Electrochemical Reaction Mechanism Research Articles

Probing the Effect of pH Value and Voltage on the Near‐Surface Proton Concentration at the Electrochemical Interface by In Situ Electrochemical Surface‐Enhanced Raman Spectroscopy (EC‐SERS)

ABSTRACTUnderstanding the variation of proton concentration near the surface of the electrochemical interface is of great significance for understanding the mechanism of electrochemical reactions. In this work, 4‐Mpy molecules that are protonated and deprotonated depending on the surrounding pH value adsorb on the Au nanoparticle film electrode with high SERS activity, and by virtue of the highly interfacial‐sensitive EC‐SERS technique, we systematically studied the effects of electrolyte pH value and external voltage on the protonation and deprotonation of 4‐Mpy at the interface between Au‐NP film electrode and phosphate buffer, to analyze the changes of near‐surface proton concentration at the electrochemical interface. It is found that the pH value of the electrolyte plays a decisive role in the protonation process of 4‐Mpy at the electrode interface at low reduction voltage (< −0.1 V). In acidic and neutral solution, 4‐Mpy exists mainly in protonated form on the electrode surface. However, in alkaline solutions, 4‐Mpy exists mainly on the electrode surface in the form of deprotonation. At high reduction voltage (≥ −0.1 V), the protonation and deprotonation of 4‐Mpy on the electrode surface are mainly determined by the adsorption structure of 4‐Mpy on the electrode surface. At the same time, we conducted a comparative study of 2‐Mpy and 4‐Mpy molecules and found that the adsorption modes were different depending on the position of the N atom. 2‐Mpy is inclined adsorbed on the surface of the Au‐NP film electrode, and 4‐Mpy is vertically adsorbed on the surface of the Au‐NP film electrode.

Microscopic characteristics and corrosion rate modeling in galvanized high-strength steel wires

The electrochemical reaction mechanism of galvanized high-strength steel wires (GHSSWs) has not been fully elucidated. Scholars have observed a significant discrepancy between the theoretical mass loss rate calculated using the Faraday equation for electrochemical corrosion and the experimental values. To address this issue, this study conducted electrochemical corrosion tests on 195 sets of GHSSWs. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and non-contact 3D scanning systems were used to characterize the surface morphology and elemental composition of specimens before and after rust removal, revealing the reaction mechanism during electrochemical corrosion in GHSSWs. The correlation between corrosion length, current intensity, and electrolysis time with the corrosion rate was investigated, and a correction function for mass loss in GHSSWs under constant current electrochemical corrosion was established. The results indicate that during the initial stage of electrochemical corrosion in GHSSWs, internal stress between the corrosion products and the GHSSWs substrate leads to the formation of apparent cracks in the corroded wire, increasing the contact area between the specimen and the electrolyte and accelerating the corrosion process. In later stages, the formation of needle-like α-FeOOH corrosion products provides protective effects, leading to a decrease in the corrosion rate.

Layered MnO2@PDA as cathode material toward high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) can benefit from a deep understanding of the electrochemical reaction mechanism of cathode materials, which can assist in resolving issues such as cathode dissolution and electrostatic interactions. We reported a straightforward two-step synthesis of polydopamine coated MnO2 (MnO2@PDA) and revealed the energy storage mechanisms in AZIBs. The layered structure of MnO2 creates a generous passage for the insertion of H+/Zn2+ ions. Simultaneously, the plethora of functional groups within PDA exerts a robust desolvation effect, bolstering the transfer rate of H+/Zn2+. This effect significantly enhances the overall efficiency and performance of cathode. The AZIBs, incorporating MnO2@PDA cathode material, consequently exhibit a satisfactory cycling capacity (412 mAh g−1 at 0.1 A g−1) and a superb specific energy (561.6 Wh kg−1 at 136.34 W kg−1). This work provides a new path for design strategies and catalytic mechanisms of MnO2@PDA cathode.

Revealing Asymmetric Phase Transformation of the BiVO4 Anodes for Potassium-Ion Batteries by In Situ Transmission Electron Microscopy.

