PROFESSIONAL EXPERIENCE

Professor, Soochow University, China, 2016-present

R & D scientist, Afton Chemical Corporation，Richmond, USA , 2015-2016

Senior Scientist, Halliburton Company, Houston, USA, 2013-2015

Research Associate, Houghton International Inc., Philadelphia, USA , 2012-2013

Research Associate, National Institute of Standards and Technology (NIST), USA, 2009-2012

EDUCATION

Ph.D. University of California, Davis, U.S.A.

M.S. in School of chemistry and chemical engineering, Shanghai Jiaotong University, China.

B.S. in School of chemistry and chemical engineering, Shanghai Jiaotong University, China.

HONORS

National Young Talents (Oversea).

Six talent peaks in Jiangsu Province: Innovative Talents, 2016.

Specially-Appointed Professor of Jiangsu Province, 2018.

Research Interests

Solid-state Lithium Metal Batteries

In view of the ultrahigh theoretical capacity (3860 mAh/g) and the lowest redox potential (−3.04 V vs. standard hydrogen electrode) of metallic lithium, lithium metal battery (LMB), among the various energy storage solutions, has been viewed as the promising next-gen battery to overcome the current capacity limit of lithium ion batteries (LIBs). However, the hostless nature of Li metal anode (LMA) causes issues such as infinite volume expansion, non-stable solid-electrolyte interphase (SEI), uncontrollable dendrite growth and dead Li formation, which in turn lead to the low Coulombic efficiency (CE), high voltage polarization and poor cycle life of LMBs. Moreover, owing to the high activity of metallic lithium, safety hazards caused by short circuit and thermal runaways further limit their practical applications. Thus, it is imperative to seek for innovative solutions and materials to passivate the metallic lithium and minimize its usage by maximizing the Li plating/stripping efficiency, and solidify the conventional liquid electrolytes to avoid safety issues.

In the examples below, we show that the compartmentalization of bulk Li deposition into 3D matric Li storage is a useful tactic to attain homogeneous Li plating/stripping, in which Li ions are guided by lithiophilic moieties to impregnate the compartments. This allows us to distill the strategic merits of guided and compartmentalized Li deposition to afford a reversible and uniform Li plating/stripping.

Borrowing the “blockchain” terminology from data mining, we devise a novel strategy of Li deposition by utilizing the conductive N-rich polypyrrole (PPy) as the “chain” to fill and interlink the “blocks” of MOF cavities. As such, during Li plating/ stripping the lithiophilic PPy helps to guide the infiltration/ extrusion of Li+ ions and serves as the nucleation sites for isotropic Li deposition, while the MOF pores enable the compartmentalization of the bulk Li deposition and provide spatial confinement for accommodating 3D matrix Li storage. This allows us to simultaneously obtain a highly lithiophilic surface and homogenize the Li+ mass and charge transport, leading to low-barrier and dendrite-free Li plating/stripping with superb Coulombic efficiencies in half, symmetric and full cells.

For details, please refer to Angewandte Chemie., 2022, 134, e202116291.

Following the same vein, we modify the Cu current collector with mercapto metal organic frameworks (MOFs) impregnating Ag nanoparticles (NPs), aiming to develop anode-free LMBs engaging no Li disks or foils. While the polar mercapto groups facilitate and guide Li⁺ transport, the highly lithiophilic Ag NPs help to enhance the electric conductivity and lower the energy barrier of Li nucleation. Furthermore, the MOF pores allow compartmentalizing bulk Li into a 3D matric Li storage so that not only the local current density is reduced, but also is the plating/stripping reversibility greatly enhanced. As a result,full cells pairing the prelithiated Ag@Zr-DMBD/Cu anodes with LiFePO₄ cathodes demonstrate a high initial specific capacity, Coulombic efficiency, and long-term cycling stability.

For details, please refer to Adv. Mater., 2023, 2303489.

Research Interests

Metal-Air Batteries

Rechargeable metal air batteries represent one of the most tempting chemical energy storage solutions owing to advantages in energy density, operational safety, environmental benignity and low cost. However, their prevailing implementation is contingent upon successfully addressing two key challenges on both the anode and cathode sides. At the anode side, reversible metal oxidation and reduction is the prerequisite for a good cycling performance, which is plagued by issues such as parasitic side reactions, anode corrosion and dendrite formation. At the cathode side, reversible oxygen conversion is crucial for achieving high energy efficiency, involving the multi-electron participated oxygen evolution (OER) and oxygen reduction (ORR) reactions with notorious sluggish kinetics, and therefore demands highly active and durable catalysts composed of earth-abundant elements.

