Abstract
Rational design of single atom catalyst is critical for efficient sustainable energy conversion. However, the atomic-level control of active sites is essential for electrocatalytic materials ...in alkaline electrolyte. Moreover, well-defined surface structures lead to in-depth understanding of catalytic mechanisms. Herein, we report a single-atomic-site ruthenium stabilized on defective nickel-iron layered double hydroxide nanosheets (Ru
1
/D-NiFe LDH). Under precise regulation of local coordination environments of catalytically active sites and the existence of the defects, Ru
1
/D-NiFe LDH delivers an ultralow overpotential of 18 mV at 10 mA cm
−2
for hydrogen evolution reaction, surpassing the commercial Pt/C catalyst. Density functional theory calculations reveal that Ru
1
/D-NiFe LDH optimizes the adsorption energies of intermediates for hydrogen evolution reaction and promotes the O–O coupling at a Ru–O active site for oxygen evolution reaction. The Ru
1
/D-NiFe LDH as an ideal model reveals superior water splitting performance with potential for the development of promising water-alkali electrocatalysts.
Condensation of fac-Re(5,6-diamino-1,10-phenanthroline)(CO)3Cl to o-quinone edge defects on graphitic carbon surfaces generates graphite-conjugated rhenium (GCC-Re) catalysts that are highly active ...for CO2 reduction to CO in acetonitrile electrolyte. X-ray photoelectron and X-ray absorption spectroscopies establish the formation of surface-bound Re centers with well-defined coordination environments. GCC-Re species on glassy carbon surfaces display catalytic currents greater than 50 mA cm−2 with 96 ± 3% Faradaic efficiency for CO production. Normalized for the number of Re active sites, GCC-Re catalysts exhibit higher turnover frequencies than that of a soluble molecular analogue, fac-Re(1,10-phenanthroline)(CO)3Cl, and turnover numbers greater than 12,000. In contrast to the molecular analogue, GCC-Re surfaces display a Tafel slope of 150 mV/decade, indicative of a catalytic mechanism involving rate-limiting one-electron transfer. This work establishes graphite-conjugation as a powerful strategy for generating well-defined, tunable, heterogeneous electrocatalysts on ubiquitous graphitic carbon surfaces.
Abstract
Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their active site ...structures remain poorly understood. A leading postulate is that the iron-containing active sites exist primarily in a pyridinic Fe-N
4
ligation environment, yet, molecular model catalysts generally feature pyrrolic coordination. Herein, we report a molecular pyridinic hexaazacyclophane macrocycle, (phen
2
N
2
)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for ORR to a typical Fe-N-C material and prototypical pyrrolic iron macrocycles. N 1s XPS and XAS signatures for (phen
2
N
2
)Fe are remarkably similar to those of Fe-N-C. Electrochemical studies reveal that (phen
2
N
2
)Fe has a relatively high Fe(III/II) potential with a correlated ORR onset potential within 150 mV of Fe-N-C. Unlike the pyrrolic macrocycles, (phen
2
N
2
)Fe displays excellent selectivity for four-electron ORR, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data demonstrate that (phen
2
N
2
)Fe is a more effective model of Fe-N-C active sites relative to the pyrrolic iron macrocycles, thereby establishing a new molecular platform that can aid understanding of this important class of catalytic materials.
Noble-metal alloys are widely used as heterogeneous catalysts. However, due to the existence of scaling properties of adsorption energies on transition metal surfaces, the enhancement of catalytic ...activity is frequently accompanied by side reactions leading to a reduction in selectivity for the target product. Herein, we describe an approach to breaking the scaling relationship for propane dehydrogenation, an industrially important reaction, by assembling single atom alloys (SAAs), to achieve simultaneous enhancement of propylene selectivity and propane conversion. We synthesize γ-alumina-supported platinum/copper SAA catalysts by incipient wetness co-impregnation method with a high copper to platinum ratio. Single platinum atoms dispersed on copper nanoparticles dramatically enhance the desorption of surface-bounded propylene and prohibit its further dehydrogenation, resulting in high propylene selectivity (~90%). Unlike previous reported SAA applications at low temperatures (<400 °C), Pt/Cu SAA shows excellent stability of more than 120 h of operation under atmospheric pressure at 520 °C.
Oxygen evolution reaction (OER) is a pivotal process in many energy conversion and storage techniques, such as water splitting, regenerative fuel cells, and rechargeable metal-air batteries. The ...synthesis of stable, efficient, non-noble metal-based electrocatalysts for OER has been a long-standing challenge. In this work, a facile and scalable method to synthesize hollow and conductive iron–cobalt phosphide (Fe–Co–P) alloy nanostructures using an Fe–Co metal organic complex as a precursor is described. The Fe–Co–P alloy exhibits excellent OER activity with a specific current density of 10 mA/cm2 being achieved at an overpotential as low as 252 mV. The current density at 1.5 V (vs reversible hydrogen electrode) of the Fe–Co–P catalyst is 30.7 mA/cm2, which is more than 3 orders of magnitude greater than that obtained with state-of-the-art Fe–Co oxide catalysts. Our mechanistic experiments and theoretical analysis suggest that the electrochemical-induced high-valent iron stabilizes the cobalt in a low-valent state, leading to the simultaneous enhancement of activity and stability of the OER catalyst.
