Pd NCs Research Articles

An “on-off” ratiometric electrochemiluminescence biosensor based on LSPR-enhanced by Ag@Au nanostructures combined with Pd NCs catalysing a single luminophore for MiRNA let-7a detection

In this study, we reported a ratiometric electrochemiluminescence (ECL) biosensor based on localized surface plasmon resonance (LSPR)-enhanced Ag@Au nanostructures combined with palladium nanoclusters (Pd NCs) catalyzing the luminol-gold nanoparticles (L-Au NPs). Firstly, L-Au NPs were synthesized, hydrogen peroxide (H2O2) was used as a co-reactant, and Ag@Au nanostructures acted as an LSPR source to enhance the initial signal at the anode. Next, with the help of strand displacement amplification (SDA), the trace target miRNA let-7a was able to be converted to a number of output DNA. And then the Visual DNA Strand Displacement (DSD) was used to evaluate the conversion efficiency of miRNA let-7a into output DNA, thereby verifying that the SDA achieved signal amplification in the construction of biosensor. It was thereafter experimentally verified that the first decrease in anodic signal was achieved by strand amplification based on magnetic beads and polymerase excitation. In contrast, Pd NCs were synthesized using double-stranded DNA (dsDNA) as a template and excited with a cathodic signal, while a second decrease of the anodic signal was also achieved. The developed ratiometric ECL biosensor demonstrated a sensitive detection of miRNA let-7a with a linear range from 0.1 pM to 10 aM and a detection limit of 5.45 aM (S/N = 3). In conclusion, the study presented a new idea for the construction of ratiometric ECL sensors based on a single luminophore, providing technical support for the early diagnosis of cancer.

Supported palladium nanocubes reduced by graphene oxide and surface-cleaned for enhanced electrocatalytic activity

Highly dispersed Pd nanocubes (Pd NCs) supported on the surface of partially reduced graphene oxide (pRGO) were successfully prepared by a facile procedure. GO was used as reductant and support without any other external reducing agent been introduced, and potassium iodide (KI) was used as capping agent for morphology control respectively. Catalytic activities for ethanol oxidation and methanol oxidation were greatly enhanced after excess iodine on the surface of Pd NCs was removed by being surface-treated with NaBH4 solution.

Atomically precise Pdm(SR)n nanoclusters for efficient hydrogen evolution reaction

Thiolate (SR) protected noble metal nanoclusters have grasped immense attention because of their promising applications in electrocatalysis, electrochemical sensors, photoluminescencse, supercapacitor and energy production. Among the noble metals, numerous reports have highlighted interesting results for Au25(SR)18, Au22(SR)18 and Ag44(SR)30 clusters but Pd and Pt nanoclusters are less addressed. Room temperature ionic liquids (RTIL) show enhanced electrocatalytic activity and stability as a binding matrix as compared to commercial binders like Nafion, Polyvinylidene fluoride (PVDF) and so on. Here, we have synthesised water-soluble thiolate 3-mercaptopropyl sulfonate (MPS) capped Palladium nanoclusters (Pd-MPS NCs). Further, Poly Acrylamide Gel Electrophoresis (PAGE), a separation technique was used to isolate size-dependent NCs and their electrocatalytic activity for the hydrogen evolution reaction (HER) with room temperature ionic liquid as a binding matrix was demonstrated. The electron microscope images of isolated Pd-MPS NCs from these three bands (obtained from PAGE separation) resulted with size ranges of 0.8-1.8 nm, 2-4 nm and 4.2-8 nm respectively. Among the three bands obtained from PAGE gel from the crude Pd NCs, the ultrasmall Pdm(SR)n NCs was isolated from the lower band resulted in high HER activity with less overpotential of 197 mV and a Tafel slope of 125.2 mV dec-1 as compared to Pd-MPS NCs obtained from the other two distinctive bands.

Quantitative Study on the Influence of Bromide Ions toward the Reduction Kinetics for Size-Tunable Palladium Nanocubes.

