Electrochemical Interface Research Articles

Enhancing Hydrogen Oxidation and Evolution Kinetics by Tuning the Interfacial Hydrogen-Bonding Environment on Functionalized Platinum Surfaces.

Developing efficient catalytic systems for the hydrogen oxidation and evolution reactions (HOR/HER) is essential in the world's transition to renewable energy. There is a growing recognition that the HOR/HER activity depends on properties of the electrochemical interface, rather than just the composition and structure of the catalyst. Herein, we demonstrate that specifically adsorbed organic additives (theophylline derivatives) could enhance the intrinsic HOR/HER activity in base on polycrystalline Pt by up to a factor of 3 via introducing weakly hydrogen-bonded water, as confirmed by in situ surface enhanced infrared and Raman spectroscopies. Optimal HOR/HER activity is achieved on a 7-n-butyltheophylline decorated Pt surface, which sufficiently disrupts the hydrogen bonding network in the double layer without depleting the interfacial water. This work demonstrates the promise of electrochemical interfacial engineering as a strategy to boost electrocatalytic performance.

In Situ Raman Observation of Dynamically Structural Transformation Induced by Electrochemical Lithium Intercalation and Deintercalation from Multi‐Electrochromic V2O5 Thin Films

AbstractUnderstanding the dynamic nature of electrochemical interface induced by ion transfer is of great significance. Herein, in situ Raman spectroscopy combined with electrochemistry has been developed to real‐time monitor the transfer of lithium ions at electrode‐electrolyte interface and reveal the associated structure and performance variation of the vanadium pentoxide (V2O5) thin films on the indium tin oxide/silver/aluminum zinc oxide/poly(ethylene terephthalate) (ITO/Ag/AZO/PET) substrates. It is demonstrated that the Raman active/silent states of the vibrational modes of VO, V3O, and VO bonds, as well as the transformation of the V2O5 thin films from V2O5 to lithium vanadate (LixV2O5), can be reversibly changed with reversible extraction/insertion of lithium ions. In situ UV‐vis spectroscopy in combination with in situ Raman analysis is applied to show that the reversible evolutions involving V2O5/LixV2O5 and VO bonding characteristic contribute to the multi‐color electrochromic characteristic of the V2O5 thin films enabling a superior optical modulation of up to 75.41%. This experimental approach establishes a significative guideline for the more elaborate research on the dynamic nature of electrochemical interface.

Learning from the Heterogeneity at Electrochemical Interfaces.

Understanding the structure-activity relationship at electrochemical interfaces is crucial in improving the performance of practical electrochemical devices, ranging from fuel cells, electrolyzers, and batteries to electrochemical sensors. However, functional electrochemical interfaces are often complex and contain various surface structures, creating heterogeneity in electrochemical activity. In this Perspective, we highlight the role of heterogeneity in electrochemistry, especially in the context of electrocatalysis. Current methods for revealing the heterogeneity at electrochemical interfaces, including nanoelectrochemistry tools and single-entity approaches, are discussed. Lastly, we provide perspectives on what one can learn by studying heterogeneity and how one can use heterogeneity to design more efficient electrochemical devices.

A Review of the Application of Modified Separators in Inhibiting the "shuttle effect" of Lithium-Sulfur Batteries.

Lithium-sulfur batteries with high theoretical specific capacity and high energy density are considered to be one of the most promising energy storage devices. However, the “shuttle effect” caused by the soluble polysulphide intermediates migrating back and forth between the positive and negative electrodes significantly reduces the active substance content of the battery and hinders the commercial applications of lithium–sulfur batteries. The separator being far from the electrochemical reaction interface and in close contact with the electrode poses an important barrier to polysulfide shuttle. Therefore, the electrochemical performance including coulombic efficiency and cycle stability of lithium–sulfur batteries can be effectively improved by rationally designing the separator. In this paper, the research progress of the modification of lithium–sulfur battery separators is reviewed from the perspectives of adsorption effect, electrostatic effect, and steric hindrance effect, and a novel modification of the lithium–sulfur battery separator is prospected.

Electrokinetically augmented load bearing capacity of a deformable microfluidic channel

Electrokinetics of deformable interfaces holds the key in developing bio-mimetic micro-devices for probing microvascular physiology and performing in vitro bio-analytical procedures. While such systems have been analyzed in the literature with the aid of a set of simplifying assumptions to some extent, implications of axial modulations in the surface potential and interfacial slip, otherwise ominous artifacts of the coupling between intrinsic electro-chemistry and substrate wettability in practical realms of surface engineering, remain grossly unaddressed in the same context. Here, we bring out the interplay of the wall compliance, periodically modulated surface potential, and patterned interfacial slip that is itself coupled with the interfacial electrochemistry, toward altering the internal hydrodynamics of a deformable microfluidic channel. Manifested in terms of a perturbed pressure field, this essentially leads to an alteration in the load bearing capacity of the concerned electro-mechanical system. By exploiting this unique coupling of the interfacial electro-mechanics, hydrodynamics, and substrate elasticity, we further demonstrate the plausibility of a significant augmentation in the load bearing capacity of the resulting system, over favorable parametric regimes. This opens up emerging possibilities of developing novel electro-kinetically modulated lubricated systems with giant augmentations in their load bearing performance.

