mA/cm2and a high mass activity of 7834 A/gPd+Ptat −0.05 V, both largely surpassing those of commercial Pt/C (30 mV, 1486 A/gPt). In addition, AL-Pt/Pd3Pb shows excellent stability and robustness. Theoretical calculations show that the improved activity is mainly derived from the charge transfer from Pd3Pb to Pt, resulting in a strong electrostatic interaction that can stabilize the transition state and lower the barrier.

Developing an active and stable metal single-atom catalyst (SAC) is challenging due to the high surface free energy of metal atoms. In this work, we report that tailoring of the 5dstate of Pt1single atoms on Co3O4through strong electronic metal–support interactions (EMSIs) boosts the activity up to 68-fold higher than those on other supports in dehydrogenation of ammonia borane for room-temperature hydrogen generation. More importantly, this catalyst also exhibits excellent stability against sintering and leaching, in sharp contrast to the rapid deactivation observed on other Pt single-atom and nanoparticle catalysts. Detailed spectroscopic characterization and theoretical calculations revealed that the EMSI tailors the unoccupied 5dstate of Pt1single atoms, which modulates the adsorption of ammonia borane and facilities hydrogen desorption, thus leading to the high activity. Such extraordinary electronic promotion was further demonstrated on Pd1/Co3O4and in hydrogenation reactions, providing a new promising way to design advanced SACs with high activity and stability.

Herein, we report a novel carbothermal welding strategy to prepare atomically dispersed Pd sites anchored on a three-dimensional (3D) ZrO2nanonet (Pd1@ZrO2) via two-step pyrolysis, which were evolved from isolated Pd sites anchored on linker-derived nitrogen-doped carbon (Pd1@NC/ZrO2). First, the NH2–H2BDC linkers and Zr6-based [Zr6(μ3-O)4(μ3-OH)4]12+nodes of UiO-66-NH2were transformed into amorphous N-doped carbon skeletons (NC) and ZrO2nanoclusters under an argon atmosphere, respectively. The NC supports can simultaneously reduce and anchor the Pd sites, forming isolated Pd1–N/C sites. Then, switching the argon to air, the carbonaceous skeletons are gasified and the ZrO2nanoclusters are welded into a rigid and porous nanonet. Moreover, the reductive carbon will result in abundant oxygen (O*) defects, which could help to capture the migratory Pd1species, leaving a sintering-resistant Pd1@ZrO2catalyst via atom trapping. This Pd1@ZrO2nanonet can act as a semi-homogeneous catalyst to boost the direct synthesis of indole through hydrogenation and intramolecular condensation processes, with an excellent turnover frequency (1109.2 h–1) and 94% selectivity.

Metal single-atom catalysts (SACs) have received significant attention in the catalysis field due to maximized atom efficiency and their unique catalytic properties. The support could have prominent influences on the catalytic performance. However, the support effect on metal SACs has been much less explored. We found that the Pd1/graphene catalyst exhibited remarkably higher activity than Pd1/C3N4in both reactions, but the alkene selectivity showed a different trend. In hydrogenation of acetylene, considerably higher ethylene selectivity was observed on Pd1/C3N4. While in hydrogenation of 1,3-butadiene, Pd1/graphene showed a significantly higher 1-butene selectivity, along with less n-butene isomer production. Higher activity of Pd1/graphene could be related with the lower Pd valence state revealed by X-ray photoemission spectroscopy and higher accessibility Pd1single atoms due to the slower coking rate. Meanwhile, different selectivities on these two samples might be attributed to the porosity and acidity of support and the variation of charge-induced Pd–substrate interaction. In brief, our work clearly demonstrated a remarkable support effect on the catalytic properties of Pd1SACs in hydrogenation reactions, which brings new insight into the design of highly active and selective SACs.

