Ruthenium atomically dispersed in carbon outperforms platinum toward hydrogen evolution in alkaline media.

Hydrogen evolution reaction is an important process in electrochemical energy technologies. Herein, ruthenium and nitrogen codoped carbon nanowires are prepared as effective hydrogen evolution catalysts. The catalytic performance is markedly better than that of commercial platinum catalyst, with an overpotential of only -12 mV to reach the current density of 10 mV cm-2 in 1 M KOH and -47 mV in 0.1 M KOH. Comparisons with control experiments suggest that the remarkable activity is mainly ascribed to individual ruthenium atoms embedded within the carbon matrix, with minimal contributions from ruthenium nanoparticles. Consistent results are obtained in first-principles calculations, where RuCxNy moieties are found to show a much lower hydrogen binding energy than ruthenium nanoparticles, and a lower kinetic barrier for water dissociation than platinum. Among these, RuC2N2 stands out as the most active catalytic center, where both ruthenium and adjacent carbon atoms are the possible active sites

Nanowrinkled Carbon Aerogels Embedded with FeN x Sites as Effective Oxygen Electrodes for Rechargeable Zinc-Air Battery.

Rational design of single-metal atom sites in carbon substrates by a flexible strategy is highly desired for the preparation of high-performance catalysts for metal-air batteries. In this study, biomass hydrogel reactors are utilized as structural templates to prepare carbon aerogels embedded with single iron atoms by controlled pyrolysis. The tortuous and interlaced hydrogel chains lead to the formation of abundant nanowrinkles in the porous carbon aerogels, and single iron atoms are dispersed and stabilized within the defective carbon skeletons. X-ray absorption spectroscopy measurements indicate that the iron centers are mostly involved in the coordination structure of FeN4, with a minor fraction (ca. 1/5) in the form of FeN3C. First-principles calculations show that the FeN x sites in the Stone-Wales configurations induced by the nanowrinkles of the hierarchically porous carbon aerogels show a much lower free energy than the normal counterparts. The resulting iron and nitrogen-codoped carbon aerogels exhibit excellent and reversible oxygen electrocatalytic activity, and can be used as bifunctional cathode catalysts in rechargeable Zn-air batteries, with a performance even better than that based on commercial Pt/C and RuO2 catalysts. Results from this study highlight the significance of structural distortions of the metal sites in carbon matrices in the design and engineering of highly active single-atom catalysts

Rational Design of High-Performance Electrocatalysts for Electrochemical Energy Technologies: From Structural Engineering of Nanocomposite Catalysts to Mechanistic Understanding of Electrocatalytic Activity

