Dispersed Metal Nanoparticles Research Articles

Furfural Hydrogenation Over Reduced Pure (LaBO3) and Substituted (LaB0.5B'0.5O3) (B, B': Fe, Co, Ni) Perovskites

AbstractA series of pure and 50 % substituted Fe‐containing (LaFeO3, LaFe0.5Ni0.5O3 and LaFe0.5Co0.5O3) and Co/Ni‐containing (LaCoO3, LaNiO3, and LaCo0.5Ni0.5O3) perovskites were used as precursors to synthesize metallic reduced catalysts to be tested for the liquid hydrogenation of furfural. The catalytic reaction was carried out in a batch reactor at 200 °C and 3.0 MPa of H2 pressure. The calcined perovskites and reduced catalysts were characterized by X‐ray diffraction (XRD), N2 physisorption at 77 K, temperature programmed reduction (H2‐TPR), temperature programmed CO2 and NH3 desorption (CO2‐TPD and NH3‐TPD), Atomic Absorption Spectroscopy (AAS) and X‐ray photoelectron spectroscopy (XPS) techniques. The LaCo0.5Ni0.5O3 reduced catalyst display the highest activity in furfural conversion, which was attributed to a cooperative effect between highly dispersed nickel and cobalt metal nanoparticles after reduction process. The effect of the nature of B‐cation have a high impact on the products selectivity in the hydrogenation of furfural, suggesting that enriched‐Ni metal surface was selectivity to tetrahydrofurfuryl alcohol, meanwhile enriched‐Co metal surface was selective to furfuryl alcohol formation, which was also supported with adsorption mode of furfural over the active sites obtained by quantum calculation.

Porous CN@MOF derived N, S-doped hierarchical framework carrying Co3Fe7/Fe0.8Co0.2S heterojunction: An efficient bifunctional cathode catalyst for Zn–air battery

The exploiting of bifunctional transition metal electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is of significance for the commercialization of rechargeable zinc-air batteries (ZABs). Herein, the N and S atoms-doped hierarchical carbon framework hosting the Co3Fe7/Fe0.8Co0.2S heterojunction is synthesized by employing porous g-C3N4 as framework and spacer, and FeCo-ZIF as metal source followed by sulfidation and pyrolysis. The detailed characterization confirms that the porous g-C3N4 plays a crucial role in improving the dispersion of metal nanoparticles. The obtained FeCo-Sx@NSC-900 catalysts exhibit layered accumulation configuration with uniformly distributed metal nanoparticles. Moreover, the typical carbon@metal nanoparticles and heterojunction structure can be observed from the HRTEM (High-Resolution Transmission Electron Microscopy) and HAADF-STEM (high-angle annular dark-field STEM) analysis results. The optimal FeCo-Sx@NSC-900 catalysts deliver exceptional ORR and OER performance with a potential difference between ORR and OER of merely 0.713 V, which is superior to the commercial Pt/C+RuO2 catalysts and other monometallic catalysts. Additionally, the ZAB assembled with the optimal FeCo-Sx@NSC-900 catalysts as cathode affords a good battery performance with high OCV (1.50 V), large power density (172 mW/cm2), good discharge stability, large specific capacity, and long-term charge/discharge stability (>300 cycles).

Facile synthesis of carbon supported ternary nickel-cobalt-iron nanocatalyst for the hydrodechlorination of 2-chlorophenol