Developing efficient and durable oxygen evolution electrocatalyst is of paramount importance for the large-scale supply of renewable energy sources. Herein, we report a design of significant surface hydrophilicity based on the cobalt oxyhydroxide (CoOOH) nanosheets to greatly improve the surface hydroxyl species adsorption and reaction kinetics at the Helmholtz double layer for high-efficiency water oxidation activity. The as-designed CoOOH-Graphene nanosheets achieve a small surface water contact angle of ~23° and a large double-layer capacitance (Cdl) of 8.44 mF/cm2, thus could evidently strengthen surface species adsorption and trigger electrochemical oxygen evolution reaction (OER) under a quite low onset potential of 200 mV with an excellent Tafel slope of 32 mV/dec. X-ray absorption spectroscopy and first-principles calculations demonstrate that the strong interface electron coupling between CoOOH and graphene extracts partial electrons from the active sties and increases the electron state density around the Fermi level, and effectively promotes the surface intermediates formation for efficient OER.

We reported that atomically dispersed Pd on graphene can be fabricated using the atomic layer deposition technique. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy both confirmed that isolated Pd single atoms dominantly existed on the graphene support. In selective hydrogenation of 1,3-butadiene, the single-atom Pd1/graphene catalyst showed about 100% butenes selectivity at 95% conversion at a mild reaction condition of about 50 °C, which is likely due to the changes of 1,3-butadiene adsorption mode and enhanced steric effect on the isolated Pd atoms. More importantly, excellent durability against deactivation via either aggregation of metal atoms or carbonaceous deposits during a total 100 h of reaction time on stream was achieved. Therefore, the single-atom catalysts may open up more opportunities to optimize the activity, selectivity, and durability in selective hydrogenation reactions.

The catalytic performance is determined by the electronic structure near the Fermi level. This study presents an effective and simple screening descriptor, i.e., the one-dimensional density of states (1D-DOS) fingerprint similarity, to identify potential catalysts for the sulfur reduction reaction (SRR) in lithium–sulfur batteries. The Δ1D-DOS in relation to the benchmark W2CS2was calculated. This method effectively distinguishes and identifies 30 potential candidates for the SRR from 420 types of MXenes. Further analysis of the Gibbs free energy profiles reveals that MXene candidates exhibit promising thermodynamic properties for SRR, with the protocol achieving an accuracy rate exceeding 93%. Based on the crystal orbital Hamilton population (COHP) and differential charge analysis, it is confirmed that the Δ1D-DOS could effectively differentiate the interaction between MXenes and lithium polysulfide (LiPS) intermediates. This study underscores the importance of the electronic fingerprint in catalytic performance and thus may pave a new way for future high-throughput material screening for energy storage applications.

As one of the potential catalysts, disordered solid solution alloys can offer a wealth of catalytic sites. However, accurately evaluating their activity localization structure and overall activity from each individual site remains a formidable challenge. Herein, an approach based on density functional theory and machine learning was used to obtain a large number of sites of the Pt–Ru alloy as the model multisite catalyst for the hydrogen evolution reaction. Subsequently, a series of statistical approaches were employed to unveil the relationship between the geometric structure and overall activity. Based on the radial frequency distribution of metal elements and the distribution of ΔGH, we have identified the surface and subsurface sites occupied by Pt and Ru, respectively, as the most active sites. Particularly, the concept of equivalent site ratio predicts that the overall activity is highest when the Ru content is 20–30%. Furthermore, a series of Pt–Ru alloys were synthesized to validate the proposed theory. This provides crucial insights into understanding the origin of catalytic activity in alloys and thus will better guide the rational development of targeted multisite catalysts.

