Shihe Yang

Bio: Shihe Yang is an academic researcher from Peking University. The author has contributed to research in topics: Perovskite (structure) & Materials science. The author has an hindex of 113, co-authored 671 publications receiving 42906 citations. Previous affiliations of Shihe Yang include University of Hong Kong & Rice University.

Design Hierarchical Electrodes with Highly Conductive NiCo2S4 Nanotube Arrays Grown on Carbon Fiber Paper for High-Performance Pseudocapacitors

Abstract: We report on the development of highly conductive NiCo2S4 single crystalline nanotube arrays grown on a flexible carbon fiber paper (CFP), which can serve not only as a good pseudocapacitive material but also as a three-dimensional (3D) conductive scaffold for loading additional electroactive materials. The resulting pseudocapacitive electrode is found to be superior to that based on the sibling NiCo2O4 nanorod arrays, which are currently used in supercapacitor research due to the much higher electrical conductivity of NiCo2S4. A series of electroactive metal oxide materials, including CoxNi1–x(OH)2, MnO2, and FeOOH, were deposited on the NiCo2S4 nanotube arrays by facile electrodeposition and their pseudocapacitive properties were explored. Remarkably, the as-formed CoxNi1–x(OH)2/NiCo2S4 nanotube array electrodes showed the highest discharge areal capacitance (2.86 F cm–2 at 4 mA cm–2), good rate capability (still 2.41 F cm–2 at 20 mA cm–2), and excellent cycling stability (∼4% loss after the repetitive ...

A Strongly Coupled Graphene and FeNi Double Hydroxide Hybrid as an Excellent Electrocatalyst for the Oxygen Evolution Reaction

Abstract: Cost-effective electrocatalysts for the oxygen evolu- tion reaction (OER) are critical to energy conversion and storage processes. A novel strategy is used to synthesize a non- noble-metal-based electrocatalyst of the OER by finely com- bining layered FeNi double hydroxide that is catalytically active and electric conducting graphene sheets, taking advant- age of the electrostatic attraction between the two positively charged nanosheets. The synergy between the catalytic activity of the double hydroxide and the enhanced electron transport arising from the graphene resulted in superior electrocatalytic properties of the FeNi-GO hybrids for the OER with over- potentials as low as 0.21 V, which was further reduced to 0.195 V after the reduction treatment. Moreover, the turnover frequency at the overpotential of 0.3 V has reached 1 s 1 , which is much higher than those previously reported for non-noble- metal-based electrocatalysts. The growing demand for energy and the increasing concerns about environment pollution from fossil fuels are stimulating intense research interest in energy conversion and storage from alternative sustainable energy sources. As one of the most important process to produce and store renewable energy in chemical form, the oxygen evolution reaction (OER) has led to many studies in recent years. However, the kinetics of OER is sluggish. Therefore, an effective electro- catalyst is needed to accelerate the reaction and reduce the large overpotential and thus improve the energy conversion efficiency. Metal oxides are the most active and durable electrocatalysts for OER, among which IrO2 and RuO2 are thought to be best OER catalysts in both acidic and alkaline solutions. (1) However, the high cost and element scarcity greatly hindered the widespread use of these noble-metal oxide catalysts. Therefore, it is desirable to develop efficient alternative catalysts based on inexpensive and earth-abun- dant elements without compromising good catalytic activity and durability for OER. Recently, extensive efforts have been made to use perovskites (2) and first-row transition-metal- based materials (3) as low-cost catalysts or electrode materials

Cation and anion immobilization through chemical bonding enhancement with fluorides for stable halide perovskite solar cells