Introduction: Chlorophenols (CPs) have become prevalent in the manufacture of herbicides, fungicides, pesticides, insecticides, pharmaceuticals, and dyes, contributing significantly to water pollution. Addressing this challenge, various treatment methods such as incineration, electrochemistry, photochemistry, biotechnology, and catalytic hydrodechlorination have been explored to reduce toxic chlorophenol contaminants. Hydrodechlorination stands out as an efficient technique for the removal of chlorine atoms. The dispersion of metal nanoparticles on supported materials significantly enhances the catalytic activity by increasing the specific surface area. Among these, carbon-supported nickel-cobalt-iron nanoparticles emerge as promising catalysts for the hydrodechlorination of 2-chlorophenol. Method: This study employs a chemical reduction method at high temperatures under an inert gas atmosphere to synthesize carbon-supported ternary nickel-cobalt-iron nanocatalysts, aiming to detoxify soil and water from pesticide residues. The physicochemical properties of these nanocatalysts were characterized using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Their catalytic activity was assessed through gas chromatography with a flame ionization detector (FID). Results: The analysis revealed that metallic nanoparticles are uniformly dispersed on the carbon support, with particle sizes ranging from 10 to 60 nm and an average size of 30 nm. The hydrodechlorination (HDC) of 2-chlorophenol (2-CP) achieved satisfactory conversions under various reaction conditions. Conclusion: The carbon-supported nickel-cobalt-iron nanoparticles demonstrated effective catalytic activity for the hydrodechlorination of 2-chlorophenol, highlighting their potential for application in the treatment of chloroorganic contaminations in the future.

Anchoring highly dispersed metal nanoparticles by strong electrostatic adsorption (SEA) on a dealuminated beta zeolite for catalysis

Enhanced interaction between metal precursors and silanol nests was demonstrated on a silanol-rich dealuminated beta zeolite by strong electrostatic adsorption, leading to the formation of highly dispersed Ni nanoparticles for effective catalysis.

In Situ Anchoring of Small-Sized Silver Nanoparticles on Porphyrinic Triazine-Based Frameworks for the Conversion of CO2 into α-Alkylidene Cyclic Carbonates with Outstanding Catalytic Activities under Ambient Conditions.

The preparation of catalytic hybrid materials by introducing highly dispersed metallic nanoparticles into porous organic polymers (POPs) may be an ideal and promising strategy for integrated CO2 capture and conversion. In terms of the carboxylative cyclization of propargyl alcohols with CO2, the anchoring of silver nanoparticles (AgNPs) on functional POPs to fabricate efficient heterogeneous catalysts is considered to be quite intriguing but remains challenging. In the contribution, well-dispersed AgNPs were successfully anchored onto the porphyrinic triazine-based frameworks by a simple "liquid impregnation and in situ reduction" strategy. The presence of N-rich dual active sites, porphyrin and triazine, which acted as the electron donor and acceptor, respectively, offered a huge opportunity for the nucleation and growth of metal nanoparticles. Significantly, the as-prepared catalyst Ag/TPP-CTF shows excellent catalytic activity (up to 99%) toward the carboxylative cyclization of propargyl alcohols with CO2 at room temperature, achieving record-breaking activities (TOF up to 615 h-1 at 1 bar and 3077 h-1 at 10 bar). Moreover, the catalyst can be easily recovered and reused at least 10 times with retention of high catalytic activity. The possible mechanism involves small-sized AgNP-mediated alkyne activation, which may promote highly efficient and green conversion of CO2. This work paves the way for immobilizing metal nanoparticles onto functional POPs by surface structure changes for enhanced CO2 catalysis.

MoO2-C@MoS2: A unique cocatalyst with LSPR effect for enhanced quasi-full-spectrum photocatalytic hydrogen evolution of CdS

A well-designed cocatalyst structure can improve the light-harvesting and quantum efficiency of photocatalysis. A multidimensional MoO2-C@MoS2 (MOCS) cocatalyst was successfully synthesized by post-sulfidation of MoO2-C nanorods. This controlled sulfidation process effectively inhibits the undesired oxidation of MoO2, stabilizing its metallicity and creating a synergistic effect for H2 evolution. Firstly, the highly dispersed metallic MoO2 nanoparticles induce localized surface plasmon resonance effects, expanding the light-harvesting range and generating abundant hot electrons. Secondly, the build-in electrostatic field and highly conductive carbon framework facilitates efficient interfacial electrons transfer. Thirdly, the amorphous MoOx and fragmented few-layers MoS2 in MOCS provide dual active sites with superior intrinsic activity for H2 evolution. Moreover, the unique multi-interface structure of MOCS optimizes the separation and reaction of charge carriers. As a result, the 20 wt% MOCS/CdS system show an excellent quasi-full-spectrum driven photocatalytic H2 evolution activity of 48.41 mmol/h·g, with 4.03 mmol/h·g in near-infrared region (> 800 nm).