Electronic metal–support interactions (EMSIs) have opened a new way to tailor the electronic and catalytic properties of supported catalysts. Herein, we demonstrate the EMSIs between Pt nanoparticles and Co(OH)2flakes grown on SiO2and show its beneficial effect on enhancing the CO oxidation activity. The EMSI characteristics of the Pt–Co(OH)2/SiO2catalyst are identified by in situ X-ray absorption fine structure (XAFS) spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and transmission electron microscopy. Quantitative XAFS analysis reveals the presence of metallic-like Pt–Co bonds. The formation of Pt–Co intermetallic bonds allows for electron donation form Co to Pt, leading to the negative charging of the Pt atoms as evidenced by reduced Pt 2p-to-5d electron-transition intensity detected by XAFS spectroscopy and the emergence of a CO adsorption band at 2063 cm–1in DRIFTS. The significance of EMSIs is manifested by comparing the CO oxidation activity over the Pt–Co(OH)2/SiO2and Pt/SiO2catalysts with similar Pt loadings. Pt–Co(OH)2/SiO2is superior to Pt/SiO2in both the apparent activation energy (19 vs 64 kJ/mol) and the turnover frequency (0.03 vs 0.003 s–1at 37 °C). The enhanced activity is attributed to the negative charging of Pt, which downshifts the d-band center and reduces the CO adsorption strength.

Proton-exchange-membrane fuel cells (PEMFCs) are attractive next-generation power sources for use in vehicles and other applications1, with development efforts focusing on improving the catalyst system of the fuel cell. One problem is catalyst poisoning by impurity gases such as carbon monoxide (CO), which typically comprises about one per cent of hydrogen fuel2–4. A possible solution is on-board hydrogen purification, which involves preferential oxidation of CO in hydrogen (PROX)3–7. However, this approach is challenging8–15because the catalyst needs to be active and selective towards CO oxidation over a broad range of low temperatures so that CO is efficiently removed (to below 50 parts per million) during continuous PEMFC operation (at about 353 kelvin) and, in the case of automotive fuel cells, during frequent cold-start periods. Here we show that atomically dispersed iron hydroxide, selectively deposited on silica-supported platinum (Pt) nanoparticles, enables complete and 100 per cent selective CO removal through the PROX reaction over the broad temperature range of 198 to 380 kelvin. We find that the mass-specific activity of this system is about 30 times higher than that of more conventional catalysts consisting of Pt on iron oxide supports. In situ X-ray absorption fine-structure measurements reveal that most of the iron hydroxide exists as Fe1(OH)xclusters anchored on the Pt nanoparticles, with density functional theory calculations indicating that Fe1(OH)x–Pt single interfacial sites can readily react with CO and facilitate oxygen activation. These findings suggest that in addition to strategies that target oxide-supported precious-metal nanoparticles or isolated metal atoms, the deposition of isolated transition-metal complexes offers new ways of designing highly active metal catalysts.

Layered metal dichalcogenides have shown intriguing physical phenomena depending on their complex layer stackings and unique architectures. Here, we report novel microscale kirigami structures of multilayered WSe2formed by a simple chemical vapor deposition and etching method. Scanning electron microscopy and atomic force microscopy reveal the unusual structure features of curved concave edges, panhandles, and sawtooth corners of these intricate multilayer architectures that result from etching. The structure–symmetry relationship and layer stackings of these WSe2kirigami were elucidated by second-harmonic generation imaging and micro-Raman spectroscopy. We propose an etching model in which the etching behaviors of WSe2multilayers are governed by the layer stacking of the bottom trilayer, which can successfully explain the formation process of WSe2kirigami. This chemical etching approach could be applied to other metal dichalcogenide materials and open up new possibilities for creating novel and complex platforms for studying the rich physical properties in two-dimensional materials.