Potassium-ion batteries (PIBs) have emerged as a promising alternative to lithium-ion batteries (LIBs), thanks to the cost-effectiveness of potassium resources and a favorable redox potential of approximately -2.936 V. The monoclinic BiVO4, known for its layered structure, shows noteworthy electrochemical properties when utilized as an anode material for both LIBs and sodium-ion batteries. However, the fundamental electrochemical reaction mechanisms of the BiVO4 anode during the potassium insertion/extraction processes remain unclear. Here, we constructed a BiVO4 anode PIB inside the transmission electron microscope (TEM) to explore the real-time potassiation/depotassiation behaviors of BiVO4 during electrochemical cycling. Utilizing the state-of-art in situ TEM technique, the BiVO4 nanorods are found to undergo an asymmetric phase transformation for the first time, where the pristine BiVO4 material is transformed into an amorphous KxBiVO4 phase after the first cycle. More interestingly, the anode materials near and far from the potassium source exhibit opposite volume-changing trends under the same voltage potential. Also, this phenomenon should be attributed to the mass flow of the unstable K-Bi alloy under the electric field. Our findings provide significant insights into the electrochemical mechanism of BiVO4 nanorods during the potassiation/depotassiation process, with the hope of assistance in designing anodes for high-performance PIBs.

Rectification of high-frequency artifacts in EIS data of three-electrode Li-ion cells

The use of a reference electrode and the analysis of Electrochemical Impedance Spectroscopy (EIS) data recorded in three-electrode configuration are beneficial for understanding the underlying electrochemical reaction mechanisms in Li-ion batteries. However, analysis of EIS data recorded both in two-electrode and especially three-electrode configurations is prone to misinterpretation due to presence of unidentified artifacts. Using the commercially available instrument (Biologic VMP3), EIS data is recorded simultaneously for both working and counter electrodes in three-electrode five-wire configuration and are algebraically summed to obtain the data for two-electrode configuration. This data is then compared to that recorded in two-electrode configuration. This arrangement of instrument helps in identifying the otherwise hidden and anomalous features, such as a high-frequency arc and extended solid electrolyte interphase (SEI) region, in the three-electrode configuration and the reason for their absence in the two-electrode configuration. Moreover, these additional features are found State-of-Charge (SoC) i.e., cell-electrochemistry dependent and can be highly influenced by the resistance of current/potential measuring leads. Additionally, a new methodology is established to rectify the EIS data and obtain ‘artifact-free’ electrochemical data.

Electrochemical behavior and reaction mechanism of nano-BiOBr/rGO composite micro flower with strong interface coupling as potassium-ion battery anodes

To explore the potential of bismuth oxybromide (BiOBr) as anodes for high-performance potassium (K)-ion batteries and understand its potassium storage mechanism, a novel nano-BiOBr/reduced graphene oxide (rGO) composite micro flower (labelled as SI-coupled nano-BiOBr/rGO micro flower), where nano-BiOBr slices are firmly anchored on rGO by strong interface coupling, is constructed. Unique microstructure accompanied by C-Bi bonds at the interface between BiOBr and rGO endows it with abundant high-speed charge transfer channels and excellent structural stability. As a result, it exhibits an excellent rate performance (a high reversible capacity of 278 mAh/g at 5 A/g) and a remarkable long-term cycling stability maintaining 95.4 % after 1000 cycles at 2.5 A/g. Furthermore, it is also found that SI-coupled nano-BiOBr/rGO micro flower anode undergoes intercalation, conversion, and alloying (BiOBr → KzBiOBr → Bi → KBi2 → K3Bi2 → K3Bi) at the initial discharge process, and the subsequent charge process is only reversible dealloying and conversion reaction (K3Bi → K3Bi2 → KBi2 → Bi → BiOxBry). This work not only demonstrates the large potential of BiOBr as high-performance K-ion battery anodes, but also elucidates for the first time its K storage mechanism.

A general methodology for the in situ construction of MxSy@N,S-C composites from L-cysteine for sodium-ion battery applications

