Showing papers on "Noble metal published in 2019"

A universal synthesis strategy for P-rich noble metal diphosphide-based electrocatalysts for the hydrogen evolution reaction

Abstract: Highly efficient, stable and cost-efficient electrocatalysts for hydrogen generation via water splitting have become in increasing demand for future energy systems. Hitherto, P-rich noble metal polyphosphides which can decrease noble metal (such as Rh, Pd, or Ir) dosage are important to probe potential high-performance HER electrocatalysts. Nevertheless, they are difficult to synthesize at ambient pressure and moderate temperatures. Herein, for the first time, we report a novel iridium diphosphide (IrP2) electrocatalyst embedded within an ultrathin nitrogen-doped carbon (NC) layer (IrP2@NC) synthesized at ambient pressure and moderate temperature (900 °C). Subsequent electrochemical tests revealed that such a P-rich IrP2@NC catalyst possesses the highest hydrogen evolution reaction (HER) activity among all the documented transition metal phosphide electrocatalysts, including the commercial Pt/C, with ultralow overpotentials of 8 and 28 mV to achieve 10 mA cm−2 in 0.5 M H2SO4 and 1.0 M KOH, respectively. Combined density functional theory (DFT) computational studies suggest that the introduction of phosphorus into iridium can weaken the H adsorption strength of IrP2, beneficial for boosting HER activity. More importantly, this synthetic strategy for P-rich IrP2@NC can also be applied to other noble metal diphosphides (RhP2@NC and Pd5P2@NC, etc.). This work presents a particularly efficient and stable P-rich transition metal polyphosphide with advanced HER performance and beyond.

Redox-Inert Fe3+ Ions in Octahedral Sites of Co-Fe Spinel Oxides with Enhanced Oxygen Catalytic Activity for Rechargeable Zinc–Air Batteries

Abstract: Bimetallic cobalt-based spinel is sparking much interest, most notably for its excellent bifunctional performance. However, the effect of Fe3+ doping in Co3 O4 spinel remains poorly understood, mainly because the surface state of a catalyst is difficult to characterize. Herein, a bifunctional oxygen electrode composed of spinel Co2 FeO4 /(Co0.72 Fe0.28 )Td (Co1.28 Fe0.72 )Oct O4 nanoparticles grown on N-doped carbon nanotubes (NCNTs) is designed, which exhibits superior performance to state-of-the-art noble metal catalysts. Theoretical calculations and magnetic measurements reveal that the introduction of Fe3+ ions into the Co3 O4 network causes delocalization of the Co 3d electrons and spin-state transition. Fe3+ ions can effectively activate adjacent Co3+ ions under the action of both spin and charge effect, resulting in the enhanced intrinsic oxygen catalytic activity of the hybrid spinel Co2 FeO4 . This work provides not only a promising bifunctional electrode for zinc-air batteries, but also offers a new insight to understand the Co-Fe spinel oxides for oxygen electrocatalysis.

Rational Design of Crystalline Covalent Organic Frameworks for Efficient CO 2 Photoreduction with H 2 O

Abstract: Solar energy-driven conversion of CO2 into fuels with H2 O as a sacrificial agent is a challenging research field in photosynthesis. Herein, a series of crystalline porphyrin-tetrathiafulvalene covalent organic frameworks (COFs) are synthesized and used as photocatalysts for reducing CO2 with H2 O, in the absence of additional photosensitizer, sacrificial agents, and noble metal co-catalysts. The effective photogenerated electrons transfer from tetrathiafulvalene to porphyrin by covalent bonding, resulting in the separated electrons and holes, respectively, for CO2 reduction and H2 O oxidation. By adjusting the band structures of TTCOFs, TTCOF-Zn achieved the highest photocatalytic CO production of 12.33 μmol with circa 100 % selectivity, along with H2 O oxidation to O2 . Furthermore, DFT calculations combined with a crystal structure model confirmed the structure-function relationship. Our work provides a new sight for designing more efficient artificial crystalline photocatalysts.