During the preparation of nanocrystals, regulating the dosage of key additives in the reaction system and the reaction temperature commonly affects the sizes and morphologies of the products. Despite the fact that bromide ions play a pivotal role in the synthesis of palladium nanocubes (Pd NCs), there is still a lack of quantitative and in-depth research on how the ions affect the reduction kinetics of Pd precursors and further on products. In this work, Pd NCs with different sizes have been prepared under various reaction conditions coupled to a systematic mechanism study. Quantitative measurements demonstrate that the reduction processes could be considered quasi-first-order reactions, and the corresponding kinetic parameters have been obtained. Furthermore, a linear relationship is discovered between k and the average size (d) of Pd NCs. The investigation on the growth patterns of four chosen systems reveals that given reaction conditions lead to certain results with unique growth patterns.

Systematic Study on the Precursor Reduction Kinetics and Growth Pattern for Size-Tunable Palladium Nanocubes.

Unveiling the underlying chemistry during the growth of well-defined nanocrystals is a fundamental but challenging task in materials chemistry. Herein, Pd NCs with tunable sizes ranging from 4.5 to 23.5 nm have been synthesized in the presence of potassium acetate (KOAc). The Pd precursor variation trends of these preparation systems along with reaction time have been determined using a UV-vis spectrometer, and corresponding reduction kinetic parameters, including the apparent reduction rate constant (k) and activation energy (Ea), are calculated by regarding the reduction processes as quasi-first-order reactions. It is confirmed that the introduction of KOAc does not affect the value of the Ea of different reaction systems. The interrelationship of k, product size (d), and reaction temperature (T) is discussed in depth. Results indicate that the three parameters are closely related, and for given reaction systems, they are specified. With the careful investigation of six specific systems (reaction systems with 10 mM, 20 mM KOAc at 55 °C, with 5 mM, 10 mM KOAc at 65 °C, without KOAc at 75 °C, and with 5 mM KOAc at 85 °C), the growth pattern of Pd NCs is described with an empirical expression and is further confirmed as a synergistic result of k and T.

Electrochemical Behavior and Shape Evolution of Structured Pd Nanoparticles in Alkaline Media─Influence of Electrochemically Absorbed Hydrogen.

We report on the electrochemical behavior and shape evolution of Pd nanocubes (Pd NCs) and Pd nanooctahedrons (Pd NOs) with an average size of 9.8 and 6.9 nm, respectively, in aqueous alkaline medium in the potential range of the underpotential deposition of H (UPD H) and H absorption. While the Pd NCs and Pd NOs remain stable in the potential region of the UPD H, H absorption and desorption of absorbed H (Habs) induce structural changes to the Pd NPs, as indicated by the results of electrochemical measurements and identical location-transmission electron microscopy (IL-TEM) analyses. Because both Pd NCs and Pd NOs are known to be stable in the potential region of H absorption and Habs desorption in acidic medium and maintain their structure, the irreversible structural changes are attributed to their interfacial interaction with the aqueous alkaline medium. In the alkaline medium, the nanoparticle surface/electrolyte interfacial structure plays an essential role in the mechanism of Habs desorption that is observed at higher potentials than that in the acidic medium. Hydrogen desorption is substantially hindered due to the structure of the water network adjacent to the Pd nanoparticles or the interaction between hydrated cations and adsorbed OH on the nanoparticle surface, resulting in the trapping of a small amount of H (incomplete Habs desorption). It is proposed that H trapping and associated structural strain lead to the deformation of the Pd nanoparticles and the loss of their initial structure.

