Plasmon-Mediated Photoelectrochemical Hot-Hole Oxidation Coupling Reactions of Adenine on Nanostructured Silver Electrodes.

Surface-enhanced Raman spectroscopy (SERS) has been widely applied in the identification and characterization of DNA structures with high efficiency. Especially, the SERS signals of the adenine group have exhibited high detection sensitivity in several biomolecular systems. However, there is still no unanimous conclusion regarding the interpretation of some special kinds of SERS signals of adenine and its derivatives on silver colloids and electrodes. This Letter presents a new photochemical azo coupling reaction for adenyl residues, in which the adenine is selectively oxidized to (E)-1,2-di(7H-purin-6-yl) diazene (azopurine) in the presence of silver ions, silver colloids, and electrodes of nanostructures under visible light irradiation. The product, azopurine, is first found to be responsible for the SERS signals. This photoelectrochemical oxidative coupling reaction of adenine and its derivatives is promoted by plasmon-mediated hot holes and is regulated by positive potentials and pH of solutions, which opens up new avenues for studying azo coupling in the photoelectrochemistry of adenine-containing biomolecules on electrode surfaces of plasmonic metal nanostructures.

External-Shell Oxygen Enabling the Local Environment Modulation of Unsaturated NbN3 for Efficient Electrosynthesis of Hydrogen Peroxide.

Single-atom catalysts with a tunable coordination structure have shown grand potential in flexibly altering the selectivity of oxygen reduction reaction (ORR) toward the desired pathway. However, rationally mediating the ORR pathway by modulating the local coordination number of the single-metal sites is still challenging. Herein, we prepare the Nb single-atom catalysts (SACs) with an external-shell oxygen-modulated unsaturated NbN3 site in carbon nitride and the NbN4 site anchored in nitrogen-doped carbon carriers, respectively. Compared with typical NbN4 moieties for 4e- ORR, the as-prepared NbN3 SACs exhibit excellent 2e- ORR activity in 0.1 M KOH, with the onset overpotential close to zero (9 mV) and the H2O2 selectivity above 95%, making it one of the state-of-the-art catalysts in the electrosynthesis of hydrogen peroxide. Density functional theory (DFT) theoretical calculations indicate the unsaturated Nb-N3 moieties and the adjacent oxygen groups optimize the interface bond strength of pivotal intermediates (OOH*) for producing H2O2, thus accelerating the 2e- ORR pathway. Our findings may provide a novel platform for developing SACs with high activity and tunable selectivity.

Ultrathin Pd3 Pt1 Rh0.1 Nanorings with Strong C-C Bond Breaking Ability for the Ethanol Oxidation Reaction.

Ethanol as a fuel for direct ethanol fuel cells (DEFCs) has the advantages of being highly energetic, environmentally friendly, and low-cost, while the slow anodic ethanol oxidation reaction (EOR), intermediate poisoning effect, and incomplete oxidation of ethanol became obstacles to the development of DEFCs. Herein, a 2D ternary cyclic Pd3 Pt1 Rh0.1 nanorings (NRs) catalyst with efficient EOR performance is prepared via a facile one-pot solvothermal approach, and systematic studies are carried out to reveal the mechanisms of the enhanced performance and C-C bond selectivity. In particular, the optimized catalyst exhibits impressive mass activity, stability, toxicity resistance, and C-C bond cleavage ability. It's proposed that the considerable performance is attributed to the unique hollow structure, providing abundant active sites. The high toxicity resistance is not only attributed to the electronic modulation of the catalyst material by Rh atoms, but also depends on the excellent water activation properties of Rh, which contribute to the removal of intermediates, such as CO. In addition, the density functional theory calculations showed that the introduction of Rh significantly enhances the C-C bond cleavage ability of the catalyst, further improving the EOR activity.

Expanding the active charge carriers of polymer electrolytes in lithium-based batteries using an anion-hosting cathode.

Ionic-conductive polymers are appealing electrolyte materials for solid-state lithium-based batteries. However, these polymers are detrimentally affected by the electrochemically-inactive anion migration that limits the ionic conductivity and accelerates cell failure. To circumvent this issue, we propose the use of polyvinyl ferrocene (PVF) as positive electrode active material. The PVF acts as an anion-acceptor during redox processes, thus simultaneously setting anions and lithium ions as effective charge carriers. We report the testing of various Li||PVF lab-scale cells using polyethylene oxide (PEO) matrix and Li-containing salts with different anions. Interestingly, the cells using the PEO-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solid electrolyte deliver an initial capacity of 108 mAh g-1 at 100 µA cm-2 and 60 °C, and a discharge capacity retention of 70% (i.e., 70 mAh g-1) after 2800 cycles at 300 µA cm-2 and 60 °C. The Li|PEO-LiTFSI|PVF cells tested at 50 µA cm-2 and 30 °C can also deliver an initial discharge capacity of around 98 mAh g-1 with an electrolyte ionic conductivity in the order of 10-5 S cm-1.

