The Top Ten Scientific Questions in Electrochemistry
Chinese Society of Electrochemistry
DOI Link: https://doi.org/10.61558/2993-074X.3444
Contents
- How to Detect or Simulate the Dynamic Structural Changes of Complex Electrochemical Interfaces under In-Situ/Operando Conditions at the Microscale, and Establish Their Relationships with Macroscopic Electrochemical Performance?
- How to Understand and Regulate the Nucleation and Growth of Metal Lithium at the Anode, and Develop Strategies for Suppressing Dendrite Formation？
- How to Obtain High-Performance Alkali-Metal-Ion Solid-State Electrolytes for Solid State Batteries?
- How to Develop Aqueous Battery Systems with High Energy Density and Multi-Electron Transfer Reaction？
- How to Rationally Design Efficient and Long-Lasting Low/Non-Platinum Electrocatalysts and Their Large-Scale Production?
- How to Construct High-Efficiency Three-Phase Interface and Gain Insights into Enhanced Charge/Mass Transportation Mechanism within a Gas Diffusion Electrode?
- How to Decipher the Relationships among Human Diseases and Electron Transfer, Energy Conversion/Substance Transformation in Biological Processes? And How to Modulate Them with Electrochemical Methods?
- How to Break Through the Shockley-Queisser Limit of Energy Conversion Efficiency in Solar Cell?
- How to Further Reveal the Kinetic Mechanism of Multi-Steps Electrode Reactions for a Complex Corrosion System, and How to Precisely Modulate Anodic and Cathodic Processes, as Well as Their Closely Associated Interfacial Reactions?
- How to Electrochemically and Precisely Synthesize High Value-Added Organic Chemicals with High Efficiency and High Selectivity？
1. How to Detect or Simulate the Dynamic Structural Changes of Complex Electrochemical Interfaces under In-Situ/Operando Conditions at the Microscale, and Establish Their Relationships with Macroscopic Electrochemical Performance?
CHENG Jun, CAI Wenbin
The electrochemical interface plays a central role in many important electrochemical applications, serving as an important reaction site for material transformation and energy conversion. With the rapid development of modern society, the requirements for the performances of electrochemical devices and systems continue to be climbed, such as the needs for batteries and fuel cells with higher energy and power densities, higher safety, and longer lifetime, the needs for low energy consumption in H2-production and CO2 reduction electrolyzers, and the needs for achieving Cu superfilling in trenches and vias with multiscale down to 10 nm for chip fabrication (Damascene interconnection). It is thus highly demanded to maximize by design the physicochemical properties of electrode-electrolyte materials and interfaces, based on a comprehensive and clear understanding of the microstructure, mechanism, and regulations of the electrochemical interface. However, under in-situ/operando conditions, the electrochemical interface has extremely high chemical complexity and is under dynamic change. The traditional theories describing electric double layer, charge transport and transfer in relatively simple occasions such as dilute solutions, near-equilibrium conditions, and solid-liquid interfaces, cannot be applied to modern electrochemical systems characterized by highly concentrated solutions, confinement environments, far-from-equilibrium conditions, solid-solid and solid-liquid-gas triple-phase interfaces, etc. How to detect the microstructures and reaction processes of such complex electrochemical interfaces is a great challenge for both experimental characterization and computational simulation. It is urgently needed to develop new experimental methods such as synchrotron radiation characterization, multi-modal spectroscopy and high-resolution dynamic imaging to obtain dynamic evolution information of electrochemical interfaces at real time, in-situ, and on-site conditions, at the molecular level, with high energy, and high spatial and high temporal resolutions. Combining first-principles calculations with multi-scale simulations, simulation methods for cross-scale modelling of electrochemical interfaces can be developed. By fully utilizing AI methods, we can develop standardized and automated computational and experimental integration platforms to accelerate the acquisition of experimental and computational data for electrochemical systems, establish open source shared computational and experimental databases, and ultimately achieve rational design and intelligent optimization of high-performance electrochemical materials and devices.