Synergistic integration of few-layer thick MXenes and small Pd nanocubes for enhanced electrochemical nitrofurantoin detection: Implications in pharmaceutical pollutant monitoring

Direct electrochemical detection of clinically significant and emerging pharmaceutical pollutants, such as nitrofurantoin, is a critical challenge. Herein, we propose an efficient electroactive platform composed of Pd nanocubes (Pd NCs) embedded within partially oxidized MXenes (Ti3C2Tx-TiO2). This proximity between Pd NCs, in-situ generated TiO2, and Ti3C2Tx results in a highly compact and efficient architecture, facilitating enhanced charge transfer and electrocatalytic activity, which results in an efficient cathodic reduction to NFT at a much lower-over potential of − 0.4 V. The optimal composite configuration (Pd-Ti3C2Tx-P) enabled NFT detection in a dynamic concentration range from 1 to 140 nM, with a detection sensitivity reaching down to 0.01 nM (S/N = 3) against Ag/AgCl as the reference electrode. Furthermore, the developed sensor demonstrated outstanding selectivity toward NFT while tolerating probable interfering substances such as biomolecules, drugs, and metal ions. The sensor can detect NFT selectively in complicated environmental matrices such as hospital waste effluent samples. The proposed design offers a simple route to construct advanced electrocatalytic sensors with potential applications in monitoring emerging pharmaceutical pollutants.

High dispersion Pd nanoclusters modified sulfur-rich vacancies ZnIn2S4 for high-performance hydrogen evolution

Hydrogen energy is regarded as the clean energy alternative for fossil energy. Hydrogen evolution reaction (HER) is a sustainable way for the production of hydrogen energy. However, commercial platinum (Pt) catalysts for HER are expensive and scarce, which will not fully meet the demand of the future market. Therefore, scientists have been actively exploring alternatives to Pt-based catalysts. Studies have shown that palladium (Pd) and Pt have similar catalytic activity in HER. Small molecular Pd nanoclusters can be used as a perfect HER activity center. Herein, anchoring of Pd nanoclusters (Pd NCs) on sulfur-vacancy-enriched ZnIn2S4 nanosheets (Pd/ZIS-T) has been successfully achieved. The zeta potential value for ZnIn2S4 is −59.9 mV, indicating that the surface of ZnIn2S4 is abundant negatively charged in deionized water, thus providing plentiful anchoring sites to absorb Pd2+. The results show that the synergistic effect of Pd NCs and sulfur vacancies will endow the obtained catalyst with excellent electrocatalytic activity and stability. It also managed to reducing costs by reducing noble metal content. In particular, the Pd/ZIS-T electrocatalyst with excellent performance delivered low overpotential of 25 mV at 10 mA cm−2 and small Tafel slope of 33 mV dec-1 in acidic electrolyte.

Nearly monodisperse Cu|pd alloyed Nanocrystals: Ultrasound induced stepwise thermoreduction in organic Medium, and catalytic alcoholysis for hydrogen evolution

Active search for efficient and inexpensive catalyst is the basic premise and urgent requirement to promote the practicality of the new hydrogen storage material-ammonia borane. We herein propose an ultrasonic-induced stepwise thermoreduction protocol to fabricate serial bimetal Cu|Pd alloyed nanocrystals with various metal molar ratios, and scientifically evaluate respective catalytic activity for alcoholyzing ammonia borane. Comprehensive characterizations and analysis confirm that the as-fabricated Cu|Pd crystalline grains appear as nearly monodisperse microspheres with mean size of about 10 nm, taking on almost superlattice arrangement. The ultrasound and precursor molar ratio can affect grain size and dispersity to varying degrees. Regardless of the Pd/Cu molar ratio, alloy phase microstructure can be formed. The Pd-rich nanoagent Cu40Pd60 unfold the upmost catalytic ability for alcoholyzing ammonia borane, even exceeding Pd NCs, with the turnover frequency (TOF) value of 66.51 mol (H2)·min−1·(mol Pd)-1 and apparent activation energy of 30.35 kJ·mol−1. Moreover, the Cu40Pd60 nanocrystals possess the exceptional stability with only 10% loss of the original catalytic activity after 5 round cyclic utilization. The catalytic methanolysis at the given conditions is identified as first-order reaction. The current findings can enrich the family of the serial bimetal alloyed nanocatalyst, also offer an optional strategy for fabricating the poly-metal composite catalysts with high activity.