Scalable Molten Salt Synthesis of Platinum Alloys Planted in Metal-Nitrogen-Graphene for Efficient Oxygen Reduction.

Fuel cells are considered as a promising alternative to the existing traditional energy systems towards a sustainable future. Nevertheless, the synthesis of efficient and robust platinum (Pt) based catalysts remains a challenge for practical applications. In this work, we present a simple and scalable molten-salt synthesis method for producing a low-platinum (Pt) nanoalloy implanted in metal-nitrogen-graphene. The as-prepared low-Pt alloyed graphene exhibits a high oxygen reduction activity of 1.29 A mgPt -1 and excellent durability over 30 000 potential cycles. The catalyst nanoarchitecture of graphene encased Pt nanoalloy provides a robust capability against nanoparticle migration and corrosion due to a strong metal-support interaction. Similarly, advanced characterization and theoretical calculations show that the multiple active sites in platinum alloyed graphene synergistically account for the improved oxygen reduction. This work not only provides an efficient and robust low-Pt catalyst but also a facile design idea and scalable preparation technique for integrated catalysts to achieve more profound applications in fuel cells and beyond.

Boosting Oxygen Reduction via Integrated Construction and Synergistic Catalysis of Porous Platinum Alloy and Defective Graphitic Carbon.

Integrated fabrication through the strong interaction between catalyst and carrier is crucial to realize efficient oxygen electrocatalysis for fuel cells. We report herein a porous Pt-rich alloy encapsulated by graphitic carbon via integration engineering, where a synergistic catalysis between ternary PtCuCo alloy and graphitic Co-N-C results in the optimized reaction pathway and improved oxygen reduction reaction (ORR) performance. The hybrid catalyst PtCuCo@Co-N-C delivers a mass activity of 1.14 A mgPt -1 at 0.9 V vs. RHE and a peak power density of 960 mW cm-2 in the full-cell assessment, outperforming commercial Pt/C catalyst (0.12 A mgPt -1 and 780 mW cm-2 ). Experimental results combined with theoretical simulations suggest that the mutual assistance between porous Pt alloy and Co-N-C accounts for the enhanced catalytic performance. Such integrated engineering concept is significant for strengthening the anti-corrosion capabilities and improving the ORR performance of Pt-based catalysts.

Lewis Acid Site-Promoted Single-Atomic Cu Catalyzes Electrochemical CO2 Methanation.

Developing an efficient catalyst for the electrocatalytic CO2 reduction reaction (CO2RR) is highly desired because of environmental and energy issues. Herein, we report a single-atomic-site Cu catalyst supported by a Lewis acid for electrocatalytic CO2 reduction to CH4. Theoretical calculations suggested that Lewis acid sites in metal oxides (e.g., Al2O3, Cr2O3) can regulate the electronic structure of Cu atoms by optimizing intermediate absorption to promote CO2 methanation. Based on these theoretical results, ultrathin porous Al2O3 with enriched Lewis acid sites was explored as an anchor for Cu single atoms; this modification achieved a faradaic efficiency (FE) of 62% at -1.2 V (vs RHE) with a corresponding current density of 153.0 mA cm-2 for CH4 formation. This work demonstrates an effective strategy for tailoring the electronic structure of Cu single atoms for the highly efficient reduction of CO2 into CH4.

Real-time dynamics and structures of supported subnanometer catalysts via multiscale simulations.

Understanding the performance of subnanometer catalysts and how catalyst treatment and exposure to spectroscopic probe molecules change the structure requires accurate structure determination under working conditions. Experiments lack simultaneous temporal and spatial resolution and could alter the structure, and similar challenges hinder first-principles calculations from answering these questions. Here, we introduce a multiscale modeling framework to follow the evolution of subnanometer clusters at experimentally relevant time scales. We demonstrate its feasibility on Pd adsorbed on CeO2(111) at various catalyst loadings, temperatures, and exposures to CO. We show that sintering occurs in seconds even at room temperature and is mainly driven by free energy reduction. It leads to a kinetically (far from equilibrium) frozen ensemble of quasi-two-dimensional structures that CO chemisorption and infrared experiments probe. CO adsorption makes structures flatter and smaller. High temperatures drive very rapid sintering toward larger, stable/metastable equilibrium structures, where CO induces secondary structure changes only.

