Showing papers in "ACS Catalysis in 2017"
TL;DR: In this article, a hierarchical MoS2-Ni3S2 heteronanorod supported by Ni foam was proposed for hydrogen evolution reaction (HER) and oxygen evolution reaction.
Abstract: Exploring noble-metal-free electrocatalysts with high efficiency for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) holds promise for advancing the production of H2 fuel through water splitting. Herein, one-pot synthesis was introduced for MoS2–Ni3S2 heteronanorods supported by Ni foam (MoS2–Ni3S2 HNRs/NF), in which the Ni3S2 nanorods were hierarchically integrated with MoS2 nanosheets. The hierarchical MoS2–Ni3S2 heteronanorods allow not only the good exposure of highly active heterointerfaces but also the facilitated charge transport along Ni3S2 nanorods anchored on conducting nickel foam, accomplishing the promoted kinetics and activity for HER, OER, and overall water splitting. The optimal MoS2–Ni3S2 HNRs/NF presents low overpotentials (η10) of 98 and 249 mV to reach a current density of 10 mA cm–2 in 1.0 M KOH for HER and OER, respectively. Assembled as an electrolyzer for overall water splitting, such heteronanorods show a quite low cell voltage of 1.50 V at 10 mA...
858 citations
TL;DR: In this paper, the development of technology for clean-energy production has become the major research priority worldwide, and the globalization of advanced energy conversion technologies like rechargeable metal-air batteries, regenerated fuel cells, and water splitting devices has been majorly benefitted by the developing of apposite catalytic materials that can proficiently carry out the pertinent electrochemical processes like oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction(HER), and water hydrolysis.
Abstract: The persistently increasing energy consumption and the low abundance of conventional fuels have raised serious concerns all over the world. Thus, the development of technology for clean-energy production has become the major research priority worldwide. The globalization of advanced energy conversion technologies like rechargeable metal–air batteries, regenerated fuel cells, and water-splitting devices has been majorly benefitted by the development of apposite catalytic materials that can proficiently carry out the pertinent electrochemical processes like oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and water hydrolysis. Despite a handful of superbly performing commercial catalysts, the high cost and low electrochemical stability of precursors have consistently discouraged their long-term viability. As a promising substitute of conventional platinum-, palladium-, iridium-, gold-, silver-, and ruthenium-based catalysts, various transition-metal (TM) i...
774 citations
TL;DR: In this article, the authors demonstrate that 2D MXenes, like Ti2C, V2C and Ti3C2, are terminated by a mixture of oxygen atoms and hydroxyl.
Abstract: Developing highly conductive, stable, and active nonprecious hydrogen evolution reaction (HER) catalysts is a key step for the proposed hydrogen economy. However, few catalysts, except for noble metals, meet all the requirements. By using state-of-the-art density functional calculations, herein we demonstrate that 2D MXenes, like Ti2C, V2C, and Ti3C2, are terminated by a mixture of oxygen atoms and hydroxyl, while Nb2C and Nb4C3O2 are fully terminated by oxygen atoms under standard conditions [pH 0, p(H2) = 1 bar, U = 0 V vs standard hydrogen electrode], findings in good agreement with experimental observation. Furthermore, all these MXenes are conductive under standard conditions, thus allowing high charge transfer kinetics during the HER. Remarkably, the Gibbs free energy for the adsorption of atomic hydrogen (ΔGH*0) on the terminated O atoms (e.g., Ti2CO2) is close to the ideal value (0 eV). Our results demonstrate terminated oxygens as catalytic active sites for the HER at these materials and highligh...
726 citations
616 citations
TL;DR: In this paper, the fundamental aspects of photocatalytic water splitting into hydrogen and oxygen by using light from the solar spectrum, which is one of the most investigated photosynthetic reactions, are discussed.
Abstract: A widely used term, “photocatalysis”, generally addresses photocatalytic (energetically downhill) and photosynthetic (energetically uphill) reactions and refers to the use of photonic energy as a driving force for chemical transformations, i.e., electron reorganization to form/break chemical bonds. Although there are many such important reactions, this contribution focuses on the fundamental aspects of photocatalytic water splitting into hydrogen and oxygen by using light from the solar spectrum, which is one of the most investigated photosynthetic reactions. Photocatalytic water splitting using solar energy is considered to be artificial photosynthesis that produces a solar fuel because the reaction mimics nature’s photosynthesis not only in its redox reaction type but also in its thermodynamics (water splitting: 1.23 eV vs glucose formation: 1.24 eV). To achieve efficient photocatalytic water splitting, all of the parameters, though involved at different time scales and spatial resolutions, should be op...