Zn2+-responsive palladium nanoclusters synergistically manage Alzheimer’s disease through neuroprotection and inhibition of oxidative stress

The current focus on inhibiting β-Amyloid (Aβ) aggregation has shown great limitations for the management of Alzheimer's disease (AD). Multi-target strategies that synergistically exert neuroprotective effects and alleviate oxidative stress are effective strategies to modulate the AD microenvironment. Herein, a novel Zn2+-responsive nano-drug delivery platform (NWP) is developed using palladium nanoclusters (Pd NCs) as carriers, loaded with nerve growth factor (NGF), capped by supramolecular nanovalves containing carboxyl pillars[5]arenes (WP5) for the treatment of AD. Pd NCs have both OH elimination and catalase activities to alleviate oxidative stress. The larger specific surface area could significantly improve the loading capacity of NGF. The supramolecular nanovalve constructed by WP5 achieves precise targeting and controlled release of NGF with Zn2+ responsiveness, thereby improving the utilization of loading drugs. In vitro and in vivo experiments demonstrates that NWP effectively scavenges reactive oxygen species (ROS), protects neuronal cells from oxidative damage and modulates microglial polarization (the pro-inflammatory M1-phenotype microglial transition to the anti-inflammatory M2-phenotype), thus reducing the release of pro-inflammatory factors and alleviating neuroinflammation. Furthermore, intracerebral injection of NWP significantly ameliorates the learning and memory deficits of AD model mice. Overall, this Zn2+-responsive multi-target therapy provides a new option for AD.

Controllable Deposition of Bi onto Pd for Selective Hydrogenation of Acetylene.

The rational regulation of catalyst active sites at atomic scale is a key approach to unveil the relationship between structure and catalytic performance. Herein, we reported a strategy for the controllable deposition of Bi on Pd nanocubes (Pd NCs) in the priority order from corners to edges and then to facets (Pd NCs@Bi). The spherical aberration-corrected scanning transmission electron microscopy (ac-STEM) results indicated that Bi2O3 with an amorphous structure covers the specific sites of Pd NCs. When only the corners and edges of the Pd NCs were covered, the supported Pd NCs@Bi catalyst exhibited an optimal trade-off between high conversion and selectivity in the hydrogenation of acetylene to ethylene under ethylene-rich conditions (99.7% C2H2 conversion and 94.3% C2H4 selectivity at 170 °C) with remarkable long-term stability. According to the H2-TPR and C2H4-TPD measurements, the moderate hydrogen dissociation and the weak ethylene adsorption are responsible for this excellent catalytic performance. Following these results, the selectively Bi-deposited Pd nanoparticle catalysts showed incredible acetylene hydrogenation performance, which provides a feasible perspective to design and develop highly selective hydrogenation catalysts for industrial applications.

Ratiometric Electrochemiluminescence Sensing of Carcinoembryonic Antigen Based on Luminol.

Ratiometric electrochemiluminescence (ECL) sensors can efficiently remove environmental interference to attain precise detection. Nonetheless, two eligible luminophores or coreactants were usually needed, increasing the complexity and restricting their practical application. In this study, a single luminophore of luminol with a single coreactant of H2O2 was employed to construct a dual-potential ratiometric ECL sensor for the detection of carcinoembryonic antigen (CEA). The produced palladium nanoclusters (Pd NCs) employing a DNA duplex as a template could not only stimulate luminol to produce cathodic ECL (Icathodic) but also quench its anodic ECL (Ianodic). During the detection process, CEA could damage the double-stranded structure and reduce the Pd NCs' amount, triggering a significant decrease in the ratio of Icathodic to Ianodic (Icathodic/Ianodic) and thereby achieving sensitive CEA's detection. Furthermore, the Icathodic/Ianodic was independent of the H2O2 concentration, which avoided a prejudicial effect from H2O2 decomposition and considerably enhanced the detection's reliability. The developed ratiometric ECL sensor demonstrated a sensitive detection toward CEA with a wide linear range from 100 ag/mL to 10 ng/mL and a detection limit of 87.1 ag/mL (S/N = 3). In conclusion, this study offers a new idea for constructing ratiometric ECL sensors based on a single luminophore and technical support for cancer's early diagnosis.

