Atomically dispersed iron hydroxide anchored on Pt for preferential oxidation of CO in H2.

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 challenging8-15 because 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)x clusters 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.

Boosting Electrocatalytic Ammonia Synthesis via Synergistic Effect of Iron-Based Single Atoms and Clusters.

Electrocatalytic reduction of nitrate to ammonia (NO3RR) is gaining attention for low carbon emissions and environmental protection. However, low ammonia production rate and poor selectivity have remained major challenges in this multi-proton coupling process. Herein, we report a facile strategy toward a novel Fe-based hybrid structure composed of Fe single atoms and Fe3C atomic clusters that demonstrates outstanding performance for synergistic electrocatalytic NO3RR. By operando synchrotron Fourier transform infrared spectroscopy and theoretical computation, we clarify that Fe single atoms serve as the active site for NO3RR, while Fe3C clusters facilitate H2O dissociation to provide protons (*H) for continued hydrogenation reactions. As a result, the Fe-based electrocatalyst exhibits ammonia Faradaic efficiency of nearly 100%, with a corresponding production rate of 24768 µg h-1 cm-2 at -0.4 V vs RHE, exceeding most reported metal-based catalysts. This research provides valuable guidance toward multi-step reactions.

Self-Assembly Intermetallic PtCu3 Core with High-Index Faceted Pt Shell for High-Efficiency Oxygen Reduction.

Rational design of well-defined active sites is crucial for promoting sluggish oxygen reduction reactions. Herein, leveraging the surfactant-oriented and solvent-ligand effects, we develop a facile self-assembly strategy to construct a core-shell catalyst comprising a high-index Pt shell encapsulating a PtCu3 intermetallic core with efficient oxygen-reduction performance. Without undergoing a high-temperature route, the ordered PtCu3 is directly fabricated through the accelerated reduction of Cu2+, followed by the deposition of the remaining Pt precursor onto its surface, forming high-index steps oriented by the steric hindrance of surfactant. This approach results in a high half-wave potential of 0.911 V versus reversible hydrogen electrode, with negligible deactivation even after 15000-cycle operation. Operando spectroscopies identify that this core-shell catalyst facilitates the conversion of oxygen-involving intermediates and ensures antidissolution ability. Theoretical investigations rationalize that this improvement is attributed to reinforced electronic interactions around high-index Pt, stabilizing the binding strength of rate-determining OHads species.

Visualization of the Distance-Dependent Synergistic Interaction in Heterogeneous Dual-Site Catalysis.

Understanding the characteristics of interfacial hydroxyl (OH) at the solid/liquid electrochemical interface is crucial for deciphering synergistic catalysis. However, it remains challenging to elucidate the influences of spatial distance between interfacial OH and neighboring reactants on reaction kinetics at the atomic level. Herein, we visualize the distance-dependent synergistic interaction in heterogeneous dual-site catalysis by using ex-situ infrared nanospectroscopy and in situ infrared spectroscopy techniques. These spectroscopic techniques achieve direct identification of the spatial distribution of synergistic species and reveal that OH facilitates the reactant deprotonation process depending on site distances in dual-site catalysts. Via modulating Ir-Co pair distances, we find that the dynamic equilibrium between generation and consumption of OH accounts for high-efficiency synergism at the optimized distance of 7.9 Å. At farther or shorter distances, spatial inaccessibility and resistance of OH with intermediates lead to OH accumulation, thereby diminishing the synergistic effect. Hence, a volcano-shaped curve has been established between the spatial distance and mass activity using formic acid oxidation as the probe reaction. This notion could also be extended to oxophilic metals, like Ir-Ru pairs, where volcano curves and dynamic equilibrium further evidence the universal significance of spatial distances.

Open Nitrogen Site-Induced Kinetic Resolution and Catalysis of a Gold Nanocluster.

The emerging metal nanocluster provides a platform for the investigation of structural features, unique properties, and structure-property correlation of nanomaterials at the atomic level. Construction of open sites on the surface of the metal nanocluster is a long-pursued but challenging goal. Herein, we realized the construction of "open organic sites" in a metal nanocluster for the first time. Specifically, we introduce the PNP (2,6-bis(diphenylphosphinomethyl)pyridine) pincer ligand in the synthesis of the gold nanocluster, enabling the construction of a structurally precise Au8(PNP)4 nanocluster. The rigidity and the unique bonding mode of PNP lead to open nitrogen sites on the surface of the Au8(PNP)4 nanocluster, which have been utilized as multifunctional sites in this work for efficient kinetic resolution and catalysis. The gold pincer nanocluster and the open nitrogen site-induced performance will be enlightening for the construction of multifunctional metal nanoclusters.