590 citations
TL;DR: In this article, a joint experimental and theoretical investigation of the electrochemical reduction of CO2 to HCOO- on polycrystalline Sn surfaces, which have been identified as promising catalysts for selectively producing HCOO−, was conducted.
Abstract: Increases in energy demand and in chemical production, together with the rise in CO2 levels in the atmosphere, motivate the development of renewable energy sources. Electrochemical CO2 reduction to fuels and chemicals is an appealing alternative to traditional pathways to fuels and chemicals due to its intrinsic ability to couple to solar and wind energy sources. Formate (HCOO–) is a key chemical for many industries; however, greater understanding is needed regarding the mechanism and key intermediates for HCOO– production. This work reports a joint experimental and theoretical investigation of the electrochemical reduction of CO2 to HCOO– on polycrystalline Sn surfaces, which have been identified as promising catalysts for selectively producing HCOO–. Our results show that Sn electrodes produce HCOO–, carbon monoxide (CO), and hydrogen (H2) across a range of potentials and that HCOO– production becomes favored at potentials more negative than −0.8 V vs RHE, reaching a maximum Faradaic efficiency of 70% a...
540 citations
TL;DR: In this paper, the authors consider an additional aspect related to the formation of a metal/oxide interface, which can be realized when small metal nanoparticles are deposited on the surface of an oxide support or when a nanostructured oxide, either a nanoparticle or a thin film, is grown on a metal.
Abstract: Reducibility is an essential characteristic of oxide catalysts in oxidation reactions following the Mars–van Krevelen mechanism. A typical descriptor of the reducibility of an oxide is the cost of formation of an oxygen vacancy, which measures the tendency of the oxide to lose oxygen or to donate it to an adsorbed species with consequent change in the surface composition, from MnOm to MnOm–x. The oxide reducibility, however, can be modified in various ways: for instance, by doping and/or nanostructuring. In this review we consider an additional aspect, related to the formation of a metal/oxide interface. This can be realized when small metal nanoparticles are deposited on the surface of an oxide support or when a nanostructured oxide, either a nanoparticle or a thin film, is grown on a metal. In the past decade, both theory and experiment indicate a particularly high reactivity of the oxygen atoms at the boundary region between a metal and an oxide. Oxygen atoms can be removed from interface sites at much...
528 citations
TL;DR: In this article, the shape and size of catalyst particles and the interface between different components of heterogeneous catalysts at the nanometer level can radically alter their performances, particularly for CeO2-based catalysts, where the precise control of surface atomic arrangements can modify the reactivity of Ce4+/Ce3+ ions, changing the oxygen release/uptake characteristics of ceria.
Abstract: Engineering the shape and size of catalyst particles and the interface between different components of heterogeneous catalysts at the nanometer level can radically alter their performances. This is particularly true with CeO2-based catalysts, where the precise control of surface atomic arrangements can modify the reactivity of Ce4+/Ce3+ ions, changing the oxygen release/uptake characteristics of ceria, which, in turn, strongly affects catalytic performance in several reactions like CO, soot, and VOC oxidation, WGS, hydrogenation, acid–base reactions, and so on. Despite the fact that many of these catalysts are polycrystalline with rather ill-defined morphologies, experimental and theoretical studies on well-defined nanocrystals have clearly established that the exposure of specific facets can increase/decrease surface oxygen reactivity and metal–support interaction (for supported metal nanoparticles), consequently affecting catalytic reactions. Here, we want to address the most recent developments in this...
497 citations
TL;DR: In this article, the most recent advances related to these issues are discussed in this review, and key parameters controlling the catalysis efficiency have been deciphered, opening the way to the design of future, more efficient and durable catalysts, as well as to the development of electrochemical or photoelectrochemical cells, all being key steps for the emergence of applied devices.