2. How to Understand and Regulate the Nucleation and Growth of Metal Lithium at the Anode, and Develop Strategies for Suppressing Dendrite Formation？
GUO Yuguo
Metallic lithium (Li), due to its high theoretical specific capacity and low potential, is considered an ideal anode material for the next-generation high-energy rechargeable batteries. However, the Li-metal anode tends to form dendrites during the electrochemical deposition process, which could lead to deteriorated battery cycling and potential safety problems. Unrevealing the nucleation and growth mechanisms of Li-metal anode during the electrochemical process and developing effective dendrite-suppression strategies constitute the critical science problem in the fundamental research of rechargeable Li-metal batteries. Currently, based on the in situ electrochemical characterization techniques and theoretical simulation methods, a preliminary understanding about the nucleation and growth of Li dendrites has been provided. Several models, such as the space charge model, the deposition-dissolution model, and the heterogeneous nucleation model, have been proposed to describe the dendrite propagation mechanism, and the corresponding dendrite-suppression strategies, including the three-dimensional current collector and artificial Li-electrolyte interface, have been developed. However, the Li deposition behavior in practical batteries is usually influenced by multiple factors, and it remains difficult, by employing the existing theoretical models, to predict the dendrite growth behavior during battery operation. Besides, the effectiveness of the present dendrite-suppression strategies has not been verified in a long-term and wide-area study. In the future, in situ and operando electrochemical characterization techniques with high spatiotemporal resolution are to be developed to collect information at multi-scales and multi-dimensions, about the evolution of fine structures, phases and physical states for nucleation and growth of Li metal (dendrites) in a real electrochemical process. The advancement in characterization technique is of great significance to understanding the dendrite evolution in a battery. Meanwhile, attention will be paid on comprehending the coupled influence by multiple factors (including thermodynamics, mass transfer kinetics and stress-strain responses) on the electrodeposition of Li metal, establishing accurate theoretical models for nucleation and growth of Li dendrites, and exploring new strategies of exploring effective additives of electrolyte to regulate Li nucleation and growth under the working conditions, resolving intrinsically the safety issue of lithium metal anode. A joint effort will facilitate sustainable development of high-energy rechargeable Li-metal batteries.
3. How to Obtain High-Performance Alkali-Metal-Ion Solid-State Electrolytes for Solid State Batteries?
DENG Yicheng, TANG Guo, AI Xinping
Solid state alkali-metal secondary batteries (SSABs) have received considerable attention as a next-generation electrochemical energy-storage technology with high energy density and safety. However, due to the poor performance of solid state electrolytes, the development of SSABs has lagged far behind expectations. Alkali-metal-ion solid electrolytes can be divided into three categories according to their chemical composition: sulfides, oxides and polymers, nevertheless, each one has its own merits and demerits, and none of them can fully meet the needs of SSABs at the current stage. Sulfide electrolytes have high ionic conductivities but narrow electrochemical windows. Oxide electrolytes have high chemical and electrochemical stability, but poor shape adaptability owing to their high Young's modulus. Polymer electrolytes have excellent flexibility and good processability, but their ionic conductivities are considerably low. Therefore, advanced solid state electrolytes with high ionic conductivity, wide electrochemical window and excellent interface shape- adaptability are still the key for the development of SSABs technology. Judging from the current research, a possible route is to construct soft solid-state electrolytes by compositing flexible electrolytes (polymers, plastic crystals, ionic gels, etc.) with rigid inorganic and organic nano-solid materials. According to this judgement, more attention should be paid to the plastic crystal-polymer composite electrolytes, ionic gel-organic frame material (MOF, COF) composite electrolytes, inorganic ion conductor-polymer composite electrolytes, and their multicomponent composites.
