A research group led by Profs. BAO Xinhe, WANG Guoxiong and GAO Dunfeng from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has revealed the mechanism of coverage-driven selectivity switch from ethylene to acetate in high-rate CO2/CO electrolysis.The study was published in Nature Nanotechnology on Jan. 12.Electrolysis of CO2 to valuable chemicals and fuels with power supply derived from renewable energy has emerged as a promising carbon capture, utilization, and storage technology.To push the CO2 electrolysis process towards practical application, high selectivity of multicarbon (C2+) products at industrial current densities is highly desirable. Moreover, tuning the microenvironments near catalyst surfaces has also been demonstrated to be effective in facilitating C–C coupling and improving C2+ production.In this study, the researchers tuned the catalyst microenvironment using mixed CO/CO2 feeds that were typical composition of waste gases from steel plants and incomplete industrial combustion of fossil fuels. Specifically, they investigated CO/CO2 co-electrolysis over a nanoporous CuO nanosheet catalyst in an alkaline membrane electrode assembly (MEA) electrolyzer at high current densities."With increasing CO pressure in the feed, the major product gradually shifted from ethylene to acetate and the current density remarkably increased, up to 3.0 A cm-2 under 0.6 MPa pure CO feed," said Prof. WANG."The selectivity switch was induced by *CO coverage and local pH. Ethylene was preferentially generated at low *CO coverage, whereas acetate formation was favorable at high *CO coverage and high local pH," said Prof. GAO.The researchers further improved electrolysis performance by optimizing electrolysis conditions. The Faradaic efficiency and partial current density of C2+ products reached 90.0% and 3.1 A cm-2, corresponding to a carbon selectivity of 100.0% and yield of 75.0%, outperforming thermocatalytic CO hydrogenation.The scale-up of the CO electrolysis process was demonstrated using an electrolyzer stack composed of four 100 cm2 MEAs, with the highest ethylene formation rate of 457.5 mL min-1 at 150 A and acetate formation rate of 2.97 g min-1 at 250 A."Our work highlights the promise of tuning catalyst microenvironments for selective production of single C2+ products such as acetate and ethylene, and presents an effective scale-up demonstration of high-rate CO2/CO electrolysis towards practical application," said Prof. WANG.

The impact of the direction of the chemical bond of colliding molecules on their chemical reactions has been observed in collisions of non-polar molecules for the first time. This observation and its theoretical underpinnings potentially offer a new way to control chemical reactions beyond the traditional chemical-reaction parameters of temperature, pressure and the addition of catalysts.Researchers have observed steric effects—the interactions of molecules depending on their spatial orientation (not just between their electrons involved in bonding)—in a chemical reaction involving non-polar molecules for the first time. The breakthrough opens the door to an entirely new way to control the products of chemical reactions.A paper describing the research team's findings was published in the journal Science on Jan. 12.One of the central goals of chemistry is to develop new methods of controlling chemical reactions. For the most part, control of chemical reactions involves understanding of the interactions between the electrons of different atoms. These "electronic" effects govern many of the properties and behavior of chemicals and the changes they undergo during reactions.But the relative spatial arrangement of atoms within molecules also impacts their properties, behavior and the changes they can undergo. Many people will be familiar with the story of thalidomide, the drug responsible for a number of severe birth defects in the 1950s. The error that occurred that caused the tragedy was related to how a chemical with an identical formula to another one—but a mirror-image structure—can have different biological effects.The study of how these spatial arrangements impact chemical reactions—so-called 'steric effects'—and how to manipulate such effects make up the subdiscipline known as stereochemistry, sometimes called '3D chemistry' for its focus on the orientations of atoms and molecules in three-dimensional space.These effects are the result of repulsive forces between overlapping electron clouds. The complement of opposite and like charges produce a particular 3D shape in a molecule, including the angles between atoms and the axis of the chemical bond ('bond axis').The researchers specialise in their lab in attempting to control the direction of the bond axis of molecules involved in chemical reactions—a way to manipulate chemical reactions beyond traditional methods such as adding suitable catalysts and changing the temperature or pressure of a reaction mixture."In many people's minds and even in some chemistry textbooks, the