Lattice oxygen self-spillover on reducible oxide supported metal cluster: the water-gas shift reaction on Cu/CeO2 catalyst.

In this work we have tackled one of the most challenging problems in nanocatalysis namely understanding the role of reducible oxide supports in metal catalyzed reactions. As a prototypical example, the very well-studied water gas shift reaction catalyzed by CeO2 supported Cu nanoclusters is chosen to probe how the reducible oxide support modifies the catalyst structures, catalytically active sites and even the reaction mechanisms. By employing density functional theory calculations in conjunction with a genetic algorithm and ab initio molecular dynamics simulations, we have identified an unprecedented spillover of the surface lattice oxygen from the ceria support to the Cu cluster, which is rarely considered previously but may widely exist in oxide supported metal catalysts under realistic conditions. The oxygen spillover causes a highly energetic preference of the monolayered configuration of the supported Cu nanocluster, compared to multilayered configurations. Due to the strong metal-oxide interaction, after the O spillover the monolayered cluster is highly oxidized by transferring electrons to the Ce 4f orbitals. The water-gas-shift reaction is further found to more favorably take place on the supported copper monolayer than the copper-ceria periphery, where the on-site oxygen and the adjacent oxidized Cu sites account for the catalytically active sites, synergistically facilitating the water dissociation and the carboxyl formation. The present work provides mechanistic insights into the strong metal-support interaction and its role in catalytic reactions, which may pave a way towards the rational design of metal-oxide catalysts with promising stability, dispersion and catalytic activity.

Improved Pd/CeO2 Catalysts for Low-Temperature NO Reduction: Activation of CeO2 Lattice Oxygen by Fe Doping.

Developing better three-way catalysts with improved low-temperature performance is essential for cold start emission control. Density functional theory in combination with microkinetics simulations is used to predict reactivity of CO/NO/H2 mixtures on a small Pd cluster on CeO2(111). At low temperatures, N2O formation occurs via a N2O2 dimer over metallic Pd3. Part of the N2O intermediate product re-oxidizes Pd, limiting NO conversion and requiring rich conditions to obtain high N2 selectivity. High N2 selectivity at elevated temperatures is due to N2O decomposition on oxygen vacancies. Doping CeO2 by Fe is predicted to lead to more oxygen vacancies and a higher N2 selectivity, which is validated by the lower onset of N2 formation for a Pd catalyst supported on Fe-doped CeO2 prepared by flame spray pyrolysis. Activating ceria surface oxygen by transition metal doping is a promising strategy to improve the performance of three-way catalysts.

Mechanistic Investigation on Copper-Arylacetylide Polymerization and Sensing Applications.

Exploration of new polymerization reactions is very intriguing in fundamental and practical research, which will advance reaction theories and produce various functional materials. Herein, we report a new polymerization method based on the reaction of CuI and arylacetylide, which generates linear polymers with high molecular weight and low polydispersity index of molecular weight. The Cu-arylacetylide polymerization exhibits different characteristics with traditional polymerizations such as mild reaction temperature, air atmosphere reaction, high molecular weight, fast polymerization rate, and imprecise molar ratio between monomers. The bond formation path and activation energy of each step was investigated by density functional theory calculations to understand the reaction mechanism. The poly(Cu-arylacetylide)s exhibit strong fluorescence emission and inherent semiconductive properties, which have been used to fabricate an electronic device for streptavidin sensing.

Direct integration of ultralow-platinum alloy into nanocarbon architectures for efficient oxygen reduction in fuel cells.