4. How to Develop Aqueous Battery Systems with High Energy Density and Multi-Electron Transfer Reaction？
LI Xianfeng
Aqueous batteries play an important role in large-scale energy storage due to the advantages of high safety, high power density, and long cycle life. High energy density is the technical guarantee for the goals of miniaturization, integration, and portability of battery devices, and is the future trend of battery development. However, common aqueous batteries are endowed with low energy density due to the side reactions of water electrolysis and are difficult to be used as power batteries, which limits their application scenarios. Traditional power batteries suffer from safety issues due to the flammable nature of organic electrolytes. The energy density of an aqueous battery is highly related to the battery voltage, concentration of redox species, and electron transfer number per redox molecule. Therefore, achieving multi-electron transfer electrochemical reactions is an important strategy to construct a high energy density battery system. However, the electrochemical kinetic and reversibility of multi-electron transfer reactions are usually poor in aqueous batteries, and there is a lack of profound understanding in their micro electrochemical mechanisms. Multi-electron transfer reactions often involve multiple intermediate state products and intermediate steps. Many intermediate states usually suffer from poor stability, short existence time, and complex forms of existence, making it difficult to observe the structure, interface adsorption and desorption, and charge transfer behavior at the molecular scale, and thus, difficult to revealing the microscopic mechanism of multi-electron transfer. In response to the complex process of multi-electron transfer reactions, it is necessary to develop new methods for multi-scale, high-resolution, and highly sensitive observation of multi-electron transfer processes, and therefore, to clarify the intermediate state, and understand their solvation structure, electrode surface adsorption and desorption, electron transfer behaviors, as well as to realize precise control of electrochemical reaction processes, and complete the adaptation of multi-electron reactions with key materials such as membranes and electrodes, ultimately providing theoretical basis and technical support for the establishment of high-energy density flow batteries.
5. How to Rationally Design Efficient and Long-Lasting Low/Non-Platinum Electrocatalysts and Their Large-Scale Production?
WEI Zidong, XIANG Yan
Electrocatalysts are crucial materials for fuel cells, directly impacting the cost, performance, and lifespan of the cells. Platinum (Pt)-based electrocatalysts, due to their excellent catalytic activity and stability in a wide range of solutions, are currently irreplaceable in polymer electrolyte membrane fuel cells, constituting approximately 40% of the electrode cost. However, as one of the rare precious metals in the world, Pt reserves are globally identified to be about 70,000 tons with an annual production of around 250 tons. Even at a technological level of 0.125 gPt/kW, it is estimated that global consumption will reach 900 tons of Pt per year, representing a three to fourfold increase over current production levels, which will severely restrict the development of fuel cell technology. The major scientific challenge in the field of fuel cells is the design of novel, highly active, and long-lasting low/non-Pt catalysts that meet the demands of complex operating conditions. Strategies such as comprehending the mechanisms behind catalyst failure in operational conditions, precisely fine-tuning catalyst composition, morphology, and atomic arrangement, in conjunction with advanced approaches such as surface/interface and nano-confinement, and modulation of coordination environments, are essential. Meanwhile, efficient mass production methods for these advanced catalysts must be devised.
6. How to Construct High-Efficiency Three-Phase Interface and Gain Insights into Enhanced Charge/Mass Transportation Mechanism within a Gas Diffusion Electrode?
XING Wei
The structure, composition, and surface properties of three-phase interface where electrochemical reaction takes place are significant in determining the performance for a variety of electrochemical energy conversion and storage devices, including fuel cells, water electrolyzers, carbon-dioxide electrolyzers and electrosynthesis. As the three-phase interface in a gas diffusion electrode (GDE) is commonly composed of ionomer and catalyst, how to regulate the ionomer-catalyst structure is a prerequisite to maximize the utilization of catalyst. For instance, an engineering novel interface structure, i.e., a three-dimensionally ordered structure, hierarchically porous structure, and ionomer-gradient distribution structure, is promising to facilitate mass transfer and water/heat management, thus enabling complete performance expression of the as-designed GDE. The delicate design of catalyst-ionomer structure is particularly important for the low catalyst loading GDE, where high local transport resistance associated with the permeation and diffusion of reactants results in considerable overpotential. To this regard, developing porous support materials with high surface area and graphitic degree, and self-polymerized microporous ionomers with high conductivity and water uptake provide an appealing approach to lower local transport resistance.