High-capacity metal sulfides have been extensively investigated as cathode materials for secondary batteries. Despite their high capacity, the redox potential of metal sulfides is limited to 2.7 V. Therefore, researchers explored its application as a negative electrode material and discovered its exceptional electrochemical performance. However, the conventional methods for synthesizing transition metal sulfides (TMS) inevitably require an external source of sulfur for secondary sulfidation, resulting in energy dissipation. In this study, L-cystine was adopted as a polydentate ligand for the synthesis of MxSy@N, SC metal-organic frameworks, which can confine the desired carbon, nitrogen, and sulfur sources within the framework. This approach facilitates one-step sintering to obtain nitrogen-doped transition metal sulfides. The structure composition and electrochemical reaction mechanism of FeS@N,S-C as the negative electrode in Na-ion batteries were studied through scanning electron microscopy (SEM)/transmission electron microscopy (TEM) and X-ray diffraction (XRD)/X-ray photoelectron spectroscopy (XPS) analysis. The electrochemical properties of FeS@N,S-C materials were test as an example. The FeS@N, SC composite exhibited a reversible Na+ storage capacity of 724.4 mAh g−1 at a current density of 200 mA g−1, and still maintained a reversible capacity of 600.7 mAh g−1 at a current density of 2000 mA g−1, demonstrating excellent rate performance. After 200 cycles, the material was still able to retain 97.3 % of the discharge specific capacity, demonstrating fine cycle performance. It shows that the FeS@N, SC composite has rapid electron conduction ability and high sodium ion diffusion coefficient. At the same time, a rapidly charge-discharge process can be achieved with a large capacitive contribution, indicating the great potential of this material as a sodium-ion battery.

Fluorine and boron co doped porous carbon materials as an electrochemical platform in trace-level sodium nitrite sensing

Sodium nitrite (NaNO2) is a common chemical oilfield tracer in the field of reservoir geological analysis. A simple, sensitive, and accurate electrochemical detection method for detection of NaNO2 has been studied. The electrode carbon porous material was based on coal tar pitch n-pentane insoluble extractants (CTPNI) and doped with the elements of fluorine (F) and boron (B) and labeled as FB-CTPNI-PC and an electrochemical sensor modified with FB-CTPNI-PC material was constructed for rapid detection of NaNO2. The characterization results of SEM and TEM indicate that this material has certain number of pore structures, also the BET analysis showed that has main pore size distribution is around the range of 2–20 nm, with abundant mesoporous structure. Moreover, the modified electrode has a good electrocatalytic effect on NaNO2. The electrochemical reaction mechanism of NaNO2 on the surface of the modified electrode was a diffusion-controlled process involving protons. The detection range of NaNO2 can reach 0.1 mM–9.5 mM. When the S/N is 3, the sensitivity is 219.8592 A·L·cm2·mol−1 and the detection limit (LOD) is 0.011 μM. The constructed electrochemical sensor has been applied to the rapid detection of NaNO2 in real oilfield water, with recovery rates ranging from 99.7 % to 103.4 %. It is also roughly consistent with the results of ion chromatography (IC) in detecting NaNO2 in oilfield water, indicating that the sensor has high accuracy. This has provided a new prospect for oil filed tracer and detection technologies.

Recent Advances in On-Line Mass Spectrometry Toolbox for Mechanistic Studies of Organic Electrochemical Reactions.

Electrochemical reactions are very complex and involve a variety of physicochemical processes. Accurate and systematic monitoring of intermediate process changes during the reaction is essential for understanding the mechanism of electrochemical reactions and is the basis for rational design of new electrochemical reactions. On-line electrochemical analysis based on mass spectrometry (MS) has become an important tool for studying electrochemical reactions. This technique is based on different ionization and sampling means and realizes on-line analysis of electrochemical reactions by establishing electrochemistry-MS (EC-MS) coupling devices. In particular, it provides key evidence for elucidating the reaction mechanism by capturing and identifying the reactive reaction intermediates. This review will categorize various EC-MS devices and the organic electrochemical reaction systems they study, highlighting the latest research progress in recent years. It will also analyze the properties of various devices and look forward to the future development of EC-MS.

Electrocatalytic degradation of flutamide an anti-prostate cancer drug and its metabolite 4-nitro-3-(trifluoromethyl) aniline using a simple graphite/β-PbO2 electrode

Flutamide is an anti-androgen drug used to treat prostate cancer. It has been determined that this drug exists in aqueous environments at ng/L levels. On the other hand, the environmental impacts of flutamide (FLU) have not yet been determined. This paper reports a simple electrocatalytic convergent-paired strategy for the degradation of FLU and its metabolite 4-nitro-3-(trifluoromethyl) aniline (NTA) using a simple graphite/β-PbO2 anode. The prepared electrode has good electrochemical stability and lifetime (more than 60 h). The results showed that the degradation efficiency of FLU and NTA under optimal conditions (pH 5.0, pollutant concentration 138 ppm and applied current density 4.9 mA/cm2) is 86 and 99 %, respectively. Also, in the solution containing both FLU and NTA with a concentration of 138 ppm of each compound, the degradation efficiency of FLU and NTA is 82 % and 92 %, respectively. Furthermore, we have comprehensively investigated the electrochemical behavior of FLU and NTA and we compared the electrochemical similarities and differences of the drug with its metabolite, and also reported important data such as electrochemical reaction mechanism, pH-potential relationship, and drug absorption/diffusion activity.

