Mingyun Guan

Bio: Mingyun Guan is an academic researcher from Stanford University. The author has contributed to research in topics: Electrochemistry & Materials science. The author has an hindex of 3, co-authored 4 publications receiving 3238 citations.

An ultrafast rechargeable aluminium-ion battery

Abstract: An aluminium-ion battery is reported that can charge within one minute, and offers improved cycle life compared to previous devices; it operates through the electrochemical deposition and dissolution of aluminium at the anode, and the intercalation/de-intercalation of chloroaluminate anions into a novel graphitic-foam cathode. The low cost and useful electrical properties of aluminium suggest that rechargeable Al-ion batteries could offer viable and safe battery technology, but problems with cathode materials, poor cycling performance and other complications have persisted. Here Hongjie Dai and colleagues describe an Al-ion battery that can charge within one minute and offers substantially improved cycle life with little decay in capacity compared to previous devices reported in the literature. The battery operates through the electrochemical deposition and dissolution of Al and intercalation/de-intercalation of chloroaluminate anions into a novel 3D graphitic foam cathode using a non-flammable ionic liquid electrolyte. The development of new rechargeable battery systems could fuel various energy applications, from personal electronics to grid storage1,2. Rechargeable aluminium-based batteries offer the possibilities of low cost and low flammability, together with three-electron-redox properties leading to high capacity3. However, research efforts over the past 30 years have encountered numerous problems, such as cathode material disintegration4, low cell discharge voltage (about 0.55 volts; ref. 5), capacitive behaviour without discharge voltage plateaus (1.1–0.2 volts6 or 1.8–0.8 volts7) and insufficient cycle life (less than 100 cycles) with rapid capacity decay (by 26–85 per cent over 100 cycles)4,5,6,7. Here we present a rechargeable aluminium battery with high-rate capability that uses an aluminium metal anode and a three-dimensional graphitic-foam cathode. The battery operates through the electrochemical deposition and dissolution of aluminium at the anode, and intercalation/de-intercalation of chloroaluminate anions in the graphite, using a non-flammable ionic liquid electrolyte. The cell exhibits well-defined discharge voltage plateaus near 2 volts, a specific capacity of about 70 mA h g–1 and a Coulombic efficiency of approximately 98 per cent. The cathode was found to enable fast anion diffusion and intercalation, affording charging times of around one minute with a current density of ~4,000 mA g–1 (equivalent to ~3,000 W kg–1), and to withstand more than 7,500 cycles without capacity decay.

Nanoscale nickel oxide/nickel heterostructures for active hydrogen evolution electrocatalysis

Abstract: There is ongoing research into new electrocatalysts for hydrogen production from water splitting. Here, the authors report the electrocatalytic performance of nickel/nickel oxide heterostructures on carbon nanotubes, and are able to assemble a water electrolyzer operated by a single-cell 1.5 V battery.

Highly Active and Stable Hybrid Catalyst of Cobalt-Doped FeS2 Nanosheets–Carbon Nanotubes for Hydrogen Evolution Reaction

Abstract: Hydrogen evolution reaction (HER) from water through electrocatalysis using cost-effective materials to replace precious Pt catalysts holds great promise for clean energy technologies. In this work we developed a highly active and stable catalyst containing Co doped earth abundant iron pyrite FeS2 nanosheets hybridized with carbon nanotubes (Fe1–xCoxS2/CNT hybrid catalysts) for HER in acidic solutions. The pyrite phase of Fe1–xCoxS2/CNT was characterized by powder X-ray diffraction and absorption spectroscopy. Electrochemical measurements showed a low overpotential of ∼0.12 V at 20 mA/cm2, small Tafel slope of ∼46 mV/decade, and long-term durability over 40 h of HER operation using bulk quantities of Fe0.9Co0.1S2/CNT hybrid catalysts at high loadings (∼7 mg/cm2). Density functional theory calculation revealed that the origin of high catalytic activity stemmed from a large reduction of the kinetic energy barrier of H atom adsorption on FeS2 surface upon Co doping in the iron pyrite structure. It is also fo...