Tuning structures of Pt shells on Pd nanocubes as neutral glucose oxidation catalysts and sensors

Nanocrystals with high-indexed facets and low-coordinated atoms exhibit promising electrocatalytic activities. Herein, different Pt shell structures on the surface of Pd nanocubes (Pd@Pt NCs) were synthesised by varying the concentration of Pt precursors. The concave Pd@Pt NCs were used as electrocatalysts for neutral glucose oxidation reactions (GORs); the effect of Pt structure on the catalytic performance was studied. In sequential catalysis, stellated Pd@Pt NCs (Pd@Pt SNC) with (211) facets had an electron transfer number (Ne) of 12.69 and a specific activity of 4.69 × 10−9 mol·g·m−2, markedly higher than that of the other concave Pd@Pt NCs. In transient catalysis, Pd NCs with Pt-coated corners (Pd@Pt CNCC) containing (210) and (950) facets demonstrated a sensitivity of 11.06 μA·mM−1·cm−2 and a linear analysis range (2.4–10.6 mM). The high recoveries (98.80%–99.85%) and low relative standards (≤1.06%) in the serum sample corroborate the potential of Pd@Pt CNCC as an enzyme-free glucose sensor.

Palladium nanocrystals-embedded covalent organic framework as an efficient catalyst for Heck cross-coupling reaction

Nanoparticles, such as noble metal nanoparticles and covalent organic frameworks (COFs), advance heterogeneous catalysis. Three COFs were synthesized via the solvothermal method using tricarboxylic acids (tricarboxylic benzene (2,4,6-tri-p-carboxyphenylpyridine (H 3 L2), 4,4′,4''-tri carboxyl triphenylamine (H 3 L1), and trimesic acid (H 3 BTC)) and 1,3,5-triazine-2,4,6-triamine moieties. The synthesized COFs were potentially used as supports for the in-situ growth of palladium nanocrystals (Pd NCs), offering a particle size of 1–5 nm. X-ray diffraction (XRD), Fourier transforms infrared (FT-IR), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), nitrogen adsorption-desorption isotherms, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) characterized the materials. Using Heck cross-coupling reaction, Pd NCs@COFs were used as catalysts to synthesize different organic molecules via carbon-carbon (C–C) formation. They exhibit complete conversion (100%) for vinyl derivatives and aryl halides (Bromo- and Chloro-derivatives) with good stability. Pd NCs@COFs maintain high catalytic activity over four consecutive cycles. • Synthesis of two new Covalent organic frameworks (COFs). • In-situ growth of palladium nanocrystals into COFs. • Applications of Pd NCs@COFs for C–C cross-coupling reactions via Heck Reaction. • Record high heterogeneous catalytic performance of the prepared catalysts.

Hierarchical-Structured Pd Nanoclusters Catalysts x-PdNCs/CoAl(O)/rGO-T by the Captopril-Capped Pd Cluster Precursor Method for the Highly Efficient 4-Nitrophenol Reduction.

