Hailiang Wang

Bio: Hailiang Wang is an academic researcher from Yale University. The author has contributed to research in topics: Catalysis & Graphene. The author has an hindex of 78, co-authored 180 publications receiving 46844 citations. Previous affiliations of Hailiang Wang include University of California, Berkeley & Stanford University.

Co3O4 nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction

Abstract: Catalysts for oxygen reduction and evolution reactions are at the heart of key renewable-energy technologies including fuel cells and water splitting. Despite tremendous efforts, developing oxygen electrode catalysts with high activity at low cost remains a great challenge. Here, we report a hybrid material consisting of Co₃O₄ nanocrystals grown on reduced graphene oxide as a high-performance bi-functional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Although Co₃O₄ or graphene oxide alone has little catalytic activity, their hybrid exhibits an unexpected, surprisingly high ORR activity that is further enhanced by nitrogen doping of graphene. The Co₃O₄/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions. The same hybrid is also highly active for OER, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER. The unusual catalytic activity arises from synergetic chemical coupling effects between Co₃O₄ and graphene.

MoS2 Nanoparticles Grown on Graphene: An Advanced Catalyst for the Hydrogen Evolution Reaction

Abstract: Advanced materials for electrocatalytic and photoelectrochemical water splitting are central to the area of renewable energy. In this work, we developed a selective solvothermal synthesis of MoS2 nanoparticles on reduced graphene oxide (RGO) sheets suspended in solution. The resulting MoS2/RGO hybrid material possessed nanoscopic few-layer MoS2 structures with an abundance of exposed edges stacked onto graphene, in strong contrast to large aggregated MoS2 particles grown freely in solution without GO. The MoS2/RGO hybrid exhibited superior electrocatalytic activity in the hydrogen evolution reaction (HER) relative to other MoS2 catalysts. A Tafel slope of ∼41 mV/decade was measured for MoS2 catalysts in the HER for the first time; this exceeds by far the activity of previous MoS2 catalysts and results from the abundance of catalytic edge sites on the MoS2 nanoparticles and the excellent electrical coupling to the underlying graphene network. The ∼41 mV/decade Tafel slope suggested the Volmer–Heyrovsky mec...

An Advanced Ni–Fe Layered Double Hydroxide Electrocatalyst for Water Oxidation

Abstract: Highly active, durable, and cost-effective electrocatalysts for water oxidation to evolve oxygen gas hold a key to a range of renewable energy solutions, including water-splitting and rechargeable metal–air batteries. Here, we report the synthesis of ultrathin nickel–iron layered double hydroxide (NiFe-LDH) nanoplates on mildly oxidized multiwalled carbon nanotubes (CNTs). Incorporation of Fe into the nickel hydroxide induced the formation of NiFe-LDH. The crystalline NiFe-LDH phase in nanoplate form is found to be highly active for oxygen evolution reaction in alkaline solutions. For NiFe-LDH grown on a network of CNTs, the resulting NiFe-LDH/CNT complex exhibits higher electrocatalytic activity and stability for oxygen evolution than commercial precious metal Ir catalysts.

Graphene-Wrapped Sulfur Particles as a Rechargeable Lithium–Sulfur Battery Cathode Material with High Capacity and Cycling Stability

Abstract: We report the synthesis of a graphene–sulfur composite material by wrapping poly(ethylene glycol) (PEG) coated submicrometer sulfur particles with mildly oxidized graphene oxide sheets decorated by carbon black nanoparticles. The PEG and graphene coating layers are important to accommodating volume expansion of the coated sulfur particles during discharge, trapping soluble polysulfide intermediates, and rendering the sulfur particles electrically conducting. The resulting graphene–sulfur composite showed high and stable specific capacities up to ∼600 mAh/g over more than 100 cycles, representing a promising cathode material for rechargeable lithium batteries with high energy density.

N-doping of graphene through electrothermal reactions with ammonia.

Abstract: Graphene is readily p-doped by adsorbates, but for device applications, it would be useful to access the n-doped material. Individual graphene nanoribbons were covalently functionalized by nitrogen species through high-power electrical joule heating in ammonia gas, leading to n-type electronic doping consistent with theory. The formation of the carbon-nitrogen bond should occur mostly at the edges of graphene where chemical reactivity is high. X-ray photoelectron spectroscopy and nanometer-scale secondary ion mass spectroscopy confirm the carbon-nitrogen species in graphene thermally annealed in ammonia. We fabricated an n-type graphene field-effect transistor that operates at room temperature.