Edge-Rich Pt-O-Ce Sites in CeO2 Supported Patchy Atomic-Layer Pt Enable a Non-CO Pathway for Efficient Methanol Oxidation.

Rational design of efficient methanol oxidation reaction (MOR) catalyst that undergo non-CO pathway is essential to resolve the long-standing poisoning issue. However, it remains a huge challenge due to the rather difficulty in maximizing the non-CO pathway by the selective coupling between the key *CHO and *OH intermediates. Here, we report a high-performance electrocatalyst of patchy atomic-layer Pt epitaxial growth on CeO2 nanocube (Pt ALs/CeO2) with maximum electronic metal-support interaction for enhancing the coupling selectively. The small-size monolayer material achieves an optimal geometrical distance between edge Pt-O-Ce sites and *OH absorbed on CeO2, which well restrains the dehydrogenation of *CHO, resulting in the non-CO pathway. Meanwhile, the *CHO/*CO intermediate generated at inner Pt-O-Ce sites can migrate to edge, inducing the subsequent coupling reaction, thus avoiding poisoning while promoting reaction efficiency. Consequently, Pt ALs/CeO2 exhibits exceptionally catalytic stability with negligible degradation even under 1000 s pure CO poisoning operation and high mass activity (14.87 A/mgPt), enabling it one of the best-performing alkali-stable MOR catalysts.

Ligand Assisted Thermal Atomization of Palladium Clusters: An Inspiring Approach for the Rational Design of Atomically Dispersed Metal Catalysts.

The transformation from metal nanocluster catalysts to metal single-atom catalysts is an important procedure in the rational design of atomically dispersed metal catalysts (ADCs). However, the conversion methods often involve high annealing temperature as well as reducing atmosphere. Herein, we reported a continuous and convenient approach to transfer Pd nanocluster into Pd single-atom in a ligand assisted annealing procedure, by which means we reduced its activating temperature low to 400 °C. Using ex-situ microscopy and spectroscopy, we comprehensively monitored the structural evolution of Pd species though the whole atomization process. Theoretical calculation revealed that the structural instability caused by remaining Cl ligands was the main reason for this low-temperature transformation. The present atomization strategy and mechanistic knowledge for the conversion from cluster to atomic dispersion provides guidelines for the rational design of ADCs.

Understanding Synergistic Catalysis on Cu-Se Dual Atom Sites via Operando X-ray Absorption Spectroscopy in Oxygen Reduction Reaction.

The construction and understanding of synergy in well-defined dual-atom active sites is an available avenue to promote multistep tandem catalytic reactions. Herein, we construct a dual-hetero-atom catalyst that comprises adjacent Cu-N4 and Se-C3 active sites for efficient oxygen reduction reaction (ORR) activity. Operando X-ray absorption spectroscopy coupled with theoretical calculations provide in-depth insights into this dual-atom synergy mechanism for ORR under realistic device operation conditions. The heteroatom Se modulator can efficiently polarize the charge distribution around symmetrical Cu-N4 moieties, and serve as synergistic site to facilitate the second oxygen reduction step simultaneously, in which the key OOH*-(Cu1 -N4 ) transforms to O*-(Se1 -C2 ) intermediate on the dual-atom sites. Therefore, this designed catalyst achieves satisfied alkaline ORR activity with a half-wave potential of 0.905 V vs. RHE and a maximum power density of 206.5 mW cm-2 in Zn-air battery.

Partially oxidized atomic cobalt layers for carbon dioxide electroreduction to liquid fuel.

Electroreduction of CO2 into useful fuels, especially if driven by renewable energy, represents a potentially 'clean' strategy for replacing fossil feedstocks and dealing with increasing CO2 emissions and their adverse effects on climate. The critical bottleneck lies in activating CO2 into the CO2(•-) radical anion or other intermediates that can be converted further, as the activation usually requires impractically high overpotentials. Recently, electrocatalysts based on oxide-derived metal nanostructures have been shown to enable CO2 reduction at low overpotentials. However, it remains unclear how the electrocatalytic activity of these metals is influenced by their native oxides, mainly because microstructural features such as interfaces and defects influence CO2 reduction activity yet are difficult to control. To evaluate the role of the two different catalytic sites, here we fabricate two kinds of four-atom-thick layers: pure cobalt metal, and co-existing domains of cobalt metal and cobalt oxide. Cobalt mainly produces formate (HCOO(-)) during CO2 electroreduction; we find that surface cobalt atoms of the atomically thin layers have higher intrinsic activity and selectivity towards formate production, at lower overpotentials, than do surface cobalt atoms on bulk samples. Partial oxidation of the atomic layers further increases their intrinsic activity, allowing us to realize stable current densities of about 10 milliamperes per square centimetre over 40 hours, with approximately 90 per cent formate selectivity at an overpotential of only 0.24 volts, which outperforms previously reported metal or metal oxide electrodes evaluated under comparable conditions. The correct morphology and oxidation state can thus transform a material from one considered nearly non-catalytic for the CO2 electroreduction reaction into an active catalyst. These findings point to new opportunities for manipulating and improving the CO2 electroreduction properties of metal systems, especially once the influence of both the atomic-scale structure and the presence of oxide are mechanistically better understood.