Atomically dispersed metal has gained much attention because of the new opportunities they offer in catalysis. However, it is still crucial to understand the mechanism of single-atom catalysis at molecular level for expanding them to other more difficult catalytic reactions, such as ammonia synthesis from nitrogen. In fact, developing ammonia synthesis under ambient conditions to overcome the high energy consumption in well-established Haber-Bosch process has fascinated scientists for many years. Herein, we demonstrate that single Cu atom yields facile valence-electron isolation from the conjugated π electron cloud of p-CN. Electron spin resonance measurements reveal that these isolated valence electrons can be easily excited to generate free electrons under photo-illumination, thus inducing high efficient photo-induced ammonia synthesis under ambient conditions. The NH3producing rate of copper modified carbon nitride (Cu-CN) reached 186 μmol g−1h−1under visible light irradiation with the quantum efficiency achieved 1.01% at 420 nm monochromatic light. This finding surely offers a model to open up a new vista for the ammonia synthesis at gentle conditions. The introduction of single atom to isolate the valence electron also represents a new paradigm for many other photocatalytic reactions, since the most photoinduced processes have been successfully exploited sharing the same origin.

Developing effective synthetic protocols for atomically monodisperse Au nanoclusters is pivotal to their fundamental science and applications. Here, we present a novel synthetic protocol toward atomically monodisperse [Au6(PPh3)6]2+nanoclusters (abbreviated as Au6) via ammonia-induced size convergence from polydisperse Aux(x= 6–11) nanocluster mixture. The analogous ammonia-induced size conversion reactions starting from individually prepared Au7and Au9nanoclusters to Au6were traced by time-dependent ultraviolet–visible absorption and electrospray ionization mass spectra. It is observed that in both cases the size conversion is achieved through gradual release of the ion–molecule complex [NH4AuPPh3Cl]+from the larger Au nanoclusters until the formation of thermodynamically stable Au6nanoclusters with the stability against the etching reaction. The role of ammonia ions in this size convergence synthesis is to accelerate the depletion of [Au(PPh3)]+fragments from the PPh3-protected Au nanoclusters, by the formation of the stable complex [NH4AuPPh3Cl]+.

Developing high-performance oxygen evolution reaction (OER) electrocatalysts is of great importance for sustainable and renewable energy conversion and storage. Here, via delocalizing the electron population around the active sites of layered hydrotalcites, we significantly facilitate the electron donation from the active sites in Cr-doped Ni0.75Fe0.25(OH)2.25and greatly reduce the charge transfer barrier by 1 order of magnitude for high OER activity. The Cr-doped Ni0.75Fe0.25(OH)2.25hydrotalcite nanosheets could thus achieve a small overpotential of 235 mV at 10 mA/cm2with an excellent Tafel slope of ∼39 mV/dec. The X-ray absorption fine structure spectroscopy and theoretical calculations reveal that the incorporated Cr ions are substituted for Fe sites in Ni0.75Fe0.25(OH)2.25and the strong overlap of dorbitals between Cr with unpaired delectrons and Fe ions promotes ∼0.3 electron π-donation from Ni2+to neighboring Cr (Fe) ions, and then evidently decreases the adsorption free energy of a water molecule to −1.45 eV for efficient OER performance.

Realizing high-efficiency hydrogen evolution in cost-effective and long-lasting electrocatalysts is critical for global production of clean and sustainable chemical fuels. Here, via modulating the metallic 1T phase in 2H MoS2nanosheets, we greatly improved the conductivity and effective active sites for highly efficient electrocatalytic hydrogen evolution. The as-synthesized 1T-2H MoS2electrocatalyst with a high 1T-phase content of 50% can significantly increase the charge concentration by an order of magnitude and triple the effective active surface sites, successfully boosting the hydrogen evolution reaction (HER) at a quite low overpotential of 126 mV at 10 mA/cm2and a small Tafel slope of 35 mV/dec. Ultraviolet photoelectron spectroscopy and electrochemical characterization reveal that the valence band edges of 1T-2H MoS2are upshifted by 0.15–0.36 eV, which obviously enhances the charge transfer ability of the surface active sites in the basal plane of MoS2for high HER performance.