Reasonable design of PBA-derived interfacial modified ternary compounds and hollow structure materials in high-performance asymmetric supercapacitors

Prussian blue analogues (PBA), common metal-organic frameworks (MOFs), are typically binary metal compounds. In this study, chromium was incorporated during the preparation of nickel‑cobalt PBA, resulting in the adjustment of the micro-morphology of PBA and the synthesis of small-sized PBA (sPBA) electrode materials with diameters ranging from 20 to 30 nm. These materials underwent various interfacial modifications to yield ternary metal phosphide (sPBA-P) and hollow nanostructures (sPBA-C). Additionally, by integrating graphene oxide (GO) as the growth substrate, successful preparation of GO@sPBA-P and GO@sPBA-C electrode materials was achieved. Significantly, these materials showcase outstanding electrochemical properties and interesting interfacial reactions when employed as cathode and anode components. Through a comprehensive series of characterization analyses, the electrochemical properties and reaction mechanisms of these materials were thoroughly investigated. Ultimately, an asymmetric supercapacitor (ASC) was assembled using the synthesized GO@sPBA-P and GO@sPBA-C to explore the material's potential in energy materials applications.

Charge injection mediated by inverse micelles in nonpolar solvents: A microscopic model

HypothesisNonpolar solvents with added charge control agents are widely used in various applications, such as E-paper displays. In spite of previous work, the mechanisms governing charge generation in nonpolar liquids, particularly those induced by electrochemical reactions at the liquid-solid interface, are not completely understood. We hypothesize that a physics-based model, according to the modified Butler–Volmer equation, can be used to quantitatively predict the injection of charges and the corresponding currents, in nonpolar solvents with surfactants. Simulation and ExperimentsWe propose a model to describe the migration and charge generation of inverse micelles. In addition to the mechanisms of electromigration, diffusion and charge generation via disproportionation that were introduced in earlier models, we include charge generation via electron injection at the electrodes using a microscopically justified expression as opposed to the previously used semi-empirical approaches. To validate our model, we compare its results to experimental current measurements in a simplified, effectively 1D, geometry. FindingsWe find that the incorporation of both bulk and electrochemical reaction mechanisms in the model can effectively explain the experimental steady-state currents in a wide range of concentrations, voltages (0.5 V-5 V), and cell thicknesses. These numerical results of currents at longer time scales show a steady-state current only when both bulk and electrochemical reactions are taken into account. Moreover, we have observed in our simulation that at low applied voltages, the electric field in the bulk is fully shielded, and the steady-state current in this low-voltage regime is governed by the charge injection at the electrodes. Conversely, when the voltage is high enough and the electric field remains partially unscreened, the bulk disproportionation mechanism dominates the current generation. This also explains why we observe a non-Ohmic behavior where the steady-state currents at high voltages are independent of applied voltage. Hence, by elucidating the physical processes underlying the experimental observations, our model offers a more profound comprehension of charge transport in these systems, which could facilitate advancements in the design of enhanced E-ink displays and smart windows.

Energy storage chemistry: Atomic and electronic fundamental understanding insights for high-performance supercapacitors

The scarcity of fuels, high pollution levels, climate change, and other major environmental issues are critical challenges that modern societies are facing, mostly originating from fossil fuels-based economies. These challenges can be addressed by developing green, eco-friendly, inexpensive energy sources and energy storage devices. Electrochemical energy storage materials possess high capacitance and superior power density. To engineer highly efficient next-generation electrochemical energy storage devices, the mechanisms of electrochemical reactions and redox behavior must be probed in operational environments. They can be studied by investigating atomic and electronic structures using in situ x-ray absorption spectroscopy (XAS) analysis. Such a technique has attracted substantial research and development interest in the field of energy science for over a decade. The mechanisms of charge/discharge, carrier transport, and ion intercalation/deintercalation can be elucidated. Supercapacitors generally store energy by two specific mechanisms—pseudocapacitance and electrochemical double-layer capacitance. In situ XAS is a powerful tool for probing and understanding these mechanisms. In this Review, both soft and hard x rays are used for the in situ XAS analysis of various representative electrochemical energy storage systems. This Review also showcases some of the highly efficient energy and power density candidates. Furthermore, the importance of synchrotron-based x-ray spectroscopy characterization techniques is enlightened. The impact of the electronic structure, local atomic structure, and electronically active elements/sites of the typical electrochemical energy storage candidates in operational conditions is elucidated. Regarding electrochemical energy storage mechanisms in their respective working environments, the unknown valence states and reversible/irreversible nature of elements, local hybridization, delocalized d-electrons spin states, participation of coordination shells, disorder, and faradaic/non-faradaic behavior are thoroughly discussed. Finally, the future direction of in situ XAS analysis combined with spatial chemical mapping from operando scanning transmission x-ray microscopy and other emerging characterization techniques is presented and discussed.