Markedly Enhanced Oxygen Reduction Activity of Single-Atom Fe Catalysts via Integration with Fe Nanoclusters

Abstract: Single-atom catalysts (SACs) have emerged as one of the most promising alternatives to noble metal-based catalysts for highly efficient oxygen reduction reaction (ORR). While SACs can offer notable benefits in terms of lowering overall catalyst cost, there is still room for improvement regarding catalyst activity. To this end, we designed and successfully fabricated an ORR electrocatalyst in which atomic clusters are embedded in an atomically dispersed Fe-N-C matrix (FeAC@FeSA-N-C), as shown by comprehensive measurements using aberration-corrected scanning transmission electron microscopy (AC-STEM) and X-ray absorption spectroscopy (XAS). The half-wave potential of FeAC@FeSA-N-C is 0.912 V (versus reversible hydrogen electrode (RHE)), exceeding that of commercial Pt/C (0.897 V), FeSA-N-C (0.844 V), as well as the half-wave potentials of most reported non-platinum-group metal catalysts. The ORR activity of the designed catalyst stems from single-atom active centers but is markedly enhanced by the presence of Fe nanoclusters, as confirmed by both experimental measurements and theoretical calculations.

CO 2 electrochemical catalytic reduction with a highly active cobalt phthalocyanine

Abstract: Molecular catalysts that combine high product selectivity and high current density for CO2 electrochemical reduction to CO or other chemical feedstocks are urgently needed. While earth-abundant metal-based molecular electrocatalysts with high selectivity for CO2 to CO conversion are known, they are characterized by current densities that are significantly lower than those obtained with solid-state metal materials. Here, we report that a cobalt phthalocyanine bearing a trimethyl ammonium group appended to the phthalocyanine macrocycle is capable of reducing CO2 to CO in water with high activity over a broad pH range from 4 to 14. In a flow cell configuration operating in basic conditions, CO production occurs with excellent selectivity (ca. 95%), and good stability with a maximum partial current density of 165 mA cm−2 (at −0.92 V vs. RHE), matching the most active noble metal-based nanocatalysts. These results represent state-of-the-art performance for electrolytic carbon dioxide reduction by a molecular catalyst. Molecular electrocatalysts reducing CO2 to CO with high selectivity and high rate are urgently needed. A cobalt phthalocyanine complex is capable of reducing CO2 to CO in water with a maximum partial current density up to 165 mA cm−2, matching the most active noble metal-based nanocatalysts.

Silver decorated magnetic nanocomposite (Fe3O4@PPy-MAA/Ag) as highly active catalyst towards reduction of 4-nitrophenol and toxic organic dyes

Abstract: Developing innovative technologies for the efficient treatment of wastewater containing toxic organic pollutants is of particular importance worldwide. Removal of organic contaminants from aqueous media through chemical reduction using noble metal-based nanocatalysts, and in the presence of NaBH4, as a reducing agent, has become an established approach in the last few years. Herein, we describe a simple method for the synthesis of a magnetic conducting polymer modified with mercaptoacetic acid (MAA) and silver nanoparticles (Ag NPs) as a promising catalyst for the reduction of organic pollutants. Ag NPs were deposited on the magnetic conducting polymer by the reduction of a silver salt precursor (AgNO3) without the need for a reducing agent or stabilizer. The developed Fe3O4@PPy-MAA/Ag nanocomposite was characterised using FE-SEM, TEM, XRD, XPS, BET and ATR-FTIR. The catalytic performance of the nanocatalyst during the reduction of 4-nitrophenol (4-NP) and organic dyes, namely, methylene blue (MB) and methyl orange (MO) was assessed in aqueous medium at 25 °C. The catalyst exhibited excellent catalytic activity for the reduction of all three targeted organic pollutants (4-NP, MO and MB). The pseudo-first-order rate constants were estimated as 0.5–14.3 × 10−2 min-1, 0.52–24.2 × 10−2 s−1 and 10.1–46.8 × 10−3 s−1 for the reduction of 4-NP, MO and MB, respectively. The magnetic catalyst was separated easily from the reaction medium and recycled without significant loss of catalytic activity up to eight successive cycles. In addition to its green synthesis and reusability, findings from this study show that Fe3O4@PPy-MAA/Ag nanocomposite has the potential efficiency and stability to make it an ideal catalyst in environmental applications via chemical reduction of toxic contaminants from wastewater.