Abstract: Electrochemical and photochemical reduction of CO2, or a smart combination of both, are appealing approaches for the storage of renewable, intermittent energies and may lead to the production of fuels and of value-added chemicals. By using only earth-abundant metal (Cu, Ni, Co, Mn, Fe) complexes, cheap electrodes and/or cheap sacrificial electron donors and visible light sensitizers, systems functioning with molecular catalysts have been recently designed, showing promising results, in particular, for the two-electron reduction of the carbon dioxide. By combining experimental and mechanistic studies, key parameters controlling the catalysis efficiency have been deciphered, opening the way to the design of future, more efficient and durable catalysts, as well as to the development of electrochemical or photoelectrochemical cells, all being key steps for the emergence of applied devices. The most recent advances related to these issues are discussed in this review.
489 citations
TL;DR: In this paper, a host-guest chemistry strategy was proposed to construct Fe-mIm nanocluster (NC) (guest)@zeolite imidazole framework-8 (ZIF-8) precursors that can be transformed into Fe-N/C electrocatalysts with controllable structures.
Abstract: Even though Fe-N/C electrocatalysts with abundant Fe-Nx active sites have been developed as one of the most promising alternatives to precious metal materials for oxygen reduction reaction (ORR), further improvement of their performance requires precise control over Fe-Nx sites at the molecular level and deep understanding of the catalytic mechanism associated with each particular structure. Herein, we report a host–guest chemistry strategy to construct Fe-mIm nanocluster (NC) (guest)@zeolite imidazole framework-8 (ZIF-8) (host) precursors that can be transformed into Fe-N/C electrocatalysts with controllable structures. The ZIF-8 host network exhibits a significant host–guest relationship dependent confinement effect for the Fe-mIm NCs during the pyrolysis process, resulting in different types of Fe-Nx sites with two- to five-coordinated configurations on the porous carbon matrix confirmed by X-ray absorption near edge structure (XANES) and Fourier transform (FT) extended X-ray absorption fine structure ...
436 citations
TL;DR: In this paper, the authors reported the development of Mn-doped CoP (Mn-Co-P/Ti) nanosheets array on Ti mesh as an efficient 3D HER electrocatalyst with good stability.
Abstract: Heteratom doping is a possible way to tune the hydrogen evolution reaction (HER) catalytic capability of electrocatalysts. In this work, we report the development of Mn-doped CoP (Mn–Co–P) nanosheets array on Ti mesh (Mn–Co–P/Ti) as an efficient 3D HER electrocatalyst with good stability at all pH values. Electrochemical tests demonstrate that Mn doping leads to enhanced catalytic activity of CoP. In 0.5 M H2SO4, this Mn–Co–P/Ti catalyst drives 10 mA cm–2 at an overpotential of 49 mV, which is 32 mV less than that for CoP/Ti. To achieve the same current density, it demands overpotentials of 76 and 86 mV in 1.0 M KOH and phosphate-buffered saline, respectively. The enhanced HER activity for Mn–Co–P can be attributed to its more thermo-neutral hydrogen adsorption free energy than CoP, which is supported by density functional theory calculations.
TL;DR: In this paper, the authors describe the recent progress on engineering the electrode-electrolyte and semiconductor-cocatalyst interfaces with cocatalysts, electrolytes, and interfacial layers (interlayers) to increase the PEC efficiency.
Abstract: The efficiency of photoelectrocatalytic (PEC) water splitting is limited by the serious recombination of photogenerated charges, high overpotential, and sluggish kinetics of surface reaction. Herein we describe the recent progress on engineering the electrode–electrolyte and semiconductor–cocatalyst interfaces with cocatalysts, electrolytes, and interfacial layers (interlayers) to increase the PEC efficiency. Introducing cocatalysts has been demonstrated to be the most efficient way to lower the reaction barrier and promote charge injection to the reactants. In addition, it has been found that electrolyte ions can influence the surface catalysis remarkably. Electrolyte cations on the surface can influence the water splitting and backward reactions, and anions may take part in the proton transfer processes, indicating that fine-tuning of the electrolyte parameters turns out to be an important strategy for enhancing the PEC efficiency. Moreover, careful modification of the interface between the cocatalysts ...
TL;DR: In this article, the authors elucidated a fundamental reason underlying the selectivity of CO2 reduction toward C2 products by studying its reactivity on Cu(100), Cu(111), and Cu(110) single-crystal surfaces.