Structural and electrocatalytic properties of copper clusters: A study via deep learning and first principles.

Determining the atomic structure of clusters has been a long-term challenge in theoretical calculations due to the high computational cost of density-functional theory (DFT). Deep learning potential (DP), as an alternative way, has been demonstrated to be able to conduct cluster simulations with close-to DFT accuracy but at a much lower computational cost. In this work, we update 34 structures of the 41 Cu clusters with atomic numbers ranging from 10 to 50 by combining global optimization and the DP model. The calculations show that the configuration of small Cun clusters (n = 10-15) tends to be oblate and it gradually transforms into a cage-like configuration as the size increases (n > 15). Based on the updated structures, their relative stability and electronic properties are extensively studied. In addition, we select three different clusters (Cu13, Cu38, and Cu49) to study their electrocatalytic ability of CO2 reduction. The simulation indicates that the main product is CO for these three clusters, while the selectivity of hydrocarbons is inhibited. This work is expected to clarify the ground-state structures and fundamental properties of Cun clusters, and to guide experiments for the design of Cu-based catalysts.

Construction of direct Z-Scheme photocatalysts for overall water splitting using two-dimensional van der waals heterojunctions of metal dichalcogenides.

The direct Z-scheme system constructed by two-dimensional (2D) materials is an efficient route for hydrogen production from photocatalytic water splitting. In the present work, the 2D van der Waals (vdW) heterojunctions of MoSe2 /SnS2 , MoSe2 /SnSe2 , MoSe2 /CrS2 , MoTe2 /SnS2 , MoTe2 /SnSe2 , and MoTe2 /CrS2 are proposed to be promising candidates for direct Z-scheme photocatalysts and verified by first principles calculations. Perpendicular electric field is induced in these 2D vdW heterojunctions, which enhances the efficiency of solar energy utilization. Replacing MoSe2 with MoTe2 not only facilitates the interlayer carrier migration, but also improves the optical absorption properties for these heterojunctions. Excitingly, the 2D vdW MoTe2 /CrS2 heterojunction is demonstrated, for the first time, to be 2D near-infrared-light driven photocatalyst for direct Z-scheme water splitting. © 2018 Wiley Periodicals, Inc.

Intrinsic Electric Fields in Two-dimensional Materials Boost the Solar-to-Hydrogen Efficiency for Photocatalytic Water Splitting.

Two-dimensional (2D) materials with the vertical intrinsic electric fields show great promise in inhibiting the recombination of photogenerated carriers and widening light absorption region for the photocatalytic applications. For the first time, we investigated the potential feasibility of the experimentally attainable 2D M2X3 (M = Al, Ga, In; X = S, Se, Te) family featuring out-of-plane ferroelectricity used in photocatalytic water splitting. By using first-principles calculations, all the nine members of 2D M2X3 are verified to be available photocatalysts for overall water splitting. The predicted solar-to-hydrogen efficiency of Al2Te3, Ga2Se3, Ga2Te3, In2S3, In2Se3, and In2Te3 are larger than 10%. Excitingly, In2Te3 is manifested to be an infrared-light driven photocatalyst, and its solar-to-hydrogen efficiency limit using the full solar spectrum even reaches up to 32.1%, which breaks the conventional theoretical efficiency limit.

Atomic-Level Insight into Optimizing the Hydrogen Evolution Pathway over a Co1 -N4 Single-Site Photocatalyst.

Knowledge of the photocatalytic H2 evolution mechanism is of great importance for designing active catalysts toward a sustainable energy supply. An atomic-level insight, design, and fabrication of single-site Co1 -N4 composite as a prototypical photocatalyst for efficient H2 production is reported. Correlated atomic characterizations verify that atomically dispersed Co atoms are successfully grafted by covalently forming a Co1 -N4 structure on g-C3 N4 nanosheets by atomic layer deposition. Different from the conventional homolytic or heterolytic pathway, theoretical investigations reveal that the coordinated donor nitrogen increases the electron density and lowers the formation barrier of key Co hydride intermediate, thereby accelerating H-H coupling to facilitate H2 generation. As a result, the composite photocatalyst exhibits a robust H2 production activity up to 10.8 µmol h-1 , 11 times higher than that of pristine counterpart.