Water-soluble captopril-capped atomically precise Pd nanoclusters (Pd17Capt8 NCs: 1.3 ± 0.5 nm) produced by a simple chemical reduction were supported on preprepared hybrid Co3Al-layered double hydroxide/reduced graphene oxide (Co3Al-LDH/rGO) by a pH-adjusted electrostatic adsorption strategy followed by proper calcinations, giving a series of novel catalysts x-PdNCs/CoAl(O)/rGO-T (x (Pd loading) = 0.09, 0.17, 0.43 wt % (ICP), T = 230, 250, 280, 300, 320 °C). The characterization results show that the as-obtained catalysts possess the hierarchical nanosheet array morphology. Pd NCs with a size of ∼1.3 to 1.8 nm are highly distributed at the edge sites of the CoAl(O) nanosheets. All of the x-PdNCs/CoAl(O)/rGO-T catalysts show superior catalytic efficiency for the conversion of 4-nitrophenol to 4-aminophenol, particularly 0.17-PdNCs/CoAl(O)/rGO-300 possesses the highest performance with a turnover frequency (TOF) of 30 042 h-1, which is the highest among the reported Pd-based catalysts so far. The superior activity of 0.17-PdNCs/CoAl(O)/rGO-300 can be owing to ultrafine Pd NCs with a clean surface, the strongest PdNCs-Co2+-OH(LDH)-rGO three-phase synergy, and the much improved adsorption of the substrate via π-π stacking upon nanosheet array morphology. Meanwhile, 0.17-PdNCs/CoAl(O)/rGO-300 exhibits excellent catalytic activities for various nitroarenes and anionic azo dyes as well as good reusability with the complete reduction of 4-nitrophenol (4-NP) within 90 s after 10 successive runs. The present work provides not only a simple and convenient strategy for the synthesis of clean, efficient, and environmentally friendly supported metal nanocluster catalysts but also a new idea for the efficient catalytic degradation of environmental pollutants.

Folic acid conjugated chitosan encapsulated palladium nanoclusters for NIR triggered photothermal breast cancer treatment

This study developed folic acid (FA) conjugated chitosan (CS) encapsulated rutin (R) synthesized palladium nanoclusters (Pd NCs) for NIR triggered and folate receptor (FR) targeted triple-negative breast cancer (MDA-MB 231 cells) treatment. R-Pd NCs exhibited flower-shaped particles with an average size of <100 nm. FA-CS encapsulation concealed the flower shape of R-Pd NCs with a positive charge. The XRD spectrum confirmed the cubic crystalline structure of Pd. The FA conjugation on CS improved the cellular uptake of R-Pd NCs in MDA-MB 231 cells was confirmed by TEM. FA-CS-R-Pd NCs (+NIR) treatment was considerably inhibited the MDA-MB 231 cells proliferation evidenced by cell viability, fluorescent staining, and flow cytometry analysis. Further, in vitro hemolysis assay and in Ovo model confirmed the non-toxic nature of FA-CS-R-Pd-NCs with or without NIR radiation. Hence, this study concluded that FA-CS-R-Pd NCs can be applied for the treatment of drug-resistant breast cancer.

Graphene nanosheets supported high-defective Pd nanocrystals as an efficient electrocatalyst for hydrogen evolution reaction

Exploring efficient and stable catalysts synthesized by innovative methodologies is extremely important for hydrogen evolution reactions. Herein, we prepared the palladium nanocrystals (Pd NCs) with different morphologies (triangle, nanocubes, and nanodendrites) supported on graphene nanosheets (GNS) by facile hydrothermal method. The shape of Pd-nanodendrites/GNS can be controlled by adjusting hydrothermal reaction time. More importantly, the crystal defects in the Pd-nanodendrites/GNS, such as steps, terraces, and edge-sites atoms, will effectively serve as catalytic active sites. Compared with other morphologies, the Pd-nanodendrites/GNS exhibited superior HER activity in the 1 M KOH solution, such as small overpotential (39.6 mV) required to achieve a 10 mA cm−2 current density, ultra-low Tafel slope (29.7 mV dec−1), and lower charge transfer resistance (Rct) value of 16.2 Ω, which indicates good conductivity and high electrochemical stability. This work offers a new opportunity to design advanced electrocatalysts for highly efficient HER in alkaline media.