Insights into Structural Behaviors of Thiolated and Aminated Reduced Graphene Oxide Supports to Understand Their Effect on MOR Efficiency.

It is essential to develop novel catalysts with high catalytic activity, strong durability, and good stability for further application in methanol fuel cells. In this work, we present for the first time the effect of the chemical functional groups (thiol and amine) with different electron affinity in reduced graphene oxide supports on the morphology and catalytic activity of platinum nanoparticles for the methanol oxidation reaction. Hydroxyl groups on graphene oxide were initially brominated and then transformed to the desired functional groups. The good dispersion of metal nanoparticles over functionalized carbon substrates (particle size less than 5 nm) with good durability, even at a limited functionalization degree (less than 7%) has been demonstrated by morphological and structural studies. The durability of the catalysts was much improved via strong coordination between the metal and nitrogen or sulfur atoms. Impressively, the catalytic activity of platinum nanoparticles on aminated reduced graphene oxide was found to be much better than that on thiolated graphene oxide despite the weaker affinity between amine and noble metals. These findings support further developing new graphene derivatives with the desired functionalization for electronics and energy applications..

Carbon nanofibers anchored LZ-276 zeolite supported Pd-Cu bimetallic catalyst for Suzuki-Miyaura coupling reaction

Herein, the composite catalyst supported by Pd-Cu bimetal was prepared by hydrothermal synthesis method using carbon nanofibers anchored LZ-276 zeolite as carrier. The addition of Cu not only save cost but also realize the high dispersion of metal nanoparticles. Under the optimized reaction conditions, the catalyst exhibits excellent catalytic activity and cycle stability in the Suzuki-Miyaura reaction. The designed structure effectively improves the catalytic performance of metal nanoparticles catalyzed reaction, and would inhibit the leaching or aggregation of metal particles. The strategy of reducing the noble metals dosage by using non-noble metals to replace noble metals reduces the catalyst costs, and thus holding great promise for industrial application.

Nanocrystalline BEA-CNT Composites with High Metal Dispersion Obtained via Inter-Zeolite Transformation for Antibacterial Application.

The rational design of interface materials containing carbon nanotubes (CNTs) and zeolites (zeolite-CNTs) is a promising perspective in chemical and biochemical communities because they exhibit several outstanding properties such as tunable hydrophobicity-hydrophilicity at interfaces. In this contribution, we report the fabrication of Ag-incorporated nanocrystalline BEA-carbon nanotube (CNT) composites via the one-pot inter-zeolite transformation of the micron-sized FAU-CNT composite in the presence of a Ag precursor. By varying the crystallization time, the inter-zeolite transformation mechanism was explored. Indeed, this process involves an amorphous intermediate of aluminosilicate species with a significant change of the crystal morphology in the presence of CNTs in the synthesis gel. Interestingly, the redispersion of metal particles was observed after the inter-zeolite transformation process, resulting in the high dispersion of metal nanoparticles over BEA nanocrystals. Notably, it was revealed that the Ag sites were also stabilized in the presence of CNT interfaces, leading to the availability of highly active Ag+ ions. To illustrate the beneficial aspect of designer materials, the synthesized Ag-incorporated BEA-CNT composites exhibited high antibacterial activity againstEscherichia coli due to the synergistic effect of the active Ag+ species and appropriate hydrophobic and hydrophilic properties of the hybrid material interfaces. This first example opens up perspectives of the rational design of zeolite-CNT interfaces with high metal dispersion via the inter-zeolite transformation approach for biomedical applications.

Highly dispersed gold nanoparticles anchoring on COFTAPB-DMTP for electrochemical detection of paracetamol