Intercalation of Al3+ into Prussian Blue Analogues from Nonaqueous Electrolytes.

Nonaqueous aluminum-ion batteries (AIBs) provide advantages, such as high energy density, enhanced safety, and reduced corrosion, making them ideal for advanced energy storage solutions. A key challenge faced by AIBs is the lack of suitable cathode materials for rapid Al-ion insertion /extraction. Herein, K2Mn[Fe(CN)6] 2H2O (KMHCF) is innovatively chosen as a model to investigate the aluminum storage performance of Prussian blue analogues in nonaqueous AIBs. As anticipated, the KMHCF allows for reversible aluminum storage and exhibits characteristic charge/discharge plateaus. Furthermore, carbon combined highly crystalline KMHCF (HC-KMHCF@C) is synthesized through a chelator-assisted preparation method in combination with an in situ carbon compositing technique. With reduced [Fe(CN)6]4⁻ defects, lower interstitial water content, and enhanced conductivity, HC-KMHCF@C exhibits a high aluminum storage capacity (146.2 mAh g⁻¹ at 0.5 A g⁻¹) and satisfactory cycling performance (maintaining 86.4 mAh g⁻¹ after 800 cycles). The electrochemical reaction mechanism of HC-KMHCF@C is investigated in detail. During the initial charge, K⁺ ions are extracted, shifting the structure from monoclinic to cubic. In subsequent cycles, reversible Al3+ insertion and extraction cause the structure to alternate between monoclinic and cubic phases.

Incorporating Ag into Nd-Succinate MOF: Tunned electrochemical supercapacitor behaviour of Ag modified Nd-Succinate and electrochemical reaction mechanism

The electrode materials must be tailored to achieve higher energy and power densities and thus improve the supercapacitor's performance. This study explores the impact of incorporating Silver (Ag) into a Neodymium-Succinate Metal Organic Framework (Nd-Succinate) on supercapacitor behaviour. Initially, the Nd-Succinate MOF was characterized by structural, morphological, and spectroscopic characterizations. Subsequently, Ag/Nd-Succinate was synthesized and characterized. The electrochemical performance of Ag/Nd-Succinate was evaluated in a 6 M KOH electrolyte; the results indicated a significant enhancement in supercapacitor performance upon incorporating Ag into parent Nd-Succinate. From galvanostatic Charge-Discharge cycles (GCD), the capacitance for Ag/Nd-Succinate was determined to be 1389 F/g, i.e., 42 % higher than that of bare Nd-Succinate which was measured at 978 F/g. at a current density of 1.25 A/g. Ag/Nd-Succinate showcased an 89 % retention value for multiple retention cycles, slightly higher than the retention value obtained (84 %) for Nd-Succinate. The results of electrochemical experiments (Cyclic voltammetry (CV) and Electrochemical Impedance Spectra (EIS)) provided information about the nature of electron transfer and capacitance enhancement upon the introduction of Ag into Nd-Succinate. These findings provide valuable information on modifying MOFs and introducing metal that will help produce high-performance supercapacitor electrodes.

Transmembrane Graphene as an Electron Tunnel to Regulate the Intracellular Redox State.

Cellular redox homeostasis is essential for maintaining cellular activities, such as DNA synthesis and gene expression. Inspired by this, new therapeutic interventions have been rapidly developed to modulate the intracellular redox state using artificial transmembrane electron transport. However, current approaches that rely on external electric field polarization can disrupt cellular functions, limiting their in vivo application. Therefore, it is crucial to develop novel electric-field-free modulation methods. In this work, we for the first time found that graphene could spontaneously insert into living cell membranes and serve as an electron tunnel to regulate intracellular reactive oxygen species and NADH based on the spontaneous bipolar electrochemical reaction mechanism. This work provides a wireless and electric-field-free approach to regulating cellular redox states directly and offers possibilities for biological applications such as cell process intervention and treatment for neurodegenerative diseases.