A Sandwich-Type Electrochemical Immunosensor based on Pd Nanocubes Functionalized MoO2 Nanospheres for Highly Sensitive Detection of CEA

In this study, a sandwich-type electrochemical immunosensor was developed for detecting carcinoembryonic antigen (CEA) effectively. The proposed electrochemical immunosensor was based on gold nanocrystals (Au NDs) as the substrate material for capturing primary antibodies and using palladium nanoscale cubics (Pd NCs) loaded on amino-functionalized MoO2 nanospheres (Pd NCs/NH2-MoO2 NSs) as a secondary antibody label. Au NDs had dendritic structures that were more conducive to capturing Ab1 and can accelerate electron transfer. MoO2 had the good catalytic capacity for reduction of H2O2 and favourable electrical conductivity. Similarly, Pd NCs had excellent catalytic performance for hydrogen peroxide reduction. Hence, the obtained Pd NCs/NH2-MoO2 NSs were more effective than Pd NCs and NH2-MoO2 NSs in catalytic reduction of hydrogen attribute to a synergistic effect, showing excellent catalysis. The proposed electrochemical immunosensor had a lower detection limit of 3.3 fg ml−1 jand a wider detection range from 10 fg ml−1 to 100 ng ml−1 (S/N = 3) for the detection of CEA under optimal experimental conditions. The proposed electrochemical immunosensor showed good sensitivity, stability, selectivity, reproducibility and its good detection performance of the immunosensor indicated that it had a broad application prospect in clinical detection.

Te-Doped Pd Nanocrystal for Electrochemical Urea Production by Efficiently Coupling Carbon Dioxide Reduction with Nitrite Reduction.

The renewable electricity-driven reduction of carbon dioxide (CO2RR) is a promising technology for carbon utilization. However, it is still a challenge to broaden the application of CO2RR. Herein, we report a Te-doped Pd nanocrystals (Te-Pd NCs) for promoting urea synthesis by coupling CO2RR with electrochemical reduction of nitrite. The electrochemical synthesis of urea has been achieved with nearly 12.2% Faraday efficiency (FE) and 88.7% N atom efficiency (NE) at -1.1 V versus reversible hydrogen electrode (vs RHE), much higher than those of pure Pd NCs (4.2% FE and 21.8% NE). Significantly, an FE of ∼10.2% and an NE of ∼82.3% for urea solution production via an optimized flow cell system have been realized, where a solution with up to 0.95 wt % of urea has been obtained. Mechanistic insights show that Te-doping not only optimizes the CO2/CO adsorption but also promotes NH3 production, fully meeting the requirements of urea synthesis.

Hybrid Pd38 nanocluster/Ni(OH)2-graphene catalyst for enhanced HCOOH dehydrogenation: First principles approach

Hydrogen energy is a potential next-generation energy source for fossil fuel replacement. The development of high-efficiency materials and catalysts for storage and transportation of hydrogen energy must be achieved to realize hydrogen economy. Recently, catalyst systems such as Pd nanoclusters (Pd NCs) supported on nickel hydroxide (Ni(OH)2) have been reported to have advantages, including effective suppression of CO production and efficiency enhancement of HCOOH dehydrogenation. However, the reaction mechanism and multi-metallic interface system design of such systems have not been elucidated. Therefore, various Ni(OH)2 surfaces supported on a graphene system were designed through density functional theory calculations, and the support material was combined with Pd38NC (Pd38NC/Ni(OH)2-G). Subsequently, the adsorption behavior of HCOOH dehydrogenation intermediates was analyzed. We found a new adsorption configuration in which HCOOH* (where * and a single underline indicates the adsorbed species and adsorbed atom, respectively) was adsorbed in a more stable manner (adsorption energy, Eads= −1.22eV) on the system than HCOOH* (Eads=−1.10eV) owing to the presence of Ni(OH)2-G. This affected the next step in HCOOH dehydrogenation, i.e., formation of HCOO* species, and showed a positive effect on the HCOOH dehydrogenation. To fundamentally understand this phenomenon, electronic structure (d-band center and density of states) and stability (vacancy formation energy) analyses were performed.