Small size Au nanoparticles (AuNPs) have aroused wide interest in electrochemical sensing due to its high surface atom utilization and superior electrical conductivity. However, there was a great challenge to balance the stability and small-size of AuNPs because of their large specific surface and high surface energy. Regarding this issue, herein, COFTAPB-DMTP was proposed as guiding support substrate for the synthesis of highly dispersed and small size AuNPs, where the uniform functional sites such N, O atoms on COFTAPB-DMTP could act as anchor points to induce in-situ reduction of AuNPs, and the confinement effects from the nanopore of COFTAPB-DMTP could limit their size. Then, an electrochemical paracetamol (PA) sensor was designed based on AuNPs@COFTAPB-DMTP since the abundant active centers and outstanding electrical conductivity of highly dispersed small size AuNPs conferred the composite excellent sensing performance. Moreover, the large specific surface, ordered pore channels and abundant heteroatomic functional groups of COFTAPB-DMTP could achieve high enrichment capacity toward PA molecules on electrode surface through pore effect, hydrogen bonding and electrostatic interaction. Benefiting from the combination between AuNPs and COFTAPB-DMTP, the AuNPs@COFTAPB-DMTP based sensor presents excellent analytical performance in term of low limit of detection (22 nM), satisfactory stability, reproducibility and selectivity. It indicated that COFs can be used as promising inducible substrate material for the preparation of highly dispersed and small size metal nanoparticles.

Superior Interfacial Contact Yields Efficient Electron Transfer Rate and Enhanced Solar Photocatalytic Hydrogen Generation in M/C3N4 Schottky Junctions.

Various literature studies (Table 6) have reported that dispersion of metal nanoparticles (NPs) on graphitic carbon nitride g-C3N4 (M/CN) has considerably improved the photocatalytic hydrogen yield. It is understood that metal NPs create active sites on the surface of CN and act as a cocatalyst. However, the precise changes induced by different metal NPs on the surface of CN still elude us. Here, we report a thorough understanding and comparison of the morphology, metal-support interactions, interfacial charge transfer kinetics, and band characteristics in different M/CN (M = Pt, Pd, Au, Ag, Cu) correlated with photocatalytic activity. Among all metals, Pt/CN was found to be the best performer both under sunlight and UV-visible irradiation. Under sunlight, maximum H2@ 2.7 mmol/h/g was observed over Pt/CN followed by Pd/CN > Au/CN > Ag/CN > Cu/CN ≈ CN. The present study revealed that among all metals, Pt formed superior interfacial contact with g-C3N4 as compared to other metals. The maximum Schottky barrier height (Φb,Pt) of 0.66 V was observed at Pt/CN followed by Φb,Au/CN (0.46 V) and Φb,Pd/CN (0.05 V). The presence of electron-deficient Pt in Pt-XPS, decrease in the intensity of d-DOS of Pt near the Fermi level in VB-XPS, increase in CB tail states, and cathodic shift in Vfb in MS plots sufficiently confirmed strong metal-support interactions in Pt/CN. Due to the SPR effect, Au and Ag NPs suffered from agglomeration and poor dispersion during photodeposition. Finely dispersed Pt NPs (2-4 nm, 53% dispersion) successfully competed with shallow/deep trap states and drove the photogenerated electrons to active metallic sites in a drastically reduced time period as investigated by femtosecond transient absorption spectroscopy. Typically, an interfacial electron transfer rate, KIET,avg, of 2.5 × 1010 s-1 was observed for Pt/CN, while 0.087 × 1010 s-1 was observed in Au/CN. Band alignment/potentials at M/CN Schottky junctions were derived and most favorable in Pt/CN with CB tail states much above the water reduction potential; however, in the case of Pd, these extend much below the H+/H2 potential and hence behave like deep trap states. Thus, in Pd/CN (τ0 = 4200 ps, 49%) and Ag/CN (3870 ps, 53%), electron deep trapping dominates over charge transfer to active sites. The present study will help in designing futuristic new cocatalyst-photocatalyst systems.

Achieving super dispersed metallic nickel nanoparticles over MCM-41 for highly active and stable hydrogenation of olefins and aromatics