Abstract: Copper oxide-derived Cu catalysts are known to exhibit enhanced energetic efficiencies and selectivities towards the reduction of carbon dioxide to commercially vital C2 products such as ethylene (C2H4). However, the cause of this selectivity is not fully understood. In this work, we elucidated a fundamental reason underlying the selectivity of CO2 reduction toward C2 products by studying its reactivity on Cu(100), Cu(111), and Cu(110) single-crystal surfaces. A combination of cyclic and linear sweep voltammetries, chronoamperometry, online gas chromatography, 1H nuclear magnetic resonance spectroscopy, and density functional theory (DFT) calculations was employed for this end. A wide range of electrochemical potentials from −0.28 to −1.25 V versus the reversible hydrogen electrode was investigated. Aqueous 0.1 M KHCO3 was used as the electrolyte. We report here two general trends on Cu2O-derived Cu and Cu single-crystal surfaces: (i) the onset potential for the formation of C2H4 always starts 300–400 mV ...
TL;DR: In this article, a ternary NiCoP/carbon cloth (CC) electrocatalyst with superior catalytic activity and stability for hydrogen evolution reaction and oxygen evolution reaction was proposed.
Abstract: The investigation of high-efficiency nonprecious electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great significance for renewable energy technologies. Here, we provide a successive hydrothermal, oxidation, and phosphidation method to fabricate a 3D nest-like ternary NiCoP/carbon cloth (CC) electrocatalyst with superior catalytic activity and stability toward HER/OER. Nest-like NiCoP/CC requires overpotentials of 44 and 62 mV to reach the current density of 10 mA cm–2 in acidic and alkaline media, respectively, toward HER. For OER, the NiCoP/CC exhibits high active and durable performance with an overpotential of 242 mV at current density of 10 mA cm–2 in alkaline solutions. Furthermore, the practical application of NiCoP/CC as a bifunctional catalyst for overall water splitting reaction yields current densities of 10 and 100 mA cm–2 at 1.52 and 1.77 V, respectively.
TL;DR: This Perspective highlights advances made by the laboratory since the inception of the photoredox/Ni cross-coupling of benzyltrifluoroborates with aryl bromides and the net C–H functionalization of the radical partner in an effort to improve atom economy.
Abstract: Photoredox catalysis has experienced a revitalized interest from the synthesis community during the past decade. For example, photoredox/Ni dual catalysis protocols have been developed to overcome several inherent limitations of palladium-catalyzed cross-couplings by invoking a single-electron transmetalation pathway. This Perspective highlights advances made by our laboratory since the inception of the photoredox/Ni cross-coupling of benzyltrifluoroborates with aryl bromides. In addition to broadening the scope of trifluoroborate coupling partners, research using readily oxidized hypervalent silicates as radical precursors that demonstrate functional group compatibility is highlighted. The pursuit of electrophilic coupling partners beyond (hetero)aryl bromides has also led to the incorporation of several new classes of C(sp2)-hybridized substrates into light-mediated cross-coupling. Advances to expand the radical toolbox by utilizing feedstock chemicals (e.g., aldehydes) to access radicals that were prev...
TL;DR: In this article, an electrocatalyst for oxygen evolution reaction (OER) with a low overpotential, a low Tafel slope, a high durability, and a high turnover frequency at lower mass loadings is presented.
Abstract: Nanostructured CuCo2S4, a mixed metal thiospinel, is found to be a benchmark electrocatalyst for oxygen evolution reaction (OER) in this study with a low overpotential, a low Tafel slope, a high durability, and a high turnover frequency (TOF) at lower mass loadings. Nanosheets of CuCo2S4 are realized from a hydrothermal synthesis method in which the average thickness of the sheets is found to be in the range of 8–15 nm. Aggregated nanosheets form a highly open hierarchical structure. When used as an electrocatalyst, CuCo2S4 nanosheets offer an overpotential value of 310 mV at a 10 mA cm–2 current density, which remains consistent for 10000 measured cycles in a 1 M KOH electrolyte. A chronoamperometric study reveals constant oxygen evolution for 12 h at a 10 mV s–1 scan rate without any degradation of the activity. Furthermore, the calculated mass activity of the CuCo2S4 electrocatalyst is found to be 14.29 A/g and to afford a TOF value of 0.1431 s–1 at 310 mV at a mass loading of 0.7 mg cm–2. For comparis...
TL;DR: In this article, the authors review the history of the photocatalytic nitrogen fixation and examine current progress toward understanding and improving photofixation of nitrogen, supplemented by a quantitative review of the thermodynamic considerations and limitations for various reaction mechanism.