Li-O₂ Batteries

Nonaqueous Li-O₂ battery (LOB) has garnered tremendous attentions owing to its high theoretical energy density of >3500 Wh kg^-1 and the potential to use ambient air as the cathode active material^4-6. In general, the rechargeable LOB based on the reversible reaction of 2Li + O₂ ↔ Li₂O₂(E^Φ =2.96 V vs. Li⁺/Li)is composed of a metal Li anode, a porous O₂-diffusion cathode and a separator saturated with organic electrolyte. Due to the semi-open device configuration, LOB faces severe challenges from each of the above components, hurdling its practical deployment outside the laboratory.

In the following example, we initiate an ingenious ‘trinity’ design of LOB by employing a hollowed cobalt metal organic framework (MOF) impregnating iodized polypyrrole simultaneously as the cathode catalyst, anode protection layer and slow-release capsule of redox mediators, so as to systemically address issues of impeded mass transport and redox kinetics on the cathode, dendrite growth and surface corrosion on the anode, as well as limited intermediate solubility in the low donor-number (DN) solvent. As a result of the systemic effort, the LOBs as-constructed demonstrate ultralow discharge/charge polarization, prolonged cycle life and high discharge capacity. Mechanistic investigations attribute the superb LOB performance to the redox-mediated solution growth mechanism of crystalline Li₂O₂ with both enhanced reaction kinetics and reversibility. This study offers a paradigm in designing smart materials to raise the performance bar of Li-O₂ battery towards realistic applications.

For details, please refer to https://doi.org/10.1002/adma.202308134.

Zn-air Batteries

Zinc–air batteries or zinc–air fuel cells are metal–air batteries powered by oxidizing zinc with oxygen from the air.  Zinc–air batteries offer specific and volumetric energy densities of around 500 Wh kg⁻¹ and 1000 Wh L⁻¹, respectively, which are among the highest for a battery system. The discharge profile is largely flat with a voltage of around 1.3 V. These batteries consist of environmentally benign and low-cost components. They also have a long shelf life of several years when properly stored. The major disadvantage is their limited power output, which is mainly due to the inadequate performance of air electrodes. The other major disadvantage is the dependence of both performance and operating period on ambient conditions such as humidity and temperature.

Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), as the two key electrochemical reactions on the air cathode of rechargeable zinc-air batteries (ZABs), are notoriously sluggish in redox kinetics due to the four-electron participated charge transfer sequences. Although thermodynamically the equilibrium potential to initiate the above reversible reactions is 1.23 V vs RHE, an overpotential is always required to drive the reaction towards either direction. To minimize such overpotentials and maximize the reaction kinetics, both high-performance OER and ORR catalysts are demanded to improve the energy storage and release efficiencies of rechargeable ZABs. At present, electrocatalysts based on precious metals such as RuO2, IrO2 for OER and Pt/C for ORR still dominate due to their high Faradaic efficiency in O2 conversion. However, their high cost, scarcity, and poor durability greatly hinder further scalable applications. Furthermore, to ameliorate the contact between catalyst and current collector on electrodes involving gas reactions, design and fabrication of the freestanding, binder-free, and integral electrodes with embedded catalytic sites are highly desirable. This not only effectively addresses the durability issue of conventional ink-loading and binder-affixing electrodes, but also endows them with extra flexibility to be implemented in wearable electronic devices. 

In the following example, aiming to achieve a high exposure of active sites, a high electrolytic current density, and a high catalytic stability for practical applications, hierarchical structures of CuCoNC nanowire arrays on copper foam are fabricated by assembling nanoparticles of Co-MOF (ZIF-67) onto individual Cu(OH)₂ nanowires, followed by pyrolysis in inert gas. This allows the incorporation of multiple catalytic species into the structure, including metal nanoparticles embedded in graphitic carbon that is beneficial for HER, metal oxides favorable for OER, as well as Metal-N-C motifs advantageous for ORR. As a result, superior electrocatalytic HER, OER and ORR performance are simultaneously achieved, enabling efficient overall water splitting self-powered by zinc-air batteries fabricated using the same trifunctional CuCoNC catalyst.

For details, please refer to Applied Catalysis B Environmental, 263, 118139 (2020).

Research Interests

In-situ Monitoring of Gas electrode reactionns

In-situ ATR-SEIRAS

ATR-SEIRAS stands for attenuated total reflectance surface-enhanced infrared absorption spectroscopy. It is a surface-sensitive technique similar to surface-enhanced Raman spectroscopy (SERS). ATR-SEIRAS uses a silicon prism with one surface coated with a thin (~ 30 nm) metal film. Infrared light passes through the prism and is totally internally reflected. The evanescent wave excites surface plasmon polaritons at the metal/air interface. The increased electric field is confined to the interface, so absorption probabilities of surface molecules increase by an order of magnitude or more.