Hydrogenation of olefins and aromatics is of significance for fuel processing and hydrogen storage, and developing nickel (Ni) catalyst highly active at low reaction temperature is the key to low the process cost. Herein we developed an ammonium citrate assisted impregnation method to fabricate loaded Ni catalyst (NiM-2) for hydrogenation. The Ni2+ species are anchored on the support MCM-41 strongly and evenly in form of Ni-citrate complex via the H-bonding between Si-OH group of MCM-41 and –COO- of citrate. During reduction, the carbon layerstemporarily formed by carbonization of citrate species inhibit the transfer and sintering of Ni species, and finally induces ultra-small metallic Ni nanoparticles after carbon layers slow decomposition by Ni species. Low coordination numbers and strong electron interaction between small metallic Ni nanoparticles and MCM-41 support upshift the d-band center of metallic Ni atoms. In hydrogenation, the small particle size and easier reduction for oxidized Ni species provide abundant active sites for reaction, and the upshifted d-band center induces strongly adsorption and activation of C = C bonds, which is confirmed for the first time in our work. As a result, the catalyst exhibits superior activity compared with reported and commercial Ni-based catalysts for hydrogenation of olefins and aromatics. Specifically, the catalyst with higher Ni loading (18%) exhibits good activity under room temperature and 0.1 MPa for hydrogenation of dicyclopentadiene and are comparable to Pd catalysts, making it as one of the best non-precious metal catalysts for hydrogenation reaction. And also, NiM-2 shows extremely high stability.

Metal-organic framework-derived Co-C catalyst for the selective hydrogenation of cinnamaldehyde to cinnamic alcohol

The liquid phase selective hydrogenation of cinnamaldehyde has been investigated over the catalysts Co-C-T (T = 400–700 °C), which were derived from the carbonization of the MOF precursor Co-BTC at different temperatures in inert atmosphere. Co-C-500 exhibited a higher conversion (85.3%) than those carbonized at other temperatures, with 51.5% selectivity to cinnamyl alcohol, under a mild condition (90 °C, 4 h, 2 MPa H2, solvent: 9 ml ethanol and 1 ml water). The high catalytic activity of Co-C-500 can be ascribed to the large specific surface area of the catalyst, the uniformly dispersed metallic cobalt nanoparticles, and the more defect sites on the carbon support. Moreover, Co-C-500 showed excellent reusability in 5 successive cycles, mainly related to the uniformly dispersed cobalt nanoparticles embedded in carbon support.

Composition‐Controlled Laser‐Induced Alloying of Colloidal Au–Cu Hetero Nanoparticles

AbstractDue to their optical properties (localized surface plasmon resonance, LSPR), colloidally dispersed metal nanoparticles are well suited for selective heating by high‐energy laser radiation above their melting point without being limited by the boiling point of the solvent, which represents an excellent complement to wet‐chemical nanoparticle synthesis. By combining wet‐chemical synthesis and postsynthesis laser treatment, the advantages of both methods can be used to specifically control the properties of nanoparticles. Especially in the colloidal synthesis of nanoalloys consisting of two or more metals with different redox potentials, wet‐chemical synthesis quickly reaches its limits in terms of composition control and homogeneity. For this reason, the direct synthesis path is divided into two parts to take the strengths of both methods. After preparing Au–Cu hetero nanoparticles by wet‐chemical synthesis, nanoalloys with previous adjusted composition can be formed by postsynthesis laser treatment. The formation of these nanoalloys can be followed by different characterization methods, such as transmission electron microscopy (TEM), where the fusion of both metal domains and the formation of spherical and homogeneous Au–Cu nanoparticles can be observed. Moreover, the alloy formation can be followed by different shifts of X‐ray diffraction (XRD) reflections and LSPR maxima depending on the composition.

Chelating adsorption-engaged synthesis of ultrafine iridium nanoparticles anchored on N-doped carbon nanofibers toward highly efficient hydrogen evolution in both alkaline and acidic media

Developing highly efficient and stable precious metal electrocatalysts toward hydrogen evolution reaction (HER) is crucial for energy application, while it is still challenging to achieve highly dispersed ultrafine metal nanoparticles on some promising supports to synergistically promote their electrocatalytic performance. Herein, we propose a feasible chelating adsorption-engaged strategy by introducing de-doped polyaniline with abundant amino groups to immobilize ultrafine iridium (Ir) nanoparticles on their derived N-doped carbon nanofibers (Ir-NCNFs). Experimental results demonstrate that the synthesized Ir-NCNFs can effectively promote the charge transfer and expose more electrochemical active sites, which eventually accelerate the reaction kinetics. Thus, the synthesized Ir-NCNFs catalyst exhibits admirable HER activities in both alkaline and acidic conditions with overpotentials of only 23 and 8 mV, which are even superior or close to the benchmark Pt/C catalyst. Furthermore, the synthesized Ir-NCNFs catalyst also exhibits a long-term durability. This study affords a reliable means to construct high-performance supported ultrafine metal nanocatalysts for electrocatalytic applications to alleviate the growing demand for energy conversion.