A highly CO-tolerant atomically dispersed Pt catalyst for chemoselective hydrogenation.

Abstract: The hydrogenation activity of noble metal, especially platinum (Pt), catalysts can be easily inhibited by the presence of a trace amount of carbon monoxide (CO) in the reaction feeds. Developing CO-resistant hydrogenation catalysts with both high activity and selectivity is of great economic interest for industry as it allows the use of cheap crude hydrogen and avoids costly product separation. Here we show that atomically dispersed Pt over α-molybdenum carbide (α-MoC) constitutes a highly CO-resistant catalyst for the chemoselective hydrogenation of nitrobenzene derivatives. The Pt1/α-MoC catalyst shows promising activity in the presence of 5,000 ppm CO, and has a strong chemospecificity towards the hydrogenation of nitro groups. With the assistance of water, high hydrogenation activity can also be achieved using CO and water as a hydrogen source, without sacrificing selectivity and stability. The weakened CO binding over the electron-deficient Pt single atom and a new reaction pathway for nitro group hydrogenation confer high CO resistivity and chemoselectivity on the catalyst. Atomically dispersed Pt on an α-MoC support exhibits high CO tolerance during selective hydrogenation of nitrobenzene and its derivatives.

A general synthesis approach for amorphous noble metal nanosheets.

Abstract: Noble metal nanomaterials have been widely used as catalysts. Common techniques for the synthesis of noble metal often result in crystalline nanostructures. The synthesis of amorphous noble metal nanostructures remains a substantial challenge. We present a general route for preparing dozens of different amorphous noble metal nanosheets with thickness less than 10 nm by directly annealing the mixture of metal acetylacetonate and alkali salts. Tuning atom arrangement of the noble metals enables to optimize their catalytic properties. Amorphous Ir nanosheets exhibit a superior performance for oxygen evolution reaction under acidic media, achieving 2.5-fold, 17.6-fold improvement in mass activity (at 1.53 V vs. reversible hydrogen electrode) over crystalline Ir nanosheets and commercial IrO2 catalyst, respectively. In situ X-ray absorption fine structure spectra indicate the valance state of Ir increased to less than + 4 during the oxygen evolution reaction process and recover to its initial state after the reaction. While noble metal usage in catalysis is ubiquitous, the metals’ scarcity necessitates new materials designs for efficient utilization. Here, authors report a general strategy to prepare amorphous noble metal nanosheets and find the nanomaterials to act as efficient water-splitting electrocatalysts.

2H- and 1T- mixed phase few-layer MoS2 as a superior to Pt co-catalyst coated on TiO2 nanorod arrays for photocatalytic hydrogen evolution

Abstract: Recently, MoS2 as an efficient co-catalyst has attracted much attention for photocatalytic water splitting. MoS2 has two polymorphs: semiconducting phase (2H) and metallic phase (1T). The 2H- and 1T- MoS2 show different reaction mechanism in photocatalytic H2 evolution. However, so far, very few experiments have clearly evidenced the electron transfer process between TiO2 and mixed phase MoS2. This study for the first time has reported a simple hydrothermal synthesis method to prepare mixed phase few-layer MoS2 nanosheets coated on TiO2 nanorod arrays (MoS2@TiO2) with a conductive fluorine-doped tin oxide (FTO) as a substrate. The structure of mixed phase MoS2 was characterized carefully. The designed MoS2@TiO2 exhibits two times higher activity than Pt@TiO2 for photocatalytic H2 evolution. The reliable conclusion that the photo-generated electrons from TiO2 to MoS2 nanosheets has clearly been evidenced by photoelectrochemical analyses and in-situ KPFM experiments, and the mixed phase MoS2 here is a co-catalyst such like Pt rather than as a semiconductor. This study not only presents a series of solid experimental evidences to verify the electrons transfer process and photocatalytic mechanism, but also provides a new method in substituting MoS2 for noble metal Pt as co-catalyst in high-efficiency photocatalytic water splitting into hydrogen.