Understanding the key factor controlling phase transitions of correlated oxides by chemical doping is becoming of fundamental and technological interest. Here, we report vanadium chain symmetry as an effective means of mediating the structural phase transition (SPT) temperature in hydrothermal Cr-doped VO2. In-situ X-ray absorption fine structure spectroscopy unveils that high structural symmetry with equidistant 2.93 Å V–V zigzag chains, along with the dimerized V–V straight chain induced by Cr-doping, can stabilize VO2at elevated temperature, thus raising the critical temperature of the VO2phase transition. The Cr-doped VO2system exhibited a SPT process involving lattice expansion, accompanied by V–V chain reconstruction into the rutile phase. These findings provide novel insights and guidance in chemically tailoring the phase transition of VO2.

Engineered MXene surfaces with more −O functional groups are feasible for realizing higher energy density due to their higher theoretical capacitance. However, there have been only a few explorations of this regulation mechanism. Investigating the formation source and mechanism is conducive to expanding the adjustment method from the top-down perspective. Herein, for the first time, the formation dynamics of −O functional groups on Mo2CTxare discovered as a two-step dehydrogenation of adsorbed water through in situ near-ambient-pressure X-ray photoelectron spectroscopy, further confirmed by ab initio molecular dynamics simulations. From this, the controllable substitution of −F functional groups with −O functional groups is achieved on Mo2CTxduring electrochemical cycling in an aqueous electrolyte. The obtained Mo2CTxwith rich −O groups exhibits a high capacitance of 163.2 F g –1at 50 mV s –1, together with excellent stability. These results offer new insights toward engineering surface functional groups of MXenes for many specific applications.

Pt/Fe3O4core/shell triangular nanoprisms were synthesized using seed-mediated heteroepitaxy. Their well-defined shape, facets, and ordered-assembly allowed detailed analysis of mechanism of the heteroepitaxy. At the Pt–Fe3O4interface, existence of both lattice and chemical mismatch resulted in facet-selective epitaxy along ⟨111⟩ directions of two lattices. X-ray absorption fine structure measurements demonstrated that the Pt seed nanocrystals were composed of an iron-rich Pt–Fe metallic thin layer sandwiched between the Pt core and a Fe–O outer-surface. The Fe–O outer-surface of the seed nanocrystals presumably offered epitaxial sites for the following deposition of the Fe3O4shell. Each tip and side of a triangular nanoprism respectively possessed a groove and a ridge, and a (111) plane parallel to the basal planes linked all grooves and ridges. This interesting (111) plane approximately bisected the triangle nanoprisms and located near the Pt-seed. The outer surface of the hybrid nanocrystals was also found to be facet-selective, that is, solely {111} facets of Fe3O4lattice. These polar {111} facets allowed the surface to be only occupied with high-density iron ions, and thus offered best surface coordination for the electron donating ligands in the solution.

Humic acid (HA) and iron oxides (FeOs) commonly coexist, and their interactions alter their ability to adsorb pollutants in the environment. The influences of HA on arsenate [As(V)] adsorption on FeOs were investigated on the preformation of complexes and their coexistence with As(V) in solution. The results indicated that HA could be strongly adsorbed on FeOs, and the adsorption capacity (Qmax, mg g−1HA‐C) followed the sequence goethite (7.73) > ferrihydrite (3.14) > hematite (2.25) with a desorption rate <1%. The HA adsorbed existed uniformly on the FeOs surfaces in spot form and did not change the x‐ray diffraction (XRD) patterns of FeOs. The formation of FeOs‐HA complexes altered As(V) adsorption with a reduced adsorption capacity, prolonged reaction kinetics, and enhanced adsorption strength. The As(V) adsorption on both FeOs and FeOs‐HA complexes decreased with increasing pH (2.5–9) or decreasing ionic strength (0.2–0 M). The coexistence of HA in solution linearly decreased the As(V) adsorption on FeOs. Thus, our results demonstrated two impact pathways of HA on As(V) adsorption on FeOs: (i) blockage or occupation in the surface sites of FeOs if HA preformed complexes with FeOs and (ii) a competition to the surface sites of FeOs when HA coexisted with As(V) in the solution. Iron oxides can strongly absorb humic acid with desorption rates <1%.The humic acid adsorbed existed uniformly on the iron oxide surfaces in fluffy spot forms.Humic acid reduced the adsorption capacity and kinetics of As(V) on iron oxides but enhanced the adsorption strength.Humic acid exerted its effect on As(V) adsorption by occupation or blockage of the surface adsorption sites.Complexation of humic acid with iron oxides did not change their patterns response to pH and ionic strength.