Magnetoconvection driven melting of nanoenriched paraffin wax in cubical enclosure

The latent heat thermal energy storage using phase change material plays a vital role in thermal power production, solar energy storage and nuclear reactors. The dispersion of metallic nanoparticles into phase change material in the presence of magnetic field controls the natural convection induced melting process. This paper numerically investigates the thermo-magnetic turbulent convection induced melting of nanoenriched paraffin wax dispersed with hybrid magnetic nanoparticle pairs in a cubical enclosure with hot bottom wall. The magneto free convection effect on the melting process is investigated for high value of Hartmann number and Rayleigh number. The melting characteristics is modeled using enthalpy-porosity formulation discretized using finite difference technique and the computations are performed using an in-house three-dimensional code. It is found that the natural convection induced melting generates quadruplet thermal plume patterns from the melt zone. The dispersion of hybrid nanoparticle pairs of ferrous ferric oxide and multi-wall carbon nanotubes for particle volume fraction of 4% enhanced the melting fraction and average Nusselt number of paraffin wax by 75.21% and 42.16% respectively. The high Lorentz force developed for turbulent Hartmann number of 2000 diminished the convection induced melting phenomena. The melting time and melting rate of nanoenriched paraffin wax are a decreasing function of Hartmann number and it decreased the melt pool velocity and kinetic energy by 73.5% and 71.42%. The increase in Hartmann number decreased the average Nusselt number of nanoenhanced paraffin wax by 20.88%.

Double spatial confinement on ruthenium nanoparticles inside carbon frameworks as durable catalysts for a quasi‐solid‐state Li–O2 battery

AbstractThe rational design of large‐area exposure, nonagglomeration, and long‐range dispersion of metal nanoparticles (NPs) in the catalysts is critical for the development of energy storage and conversion systems. Little attention has been focused on modulating and developing catalyst interface contact engineering between a carbon substrate and dispersed metal. Here, a highly dispersed ultrafine ruthenium (Ru) NP strategy by double spatial confinement is proposed, that is, incorporating directed growth of metal–organic framework crystals into a bacterial cellulose templating substrate to integrate their respective merits as an excellent electrocatalytic cathode catalyst for a quasi‐solid‐state Li–O2 battery. The porous carbon matrix with highly dispersed ultrafine Ru NPs is well designed and used as cathode catalysts in a Li–O2 battery, demonstrating a high discharge areal capacity of 6.82 mAh cm–2 at 0.02 mA cm–2, a high‐rate capability of 4.93 mAh cm–2 at 0.2 mA cm–2, and stable discharge/charge cycling for up to 500 cycles (2000 h) with low overpotentials of ~1.4 V. This fundamental understanding of the structure–performance relationship demonstrates a new and promising approach to optimize highly efficient cathode catalysts for solid‐state Li–O2 batteries.

Kinetic Relevance of Surface Reactions and Lattice Diffusion in the Dynamics of Ce–Zr Oxides Reduction–Oxidation Cycles