structure and shape of a molecule are subliminally ignored in the physical picture of a chemical reaction," said Yufeng Wang, the lead author of the study and chemist with the State Key Laboratory of Molecular Reaction Dynamics at the Dalian institute of chemical physics (DICP) of the Chinese Academy of Sciences. "But molecules cannot be simply taken as a point of mass. The structure and shape of the reactant molecule can have profound influences on the chemical reaction."In turn, the mutual orientation of reactants colliding into each other also has a major effect on the outcome of the chemical reaction. Thus by controlling that orientation, it should be possible to promote or restrict the yield of the products of the reactions into specific final states or scattering angles.Experiments attempting this sort of colliding molecular-orientation control have been performed for a number of years on polar molecules. Polar molecules are those such as, most famously, water wherein due to unequal sharing of electrons between the component atoms, the molecule has an end that is negative and an end that is positive.But they have not been performed on non-polar molecules. Non-polar molecules, such as molecular oxygen or nitrogen, are composed of atoms that share electrons equally and thus have no charge. Yet there should be very large steric effects because the lack of charge will produce very weak 'steering' interactions en route to the collision.Molecular hydrogen (H2), another non-polar molecule, should be a good candidate for such orientation-control scattering experiments, not least due to its simplicity of each atom having just one proton and one electron (and thus enjoying considerable theoretical tractability).Until recently however, it has been difficult to prepare sufficient concentrations of H2 in specific quantum states for scattering experiments. But thanks to the development of a high pulsed enengy and single-longitudinal mode optical parametric oscillator/amplifier, large concentrations of H2 in specific quantum states have become available using the scheme of stimulated Raman pumping. The quantity is now sufficient to study collision dynamics and to align H2 molecules in a particular direction for steric dynamics experiments.With the advent of this new technique, the researchers wanted to see whether the predicted significant steric effects could be observed in the simplest chemical reactions involving H2 molecules.For their experiment, the researchers picked a very simple chemical reaction, the transformation of hydrogen (H) and hydrogen deuteride (HD—a hydrogen atom bonded to an atom of deuterium, an isotope of hydrogen with an extra neutron) into molecular hydrogen (H2) and deuterium (D). They collided the chemical reactants at three different collision energies, and also at two different collision geometries—one where the chemical bond was aligned parallel to the relative velocity of the collision partners and one where the bond was aligned in perpendicular fashion.The research team successfully observed the hypothesized substantial steric effects while using quantum dynamics calculations to analysis their observations in a straightforward manner. They found that when two waves together produces a larger wave in the perpendicular configuration, it plays an important role in the steric effects observed. The chemical reaction changed drastically depending on the direction of the HD bond axis.The observations and the underlying theoretical understanding open the door to a new way to control chemical reactions.The next move for the team will be to step up their game by extending this research to more complicated reactions, which will be much more challenging in terms of carrying out experiments and on the theoretical end as well. The ultimate goal is to develop more precise and effective ways of controlling chemical reactions across the board, not just with the simplest of molecules.

A research group led by Prof. WU Kaifeng from the Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences (CAS) recently reported the successful initialization, coherent quantum-state control, and readout of spins at room temperature using solution-grown quantum dots, which represents an important advance in quantum information science.The study was published in Nat. Nanotechnol. on Dec 19th.Quantum information science is concerned with the manipulation of the quantum version of information bits (called qubits). When people talk about materials for quantum information processing, they usually think of those manufactured using the most cutting-edge technologies and operating at very cold temperatures (below a few Kelvin), not the "warm and messy" materials synthesized in solution by chemists. Recent years have witnessed the discovery of isolated defects in solid-state materials (such as NV centers) that have made possible room-temperature spin-qubit manipulation, but scaled-up production of these "point defects" will eventually become a challenge.Colloidal