In Situ Characterization Techniques for Electrochemical Nitrogen Reduction Reaction.

The electrochemical reduction of nitrogen to produce ammonia is pivotal in modern society due to its environmental friendliness and the substantial influence that ammonia has on food, chemicals, and energy. However, the current electrochemical nitrogen reduction reaction (NRR) mechanism is still imperfect, which seriously impedes the development of NRR. In situ characterization techniques offer insight into the alterations taking place at the electrode/electrolyte interface throughout the NRR process, thereby helping us to explore the NRR mechanism in-depth and ultimately promote the development of efficient catalytic systems for NRR. Herein, we introduce the popular theories and mechanisms of the electrochemical NRR and provide an extensive overview on the application of various in situ characterization approaches for on-site detection of reaction intermediates and catalyst transformations during electrocatalytic NRR processes, including different optical techniques, X-ray-based techniques, electron microscopy, and scanning probe microscopy. Finally, some major challenges and future directions of these in situ techniques are proposed.

Scaling of Planar Sodium‐Nickel Chloride Battery Cells to 90 cm2 Active Area

High‐temperature sodium‐nickel chloride (Na‐NiCl2) batteries offer a competitive solution for stationary energy storage due to their long‐term stability, high energy efficiency, and sustainable raw materials. However, scaling up this technology faces challenges related to the costly integration of tubular Na‐β''‐alumina ceramic electrolytes into hermetically sealed battery cells. Alternative cell designs with a planar Na‐β''‐alumina ceramic electrolyte have been a focus of research for many years, and a series of achievements were made on cell design, on reduction of the operating temperature, and on the analysis of electrochemical reaction mechanisms. However, the data presented in these reports was derived from laboratory‐scale cells with small area (1‐5 cm2). To date, there has been no research conducted on enlarging planar cells to an economically viable size. Here we report the fabrication of large planar Na‐β''‐alumina electrolytes and their integration into planar Na‐NiCl2 cells with 90 cm2 active area and >7 Ah capacity. Our cell design enabled cycling at 300 °C for three months, transferring a cumulative capacity of 323 Ah. We discuss design and engineering considerations for large planar high‐temperature cells emphasizing the need for cell stacking to compete with tubular Na‐NiCl2 batteries in terms of mass‐specific energy.

Facile and efficient fabrication of Cu1.04Mn0.96O2 nanosheet anodes with superior electrochemical lithium storage capability

In this work, Cu1.04Mn0.96O2 nanosheets were synthesized via a simple hydrothermal method, and their electrochemical lithium storage properties and reaction mechanisms were investigated. The nanosheet structure effectively promotes electron transfer and shortens the transport path. Additionally, the partial substitution of Cu for Mn decreases the Jahn-Teller distortion of the MnO6 octahedron. Employing as an anode for Li-ion batteries, the specific capacity reached 610.91 mAh g−1 after 100 cycles at a current density of 100 mA g−1.

(Invited) Understanding Electrochemical Reaction Mechanisms of Sulfur in All-Solid-State Batteries through Operando and Theoretical Studies

All-solid-state lithium-sulfur batteries (ASLSBs) have been considered a promising next-generation energy storage technology due to their remarkable safety and high energy density. In ASLSBs, the electrochemical pathways are intrinsically different from conventional Li-S batteries using liquid electrolytes. However, the mechanism still lacks clear identification and deep understanding. Herein, for the first time, we investigated the chemistries and explored the electrochemical reaction mechanism in ASLSBs through coupling operando Raman spectroscopy and ex-situ X-ray absorption spectroscopy. We proved that no long-chain lithium polysulfides (Li2Sn, 4≤n≤8) were formed during the redox reactions, but a short-chain polysulfide (Li2S2) intermediate phase formation was identified in the conversion between active material S8 and reduction product Li2S. This evidence explains the electrochemical behavior differences of Li-S batteries when using liquid and solid electrolytes. Moreover, there are partial S8 and Li2S2 remaining at the cathode even at fully lithiation stage, suggesting the sluggish reaction kinetics in the ASLSBs. This study revealed the generation of Li2S2 intermediates in ASLSBs, inspiring future research to further improve the performance of ASLSBs through completing the conversions and promoting reaction kinetics in ASLSBs.