Abstract: Defects play an important role in the degradation processes of hybrid halide perovskite absorbers, impeding their application for solar cells. Among all defects, halide anion and organic cation vacancies are ubiquitous, promoting ion diffusion and leading to thin-film decomposition at surfaces and grain boundaries. Here, we employ fluoride to simultaneously passivate both anion and cation vacancies, by taking advantage of the extremely high electronegativity of fluoride. We obtain a power conversion efficiency of 21.46% (and a certified 21.3%-efficient cell) in a device based on the caesium, methylammonium (MA) and formamidinium (FA) triple-cation perovskite (Cs0.05FA0.54MA0.41)Pb(I0.98Br0.02)3 treated with sodium fluoride. The device retains 90% of its original power conversion efficiency after 1,000 h of operation at the maximum power point. With the help of first-principles density functional theory calculations, we argue that the fluoride ions suppress the formation of halide anion and organic cation vacancies, through a unique strengthening of the chemical bonds with the surrounding lead and organic cations. Defects and defect migration are detrimental for perovskite solar cell efficiency and long-term stability. Li et al. show that fluoride is able to suppress the formation of halide anion and organic cation vacancy defects by restraining the relative ions via ionic and hydrogen bonds.

Efficiency Enhancement of Perovskite Solar Cells through Fast Electron Extraction: The Role of Graphene Quantum Dots

Abstract: We report on a significant power conversion efficiency improvement of perovskite solar cells from 8.81% to 10.15% due to insertion of an ultrathin graphene quantum dots (GQDs) layer between perovskite and TiO2. A strong quenching of perovskite photoluminescence was observed at ∼760 nm upon the addition of the GQDs, which is pronouncedly correlated with the increase of the IPCE and the APCE of the respective cells. From the transient absorption measurements, the improved cell efficiency can be attributed to the much faster electron extraction with the presence of GQDs (90–106 ps) than without their presence (260–307 ps). This work highlights that GQDs can act as a superfast electron tunnel for optoelectronic devices.

Sequential deposition as a route to high-performance perovskite-sensitized solar cells

Abstract: Following pioneering work, solution-processable organic-inorganic hybrid perovskites-such as CH3NH3PbX3 (X = Cl, Br, I)-have attracted attention as light-harvesting materials for mesoscopic solar cells. So far, the perovskite pigment has been deposited in a single step onto mesoporous metal oxide films using a mixture of PbX2 and CH3NH3X in a common solvent. However, the uncontrolled precipitation of the perovskite produces large morphological variations, resulting in a wide spread of photovoltaic performance in the resulting devices, which hampers the prospects for practical applications. Here we describe a sequential deposition method for the formation of the perovskite pigment within the porous metal oxide film. PbI2 is first introduced from solution into a nanoporous titanium dioxide film and subsequently transformed into the perovskite by exposing it to a solution of CH3NH3I. We find that the conversion occurs within the nanoporous host as soon as the two components come into contact, permitting much better control over the perovskite morphology than is possible with the previously employed route. Using this technique for the fabrication of solid-state mesoscopic solar cells greatly increases the reproducibility of their performance and allows us to achieve a power conversion efficiency of approximately 15 per cent (measured under standard AM1.5G test conditions on solar zenith angle, solar light intensity and cell temperature). This two-step method should provide new opportunities for the fabrication of solution-processed photovoltaic cells with unprecedented power conversion efficiencies and high stability equal to or even greater than those of today's best thin-film photovoltaic devices.

Chemistry and properties of nanocrystals of different shapes.

Abstract: The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Metal–Organic Framework Materials as Chemical Sensors

Abstract: 1. INTRODUCTION Among the classes of highly porous materials, metalÀorganic frameworks (MOFs) are unparalleled in their degree of tunability and structural diversity as well as their range of chemical and physical properties. MOFs are extended crystalline structures wherein metal cations or clusters of cations (\" nodes \") are connected by multitopic organic \" strut \" or \" linker \" ions or molecules. The variety of metal ions, organic linkers, and structural motifs affords an essentially infinite number of possible combinations. 1 Furthermore, the possibility for postsynthetic modification adds an additional dimension to the synthetic variability. 2 Coupled with the growing library of experimentally determined structures, the potential to computationally predict, with good accuracy, affinities of guests for host frameworks points to the prospect of routinely predesigning frameworks to deliver desired properties. 3,4 MOFs are often compared to zeolites for their large internal surface areas, extensive porosity, and high degree of crystallinity. Correspondingly, MOFs and zeolites have been utilized for many of the same applications