quantum dots (QDs), which are tiny semiconductor nanoparticles made in solution, could be a game changer. They can be synthesized in large quantities in solution at low cost, yet with high finesse in size and shape control. Further, they are usually strongly quantum-confined, thus their carriers well isolated from the phonon bath, which could enable long-lived spin coherence at room temperature. But room-temperature coherent manipulation of spins in colloidal QDs has never been reported, in that a QD system whose spins can be simultaneously initialized, rotated, and readout at room-temperature remains to be invented.Here the authors show that solution-grown CsPbBr3 perovskite QDs can actually accomplish this intimidating goal. Polarized hole spins are obtained by sub-picosecond electron scavenging, to surface-anchored molecular acceptors, following a circularly-polarized femtosecond pulse excitation. A transverse magnetic field induces coherent Larmor precession of the hole spins. A second off-resonance femtosecond pulse coherently rotates the spins through the optical Stark effect, which is enabled by the exceptionally strong light-matter interaction of the perovskite QDs. These results represent full quantum-state control of single-hole spins at room temperature, holding great promise for a scalable and sustainable future of spin-based quantum information processing"Our success here is enabled by a very rare combination of knowledge in materials, chemistry and physics," said Prof. WU. "We fabricated strongly- and uniformly-confined CsPbBr3 QDs as the unique system for the study, and identified appropriate surface-ligand molecules to rapidly extract the electrons via charge-transfer chemistry for hole-spin initialization at room temperature. Meanwhile, we were able to utilize strong light-matter interaction of these QDs to perform coherent spin manipulation."This work was supported by the Chinese Academy of Sciences, the Ministry of Science and Technology of China and the National Natural Science Foundation of China. (Text by WU Kaifeng)

Photocatalysts can utilize sunlight to produce hydrogen from water splitting and to produce solar fuels through CO2reduction, but the essential mechanism, how photogenerated charges are involved in the photocatalysis processes, has remained elusive since the beginning of photocatalysis study. Although enormous efforts have been made in photocatalysts preparation and photocatalytic reaction tests in the past a half century of photocatalysis study, the mystery on the exact mechanism behind the process and how to make the process more effectively, do not actually know, as photocatalysts have complex nanoscale morphology features and particularly photogenerated charges in photocatalysis experiences broad lifetimes and pace, across femtosecond to seconds and subnano-meter to micro-meter.Now, the mystery is resolved. Researchers in China have mapped the spatiotemporal evolution of charge transfers in cuprous oxide photocatalyst particles (a typical photocatalysts composed of only one copper atom and one oxygen atom), integrating three different techniques to reveal a holistic picture of the complex charge-transport mechanisms.The team published their results on Oct. 12 in Nature.Photovoltage measurements on photocatalyst particles are used to spatiotemporally track the charge transfer processes on the femtosecond to second timescale at the single-particle level (Image by CHEN Ruotian)"Water-splitting reactions with photocatalyst particles are a promising route for solar hydrogen, we have focused on the photogenerated charge dynamics in photocatalysis for decades," said co-corresponding author LI Can, a professor from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS). "We believed that the photoinduced charges transfer and transport in photocatalysts, and from bulk to surface reaction sites is the key determining the photocatalytic efficiency; however, it is challenging to understand the mechanisms which spans a wide spatiotemporal range from subnanometers to micrometers and from femtoseconds to seconds."According to LI, to thoroughly track this process in a photocatalyst particle has long been thought to be a dream, and the research team has finally achieved their goal."Photocatalysis generally starts with harvesting solar energy in the particulate semiconductor material, which transforms absorbed solar photons into excited charges (electrons and holes). These excited charges participate in the photocatalytic reactions," said co-corresponding author FAN Fengtao, a professor from DICP. "The photo-generated electrons and holes require separation from their initial states and transfer to a catalyst surface, where they initiate reactions to produce chemical fuels."To transfer to the surface, the electron or hole are derived from photo-excitation, which triggers the separation from their ground states. According to Fan, the efficiency challenge arises because, at such tiny physical scales, the photocatalysts often