Understanding the atomic diffusions at the nanoscale is important for controlling the synthesis and utilization of nanomaterials. Here, using in situX-ray absorption spectroscopy coupled with theoretical calculations, we demonstrate a so far unexplored unidirectional diffusion from the Au shell to the Cu core in thermally alloying Cu@Au core@shell architecture of ca.7.1 nm. The initial diffusion step at 423 K is found to be characterized by the formation of a diffusion layer composed of a Au-dilute substitutional CuAu-like intermetallic compound with short Cu–Au bond length (2.61 Å). The diffusion further happens by the migration of the Au atoms with large disorder into the interior Cu matrix at higher temperatures (453 and 553 K). These results suggest that the structural preference of a CuAu-like compound, along with the nanosized effect, plays a critical role in determining the atomic diffusion dynamics.

Solvent has a key role in the controllable synthesis of nanocrystals (NCs). Here, using X-ray absorption spectroscopy, we demonstrate that solvent can significantly influence the adsorption of thiols on Au NCs, and thereby affects their growth. It is shown that increasing the solvent polarities leads to the higher thiol coverage on the NC surface. The high coverage of thiols then retards the growth of particles, and as a result, the NCs’ sizes decrease with the increase in the solvents’ polarities. The underlying reason for the solvent dependence is proposed to be the synergistic effects of different hydrogen bond and hydrophobic interactions between the sulfhydryl and alkyl groups of thiols with the solvents molecules. This work addresses the important role of the solvent environments in the size-controlled synthesis of NCs.

Elemental codoping has been an effective way to modify the structural and electronic properties of semiconductors. By use of X-ray diffraction and X-ray absorption fine structure spectroscopy, we show that the spatial occupations of Co and Cu codopants in ZnO thin films could be regulated by the crystal orientation of the matrix prepared by pulsed laser deposition at different temperatures. At deposition temperatures lower than 300 °C, the ZnO matrix was grown along the [201] preferential orientation, with the substitutional incorporation of Co dopants and formation of metallic Cu nanoclusters. Increasing the growth temperature to 300 °C or higher drives a transform of the ZnO film to the c-axial [002] preferred orientation. Consequently, the Cu atoms aggregate into larger fcc-structured Cu nanocrystals that attract part of the Co dopants to precipitate out as metallic clusters. The relation between the growth orientation of ZnO thin films and the occupation positions of Co/Cu codopants is discussed in terms of the temperature-dependent mobility and formation energy of the doping atoms.

Control over the anisotropic assembly of small building blocks into organized structures is considered an effective way to design organic nanosheets and atomically thick inorganic nanosheets with nonlayered structure. However, there is still no available route so far to control the assembly of inorganic and organic building blocks into a flattened hybrid nanosheet with atomic thickness. Herein, we highlight for the first time a universal in-plane coassembly process for the design and synthesis of transition-metal chalcogenide–alkylamine inorganic–organic hybrid nanosheets with atomic thickness. The structure, formation mechanism, and stability of the hybrid nanosheets were investigated in detail by taking the Co9S8–oleylamine (Co9S8–OA) hybrid nanosheets as an example. Both experimental data and theoretical simulations demonstrate that the hybrid nanosheets were formed by in-plane connection of small two-dimensional (2D) Co9S8nanoplates viaoleylamine molecules adsorbed at the side surface and corner sites of the nanoplates. X-ray absorption fine structure spectroscopy study reveals the structure distortion of the small 2D Co9S8nanoplates that endows structural stability of the atomically thick Co9S8–OA hybrid nanosheets. The brand new atomically thick nanosheets with inorganic–organic hybrid network nanostructure will not only enrich the family of atomically thick 2D nanosheets but also inspire more interest in their potential applications.