Graphene and Graphene Oxide: Synthesis, Properties, and Applications

Abstract: There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.

The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets

Abstract: Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono- or few-layered TMDs - obtained either through exfoliation of bulk materials or bottom-up syntheses - are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors.

Roll-to-roll production of 30-inch graphene films for transparent electrodes

Abstract: The outstanding electrical, mechanical and chemical properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as approximately 125 ohms square(-1) with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as approximately 30 ohms square(-1) at approximately 90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.

Combining theory and experiment in electrocatalysis: Insights into materials design

Abstract: BACKGROUND With a rising global population, increasing energy demands, and impending climate change, major concerns have been raised over the security of our energy future. Developing sustainable, fossil-free pathways to produce fuels and chemicals of global importance could play a major role in reducing carbon dioxide emissions while providing the feedstocks needed to make the products we use on a daily basis. One prospective goal is to develop electrochemical conversion processes that can convert molecules in the atmosphere (e.g., water, carbon dioxide, and nitrogen) into higher-value products (e.g., hydrogen, hydrocarbons, oxygenates, and ammonia) by coupling to renewable energy. Electrocatalysts play a key role in these energy conversion technologies because they increase the rate, efficiency, and selectivity of the chemical transformations involved. Today’s electrocatalysts, however, are inadequate. The grand challenge is to develop advanced electrocatalysts with the enhanced performance needed to enable widespread penetration of clean energy technologies. ADVANCES Over the past decade, substantial progress has been made in understanding several key electrochemical transformations, particularly those that involve water, hydrogen, and oxygen. The combination of theoretical and experimental studies working in concert has proven to be a successful strategy in this respect, yielding a framework to understand catalytic trends that can ultimately provide rational guidance toward the development of improved catalysts. Catalyst design strategies that aim to increase the number of active sites and/or increase the intrinsic activity of each active site have been successfully developed. The field of hydrogen evolution, for example, has seen important breakthroughs over the years in the development of highly active non–precious metal catalysts in acid. Notable advancements have also been made in the design of oxygen reduction and evolution catalysts, although there remains substantial room for improvement. The combination of theory and experiment elucidates the remaining challenges in developing further improved catalysts, often involving scaling relations among reactive intermediates. This understanding serves as an initial platform to design strategies to circumvent technical obstacles, opening up opportunities and approaches to develop higher-performance electrocatalysts for a wide range of reactions. OUTLOOK A systematic framework of combining theory and experiment in electrocatalysis helps to uncover broader governing principles that can be used to understand a wide variety of electrochemical transformations. These principles can be applied to other emerging and promising clean energy reactions, including hydrogen peroxide production, carbon dioxide reduction, and nitrogen reduction, among others. Although current paradigms for catalyst development have been helpful to date, a number of challenges need to be successfully addressed in order to achieve major breakthroughs. One important frontier, for example, is the development of both experimental and computational methods that can rapidly elucidate reaction mechanisms on broad classes of materials and in a wide range of operating conditions (e.g., pH, solvent, electrolyte). Such efforts would build on current frameworks for understanding catalysis to provide the deeper insights needed to fine-tune catalyst properties in an optimal manner. The long-term goal is to continue improving the activity and selectivity of these catalysts in order to realize the prospects of using renewable energy to provide the fuels and chemicals that we need for a sustainable energy future.

Co3O4 nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction

Abstract: Catalysts for oxygen reduction and evolution reactions are at the heart of key renewable-energy technologies including fuel cells and water splitting. Despite tremendous efforts, developing oxygen electrode catalysts with high activity at low cost remains a great challenge. Here, we report a hybrid material consisting of Co₃O₄ nanocrystals grown on reduced graphene oxide as a high-performance bi-functional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Although Co₃O₄ or graphene oxide alone has little catalytic activity, their hybrid exhibits an unexpected, surprisingly high ORR activity that is further enhanced by nitrogen doping of graphene. The Co₃O₄/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions. The same hybrid is also highly active for OER, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER. The unusual catalytic activity arises from synergetic chemical coupling effects between Co₃O₄ and graphene.