Abstract: Over the last century, the industrialization of agriculture and the consumption of fossil fuels have resulted in a significant imbalance and redistribution in nitrogen-containing resources. This has sparked an interest in developing more sustainable and resilient approaches for producing nitrogen-containing commodities such as fertilizers and fuels. One largely neglected but emerging approach is photocatalytic nitrogen fixation. There is significant evidence that this process occurs spontaneously in terrestrial settings, and it has been demonstrated in numerous engineered systems. Yet many questions still remain unanswered regarding the rates, mechanisms, and impacts of photocatalytically producing fixed nitrogen “out of thin air”. This work reviews the fascinating history of the reaction and examines current progress toward understanding and improving photofixation of nitrogen. This is supplemented by a quantitative review of the thermodynamic considerations and limitations for various reaction mechanism...
TL;DR: In this paper, the synthesis of CoP nanoparticles encapsulated in ultrathin nitrogen-doped porous carbon (CoP@NC) through a metal-organic framework (MOF) is reported.
Abstract: Searching for non-noble-metal-based electrocatalysts with high efficiency and durability toward the hydrogen evolution reaction (HER) is vitally necessary for the upcoming clean and renewable energy systems. Here we report the synthesis of CoP nanoparticles encapsulated in ultrathin nitrogen-doped porous carbon (CoP@NC) through a metal–organic framework (MOF) route. This hybrid exhibits remarkable electrocatalytic activity toward the HER in both acidic and alkaline media, with good stability. Experiments and theoretical calculations reveal that the carbon atoms adjacent to N dopants on the shells of CoP@NC are active sites for hydrogen evolution and that CoP and N dopants synergistically optimize the binding free energy of H* on the active sites, which results in a higher electrocatalytic activity in comparison to its counterparts without nitrogen doping and/or CoP encapsulation.
TL;DR: In this article, the development of carbon-based electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is discussed, as well as their challenges and opportunities.
Abstract: Hydrogen and oxygen evolution reactions (HER and OER) are important for many electrochemical systems. Besides traditional noble-metal-based catalysts, carbon-based materials have been found to be effective for catalyzing these reactions. Various carbon structures doped with heteroatoms (N, S, P, B, and transition metals) and graphitic-layer-encapsulated metal and compound particles have shown good activities toward HER and OER at universal pHs. In this Perspective, recent research on the development of carbon-based electrocatalysts for HER and OER, as well as their challenges and opportunities are discussed.
TL;DR: This paper showed that water can directly contribute to about 50% of CO2 production on a single-atom Pt1/CeO2 catalyst via a water-mediated Mars-van Krevelen (MvK) mechanism.
Abstract: In water-promoted CO oxidation, water was thought not to directly participate in CO2 production. Here we report that via a water-mediated Mars–van Krevelen (MvK) mechanism, water can directly contribute to about 50% of CO2 production on a single-atom Pt1/CeO2 catalyst. The origin is the facile reaction of CO with the hydroxyl from dissociated water to yield the carboxyl intermediate, which dehydrogenates subsequently with the help of a lattice hydroxyl to generate CO2 and water. The water-mediated MvK type reaction found here provides new insights in the promotion role of water in heterogeneous catalysis.
TL;DR: In this article, the fabrication methods for N-doped carbon-supported metal catalysts and the catalytic application of these fascinating materials are discussed. And the authors focus on the fabrication and fabrication methods of these materials and their application in heterogeneous catalysis.
Abstract: Developing novel and efficient catalysts is always an important theme for heterogeneous catalysis from fundamental and applied research points of view. In the past, carbon materials were used as supports for numerous heterogeneous catalysts because of their fascinating properties including high surface areas, tunable porosity, and functionality. Recently, the newly emerging N-doped carbon-supported metal catalysts have arguably experienced great progress and brought the most attention over the last decades in view of the fact that nitrogen doping can tailor the properties of carbon for various applications of interest. Compared with pristine carbon-supported metal catalysts, these catalysts normally show superior catalytic performance in many heterogeneous catalytic reactions because of the introduced various metal–support interactions from N doping. In this Perspective, we focus on the fabrication methods for N-doped carbon-supported metal catalysts and the catalytic application of these fascinating cata...
TL;DR: In this paper, the authors reported a selective conversion of CO2 to lower olefins through CO2 hydrogenation over a ZnZrO/SAPO tandem catalyst.