Platinum-copper single atom alloy catalysts with high performance towards glycerol hydrogenolysis.

Abstract: Selective hydrogenolysis of biomass-derived glycerol to propanediol is an important reaction to produce high value-added chemicals but remains a big challenge. Herein we report a PtCu single atom alloy (SAA) catalyst with single Pt atom dispersed on Cu nanoclusters, which exhibits dramatically boosted catalytic performance (yield: 98.8%) towards glycerol hydrogenolysis to 1,2-propanediol. Remarkably, the turnover frequency reaches up to 2.6 × 103 molglycerol·molPtCu–SAA−1·h−1, which is to our knowledge the largest value among reported heterogeneous metal catalysts. Both in situ experimental studies and theoretical calculations verify interface sites of PtCu–SAA serve as intrinsic active sites, in which the single Pt atom facilitates the breakage of central C–H bond whilst the terminal C–O bond undergoes dissociation adsorption on adjacent Cu atom. This interfacial synergistic catalysis based on PtCu–SAA changes the reaction pathway with a decreased activation energy, which can be extended to other noble metal alloy systems. Selective hydrogenolysis of biomass glycerol to propanediol is a promising route for the production of high-value chemicals but remains a challenge. Here, the authors find a PtCu single atom alloy catalyst exhibits remarkably boosted performance with a turnover frequency value of 2.6 × 103 molglycerol·molPtCu–SAA−1·h−1.

Self-catalyzed growth of Co, N-codoped CNTs on carbon-encased CoSx surface: a noble-metal-free bifunctional oxygen electrocatalyst for flexible solid Zn–air batteries

Abstract: The self-catalyzed growth of nanostructures on material surfaces is one of the most time- and cost-effective ways to design multifunctional catalysts for a wide range of applications. Herein, the use of this technique to develop a multicomponent composite catalyst with CoS core encapsulated in an ultrathin porous carbon shell entangled with Co, N-codoped carbon nanotubes is reported. The as-prepared catalyst has a superior catalytic activity for oxygen evolution and oxygen reduction reactions, an ultralow potential gap of 0.74 V, and outstanding durability, surpassing most previous reports. Such superiority is ascribed, in part, to the unique 3D electrode architecture of the composite, which is favorable for transporting oxygen species and electrons and creates a synergy between the components with different functionalities. Moreover, the flexible solid Zn–air battery assembled with such an air electrode shows a steady discharge voltage plateau of 1.25 V and a round-trip efficiency of 70% at 1 mA cm. This work presents a simple strategy to design highly efficient bifunctional oxygen electrocatalysts and may pave the way for the practical application of these materials in many energy conversion/storage devices.

Non-precious Co3O4-TiO2/Ti cathode based electrocatalytic nitrate reduction: Preparation, performance and mechanism

Abstract: The presence of high nitrate (NO3−) concentration in natural water constitutes a serious issue to the environment and human health. Therefore, the development of low-cost, stable non-precious metal catalysts is imminent for efficient NO3- reduction. In this study, we prepared a Co3O4-TiO2/Ti cathode via combining sol-gel and calcination methods and evaluated its performance for electrocatalytic NO3- reduction. The dispersion of the Co3O4 catalyst particles was improved by the addition of PVP to the coating liquid. The presence of anatase could effectively stabilize Co3O4 and prevent the releasing of toxic Co ions into the solution. The Co3O4-TiO2/Ti cathode with the optimized performance for NO3- reduction could be prepared by four times coating at calcination temperature of 500 °C. The electrocatalytic reduction of NO3- was negligibly impacted by solution pH in the range of 3.0–9.0, while it could be facilitated by elevating the current density from 2.5 to 25 mA cm2. Ammonium ions were the main final NO3- reduction product, and the presence of Cl- was capable to oxidize ammonium ions to N2 due to the electrochemical production of reactive chlorine species. The electrochemical analyses, scavenging experiments and density functional theory calculations collectively confirm that NO3- reduction was mainly induced by the Co2+–Co3+–Co2+ redox process instead of being directly resulted from the electrons generated at the cathode. Unlike noble metal (e.g., Pd and Ag) based catalytic reaction systems, in the present Co3O4 mediated electrocatalytic reaction process, atomic H* would more favorably turn to H2 by Heyrovsky and Tafel routes and therefore contributed marginally to the NO3- reduction. Generally, this study provided a new paradigm for designing the stable and cost-effective cathode for NO3- reduction.