The ubiquity of anthropogenic debris in hundreds of species of wildlife and the toxicity of chemicals associated with it has begun to raise concerns regarding the presence of anthropogenic debris in ...seafood. We assessed the presence of anthropogenic debris in fishes and shellfish on sale for human consumption. We sampled from markets in Makassar, Indonesia, and from California, USA. All fish and shellfish were identified to species where possible. Anthropogenic debris was extracted from the digestive tracts of fish and whole shellfish using a 10% KOH solution and quantified under a dissecting microscope. In Indonesia, anthropogenic debris was found in 28% of individual fish and in 55% of all species. Similarly, in the USA, anthropogenic debris was found in 25% of individual fish and in 67% of all species. Anthropogenic debris was also found in 33% of individual shellfish sampled. All of the anthropogenic debris recovered from fish in Indonesia was plastic, whereas anthropogenic debris recovered from fish in the USA was primarily fibers. Variations in debris types likely reflect different sources and waste management strategies between countries. We report some of the first findings of plastic debris in fishes directly sold for human consumption raising concerns regarding human health.
We report on the continuous fine-scale tuning of band gaps over 0.4 eV and of the electrical conductivity of over 4 orders of magnitude in a series of highly crystalline binary alloys of ...two-dimensional electrically conducting metal–organic frameworks M3(HITP)2 (M = Co, Ni, Cu; HITP = 2,3,6,7,10,11-hexaiminotriphenylene). The isostructurality in the M3(HITP)2 series permits the direct synthesis of binary alloys (M x M′3–x )(HITP)2 (MM′ = CuNi, CoNi, and CoCu) with metal compositions precisely controlled by precursor ratios. We attribute the continuous tuning of both band gaps and electrical conductivity to changes in free-carrier concentrations and to subtle differences in the interlayer displacement or spacing, both of which are defined by metal substitution. The activation energy of (Co x Ni3–x )(HITP)2 alloys scales inversely with an increasing Ni percentage, confirming thermally activated bulk transport.
With increasing concerns for global warming, the solar‐driven photocatalytic reduction of CO2 into chemical fuels like methanol is a propitious route to enrich energy supplies, with concomitant ...reduction of the abundant CO2 stockpiles. Herein, a novel single atom‐confinement and a strategy are reported toward single ruthenium atoms dispersion over porous carbon nitride surface. Ruthenium single atom character is well confirmed by EXAFS absorption spectrometric analysis unveiling the cationic coordination environment for the single‐atomic‐site ruthenium center, that is formed by Ru‐N/C intercalation in the first coordination shell, attaining synergism in N–Ru–N connection and interfacial carrier transfer. From time resolved fluorescence decay spectra, the average carrier lifetime of the RuSA–mC3N4 system is found to be higher compared to m‐C3N4; the fact uncovering the crucial role of single Ru atoms in promoting photocatalytic reaction system. A high yield of methanol (1500 µmol g‐1 cat. after 6 h of the reaction) using water as an electron donor and the reusability of the developed catalyst without any significant change in the efficiency represent the superior aspects for its potential application in real industrial technologies.
The synthesis and photocatalytic applications of RuSA–mC3N4 are evaluated for carbon dioxide reduction to methanol. A high yield of methanol (1500 µmol g‐1 cat. after 6 h of the reaction) is obtained. The stable catalyst could be reusable for subsequent cycles without significant change in the catalytic efficiency.
Nanoceria-supported atomic Pt catalysts (denoted as Pt1@CeO2) have been synthesized and demonstrated with advanced catalytic performance for the nonoxidative, direct conversion of methane. These ...catalysts were synthesized by calcination of Pt-impregnated porous ceria nanoparticles at high temperature (ca. 1000 °C), with the atomic dispersion of Pt characterized by combining aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses. The Pt1@CeO2 catalysts exhibited much superior catalytic performance to its nanoparticulated counterpart, achieving 14.4% of methane conversion at 975 °C and 74.6% selectivity toward C2 products (ethane, ethylene, and acetylene). Comparative studies of the Pt1@CeO2 catalysts with different loadings as well as the nanoparticulated counterpart reveal the single-atom Pt to be the active sites for selective conversion of methane into C2 hydrocarbons.
Bimetallic Pt–Co nanoparticles (NPs) were prepared and characterized by scanning transmission electron microscopy, in situ X-ray absorption spectroscopy, in situ synchrotron X-ray diffraction, and ...catalytic conversion for propane dehydrogenation with and without added H2. In addition, the surface extended X-ray absorption fine structure (EXAFS) obtained by fitting the difference spectrum between the fully reduced and room-temperature-oxidized catalysts suggest that the surface structure remains Pt3Co, although the core changes from Pt to Pt3Co and to PtCo. At low Co loading, the bimetallic nanoparticles form a Pt3Co intermetallic surface alloy with Pt-rich core. With increasing Co loading, a full alloy forms where both the surface and NP compositions are Pt3Co. A further increase in Co loading leads to a Co-rich NP core, likely PtCo, with a surface of Pt3Co. Although Pt–Co intermetallic alloys form two different phases and several morphologies, the surface structures are similar in all catalysts. Although both monometallic Pt and Co are active for alkane dehydrogenation, all bimetallic Pt–Co catalysts are significantly more olefin selective than either single metal. The turnover rates of the bimetallic catalysts indicate that Pt is the active atom with little contribution from Co atoms. The high olefin selectivity is suggested to be due to Co acting as a less active structural promoter to break up large Pt ensembles in bimetallic NPs.
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