lack the forces needed to separate the charges. Efficient separation requires a dependable electric field."To form an aligned electric field in the photocatalyst particle, we carefully engineered the morphology of cuprous oxide particles," said the first author, CHEN Ruotian Ph.D. from DICP.Called facet engineering, the work consisted of precisely tuning the ratio between two of the facets on the particles, morphing them from cubes to octahedrons and generating built-in electric fields that can aid in charge separation."Interestingly, we found that the built-in electric fields vary with the facet ratios and become prominent in the configuration as the ratio increases," CHEN said, explaining that the observed inter-facet potential differences correlate with why the charge transfer can vary in magnitude in different directions. "This phenomenon, called anisotropic charge transfer, appears optimized in the truncated octahedral configuration. However, only electrons are visible on the surface after this facet tuning, indicating that holes hardly transfer to the surface and may limit efficiency."The researchers introduced hydrogen into the photocatalyst particles, forming defects that offer a potential pathway for hole transfer to surface via a selective trapping process, which prevents the hole from recombining with an electron."We found that defects were selectively incorporated into the facets of the particles, thus allowing the hole transfer selectively to defected facets." FAN said. "Photovoltage measurements indicated that the selective defect incorporation further contributes to efficient charge separation. We also demonstrated that the photogenerated electrons and holes can be selectively extracted to specific facets, but the mechanism underlying this process is likely different for holes than for electrons."To better understand the spatiotemporal origin of the efficient charge separation within the nanosecond range, the researchers used time-resolved photoemission electron microscopy —The resulting images verified that photoelectron density varies on different facets and that the electrons move from one facet to another on ultrafast time scales."However, ultrafast transport is not expected from the conventional drift-diffusion model, even though it has long been regarded as the dominant charge separation mechanism in photocatalysis," CHEN said, referring to the idea that a charge could drift around a particle, repeatedly scattering as it encounters another component. "We ascribed the ultrafast charge transfer to the ballistic transport regime, in which the carriers propagated at extremely high speeds, as the carriers travel the length of the particle prior to scattering."Following the ultrafast charge transfer, the researchers observed a gradual increase in electrons on both facets, likely arising from the drift of electrons from bulk to the surface. To directly observe the charge transfer process, the researchers performed a transient photovoltage analysis and found that signals shifted from negative to positive as the timescale progressed from nano- to microseconds."We saw ultrafast ballistic electron transfer to one type of facet and slow defect-induced hole transfer to the other type of facet, so we can determine that the efficient spatial separation of photogenerated electrons and holes on the facets was due to the spatiotemporally anisotropic charge transfer mechanism," FAN said. "We demonstrated that the quasi-ballistic inter-facet electron transfer and spatially selective trapping are the dominant processes facilitating efficient charge separation in photocatalysis."Taken together, according to CHEN, FAN and LI, this study suggests that the dominant photocatalytic mechanisms could be manifested and tuned through rational engineering of anisotropic facets and defects."We combined three different methods — time-resolved photoemission microscopy (femto- to nanoseconds), transient surface photovoltage spectroscopy (nano- to microseconds) and surface photovoltage microscopy (microseconds to seconds) — like a relay race, for the first time, to follow the entire mechanism of electron and hole to surface reaction centers in a single photocatalyst particle," LI said. "The ability to spatiotemporally track charge transfer enables advancing experimental technique for understanding the complex mechanisms in energy conversion devices, paving the way for the rational design of photocatalysts with improved performance."CHEN Ruotian and REN Zefeng are the co-first authors. LI is also affiliated with the University of CAS and the University of Science and technology of China (USTC). Other cooperations include Shandong University and Helmholtz-Center Berlin for Materials and Energy.The Fundamental Research Center of Artificial Photosynthesis, funded by the National Natural Science Foundation of China; CAS Projects for Young Scientists in Basic Research; National Program on Key Basic Research Project; and DICP Innovation Foundation supported this work.