In addition, a comprehensive understanding on the key scientific problems associated with charge/mass transfer process in the three-phase interface lays the foundation for the interface structure design and thus the high-performance GDE. It greatly depends on the development of operando characterization techniques with high sensitivity and spatiotemporal resolution, which include X-ray transient absorption spectroscopy, sum frequency generation vibrational spectroscopy, scanning probe microscopy coupled with electrochemical spectroscopy and tip-enhanced Raman spectroscopy. These operando techniques are helpful to gain insights into transient response of mass/charge transfer and reaction kinetics within the three-phase interface at a micro-atomic scale. Combining with advanced theoretical modelling, such as quantum mechanics, multiscale simulation, big data analytics and artificial intelligence, we could dissect the dynamic evolution mechanism of three-phase interface structure under working conditions, thereby revealing the structure-property relationship at an atomic scale.
7. How to Decipher the Relationships among Human Diseases and Electron Transfer, Energy Conversion/Substance Transformation in Biological Processes? And How to Modulate Them with Electrochemical Methods?
LI Yueqi, JU Huaxian, LI Jinghong
Electron transfer and the transformation of energy/substances are commonly involved in biological activities, for example, electron transfer in cell respiration, photon-electron energy conversion in photosynthesis, molecular recognition, and interaction in cell signalling pathway, and phase separation of biological macromolecules. Because the above processes establish the physical and chemical bases for biological activities, the disorders in their regulations are closely related to the occurrence and development of a wide range of diseases. To date, it is still intriguing task to reveal the microscopic mechanisms of these key processes. The methods of electrochemistry feature outstanding sensitivity, selectivity, and spatial/temporal resolution, providing powerful tools for studying biological processes at the level of cells and molecules, demonstrating the mechanism of cell redox processes, and intervening the functions of biological molecules. The multi-scale electro-analytical technologies based on electrochemical measurement and modulation include electrochemical biosensing, membrane potential and neurotransmitter analysis, electrogenerated chemiluminescence microscopy, single-biomolecule electronic measurement, etc. In the future, combining electrochemical strategies with spectroscopy, microscope imaging, force and magnetic measurement techniques will contribute to multi-scale, multi-mode, and highly sensitive new characterizations of biological systems. This will help us to discover more microscopic properties and even quantum effects in biological systems, to understand the chemical nature and physical principles of electron transfer and the transformation of energy/substances, to explore new paradigms for the diagnosis and treatment of related diseases, and to open new ways for regulating the molecular bio-functions and for intervening the cell aging processes. The efforts will potentially lead to important, new directions in the physical science for biological systems.
8. How to Break Through the Shockley-Queisser Limit of Energy Conversion Efficiency in Solar Cell?
SHI Yuxin, FAN Louzhen
Solar cell (SC), as a type of photoelectric device, can directly convert light into electricity. Due to its advantages of environmentally friendly, low cost, and easy-to-manufacture, solar power has become one of the most important power supply systems in the world and has been widely used in various fields. As a key parameter for measuring the performance of SC, the power conversion efficiency (PCE) refers to the percentage of power converted from sunlight into electrical energy under "standard test conditions". The Shockley-Queisser (SQ) limit was first proposed by William Shockley and Hans Queisser in 1961, in which, for single-junction SC, the maximum PCE calculated by the SQ limit is 33.7%. However, for multi-junction SCs, it can reach to 68.7% under normal sunlight, or 86.8% under concentrated sunlight. Considering that these devices consist of multiple wide-bandgap bottom cells and narrow-bandgap top cells, it is crucial to effectively control the structure of connection layer, and the charge transfer between the upper and lower cells.
Electrochemical method features operational simplicity, high sensitivity, and outstanding accuracy, which serves as a powerful tool for optimizing the preparation process, adjusting the interface and bulk structure, and analyzing electrical properties and mechanisms of SC. To date, focusing on electrochemical deposition and measurement, the control of the structure of connection layers and the regulation of transport, separation, and recombination of charges in SC have been achieved. Importantly, a multi-scale and multi-level integrated electrochemical-SC system has been established to capture solar energy, convert, and store energy, significantly improving the PCE of SC. In the future, how to further optimize electrochemical methods to explore the relationship between performance and structure, and the charge balance mechanism in multi-junction SCs will be of great significance for developing new ideas to push the SQ limit.