Photocatalytic Hydrogen Production: Role of Sacrificial Reagents on the Activity of Oxide, Carbon, and Sulfide Catalysts

Abstract: Photocatalytic water splitting is a sustainable technology for the production of clean fuel in terms of hydrogen (H2). In the present study, hydrogen (H2) production efficiency of three promising photocatalysts (titania (TiO2-P25), graphitic carbon nitride (g-C3N4), and cadmium sulfide (CdS)) was evaluated in detail using various sacrificial agents. The effect of most commonly used sacrificial agents in the recent years, such as methanol, ethanol, isopropanol, ethylene glycol, glycerol, lactic acid, glucose, sodium sulfide, sodium sulfite, sodium sulfide/sodium sulfite mixture, and triethanolamine, were evaluated on TiO2-P25, g-C3N4, and CdS. H2 production experiments were carried out under simulated solar light irradiation in an immersion type photo-reactor. All the experiments were performed without any noble metal co-catalyst. Moreover, photolysis experiments were executed to study the H2 generation in the absence of a catalyst. The results were discussed specifically in terms of chemical reactions, pH of the reaction medium, hydroxyl groups, alpha hydrogen, and carbon chain length of sacrificial agents. The results revealed that glucose and glycerol are the most suitable sacrificial agents for an oxide photocatalyst. Triethanolamine is the ideal sacrificial agent for carbon and sulfide photocatalyst. A remarkable amount of H2 was produced from the photolysis of sodium sulfide and sodium sulfide/sodium sulfite mixture without any photocatalyst. The findings of this study would be highly beneficial for the selection of sacrificial agents for a particular photocatalyst.

Noble Metal-Free Nanoporous High-Entropy Alloys as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

Abstract: Developing highly efficient catalysts for oxygen evolution reactions (OER) is a key step for rechargeable metal–oxygen batteries and water splitting. Usually, binary NiFe or ternary NiCoFe nano-alloys are used as the OER catalysts. Herein, combining the precursor alloy design with chemical etching, a simple dealloying route is developed to controllably incorporate five or more nonprecious metals into one nanostructured alloy with a naturally oxidized surface, that is, nanoporous high entropy alloys (np-HEAs) covered with high-entropy (oxy)hydroxides (HEOs). It is found that the alloy composition plays a dominant role in the OER activity enhancement with the np-AlNiCoFeX (X = Mo, Nb, Cr) combination showing the highest activity. Forming quinary HEAs also greatly enhances the electrochemical cycling stabilities compared with the ternary and quaternary counterparts. The result indicates the significance of synergistically incorporating five or more metal elements in one single-phase nanostructure, which prov...

Dynamic charge and oxidation state of Pt/CeO 2 single-atom catalysts

Abstract: The catalytic activity of metals supported on oxides depends on their charge and oxidation state. Yet, the determination of the degree of charge transfer at the interface remains elusive. Here, by combining density functional theory and first-principles molecular dynamics on Pt single atoms deposited on the CeO2 (100) surface, we show that the common representation of a static metal charge is oversimplified. Instead, we identify several well-defined charge states that are dynamically interconnected and thus coexist. The origin of this new class of strong metal–support interactions is the relative position of the Ce(4f) levels with respect to those of the noble metal, allowing electron injection to (or recovery from) the support. This process is phonon-assisted, as the Ce(4f) levels adjust by surface atom displacement, and appears for other metals (Ni) and supports (TiO2). Our dynamic model explains the unique reactivity found for activated single Pt atoms on ceria able to perform CO oxidation, meeting the Department of Energy 150 °C challenge for emissions. The catalytic activity of metals supported on oxides depends on charge and oxidation states, but charge transfer at the interface is not well understood. A model investigating the dynamic charges and oxidation states of Pt/CeO2 single-atom catalysts now clarifies the nature of the active site.