Hyperdispersed Ruthenium Nanoparticles Anchored on S/N Co-doped Carbon Nanotubes as an Efficient HER Electrocatalyst

Abstract: The preparation of green hydrogen by electrolyzing water has shown great application prospects, and the noble metal Pt as catalyst for hydrogen evolution reaction (HER) is one of the main...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Abstract: Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

High-power all-solid-state batteries using sulfide superionic conductors

Abstract: Compared with lithium-ion batteries with liquid electrolytes, all-solid-state batteries offer an attractive option owing to their potential in improving the safety and achieving both high power and high energy densities. Despite extensive research efforts, the development of all-solid-state batteries still falls short of expectation largely because of the lack of suitable candidate materials for the electrolyte required for practical applications. Here we report lithium superionic conductors with an exceptionally high conductivity (25 mS cm−1 for Li9.54Si1.74P1.44S11.7Cl0.3), as well as high stability ( ∼0 V versus Li metal for Li9.6P3S12). A fabricated all-solid-state cell based on this lithium conductor is found to have very small internal resistance, especially at 100 ∘C. The cell possesses high specific power that is superior to that of conventional cells with liquid electrolytes. Stable cycling with a high current density of 18 C (charging/discharging in just three minutes; where C is the C-rate) is also demonstrated. The development of all-solid-state batteries requires fast lithium conductors. Here, the authors report a lithium compound, Li9.54Si1.74P1.44S11.7Cl0.3, with an exceptionally high conductivity and demonstrate that all-solid-state batteries based on the compound have high power densities.

A high-capacity and long-life aqueous rechargeable zinc battery using a metal oxide intercalation cathode

Abstract: Although non-aqueous Li-ion batteries possess significantly higher energy density than their aqueous counterparts, the latter can be more feasible for grid-scale applications when cost, safety and cycle life are taken into consideration. Moreover, aqueous Zn-ion batteries have an energy storage advantage over alkali-based batteries as they can employ Zn metal as the negative electrode, dramatically increasing energy density. However, their development is plagued by a limited choice of positive electrodes, which often show poor rate capability and inadequate cycle life. Here we report a vanadium oxide bronze pillared by interlayer Zn2+ ions and water (Zn0.25V2O5⋅nH2O), as the positive electrode for a Zn cell. A reversible Zn2+ ion (de)intercalation storage process at fast rates, with more than one Zn2+ per formula unit (a capacity up to 300 mAh g−1), is characterized. The Zn cell offers an energy density of ∼450 Wh l−1 and exhibits a capacity retention of more than 80% over 1,000 cycles, with no dendrite formation at the Zn electrode. High-performing positive electrode materials are crucial for the development of aqueous Zn-ion batteries. Here the authors report a battery based on reversible intercalation of Zn ions in a layered Zn0.25V2O5⋅nH2O-based positive electrode, which exhibits high-capacity and long-term cycling stability.

Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review

Abstract: Increasing demand for finding eco-friendly and everlasting energy sources is now totally depending on fuel cell technology. Though it is an eco-friendly way of producing energy for the urgent requirements, it needs to be improved to make it cheaper and more eco-friendly. Although there are several types of fuel cells, the hydrogen (H2) and oxygen (O2) fuel cell is the one with zero carbon emission and water as the only byproduct. However, supplying fuels in the purest form (at least the H2) is essential to ensure higher life cycles and less decay in cell efficiency. The current large-scale H2 production is largely dependent on steam reforming of fossil fuels, which generates CO2 along with H2 and the source of which is going to be depleted. As an alternate, electrolysis of water has been given greater attention than the steam reforming. The reasons are as follows: the very high purity of the H2 produced, the abundant source, no need for high-temperature, high-pressure reactors, and so on. In earlier days,...

Catalysis with two-dimensional materials and their heterostructures

Abstract: Graphene and other 2D atomic crystals are of considerable interest in catalysis because of their unique structural and electronic properties. Over the past decade, the materials have been used in a variety of reactions, including the oxygen reduction reaction, water splitting and CO2 activation, and have been shown to exhibit a range of catalytic mechanisms. Here, we review recent advances in the use of graphene and other 2D materials in catalytic applications, focusing in particular on the catalytic activity of heterogeneous systems such as van der Waals heterostructures (stacks of several 2D crystals). We discuss the advantages of these materials for catalysis and the different routes available to tune their electronic states and active sites. We also explore the future opportunities of these catalytic materials and the challenges they face in terms of both fundamental understanding and the development of industrial applications.