Developing sustainable, high efficiency and clean energy technologies is one of the urgent missions for modern chemistry. Fuel cells with their high energy conversion efficiency, high reliability, low CO2 emission and extensive applications, show promising outlook among all new energy devices. However, the expensive electrocatalyst and their sluggish electrode reaction kinetics greatly hamper the commercialization of fuel cells. Thus, the advanced electrocatalyst should be designed and synthesized, meanwhile, the reaction mechanism should be better understood for material structural modification and activity enhancement. My thesis focused on design, synthesis of nano materials for advanced electrocatalysts and understanding and exploring the catalytic mechanism. Based on series of research projects, a systemic strategy framework for electrocatalyst preparation and understanding is established by combination of experimental and theory method. This framework contains a wide range of aspect of electrocatalyst studies. Specifically, Chapter 1 introduces the background of fuel cell, water electrolyzer and their related critical electrochemistry reactions. A systematic overview of electrocatalyst design, modification and reaction mechanism understanding is illustrated. Based on the current and previous results, the strategy loop and the central dogma of electrocatalyst design is proposed. Each of the work introduced in other chapters was carried out based on one or several aspects of the strategy loop, which including material synthesis, activity measurement, active site revealing, electronic structure understanding, modification of electronic structure. Chapter 2, chapter 3, chapter 4 introduces series work of carbon nanowires for electrocatalyst. These works include the aspects of material synthesis, activity understanding, active site identifying or understanding the source of activity. Specifically, chapter 2 introduces the design and synthesis of a novel nitrogen and iron-doped carbon nanowires material for great activity for alkaline oxygen reduction reaction, with the performance even surpass the commercial platinum carbon. Moreover, the active site was identified, and their activity was compared as the order of Stone-Wales FeN4 sites> Normal FeN4 sites> neighboring carbon atom of nitrogen atom in the carbon matrix. In addition, the source of activity of each important activity site were also revealed. The great activity of FeN4 comes from the d-orbital of Fe atom provide great chance for oxygenous intermediate species to absorb and detach. While, the neighboring carbon to nitrogen atom have much better ability for adsorption than normal carbon, due to the charge transfer from themselves to the nearby nitrogen atoms. Chapter 3 introduces the design and synthesis of novel ruthenium and nitrogen doped carbon nanowires for excellent activity for hydrogen evolution reaction in alkaline electrolyte, with the performance better than commercial platinum carbon and other noble metal-based material as reported previously. Moreover, it was identified that the activity is coming from a novel single atom ruthenium site, RuC2N2 structure embedded in the carbon, other than ruthenium nanoparticle or normal RuN4 sites as assumed previously. The ruthenium and its neighboring carbon atoms of RuC2N2 can provide efficient water dissociation process which is critical for overall reaction. Chapter 4 introduces a typical work for adopting theoretical calculation to reveal active sties and for guiding experimental electrocatalyst synthesis. In this work, a high throughput first principle calculation was first carried out and find that the platinum needs a minimum domain size (about 0.9 nm of diameter) to maintain activity for catalyzing oxygen reduction reaction. Any platinum species smaller than that limit will suffer great difficulty of adsorbing oxygen molecules due to the lack of states and electron near Fermi level. Moreover, it was further revealed cobalt atom doping can greatly assist in oxygen adsorption when the domain size of platinum is too small. The following experimental work confirmed the theoretical finding and successfully synthesized PtCo few atom clusters as high efficiency electrocatalyst for oxygen reduction reaction, which can have an ultrahigh mass activity as much as 48 times better than commercial platinum carbon. Chapter 5 and chapter 6 mainly focus on several individual works about interfacial charge transfer of nanomaterial and its induced electrocatalytic activity enhancement. For instance, Chapter 5 introduce several works about charge transfer induced electrochemical activity enhancement. In one work, it was observed oxygen vacancy doped TiO2 can transfer electrons to the palladium nanoparticles loaded on them. This charge transfer can significantly enhance the activity of ethanol oxidation reaction catalyzed by palladium nanoparticles. In another work, it was found that black phosphorus can donate significant number of electrons to the platinum, gold and silver nanoparticle load on it. This charge transfer can induce the activity decrease for platinum nanoparticles and increase for gold and silver nanoparticles towards oxygen reduction reaction. Chapter 6 introduces developing new methods for charge transfer. Specifically, TiO2 nanoparticles functionalizing with alkyne ligand can induce significant one-way charge transfer from ligand to surface of metal oxide through M-O-C≡C- core-ligand linkages. This linkage can also induce novel states inside of band gap. Moreover, this unique charge transfer can be universally observed on other metal oxide, exhibiting a powerful ability for increasing the charge density of metal oxide catalyst. Finally, all of finding are systemically summarized in chapter 7. In addition, a perspective of future works was put forward based on the previous works

Rational Design of High-Performance Electrocatalysts for Electrochemical Energy Technologies: From Structural Engineering of Nanocomposite Catalysts to Mechanistic Understanding of Electrocatalytic Activity