Promoting electrocatalytic overall water splitting with nanohybrid of transition metal nitride-oxynitride

Abstract: Excellent Electrochemical water splitting with remarkable durability can provide a solution for the increasing global energy demand. Herein, we report an efficient and stable overall water splitting system; cobalt nitride-vanadium oxynitride nanohybrid, prepared from the polyaniline (PANI) mediated synthetic protocol. This nanohybrid produces significantly higher water oxidation, proton reduction as well as overall water splitting performances compared to the cobalt nitride, vanadium oxynitride or even noble metal catalyst systems. Only 263 mV overpotential is required to reach 10 mA cm−2 current density for oxygen evolution reaction (OER) and 118 mV for the same in case of hydrogen evolution reaction (HER). Finally, the bifunctional nanohybrid has been explored for the alkaline overall water splitting at cell voltage of 1.64 V to attain 10 mA cm−2 current density with long term stability for 100 h. Post-catalytic analyses have revealed the formation of defect rich amorphous CoOx sites leading to high OER activity, whereas crystalline Co(OH)2-Coδ+-N (0

Nickel cobalt phosphide with three-dimensional nanostructure as a highly efficient electrocatalyst for hydrogen evolution reaction in both acidic and alkaline electrolytes

Abstract: Transition metal phosphides (TMPs) are promising candidates for noble metal free electrocatalysts in water splitting applications. In this work, we present the facile synthesis of nickel cobalt phosphide electrocatalyst with three-dimensional nanostructure (3D-NiCoP) on the nickel foam, via hydrothermal reaction and phosphorization. The as-prepared electrocatalyst exhibits an excellent activity for hydrogen evolution reaction (HER) in both acidic and alkaline electrolytes, with small overpotentials to drive 10 mA/cm2 (80 mV for 0.5 M H2SO4, 105 mV for 1 M KOH), small Tafel slopes (37 mV/dec for 0.5 M H2SO4, 79 mV/dec for 1 M KOH), and satisfying durability in long-term electrolysis. 3D-NiCoP also shows a superior HER activity compared to single metal phosphide, such as cobalt phosphide and nickel phosphide. The outstanding performance for HER suggests the great potential of 3D-NiCoP as a highly efficient electrocatalyst for water splitting technology.

A sulfur-tethering synthesis strategy toward high-loading atomically dispersed noble metal catalysts.

Abstract: Metals often exhibit robust catalytic activity and specific selectivity when downsized into subnanoscale clusters and even atomic dispersion owing to the high atom utilization and unique electronic properties. However, loading of atomically dispersed metal on solid supports with high metal contents for practical catalytic applications remains a synthetic bottleneck. Here, we report the use of mesoporous sulfur-doped carbons as supports to achieve high-loading atomically dispersed noble metal catalysts. The high sulfur content and large surface area endow the supports with high-density anchor sites for fixing metal atoms via the strong chemical metal-sulfur interactions. By the sulfur-tethering strategy, we synthesize atomically dispersed Ru, Rh, Pd, Ir, and Pt catalysts with high metal loading up to 10 wt %. The prepared Pt and Ir catalysts show 30- and 20-fold higher activity than the commercial Pt/C and Ir/C catalysts for catalyzing formic acid oxidation and quinoline hydrogenation, respectively.

Noble metal free, CeO2/LaMnO3 hybrid achieving efficient photo-thermal catalytic decomposition of volatile organic compounds under IR light

Abstract: Large amounts of anthropogenic VOCs emissions give rise to photochemical smog and ground-level ozone. Currently, catalytic oxidation for VOCs elimination still requires energy-intensive high temperatures. Light-driven photo-thermocatalysis oxidation of VOCs holds great promise to substantially reduce energy consumption for sustainable development in comparison with conventional thermal-based catalytic oxidation. Herein, CeO2/LaMnO3 composite, featuring the broad light wavelength absorption (800∼1800 nm), can be used as a highly active photo-thermal responsive catalyst on VOCs decomposition under IR irradiation. The maximum photo-thermal conversion efficiency is able to reach 15.2% with a significant toluene conversion of 89% and CO2 yield of 87% under IR irradiation intensity of 280 mW/cm2, together with excellent stability of nearly 30 h. Comparative characterizations reveal that such photo-thermal catalytic activity enhancement is predominantly attributed to the synergistic effects of ultrabroadband strong light absorption, efficient light-to-heat conversion, good low temperature reducibility and high lattice oxygen mobility, originating from an intense interaction of LaMnO3 with CeO2. Toluene oxidation reaction on CeO2/LaMnO3 catalyst proceeds via a Mars-van Krevelen mechanism as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy.