The structures and dielectric properties of Pb(Fe1/2Nb1/2)1-xTixO3(PFNT, $x = 0.07$ and 0.48) single crystals were investigated using a combination of temperature-dependent dielectric, X-ray diffraction (XRD), Raman, and X-ray absorption fine structure (XAFS) spectra. Detailed structure analyses reveal that the crystal structure of PFNT ($x = 0.48$) is single-phase tetragonal perovskite, whereas that of PFNT ($x = 0.07$) is a mixture of rhombohedral and tetragonal phases. The structural differences are found to have significant connections with the dielectric properties in the temperature range of 90--300 K. Both samples exhibit a frequency-dependent dielectric anomaly, arising primarily from the 3d electrons hopping between Fe2+and Fe3+. The second dielectric anomaly, which is a weak frequency dispersion and observable only for PFNT ($x = 0.07$), was probably caused by a dipole glass behavior near the morphotropic phase boundary.

To efficiently transform absorbed photons to chemical energy is highly desired for the full utilization of visible light in solar hydrogen generation process. Here, a highly active photoanode consisting of a thin NixFe2–xO3overlayer on the surface of hematite nanotube has been constructed to raise the utilization of the photoexcited carriers by Fe2O3in the visible spectrum. We find that the obtained overlayer photoanodes promote the charge migration of photogenerated carriers to the surface, accelerating surface oxygen evolution and avoiding low-energy photoexcited holes recombination at the semiconductor–liquid junction. Relative to the pristine Fe2O3photoanodes, a sustainably high incident photon to electron conversion efficiency from 40% at 400 nm until 10% at 500 nm is observed for Ni-doped overlayer hematite, yielding ∼280% enhancement of the photoconversion efficiency. Our results provide some guidance for the future design and optimization for the structure of photoanode.

The interfacial atomic and electronic structures of ligand-protected nanomaterials are vital factors but are inadequately known. Here, we demonstrate that the adsorption geometry, as well as the electronic structures of Au–S interface, can be tailored via varying the hydrocarbon “tail” lengths of n-alkanethiol ligands. Fully n-alkanethiols (n= 3, 8, and 12) capped Au nanocrystals of 3.0 nm were characterized in solution by X-ray absorption fine structure at the Au L3-edge. With increasing alkyl length, it is found that the headgroup S atom occupies the nanocrystals surface sites with gradually higher coordinations, along with the progressively shortened Au–S bond length. As a result, the strongest Au–S interactions coming from the longest n-alkanethiols capping lead to the most significant dcharge transfer from the surface Au layer to the S atoms.

Here we report a study to improve the solar water splitting activity of TiO2photoanodes by tuning the porosity of the nanotube arrays. Through modifying the electrochemical anodization conditions, the average wall thickness and inner diameter of the synthesized TiO2nanotube arrays were controlled in the range of 8–20 nm and 40–145 nm, respectively, corresponding to a variation of the porosity from 47.1% to 75.7%. The photoelectrochemical (PEC) measurements demonstrate that the sample with maximum porosity (75.7%) shows the peak ultraviolet conversion efficiency of 7.02%. Further analysis reveals that the photoconversion efficiency increases monotonously with porosity rather than with wall thickness and/or inner diameter. We suggest that the large porosity can ensure a much shorter hole diffusion path toward wall surface and accelerate ion migration in the tube to overcome the kinetic bottleneck, thus enhancing the PEC water splitting efficiency of the TiO2nanotube arrays.