Developing sustainable, high efficiency and clean energy technologies is one of the urgent missions for modern chemistry. Fuel cells with their high energy conversion efficiency, high reliability, low CO2 emission and extensive applications, show promising outlook among all new energy devices. However, the expensive electrocatalyst and their sluggish electrode reaction kinetics greatly hamper the commercialization of fuel cells. Thus, the advanced electrocatalyst should be designed and synthesized, meanwhile, the reaction mechanism should be better understood for material structural modification and activity enhancement. My thesis focused on design, synthesis of nano materials for advanced electrocatalysts and understanding and exploring the catalytic mechanism. Based on series of research projects, a systemic strategy framework for electrocatalyst preparation and understanding is established by combination of experimental and theory method. This framework contains a wide range of aspect of electrocatalyst studies. Specifically, Chapter 1 introduces the background of fuel cell, water electrolyzer and their related critical electrochemistry reactions. A systematic overview of electrocatalyst design, modification and reaction mechanism understanding is illustrated. Based on the current and previous results, the strategy loop and the central dogma of electrocatalyst design is proposed. Each of the work introduced in other chapters was carried out based on one or several aspects of the strategy loop, which including material synthesis, activity measurement, active site revealing, electronic structure understanding, modification of electronic structure. Chapter 2, chapter 3, chapter 4 introduces series work of carbon nanowires for electrocatalyst. These works include the aspects of material synthesis, activity understanding, active site identifying or understanding the source of activity. Specifically, chapter 2 introduces the design and synthesis of a novel nitrogen and iron-doped carbon nanowires material for great activity for alkaline oxygen reduction reaction, with the performance even surpass the commercial platinum carbon. Moreover, the active site was identified, and their activity was compared as the order of Stone-Wales FeN4 sites> Normal FeN4 sites> neighboring carbon atom of nitrogen atom in the carbon matrix. In addition, the source of activity of each important activity site were also revealed. The great activity of FeN4 comes from the d-orbital of Fe atom provide great chance for oxygenous intermediate species to absorb and detach. While, the neighboring carbon to nitrogen atom have much better ability for adsorption than normal carbon, due to the charge transfer from themselves to the nearby nitrogen atoms. Chapter 3 introduces the design and synthesis of novel ruthenium and nitrogen doped carbon nanowires for excellent activity for hydrogen evolution reaction in alkaline electrolyte, with the performance better than commercial platinum carbon and other noble metal-based material as reported previously. Moreover, it was identified that the activity is coming from a novel single atom ruthenium site, RuC2N2 structure embedded in the carbon, other than ruthenium nanoparticle or normal RuN4 sites as assumed previously. The ruthenium and its neighboring carbon atoms of RuC2N2 can provide efficient water dissociation process which is critical for overall reaction. Chapter 4 introduces a typical work for adopting theoretical calculation to reveal active sties and for guiding experimental electrocatalyst synthesis. In this work, a high throughput first principle calculation was first carried out and find that the platinum needs a minimum domain size (about 0.9 nm of diameter) to maintain activity for catalyzing oxygen reduction reaction. Any platinum species smaller than that limit will suffer great difficulty of adsorbing oxygen molecules due to the lack of states and electron near Fermi level. Moreover, it was further revealed cobalt atom doping can greatly assist in oxygen adsorption when the domain size of platinum is too small. The following experimental work confirmed the theoretical finding and successfully synthesized PtCo few atom clusters as high efficiency electrocatalyst for oxygen reduction reaction, which can have an ultrahigh mass activity as much as 48 times better than commercial platinum carbon. Chapter 5 and chapter 6 mainly focus on several individual works about interfacial charge transfer of nanomaterial and its induced electrocatalytic activity enhancement. For instance, Chapter 5 introduce several works about charge transfer induced electrochemical activity enhancement. In one work, it was observed oxygen vacancy doped TiO2 can transfer electrons to the palladium nanoparticles loaded on them. This charge transfer can significantly enhance the activity of ethanol oxidation reaction catalyzed by palladium nanoparticles. In another work, it was found that black phosphorus can donate significant number of electrons to the platinum, gold and silver nanoparticle load on it. This charge transfer can induce the activity decrease for platinum nanoparticles and increase for gold and silver nanoparticles towards oxygen reduction reaction. Chapter 6 introduces developing new methods for charge transfer. Specifically, TiO2 nanoparticles functionalizing with alkyne ligand can induce significant one-way charge transfer from ligand to surface of metal oxide through M-O-C≡C- core-ligand linkages. This linkage can also induce novel states inside of band gap. Moreover, this unique charge transfer can be universally observed on other metal oxide, exhibiting a powerful ability for increasing the charge density of metal oxide catalyst. Finally, all of finding are systemically summarized in chapter 7. In addition, a perspective of future works was put forward based on the previous works