Theoretical Study of Single-Atom Catalysts for Hydrogen Evolution Reaction Based on BiTeBr Monolayer.

Developing an inexpensive and efficient catalyst for a hydrogen evolution reaction (HER) is an effective measure to alleviate the energy crisis. Single-atom catalysts (SACs) based on Janus materials demonstrated promising prospects for the HER. Herein, density functional theory calculations were conducted to systematically investigate the performance of SACs based on the BiTeBr monolayer. Among the one hundred and forty models that were constructed, fourteen SACs with potential HER activity were selected. Significantly, the SAC, in which a single Ru atom is anchored on a BiTeBr monolayer with a Bi vacancy (RuS2/VBi-BiTeBr), exhibits excellent HER activity with an ultra-low |ΔGH*| value. A further investigation revealed that RuS2/VBi-BiTeBr tends to react through the Volmer-Heyrovsky mechanism. An electronic structure analysis provided deeper insights into this phenomenon. This is because the Tafel pathway requires overcoming steric hindrance and disrupting stable electron filling states, making it challenging to proceed. This study finally employed constant potential calculations, which approximate experimental situations. The results indicated that the ΔGH* value at pH = 0 is 0.056 eV for RuS2/VBi-BiTeBr, validating the rationality of the traditional Computational Hydrogen Electrode (CHE) method for performance evaluation in this system. This work provides a reference for the research of new HER catalysts.

Platinum monolayer dispersed on MXenes for electrocatalyzed hydrogen evolution: a first-principles study.

Maximizing platinum's atomic utilization and understanding the anchoring mechanism between platinum moieties and their supports are crucial for the hydrogen evolution reaction (HER). Using density functional theory, we investigate the catalyst of a Pt monolayer on the two-dimensional Mo2TiC2 substrate (PtML/Mo2TiC2) for the reaction. This Pt monolayer shows a Pt(111)-like pattern, with its Pt-Pt bond elongated by about 0.1 Å compared to Pt(111); charge transfer from Mo2TiC2 to the Pt monolayer leads to significant charge accumulation on Pt. This substantial monolayer metal-support interaction optimizes hydrogen adsorption toward optimal HER activity under both constant charge and potential conditions, making PtML/Mo2TiC2 a promising HER catalyst. Detailed studies reveal that the dominant Volmer-Tafel mechanism in the HER occurs on the 1 monolayer hydrogen-covered PtML/Mo2TiC2 surface. The surface Pourbaix diagram identifies this as the stable surface termination under the electrochemical reaction conditions. These findings provide insights into designing stable, efficient, and low platinum-loaded HER catalysts.

Unveiling the Composition-Dependent Catalytic Mechanism of Pt-Ni Alloys for Oxygen Reduction: A First-Principles Study.

Unveiling the composition-dependent catalytic mechanism of Pt-based alloy cathodes for the oxygen reduction reaction (ORR) helps improve the proton exchange membrane fuel cells. Using density functional theory calculations, this study investigates the ORR catalytic performance of the Pt-Ni system with various compositions (1.00, ∼0.99, 0.75, 0.50, 0.25, ∼0.01, and 0.00). The ordered solid solution PtNi3(111) system shows activity comparable to Pt(111) and is cost-effective. The Ni1/Pt(111) system, featuring a single Ni atom on the Pt(111) surface as a surface single-atom alloy (SSAA), demonstrates the highest activity with an overpotential of only 0.28, which could be further reduced to 0.21 V by decreasing the surface Ni concentration to 1/16 monolayer coverage. The predicted high activity of Ni1/Pt(111) is confirmed when considering factors such as the implicit solution environment, constant potential conditions, and protonation capability. Moreover, surface-adsorbed oxygen species driven by reaction conditions stabilize these single Ni atoms of Ni1/Pt(111) by preventing segregation and dissolution processes, thereby exhibiting a dual functionality. This study reveals the composition dependence of Pt-based alloys and highlights the stability mechanisms of SSAA catalysts during the ORR.

Design, Synthesis, and 3D-QASR of 2-Ar-1,2,3-triazole Derivatives Containing Hydrazide as Potential Fungicides.