Metal-organic framework as nanoreactors to co-incorporate carbon nanodots and CdS quantum dots into the pores for improved H2 evolution without noble-metal cocatalyst

Abstract: Avoiding the utilization of noble-metal cocatalyst and the aggregation of nano photocatalysts in the preparation and photocatalytic reaction are two important aspects in the area of photocatalytic H2 evolution. In this work, for the first time, CdS quantum dots and carbon nanodots (CDs) were successfully co-immobilized in the cages of MIL-101 by one-step double solvents method followed by heating treatment. The optimum photocatalytic H2-evolution rate of CD/CdS@MIL-101(50) composite with CDs content of 5.2 wt% exhibits a H2 evolution rate of 14.66 μmol h−1 without noble metal assisted under visible-light irradiation, which is 8.5 and 18.6 times higher than that of CdS@MIL-101 and bare CdS, respectively. The improved photocatalytic H2-production activity of CD/CdS@MIL-101 ternary composite is predominantly attributed to the effect of CDs, which mainly serves as an electron collector to efficiently prolong the lifetime of the photogenerated charge carriers from CdS@MIL-101 heterostructure. This work provide a new strategy of one-step double solvents method to co-incorporate two functional species to the pores of metal-organic frameworks (MOFs) to improve the photocatalytic H2 evolution activity of host photocatalyst.

Modular Design of Noble‐Metal‐Free Mixed Metal Oxide Electrocatalysts for Complete Water Splitting

Abstract: Electrocatalytic water splitting into H2 and O2 is a key technology for carbon-neutral energy. Here, we report a modular materials design leading to noble metal-free composite electrocatalysts, which combine high electrical conductivity, high OER and HER reactivity and high durability. The scalable bottom-up fabrication allows the stable deposition of mixed metal oxide nanostructures with different functionalities on copper foam electrodes. The composite catalyst shows sustained OER and HER activity in 0.1 m aqueous KOH over prolonged periods (t>10 h) at low overpotentials (OER: ≈300 mV; HER: ≈100 mV) and high faradaic efficiencies (OER: ≈100 %, HER: ≈98 %). The new synthetic concept will enable the development of multifunctional, mixed metal oxide composites as high-performance electrocatalysts for challenging energy conversion and storage reactions.

Cu-Pd alloy nanoparticles as highly selective catalysts for efficient electrochemical reduction of CO2 to CO

Abstract: Although a copper catalyst has very interesting properties in CO2 electroreduction reaction (CO2RR), the high overpotential of this reaction and low selectivity of the catalyst for a single product are major hindrances to catalyst commercialization. In this work, monodisperse Cu-Pd nanoparticles (NPs) with various compositions are synthesized using the colloidal method. These NPs show a totally different catalytic performance than bulk Cu catalysts. Alloying Cu with Pd suppresses hydrocarbon production on the alloy NP catalyst surface. NPs with a 1:1 Cu-Pd ratio show the best catalytic activity for the conversion of CO2 to CO. At -0.9 V (vs. RHE), 87% CO Faradaic efficiency is achieved, as well as a high noble metal mass activity of 47 mA m g P d - 1 , for CO production. Density functional theory calculations suggest that the energy barrier to the CO* protonation step is increased when Pd is alloyed with Cu; this increase suppresses the reduction of CO2 to hydrocarbons. This result is a significant advance toward selective electrochemical reduction of CO2.