The 100 MW Dalian Flow Battery Energy Storage Peak-shaving Power Station, with the largest power and capacity in the world so far, was connected to the grid in Dalian, China, on September 29, and it will be put into operation in mid-October.This energy storage project is supported technically by Prof. LI Xianfeng's group from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences. And the system was built and integrated by Rongke Power Co. Ltd.The Dalian Flow Battery Energy Storage Peak-shaving Power Station was approved by the Chinese National Energy Administration in April 2016. As the first national, large-scale chemical energy storage demonstration project approved, it will eventually produce 200 megawatts (MW)/800 megawatt-hours (MWh) of electricity.The first phase of the on-grid power station project is 100 MW/400 MWh. Based on China's average daily life electricity consumption of 2 kWh per capita, the power station can meet the daily electricity demand of 200,000 residents, thus reducing the pressure on the power supply during peak periods and improving power supply reliability in the southern region of Dalian.Energy storage technology can help power systems achieve the strain and response capability needed after large-scale access to the power grid. It is also particularly important in facilitating the use of renewable energy, which is key to helping China achieve its carbon peak and carbon neutrality goals but is not always accessible due to variations in wind and sunlight, etc.The Dalian Flow Battery Energy Storage Peak-shaving Power Station, which is based on vanadium flow battery energy storage technology developed by DICP, will serve as the city's "power bank" and play the role of "peak cutting and valley filling" across the power system, thus helping Dalian make use of renewable energy, such as wind and solar energy.These renewable energy sources will be used to charge the station's batteries during the grid load valley period by converting electrical energy into battery-stored chemical energy. Later, at peak grid load, the stored chemical energy will be converted back into electrical energy and transmitted to users.The station's energy storage technology uses vanadium ions of various valence states. Electrical energy and chemical energy are converted back and forth through redox reactions of these ions in the positive and negative electrolytes, thus realizing large-scale storage and the release of electrical energy.This technology is promising in large-scale energy storage applications because of its excellent safety, good reliability, large output power and storage capacity, long life, good cost-performance, use of recyclable electrolytes, and environmental friendliness.Additionally, this technology can work with conventional thermal power, nuclear power, and other power sources, providing peak regulation and frequency regulation for the power system as well as improving its flexibility.The Dalian Flow Battery Energy Storage Peak-shaving Power Station will improve the renewable energy grid connection ratio, balance the stability of the power grid, and improve the reliability of the power grid, thus serving as a model for electricity peak-shaving and renewable energy grid management in China. (Text by LIU Tao)Fig. 1 Dalian Flow Battery Energy Storage Peak-shaving Power Station (Image by DICP)Fig. 2 Power module (Image by DICP)Fig. 3 System debugging (Image by DICP)Fig. 4 Electrolyte tanks (Image by DICP)Vanadium flow battery working mechanism (Credit to ScienceApe)

A research group led by Prof. WU Kaifeng from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Dr. Peter C. Sercel from the Center for Hybrid Organic Inorganic Semiconductors for Energy, recently reported the utilization of lattice distortion in lead halide perovskite quantum dots (QDs) to control their exciton fine structure.The study was published in Nature Materials on Sept. 8.Lattice distortion in lead halide perovskite quantum dots leads to a fine structure gap and coherent exciton quantum beating (Image by HAN Yaoyao)It is well known that shape or crystal anisotropy in QDs, which are tiny semiconductor nanoparticles, results in energy splitting of their optically bright excitons (bound electron-hole pairs), known as fine structure splitting (FSS). These excitons form an important playground for quantum information science. For example, the excitons' FSS can be exploited for coherent control of quantum states for quantum computing, or for polarization-entangled photon-pairs in quantum optics, although for the latter it is important to suppress the magnitude of splitting.Traditionally, studying FSS usually requires single or just a few QDs at liquid-helium temperature, because of its sensitivity to QD size and shape. Measuring FSS at an ensemble-level, let alone controlling it, seems impossible unless all the dots are made to be nearly identical.In this study, by using ensemble-level femtosecond polarized transient absorption, the researchers observed clear bright-exciton FSS in solution-processed CsPbI3 perovskite QDs, which is manifested as exciton quantum beats (periodic oscillations of kinetic traces)."Even more amazingly, the beat frequency, as determined by the FSS energy, of a given sample can be continuously controlled by changing the temperature. This is an unprecedented result, meaning that now scientists can facilely control FSS through temperature," said Prof. WU.The researchers also found that the temperature-dependent FSS was related to the interesting, highly-dynamic lattice of lead halide perovskites. Lowering the temperature led to a more distorted lead-iodide octahedral framework.Calculations indicated that, because these orthorhombic-phase QDs were actually still bounded by the pseudocubic family of crystal planes, the lattice distortion results in an avoided crossing fine-structure gap between bright exciton. This gap was responsible for the observed FSS, and it could be detected in spite of QD size and shape heterogeneity across an ensemble sample."Lattice distortion in CsPbI3 perovskites is well known in the photovoltaic community, as it is connected to the issue of phase stability of perovskite solar cells, but nobody has previously connected it experimentally to the exciton fine structure" said Prof. WU. "Our study demonstrates that this material property can actually be harnessed to control the bright-exciton splitting in quantum dots for quantum information technologies."