Here we report that the occupation sites of Co atoms in ZnO matrix could be effectively tuned by the concentration of Cu codopant. The Co–Cu codoping effect has been revealed by a combination of X-ray diffraction and X-ray absorption fine structure spectroscopy techniques for Zn0.95–xCuxCo0.05O (0.005 ≤ x≤ 0.08) thin films grown by pulse laser deposition at 923 K. Specifically, at the low Cu doping levels (x≤ 0.02), the Co(+2) ions are substantially incorporated into the ZnO lattice; upon increasing the Cu concentration to 0.03 or higher, partial formation of Co(0) species occurs, and its proportion rises rapidly with the Cu concentration. Further analysis shows that the Cu codopants are precipitated to form Cu(0) metallic phase in all the samples. We propose a competition mechanism between the Co(0)–Cu(0) metallic interactions and the dissolution of Co ions in ZnO to interpret these findings.

Abstract: The structures of selenium nanoparticles and nanotubes synthesized by the dismutation of precursor Na2SeSO3 under acidic condition in micellar solution are studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray absorption fine structure spectroscopy (XAFS). Spherical-like nanoparticles contain both amorphous and crystalline parts while, as shown by XRD patterns, nanotubes have the crystal structure of trigonal selenium (t-Se). They display quite different XANES spectral features indicating different local atomic arrangements. Theoretical XANES calculations show that the local structure around Se atom in the nanotubes is similar to a hexangular cylinder. Quantitative extended XAFS (EXAFS) analysis further shows that the average Se–Se bond length for both nanotubes and nanoparticles is 2.35 Å.

Abstract: The Morlet wavelet transformation (MT) was used to analyze Mn K-edge extended X-ray absorption fine structure (EXAFS) spectra of Mn-doped Si-based diluted magnetic semiconductor (DMS) thin films grown by the magnetron co-sputtering method. MT of EXAFS data shows that the Mn–Mn scattering path can be distinguished by the Mn–Si scattering path in the spectra of Mn x Si1−x DMS thin films. In all DMS thin films Mn atoms fill Si sites without forming Mn–Si compounds while Mn–Si compounds are present in the annealed analogues. From the analysis of experimental data we point out that low-concentration Mn-doped samples are characterized by a more symmetric structure.

Reversible dehydrationof complex 1switches the spin state of cobalt from low‐spin (LS) CoIIIto high‐spin (HS) CoII(see picture) and allows the magnetic moment to be varied from 0.48 μBat 120 °C to 4.15 μBat 220 °C in fully dehydrated complex 1‐220. notpH6=1,4,7‐triazacyclononane‐1,4,7‐triyl‐tris(methylenephosphonic acid).

Die reversible Dehydratisierungvon Komplex 1schaltet den Spinzustand des Cobalts von Low‐Spin(LS)‐CoIIIzu High‐Spin(HS)‐CoII(siehe Bild). Dies ermöglicht es, das magnetische Moment von 0.48 μBbei 120 °C auf 4.15 μBbei 220 °C im vollständig dehydratisierten Komplex 1‐220hochzufahren. notpH6=1,4,7‐Triazacyclononan‐1,4,7‐triyltris(methylenphosphonsäure).

The efficient absorption of visible light is crucial for improving the photocatalytic activity of foreign species-doped TiO2. With first-principles calculations, we explore the effects of phosphorus doping on mediating the photocatalytic activity of anatase. It is found that the P impurity tends to occupy the cation site in TiO2; more importantly, there exists a critical phosphorus concentration of about 0.7% for maximizing the absorption of solar light. The optical energy gap is narrowed by ∼0.3 eV at the low doping concentration of 0.7%, whereas it increases with P concentration at the higher P concentration region of 0.7−3.1 atm. %. These results suggest that the dopant concentration dependence might be responsible for numerous seeming controversies of optical absorption observed in experiments. This finding points to a possibility of tailoring the optical absorption of TiO2by varying the dopant content.