Abstract: Conversion of CO2 to value-added chemicals has been a long-standing objective, and direct hydrogenation of CO2 to lower olefins is highly desirable but still challenging. Herein, we report a selective conversion of CO2 to lower olefins through CO2 hydrogenation over a ZnZrO/SAPO tandem catalyst fabricated with a ZnO-ZrO2 solid solution and a Zn-modified SAPO-34 zeolite, which can achieve a selectivity for lower olefins as high as 80–90% among hydrocarbon products. This is realized on the basis of the dual functions of the tandem catalyst: hydrogenation of CO2 on the ZnO-ZrO2 solid solution and lower olefins production on the SAPO zeolite. The thermodynamic and kinetic coupling between the tandem reactions enable the highly efficient conversion of CO2 to lower olefins. Furthermore, this catalyst is stable toward the thermal and sulfur treatments, showing the potential industrial application.
TL;DR: In this article, a review of the development of Fe, Co, and Ni catalysts for the alkene hydrosilylation reaction, as well as the related dehydrogenative silylation, is presented.
Abstract: This review covers the advance in the development of Fe, Co, and Ni catalysts for the alkene hydrosilylation reaction, as well as the related dehydrogenative silylation reaction. The hydrosilylation of alkene is an important reaction for the synthesis of alkylsilanes that has widespread applications in numerous silicon-based materials, and for decades, this transformation has been relying on the use of Pt catalysts. Recently, the high abundance and low cost, coupled with the environmentally benign nature of the base metals have stimulated enormous research on the development of first-row transition-metal catalysts as replacements for the precious Pt catalysts. Several base-metal catalysts which have emerged during the past 5 years offer high activity, broad substrate scope, and excellent regioselectivity. Both of the anti-Markovnikov and the unusual Markovnikov additions can be achieved in a high degree of regioselectivity. The reactions of acyclic internal olefins catalyzed by the base-metal catalysts re...
TL;DR: Ni catalysis provides exciting new tools to build C-heteroatom and C-C bonds using an unconventional reactant (i.e., the amide), which is ideally suited for use in multi-step synthesis.
Abstract: Amides have been widely studied for decades, but their synthetic utility has remained limited in reactions that proceed with rupture of the amide C–N bond. Using Ni catalysis, we have found that amides can now be strategically employed in several important transformations: esterification, transamidation, Suzuki–Miyaura couplings, and Negishi couplings. These methodologies provide exciting new tools to build C–heteroatom and C–C bonds using an unconventional reactant (i.e., the amide), which is ideally suited for use in multi-step synthesis. It is expected that the area of amide C–N bond activation using nonprecious metals will continue to flourish and, in turn, will promote the growing use of amides as synthons in organic synthesis.
TL;DR: In this article, an alloyed Pd single-atom catalyst (SAC) was used for the selective hydrogenation of acetylene to ethylene under a simulated front-end hydrogenation process in industry.
Abstract: Selective hydrogenation of acetylene to ethylene is an industrially important reaction. Pd-based catalysts have been proved to be efficient for the acetylene conversion, while enhancing the selectivity to ethylene is challenging. Here, we chose Cu as the partner of Pd, fabricated an alloyed Pd single-atom catalyst (SAC), and investigated its catalytic performance for the selective hydrogenation of acetylene to ethylene under a simulated front-end hydrogenation process in industry: that is, with a high concentration of hydrogen and ethylene. The Cu-alloyed Pd SAC showed ∼85% selectivity to ethylene and 100% acetylene elimination. In comparison with the Au- or Ag-alloyed Pd SAC, the Cu-alloyed analogue exceeded both of them in conversion, while the selectivity rivaled that of the Ag-alloyed Pd SAC and surpassed that of the Au-alloyed Pd SAC. As Cu is a low-cost metal, Cu-alloyed Pd SAC would minimize the noble-metal usage and possess high utilization potential for industry. The Cu-alloyed Pd SAC was verifie...
TL;DR: In this article, a series of iron-based catalysts synthesized by pyrolysis of Fe-, N-, and C-containing precursors for the electroreduction of CO2 to CO under aqueous conditions were investigated.
Abstract: Selective electrochemical reduction of CO2 into energy-dense organic compounds is a promising strategy for using CO2 as a carbon source. Herein, we investigate a series of iron-based catalysts synthesized by pyrolysis of Fe-, N-, and C-containing precursors for the electroreduction of CO2 to CO under aqueous conditions and demonstrate that the selectivity of these materials for CO2 reduction over proton reduction is governed by the ratio of isolated FeN4 sites vs Fe-based nanoparticles. This ratio can be synthetically tuned to generate electrocatalysts producing controlled CO/H2 ratios. It notably allows preparing materials containing only FeN4 sites, which are able to selectively reduce CO2 to CO in aqueous solution with Faradaic yields of over 90% and at low overpotential.