Developing efficient platinum (Pt)-based electrocatalysts is enormously significant for fuel cells. Herein, we report an integrated electrocatalyst of ultralow-Pt alloy encapsulated into nitrogen-doped nanocarbon architecture for efficient oxygen reduction reaction. This hybrid Pt-based catalyst achieves a mass activity of 3.46 A mgpt-1 at the potential of 0.9 V vs. RHE with a negligible stability decay after 10,000 cycles. More importantly, this half-cell activity can be expressed at full cell level with a high Pt utilization of 10.22 W mgPt-1cathode and remarkable durability after 30,000 cycles in single-cell. Experimental and theoretical investigations reveal that a highly strained Pt structure with an optimal Pt-O binding energy is induced by the incorporation of Co/Ni into Pt lattice, which would account for the improved reaction kinetics. The synergistic catalysis due to nitrogen-doped nanocarbon architecture and active Pt component is responsible for the enhanced catalytic activity. Meanwhile, the strong metal-support interaction and optimized hydrophilic properties of nanocarbon matrix facilitate efficient mass transport and water management. This work may provide significant insights in designing the low-Pt integrated electrocatalysts for fuel cells and beyond.

Finite-Temperature Structures of Supported Subnanometer Catalysts Inferred via Statistical Learning and Genetic Algorithm-Based Optimization.

Single-atom catalysts (SACs) minimize noble metal utilization and can alter the activity and selectivity of supported metal nanoparticles. However, the morphology of active centers, including single atoms and subnanometer clusters of a few atoms, remains elusive due to experimental challenges. The computational cost to describe numerous cluster shapes and sizes makes direct first-principles calculations impractical. We present a computational framework to enable structure determination for single-atom and subnanometer cluster catalysts. As a case study, we obtained the low-energy structures of Pdn (n = 1-21) clusters supported on CeO2(111), which are critical components of automobile three-way catalysts. Trained on density functional theory data, a three-dimensional cluster expansion is established using statistical learning to describe the Hamiltonian and predict energies of supported Pdn clusters of any structure. Low-energy stable and metastable structures are identified using a Metropolis Monte Carlo-based genetic algorithm in the canonical ensemble at 300 K. We observe that supported single atoms sinter to form bilayer clusters, and large cluster isomers share similarities in both shape and energy. The findings elucidate the significance of the support and microstructure on cluster stability. We discovered a simple surrogate structure-energy model, where the energy per atom scales with the square root of the average first coordination number, which can be used to estimate energies and compare the stability of clusters. Our framework, applicable to any metal/support system, fills an important methodological gap to predict the stability of supported metal catalysts in the subnanometer regime.

Engineering the electronic and strained interface for high activity of PdMcore@Ptmonolayer electrocatalysts for oxygen reduction reaction.

Alloyed nanoparticles with core-shell structures provide a favorable model to modulate interfacial interaction and surface structures at the atomic level, which is important for designing electrocatalysts with high activity and durability. Herein, core-shell structured Pd3M@Pt/C nanoparticles with binary PdM alloy cores (M = Fe, Ni, and Co) and a monolayer Pt shell were successfully synthesized with diverse interfaces. Among these, Pd3Fe@Pt/C exhibited the best oxygen reduction reaction catalytic performance, roughly 5.4 times more than that of the commercial Pt/C catalyst used as reference. The significantly enhanced activity is attributed to the combined effects of strain engineering, interfacial electron transfer, and improved Pt utilization. Density functional theory simulations and extended X-ray absorption fine structure analysis revealed that engineering the alloy core with moderate lattice mismatch and alloy composition (Pd3Fe) optimizes the surface oxygen adsorption energy, thereby rendering excellent electrocatalytic activity. Future researches may use this study as a guide on the construction of highly effective core-shell electrocatalysts for various energy conversions and other applications.

Engineering bunched Pt-Ni alloy nanocages for efficient oxygen reduction in practical fuel cells.

Development of efficient and robust electrocatalysts is critical for practical fuel cells. We report one-dimensional bunched platinum-nickel (Pt-Ni) alloy nanocages with a Pt-skin structure for the oxygen reduction reaction that display high mass activity (3.52 amperes per milligram platinum) and specific activity (5.16 milliamperes per square centimeter platinum), or nearly 17 and 14 times higher as compared with a commercial platinum on carbon (Pt/C) catalyst. The catalyst exhibits high stability with negligible activity decay after 50,000 cycles. Both the experimental results and theoretical calculations reveal the existence of fewer strongly bonded platinum-oxygen (Pt-O) sites induced by the strain and ligand effects. Moreover, the fuel cell assembled by this catalyst delivers a current density of 1.5 amperes per square centimeter at 0.6 volts and can operate steadily for at least 180 hours.

Understanding the Impact of Defects on Catalytic CO Oxidation of LaFeO3-Supported Rh, Pd, and Pt Single-Atom Catalysts.