Reduction–oxidation cycles in oxides are ubiquitous in oxygen storage and transport, chemical looping processes, and fuel cells. O-atom addition and removal are mediated by coupling reactions of oxidants and reductants at surfaces with diffusion of O-atoms within oxide crystals, with either or both processes as limiting steps. CeO2–ZrO2 solid solutions (CZO) are ubiquitous in practice. They are used here to illustrate general experimental strategies and reaction–diffusion formalisms for nonideal systems that enable assessments of the kinetic relevance of the steps that mediate O-atom addition and removal in these materials; these experiments are described within the context of models that describe the driving forces for reaction and diffusion rigorously in terms of oxygen chemical potentials (μO). These strategies assess the rate consequences of varying the fluid phase redox potential, through changes in the identity and pressures of the reactants and products used in redox cycles (O2; CO/CO2; H2/H2O; N2O/N2), of introducing dispersed metal nanoparticles that capture and react lattice O-atoms in CZO using CO or H2, and of imposing intervening dwells without reaction within redox cycles. O-removal rates depend on reductant pressures, even when CO/CO2 and H2/H2O ratios are chosen to maintain the same surface μO if surface reactions were quasi-equilibrated. These data, taken together with significant rate enhancements in O-removal when Pt nanoparticles are present at CZO crystal surfaces and with similar rates before and after inert dwells, demonstrate that reduction rates by both CO and H2 are limited by surface reactions without the presence of consequential spatial gradients in μO within CZO crystals. In contrast, O-addition rates to partially reduced CZO crystals are similar for N2O and O2 reactants and are not affected by the presence of Pt nanoparticles; O-addition rates are significantly higher after intervening inert dwells during CZO oxidation, indicative of spatial gradients in μO, which relax during nonreactive periods. These methods and models, illustrated here for CZO redox cycles at conditions relevant to oxygen storage practice, allow systematic assessments of the kinetic relevance of lattice diffusion and surface reactions for systems that use solids for the reversible storage and release of atoms, irrespective of the identity of the solids or the atoms (e.g., O, H, N, and S).

Ultrasmall FeMoNi Tri-Metal nanoparticles confined by tannic acid-derived carbon as bi-functional electrocatalyst for oxygen evolution and urea oxidation

Exploration of the electrocatalysts with uniformly dispersed metal nanoparticles (NPs) is important to achieve high electrocatalytic activity, but the NPs always trend to aggregate during fabrication or application. Herein, ultrasmall FeMoNi tri-metal NPs was confined by tannic acid-derived carbon layer and utilized as bi-functional electrocatalyst. The interconnected nanosheets network with open porous structure and electrolyte/gas diffusion channels can reduce the mass transfer resistance. The tri-metal NPs with average diameter of only 11.9 nm are uniformly distributed between the space limited carbon interlayer to avoid aggregation and provide enhanced electric conductivity. Meanwhile, the physical carbon armor and electron tunneling effect can enhance the alkali resistance and electrocatalytic activity/stability of the electrocatalyst. Therefore, the optimized C@FeMoNi/CC electrode can achieve overpotential of 244 mV and potential of 1.4 V at 10 mA cm−2 for OER and UOR, respectively, and high long-term cyclic stability for 40 h. Moreover, the high-valence NiFe species are considered as the highly active centers. This plant polyphenol derived surface coating and carbonization strategy with controllable functional building blocks provides a solution for the rational design of energy conversion devices.

Loading uniformly distributed CuRu alloys on carbon nanotubes via flash Joule heating for high-performance electrocatalytic water splitting

Constructing highly efficient and stable electrocatalysts is the key to reducing the overall energy input for electrocatalytic water splitting, which ensures the reduced cost of environmentally friendly hydrogen resources with high energy density. Assisted by ultrafast pyrolysis with a flash Joule heating technique, CuRu ultrasmall alloy nanoparticles are uniformly coated on carbon nanotubes (CNTs) with tannic acid (TA) to chelate metal ions. During the pyrolysis procedure, the self-assembled TA molecules not only offer a cross-linked porous polyphenol framework but also provide more interactions to link the alloy nanoparticles and CNT substrates, forming highly conductive electrocatalysts with uniformly dispersed ultrasmall alloy metallic nanoparticles (∼ 4.3 nm in diameter) on the surface of porous CNTs (CuRu-CNTs). In particular, CuRu-CNTs with Cu-Ru alloy nanoparticles achieve the highest electrochemical activity, exhibiting tiny HER and OER overpotential of 39 mV and 330 mV at 10 mA cm−2 in 1.0 M KOH medium. The unique bifunctional feature of CuRu-CNTs allows good overall water splitting activity (10 mA cm−2 for 12 h), which is comparable with the best noble metal-based benchmark. This contribution provides a general energy saving pyrolysis method for the preparation of highly efficient, cost-effective and chemically stable electrocatalysts for water splitting.