9. How to Further Reveal the Kinetic Mechanism of Multi-Steps Electrode Reactions for a Complex Corrosion System, and How to Precisely Modulate Anodic and Cathodic Processes, as Well as Their Closely Associated Interfacial Reactions?
LIN Changjian
Corrosion results in a huge economy loss about RMB3.6 trillion a year in China (GDP 3.34%), it always consumes limited human resources and causes energy waste, pollution, quality problem, safety risk and high cost, etc. Corrosion is a complex coupling system with multi electrode reactions functioned of surrounding environment, involving mass transfer of corrosive species toward cathodic and anodic sites separately, charge transfer of Faraday reactions, electron transfer in short-circuit of corrosion cell, and transport of corrosion products, following chemical reactions and formation of corrosion products, which closely affect the corrosion form, kinetic behavior, corrosion mechanism and its regularity. It remains great challenge to further reveal the kinetic mechanism of multi-steps electrode reactions for a complex corrosion system, and to precisely modulate anodic and cathodic processes, and their closely associated interfacial reactions. Traditional research methods of corrosion electrochemistry, through electrochemical simulation, measurements of response and theoretical analysis, usually can only obtain indirect, average and statistic information for a corrosion system. It is hard to recognize the details of multi electrode reactions and essential mechanism from molecular and atomic level, and to precisely modulate electrode process and associated reactions as well for a complex corrosion system. In the new era, it needs to develop various in-situ electrochemical probes with high resolution, in-situ spectroscopic analysis in high tempolar-spatial resolution, operando atomic imaging, and AI techniques to further reveal interfacial structure of corrosion system at multi-scale. Consequently, all in-depth understanding to mechanism and kinetic regularity will benefit to realize precise modulation of anodic and cathodic processes, and the closely related reactions in a complex corrosion system.
10. How to Electrochemically and Precisely Synthesize High Value-Added Organic Chemicals with High Efficiency and High Selectivity？
LIN Haibo
Motivated by carbon peaking and carbon neutrality goals, the precise electrochemical synthesis in conjunction with renewable energy sources is expected to establish a novel paradigm in the realm of green energy conversion toward high-value chemical energy. Organic electrochemical synthesis generally occurs in an oil-water milieu, using in-situ electricity to generate reactive oxygen (or reactive hydrogen). This process selectively electro-catalyzes the oxidation (or reduction) of organic compounds into high-value organic molecules. This intricate process encompasses multi-electron (multi-proton) transfer stages and separation procedures. Organic electrosynthesis is proficient in various transformations, including the derivation of aldehydes/ketones/acids from alcohols, aldehydes/ketones/acids from alcohols, the hydrogenation of carbonyl compounds to prepare alcohols and deoxygenated coupling products, the selective hydrogenation of alkyne/olefin compounds, and the electrochemical fluorination modification of drug molecules. Presently, several challenges confront the industrialization of organic electrosynthesis, such as the selective breaking and formation mechanisms of chemical bonds in organic electrocatalytic systems, medium and surface-interface effects, the regulation rules and large-scale preparation of electrocatalysts (electrodes), material distribution and transfer at the oil/water interface, phase equilibrium rules, the material and energy transfer rules of organic electrosynthesis reactors, and the dynamic/static response characteristics and coordination matching mechanisms of organic electrosynthesis devices propelled by fluctuating electrical energy. Future efforts should be devoted to concentrate on developing lipophilic/hydrophilic dual-interface catalytic layer construction technology, and controllable preparation of high-efficiency, highly catalytic activity, highly selective, and long-life industrial electrocatalysts (electrodes), as well as the design, amplification, product separation technology, and integrated processes of efficient, high-performance, low-energy-consumption electrocatalytic organic synthesis reactors to realize efficient and highly selective electrochemical production of high-value organic chemicals driven by renewable electricity.