Role of nutrients and temperature in shaping distinct summer phytoplankton and microzooplankton population dynamics in the western North Pacific and Bering Sea

Phytoplankton growth and microzooplankton grazing are two critical processes in marine food webs, but they remain understudied in the vast area of the subarctic western Pacific and the Bering Sea. In this study, we measured phytoplankton growth and microzooplankton grazing rates in these less-explored regions to demonstrate their spatial patterns and investigate underlying mechanisms driving the planktonic food web dynamics. Our results showed that the phytoplankton growth in these regions was determined by nutrient availability and temperature. In the high-nutrient, low-chlorophyll regions (HNLC), iron availability was the primary factor limiting phytoplankton growth. In contrast, phytoplankton growth in the Gulf of Anadyr and Kamchatka Strait was mainly limited by inorganic nitrogen exhausted by the summer blooms. We found that microzooplankton grazing rate was affected by temperature and prey availability, highlighting the positive effect of temperature. Strong top-down control on phytoplankton by microzooplankton in the Gulf of Anadyr and Kamchatka Strait indicated an active microbial food web with high turnover rates. In contrast, the decoupling of phytoplankton growth and microzooplankton grazing in the HNLC regions illustrates a weak role of microzooplankton in the marine food web. These results indicated different food web structures in the areas with and without riverine iron input. By revealing the roles of temperature and nutrient or prey availability in regulating the spatial variability of plankton rates, we expect that the plankton will respond differently to ocean warming between the HNLC and coastal regions of the subarctic Pacific due to different nutrient conditions. Our study helps understand how marine plankton will respond to environmental changes at high latitudes

Ultrafast synthesis of cobalt/carbon nanocomposites by magnetic induction heating for oxygen evolution reaction

Metal/carbon nanocomposites have shown great potential as high-performance, low-cost electrocatalysts owing largely to their unique metal-support interactions. These nanocomposites are typically prepared by conventional pyrolysis that is tedious and energy-intensive. Herein, we report the ultrafast preparation of cobalt/carbon nanocomposites by magnetic induction heating (MIH) of metal organic frameworks within seconds under an inert atmosphere. The resulting samples consist of cobalt nanoparticles encapsulated within defective carbon shells, and effectively catalyze oxygen evolution reaction (OER) in alkaline media. Among the series, the sample prepared at 400 A for 10 s exhibits the best OER performance, needing a low overpotential of +308 mV to reach the current density of 10 mA cm−2, along with excellent stability, and even outperforms commercial RuO2 at high overpotentials. This is ascribed to the charge transfer between the carbon scaffold and metal nanoparticles. Operando X-ray absorption spectroscopy measurements show that the electrochemically produced CoOOH species is responsible for the high electrocatalytic performance. The results highlight the unique potential of MIH in the development of effective nanocomposite catalysts for electrochemical energy technologies

Oxygen Reduction Reaction Catalyzed by Carbon-Supported Platinum Few-Atom Clusters: Significant Enhancement by Doping of Atomic Cobalt.

Oxygen reduction reaction (ORR) plays an important role in dictating the performance of various electrochemical energy technologies. As platinum nanoparticles have served as the catalysts of choice towards ORR, minimizing the cost of the catalysts by diminishing the platinum nanoparticle size has become a critical route to advancing the technological development. Herein, first-principle calculations show that carbon-supported Pt9 clusters represent the threshold domain size, and the ORR activity can be significantly improved by doping of adjacent cobalt atoms. This is confirmed experimentally, where platinum and cobalt are dispersed in nitrogen-doped carbon nanowires in varied forms, single atoms, few-atom clusters, and nanoparticles, depending on the initial feeds. The sample consisting primarily of Pt2~7 clusters doped with atomic Co species exhibits the best mass activity among the series, with a current density of 4.16 A mgPt -1 at +0.85 V vs. RHE that is almost 50 times higher than that of commercial Pt/C