TL;DR: A systematic structural elucidation of the near surface active species of the two remarkably active nickel phosphides Ni12P5 and Ni2P on the basis of extensive analytical, microscopic, and spectroscopic investigations is reported in this paper.
Abstract: A systematic structural elucidation of the near-surface active species of the two remarkably active nickel phosphides Ni12P5 and Ni2P on the basis of extensive analytical, microscopic, and spectroscopic investigations is reported. The latter can serve as complementary efficient electrocatalysts in the hydrogen (HER) versus oxygen evolution reaction (OER) in alkaline media. In the OER Ni12P5 shows enhanced performance over Ni2P due to the higher concentration of nickel in this phase, which enables the formation of an amorphous NiOOH/Ni(OH)2 shell on a modified multiphase with a disordered phosphide/phosphite core. The situation is completely reversed in the HER, where Ni2P displayed a significant improvement in electrocatalytic activity over Ni12P5 owing to a larger concentration of phosphide/phosphate species in the shell. Moreover, the efficiently combined use of the two nickel phosphide phases deposited on nickel foam in overall electrocatalytic water splitting is demonstrated by a strikingly low cell v...
TL;DR: In this article, the role of the support may have a significant effect on the catalytic properties, similar to that of the ligand molecules in homogeneous catalysts, and the support effect was demonstrated by preparing a single-atom platinum catalyst on two different supports.
Abstract: Single-atom catalysts (SACs) provide an ideal platform for reducing noble-metal usage. SACs also exhibit unusual catalytic properties due to the absence of a metal surface. The role of the support may have a significant effect on the catalytic properties, similar to that of the ligand molecules in homogeneous catalysts. Here, the support effect was demonstrated by preparing a single-atom platinum catalyst on two different supports: titanium carbide (Pt1/TiC) and titanium nitride (Pt1/TiN). The formation of single-atom Pt was confirmed by STEM, EXAFS, and in situ IR spectroscopy. Pt1/TiC showed higher activity, selectivity, and stability for electrochemical H2O2 production than Pt1/TiN. Density functional theory calculations presented that oxygen species have strong affinity into Pt1/TiN, possibly acting as surface poisoning species, and Pt1/TiC preserves oxygen–oxygen bonds more with higher selectivity toward H2O2 production. This work clearly shows that the support in SACs actively participates in the su...
TL;DR: An overview of the catalytic properties of intermetallic compounds has been made to provide a comprehensive understanding regarding what intermetall compounds can do, their fundamental roles in enhanced catalysis, and their advantages over other inorganic materials.
Abstract: An overview of the catalytic properties of intermetallic compounds has been made to provide a comprehensive understanding regarding (1) what intermetallic catalysts can do, (2) their fundamental roles in enhanced catalysis, and (3) their advantages over other inorganic materials. A number of chemical transformations using intermetallic catalysts have been surveyed and classified into three major divisions—hydrogenation/dehydrogenation, oxidation, and steam reforming and various subsections. The fundamental roles of intermetallic phases obtained from this survey were categorized into four types of effects: (a) electronic, (b) geometric, (c) steric, and (d) ordering effects. The unprecedented steric effects governed by the specific surface structures of intermetallic compounds highlight the unique capabilities of intermetallic materials. On the basis of this overview, we have concluded that intermetallic compounds have the following advantages for fine catalyst design: (i) control of the electronic structur...
TL;DR: The α,β-unsaturated acyl azolium has emerged as a central reactive intermediate for reaction discovery using N-heterocyclic carbene catalysis as discussed by the authors.
Abstract: First reported less than a decade ago, the α,β-unsaturated acyl azolium has emerged as a central reactive intermediate for reaction discovery using N-heterocyclic carbene catalysis. In this Perspective, an introduction to the four main reactivity patterns accessible from this intermediate is provided. The Perspective is handled in a largely chronological fashion, with an emphasis on alternate approaches to the key intermediate and first-in-class reaction cascades. Finally, a brief discussion of emerging trends in this field of catalysis is presented. Although not exhaustive, the Perspective provides an overview of this active area of research and serves as a guide for future investigations.