Enhanced Electrocatalytic N2 Reduction via Partial Anion Substitution in Titanium Oxide–Carbon Composites

Abstract: The electrochemical conversion of N2 at ambient conditions using renewably generated electricity is an attractive approach for sustainable ammonia (NH3 ) production. Considering the chemical inertness of N2 , rational design of efficient and stable catalysts is required. Therefore, in this work, it is demonstrated that a C-doped TiO2 /C (C-Tix Oy /C) material derived from the metal-organic framework (MOF) MIL-125(Ti) can achieve a high Faradaic efficiency (FE) of 17.8 %, which even surpasses most of the established noble metal-based catalysts. On the basis of the experimental results and theoretical calculations, the remarkable properties of the catalysts can be attributed to the doping of carbon atoms into oxygen vacancies (OVs) and the formation of Ti-C bonds in C-Tix Oy . This binding motive is found to be energetically more favorable for N2 activation compared to the non-substituted OVs in TiO2 . This work elucidates that electrochemical N2 reduction reaction (NRR) performance can be largely improved by creating catalytically active centers through rational substitution of anions into metal oxides.

Confinement Effects in Zeolite-Confined Noble Metals

Abstract: Confinement of noble nanometals in a zeolite matrix is a promising way to special types of catalysts that show significant advantages in size control, site adjustment, and nano-architecture design. The beauty of zeolite-confined noble metals lies in their unique confinement effects on a molecular scale, and thus enables spatially confined catalysis akin to enzyme catalysis. In this Minireview, the confined synthesis strategies of zeolite-confined noble metals will be briefly discussed, showing the processes, advantages, features, and mechanisms. The confined catalysis carried on zeolite-confined noble metals will be summarized, and great emphasis will be paid to the confinement effects involving size, encapsulation, recognition, and synergy. Great progress of atomic sites in the size effect, supercage stabilization in the encapsulation effect, site adsorption in the recognition effect, and cascade reaction in the synergy effect are highlighted. This Minireview is concluded with challenges and opportunities in terms of the synthesis of zeolite-confined noble metals and their applications to design multifunctional catalysts with high catalytic activity, selectivity, and stability.

Nickel-Based Transition Metal Nitride Electrocatalysts for the Oxygen Evolution Reaction.

Abstract: Electrocatalysis is an efficient and promising means of energy conversion, with minimal environmental footprint. To enhance reaction rates, catalysts are required to minimize overpotential. Alternatives to noble metal electrocatalysts are essential to address these needs on a large scale. In this context, transition metal nitride (TMN) nanoparticles have attracted much attention owing to their high catalytic activity, distinctive electronic structures, and enhanced surface morphologies. Nickel-based materials are an ideal choice for electrocatalysts given nickel's abundance and low cost in comparison to noble metals. In this Minireview, advancements made specifically in Ni-based binary and ternary TMNs as electrocatalysts for the oxygen evolution reaction (OER) are critically evaluated. When used as OER electrocatalysts, Ni-based nanomaterials with 3 D architectures on a suitable support (e.g., a foam support) speed up electron transfer as a result of well-oriented crystal structures and also assist intermediate diffusion, during reaction, of evolved gases. 2 D Ni-based nitride sheet materials synthesized without supports usually perform better than 3 D supported electrocatalysts. The focus of this Minireview is a systematic description of OER activity for state-of-the-art Ni-based nitrides as nanostructured electrocatalysts.

Direct Hybridization of Noble Metal Nanostructures on 2D Metal-Organic Framework Nanosheets To Catalyze Hydrogen Evolution.

Abstract: Rational hybridization of two-dimensional (2D) nanomaterials with extrinsic species has shown great promise for a wide range of applications. To date, rational design and engineering of heterostructures based on 2D metal-organic frameworks (MOFs) has been rather limited. Herein, we report an efficient strategy to construct noble metal/2D MOF heterostructures, featuring the utilization of surface oxygen sites from uncoordinated MOF ligands. The incorporation of highly dispersed noble metal nanoparticles (e.g., Pt and Pd) with modulated electronic structure is enabled on a surfactant-free MOF surface. As a proof-of-concept demonstration, the 2D Ni-MOF@Pt hybrid with well-defined interfaces is applied to boost the electrochemical hydrogen evolution reaction (HER) and delivers decent electrocatalytic activity under both acidic and alkaline conditions. The present results are expected to provide new insights into furnishing MOFs with extended functionalities and applications.