In the following example, ATR-SEIRAS was employed to probe the intermediates associated with multi-carbon alcohol production on Hex-2Cu-O, a hexaphyrin compound. A prominent absorption band at 2095 cm⁻¹, attributed to the C≡O stretching mode of *CO, is observed at all potentials from −0.5 to −1.3 V, and its intensity decreases with the increasing bias. This suggests that at negative potentials more CO attend to the C–C coupling reactions to form multi-carbon products. Meanwhile, the peak shows a red shift with increasing bias, which is ascribed to the Stark shift caused by strong electronic interaction between *CO and the under-coordinated metal cluster. The peaks located at 1560 cm⁻¹ and 1436 cm⁻¹ growing conspicuously with decreasing potential can be designated to the C-O vibration of adsorbed *OC–CO(H), a strong evidence for the direct CO-CO dimerization on Cu clusters. As reported in previous studies, one of the most probable rate-limiting steps for generating C₂ intermediates is the *CO dimerization, which is greatly facilitated by concentrated CO adsorption on under-coordinated Cu sites. More importantly, the growing peak at 1360 cm⁻¹ is ascribed to the stretching of surface-bound *OCH₂CH₃ species, which is considered a key intermediate in the C₂₊ pathway to form alcohols. Note that the premature formation of intermediates before the actual show-up of the corresponding products has been often seen in literature and attributed to their strong surface absorption prior to an endothermic release step.

For details, please refer to Nature Communications, 13, 5122 (2022).

Operando Raman

Raman spectroscopy is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified. Raman spectroscopy relies upon inelastic scattering of photons, known as Raman scattering. A source of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range is used, although X-rays can also be used. The laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down. The shift in energy gives information about the vibrational modes in the system. Infrared spectroscopy typically yields similar yet complementary information.

In the following example, Operando Raman studies were carried out on a flow-cell assembly by sweeping the applied voltage from −0.2 to −1.4 V. Under negative bias, peaks at 298 cm⁻¹ (corresponding to the Cu−CO rotational mode) and between 2033–2049 cm⁻¹ (corresponding to the stretching modes of C≡O) were observed for PANI@HKUST-1, but not for HKUST-1 and PPy@HKUST-1. This provides a strong evidence for high *CO coverage at the PANI/Cu interface, which is presumably caused by PANI-induced CO₂ concentration. The C≡O stretching bands can be further deconvoluted into two bands at 2033 and 2049 cm⁻¹, of which the intensity ratio is potential dependent. While the low-frequency C≡O band (LFB) has been viewed critically contributing to the C−C coupling events, the high-frequency band (HFB) is associated with CO intermediates that are relatively static and inert. The potential-dependent C≡O vibration modes indicates a dynamic Cu/PANI interface along with the restructuring of HKUST-1. Serving also as a Lewis base, PANI has been reported capable of not only enriching local CO₂ concentration but also lowering the CO₂ activation barrier. This is indeed evidenced by the Raman signal of V_s(CO₂) detected at 991 cm⁻¹.

For details, please refer to Angewandte Chemie International Edition, 10.1002/anie.202312113 (2023).

In-situ DEMS

Differential Electrochemical Mass Spectrometry (DEMS) is an analytical technique that combines electrochemical half-cell experimentation with mass spectrometry. It allows in situ mass resolved determination of gaseous or volatile electrochemical reactants, reaction intermediates and products in real time. The experimental setup consists of an electrochemical half-cell, the membrane interface and a vacuum system including a quadrupole mass spectrometer. It can be used for online analysis of gas production during the charging and discharging processes of various energy storage devices, such as Lithium-ion, Sodium-ion, and Zinc-ion batteries. For rechargeable battery types that consume and produce gas, such as air batteries, it can be used for quantitative analysis of gas generation or consumption in real time. Obtaining the distribution of gas generation or consumption with voltage changes during battery charging and discharging is one of the important analytical tools for studying the electrochemical reaction mechanism of batteries, quickly selecting electrode materials, and evaluating electrolyte decomposition.

In the following example, in situ DEMS is utilized to interrogate the reversible Li–O₂ reaction in the Li@GA||NCO@rGA cell. By measuring the O₂ consumption/evolution and comparing it with the quantified Faradaic charge, the numbers of electron transfer per O₂ molecule were determined to be 1.8 and 2.1 for discharge and charge, respectively, which are very close to the theoretical value of 2e⁻/O₂ for reversible Li₂O₂ formation. Note that the tiny amount of CO₂ detected during the charging process could be due to the decomposition of carbon and/or electrolyte at high charging potentials.

For details, please refer to Advanced Functional Materials, 2007218 (2020).

Below are more cases for in-situ monitoring of gas evolution invarious battery types.

Lithium metal battery (button-type)

Sodium-ion battery (soft pack)