Understanding the intrinsic catalytic properties of perovskite materials can accelerate the development of highly active and abundant complex oxide catalysts. Here, we performed a first-principles density functional theory study combined with a microkinetics analysis to comprehensively investigate the influence of defects on catalytic CO oxidation of LaFeO3 catalysts containing single atoms of Rh, Pd, and Pt. La defects and subsurface O vacancies considerably affect the local electronic structure of these single atoms adsorbed at the surface or replacing Fe in the surface of the perovskite. As a consequence, not only the stability of the introduced single atoms is enhanced but also the CO and O2 adsorption energies are modified. This also affects the barriers for CO oxidation. Uniquely, we find that the presence of La defects results in a much higher CO oxidation rate for the doped perovskite surface. A linear correlation between the activation barrier for CO oxidation and the surface O vacancy formation energy for these models is identified. Additionally, the presence of subsurface O vacancies only slightly promotes CO oxidation on the LaFeO3 surface with an adsorbed Rh atom. Our findings suggest that the introduction of La defects in LaFeO3-based environmental catalysts could be a promising strategy toward improved oxidation performance. The insights revealed herein guide the design of the perovskite-based three-way catalyst through compositional variation.

Linear Activation Energy-Reaction Energy Relations for LaBO3 (B = Mn, Fe, Co, Ni) Supported Single-Atom Platinum Group Metal Catalysts for CO Oxidation.

Single-atom catalysts are at the center of attention of the heterogeneous catalysis community because they exhibit unique electronic structures distinct from nanoparticulate forms, resulting in very different catalytic performance combined with increased usage of often costly transition metals. Proper selection of a support that can stably keep the metal in a high dispersion is crucial. Here, we employ spin-polarized density functional theory and microkinetics simulations to identify optimum LaBO3 (B = Mn, Fe, Co, Ni) supported catalysts dispersing platinum group metals as atoms on their surface. We identify a strong correlation between the CO adsorption energy and the d-band center of the doped metal atom. These CO adsorption strength differences are explained in terms of the electronic structure. In general, Pd-doped surfaces exhibit substantially lower activation barriers for CO2 formation than the Rh- and Pt-doped surfaces. Strong Brønsted-Evans-Polanyi correlations are found for CO oxidation on these single-atom catalysts, providing a tool to predict promising compositions. Microkinetics simulations show that Pd-doped LaCoO3 is the most active catalyst for low-temperature CO oxidation. Moderate CO adsorption strength and low reaction barriers explain the high activity of this composition. Our approach provides guidelines for the design of highly active and cost-effective perovskite supported single-atom catalysts.

Highly Active and Stable CH4 Oxidation by Substitution of Ce4+ by Two Pd2+ Ions in CeO2(111).

Methane (CH4) combustion is an increasingly important reaction for environmental protection, for which Pd/CeO2 has emerged as the preferred catalyst. There is a lack of understanding of the nature of the active site in these catalysts. Here, we use density functional theory to understand the role of doping of Pd in the ceria surface for generating sites highly active toward the C-H bonds in CH4. Specifically, we demonstrate that two Pd2+ ions can substitute one Ce4+ ion, resulting in a very stable structure containing a highly coordinated unsaturated Pd cation that can strongly adsorb CH4 and dissociate the first C-H bond with a low energy barrier. An important aspect of the high activity of the stabilized isolated Pd cation is its ability to form a strong σ-complex with CH4, which leads to effective activation of CH4. We show that also other transition metals like Pt, Rh, and Ni can give rise to similar structures with high activity toward C-H bond dissociation. These insights provide us with a novel structural view of solid solutions of transition metals such as Pt, Pd, Ni, and Rh in CeO2, known to exhibit high activity in CH4 combustion.

Stable Pd-Doped Ceria Structures for CH4 Activation and CO Oxidation.

Doping CeO2 with Pd atoms has been associated with catalytic CO oxidation, but current surface models do not allow CO adsorption. Here, we report a new structure of Pd-doped CeO2(111), in which Pd adopts a square planar configuration instead of the previously assumed octahedral configuration. Oxygen removal from this doped structure is favorable. The resulting defective Pd-doped CeO2 surface is active for CO oxidation and is also able to cleave the first C-H bond in methane. We show how the moderate CO adsorption energy and dynamic features of the Pd atom upon CO adsorption and CO oxidation contribute to a low-barrier catalytic cycle for CO oxidation. These structures, which are also observed for Ni and Pt, can lead to a more open coordination environment around the doped-transition-metal center. These thermally stable structures are relevant to the development of single-atom catalysts.