A series of novel 2-Ar-1,2,3-triazole derivatives were designed and synthesized based on our previously discovered active compound 6d against Rhizoctonia solani. Most of these compounds exhibited good antifungal activity against R. solani at a concentration of 25 µg/mL. Based on the results of biological activity, we established a three-dimensional quantitative structure-activity relationship (3D-QSAR) model that guided the synthesis of compound 7y. Compound 7y exhibited superior activity against R. solani (EC50 = 0.47 µg/mL) compared to the positive controls hymexazol (EC50 = 12.80 µg/mL) and tebuconazole (EC50 = 0.87 µg/mL). Furthermore, compound 7y demonstrated better protective activity than the aforementioned two commercial fungicides in both detached leaf assays and greenhouse experiments, achieving 56.21% and 65.75% protective efficacy, respectively, at a concentration of 100 µg/mL. The ergosterol content was determined and molecular docking was performed to explore the mechanism of these active molecules. DFT calculation and MEP analysis were performed to illustrate the results of this study. These results suggest that compound 7y could serve as a novel 2-Ar-1,2,3-triazole lead compound for controlling R. solani.

First-Principles Insights into Tungsten Semicarbide-Based Single-Atom Catalysts: Single-Atom Migration and Mechanisms in Oxygen Reduction.

Understanding the structural evolution of single-atom catalysts (SACs) in catalytic reactions is crucial for unraveling their catalytic mechanisms. In this study, we utilize density functional theory calculations to delve into the active phase evolution and the oxygen reduction reaction (ORR) mechanism of tungsten semicarbide-based transition metal SACs (TM1/W2C). The stable crystal phases and optimal surface exposures of W2C are identified by using ab initio atomistic thermodynamics simulations. Focusing on the W-terminated (001) surface, we screen 13 stable TM1/W2C variants, ultimately selecting Pt1/W2C(001) as our primary model. The surface Pourbaix diagram, mapped for this model under ORR conditions, reveals dynamic Pt1 migration on the surface, triggered by surface oxidation. This discovery suggests a novel single-atom evolution pathway. Remarkably, this single-atom migration behavior is also discerned in seven other group VIII SACs, enhancing both their catalytic activity and their stability. Our findings offer insights into the evolution of active phases in SACs, considering substrate structural arrangement, single-atom incorporation, and self-optimization of catalysts under various conditions.

Manipulation of d-Orbital Electron Configurations in Nonplanar Fe-Based Electrocatalysts for Efficient Oxygen Reduction.

Manipulation of the spin state holds great promise to improve the electrochemical activity of transition metal-based catalysts. However, the underlying relationship between the nonplanar metal coordination environment and spin states remains to be explored. Herein, we report the precise regulation of nonplanar Fe atomic d-orbital energy level into an irregular tetrahedral crystal field configuration by introducing P atoms. With the increase of P coordination number, the spin magnetic moment decreases linearly from 3.8 µB to 0.2 µB, and the high spin content decreases linearly from 31% to 5%. Significantly, a volcanic curve between the spin states of Fe-based catalysts (Fe-NxPy) and oxygen reduction reaction (ORR) activity has been unequivocally established based on the thermodynamic results. Thus, the Fe-N3P1 catalyst with a 19% medium spin state experimentally exhibits the optimal reaction activity with a high half-wave potential of 0.92 V. These findings indicate that regulating electron spin moments through coordination engineering is a promising catalyst design strategy, providing important insights into spin catalysis.

Cu-phen Coordination Enabled Selective Electrocatalytic Reduction of CO2 to Methane.

Manipulation of selectivity in the catalytic electrochemical carbon dioxide reduction reaction (eCO2RR) poses significant challenges due to inevitable structure reconstruction. One approach is to develop effective strategies for controlling reaction pathways to gain a deeper understanding of mechanisms in robust CO2RR systems. In this work, by precise introduction of 1,10-phenanthroline as a bidentate ligand modulator, the electronic property of the copper site was effectively regulated, thereby directing selectivity switch. By modification of [Cu3(btec)(OH)2]n, the use of [Cu2(btec)(phen)2]n·(H2O)n achieved the selectivity switch from ethylene (faradaic efficiency (FE) = 41%, FEC2+ = 67%) to methane (FECH4 = 69%). Various in situ spectroscopic characterizations revealed that [Cu2(btec)(phen)2]n·(H2O)n promoted the hydrogenation of *CO intermediates, leading to methane generation instead of dimerization to form C2+ products. Acting as a delocalized π-conjugation scaffold, 1,10-phenanthroline in [Cu2(btec)(phen)2]n·(H2O)n helps stabilize Cuδ+. This work presents a novel approach to regulate the coordination environment of active sites with the aim of selectively modulating the CO2RR.