Biochar-supported Cu nanocluster as an electrochemical ultrasensitive interface for ractopamine sensing.

Electrochemical sensors actually involve an electrocatalytic process involving an efficient and selective energy conversion that is related to the morphology and size of the interface of the modified materials. Ultrasmall nanoclusters or single atoms generate a greater catalytic ability than normal nanomaterials. In this study biochar-supported Cu nanoclusters (CuNCs@CNFs) were fabricated via a carbon confinement synthesis method toward ultrasensitive electrochemical sensing of ractopamine (RAC). RAC is a β-adrenergic receptor agonist that is illegally used as a feed additive to significantly improve muscle accretion, resulting in RAC accumulation in meat-based food products. The unique structure of CuNCs@CNFs and the interconnectivity between the CuNCs and the CNFs enable the nanocomposite to significantly enhance conductivity and electrocatalytic activity. Using the CuNCs@CNFs-based sensor, RAC was determined with a high sensitivity of 1641 μA μM-1 cm-2. The feasibility of detecting RAC in spiked meat samples was also carried out with satisfactory recoveries ranging from 91.39% to 94.58%.

Au@BSA prepared under alkaline conditions as an electrochemical non-enzymatic glucose sensor interface

Au@BSA prepared under alkaline conditions as an electrochemical non-enzymatic glucose sensor interface

Interplay between electrochemistry and optical imaging: The whole is greater than the sum of the parts

Optical techniques can afford a powerful characterisation of the solid–liquid interface that is composed of an electrode immersed in an electrolyte. While a typical electrochemical measurement such as current intensity is averaged over the entire electrode surface, the access to surface heterogeneity can provide an increased level of information enabling to rationalise and optimise the performance of chemical or biochemical sensors. In this opinion article, we will briefly review the different strategies developed to translate an electrochemical process into a luminescence signal. Also, several key examples will be selected and commented in order to highlight the key advantages of coupling electrochemistry with optical imaging, essentially fluorescence and electrochemiluminescence. • Coupling electrochemistry with optical microscopy offers a unique way to image the electrochemical interface. • The main strategies rely on using pH-sensitive dyes, electrofluorogenic species or local fluorescence quenching. • The coupling gives access to surface heterogeneity to improve the performance of biosensors. • In electrochemiluminescence, mechanistic pathways are validated by imaging the working and counter electrodes.

Electrolyte-philic and thermal-resistant polyimide separator enhances the performance of flexible silicon/carbon nanofibers for lithium-ion batteries

It is still challenging to construct a stable silicon/electrolyte interface to inhibit the mechanical fracture of Si particles and repeated formation of a solid electrolyte interface layer. The separator is a vital component in lithium-ion batteries, however, commercial polyolefin separators suffer from low thermal stability and poor electrolyte wettability. Herein, a polyimide separator is reported to achieve a stable interface of silicon anode due to its high polarity, outstanding electrolyte absorption, and reduction of side reactions. The binder-free self-standing silicon carbon (Si@C) nanofiber composite is designed by a facile electrospinning method and subsequent pyrolysis, where the nanosized Si particles are confined in polyimide-derived carbon nanofibers to form a bamboo-like morphology with good flexibility. Such flexible nanofiber film with cross-linked 3D network structure is important to increase energy density of batteries, mitigate the growth of new interfaces, and avoid the known issues of side reaction during the electrochemical operation. Encouragingly, the 40 %-Si@C composite illustrates an improved lithium storage property with high reversible capacity of 1819.7 mAh g−1 at 0.2 A g−1, excellent rate capability and cycling stability, demonstrating superiority of the film electrode and polyimide separator. This work provides new insights for stabilizing the interface electrochemistry of alloy anodes for the development of next-generation flexible energy storage devices.

Enhanced interfacial electron transfer by constructing NiCo-LDH hollow nanocages decorated N-doped graphene quantum dots heterojunction for high-performance supercapacitors

Nickel–cobalt layered double hydroxides (NiCo-LDHs) are highly promising materials for energy storage electrodes. However, the poor conductivity and easy agglomeration limit their practical application. Herein, the novel hollow nanocage architecture of NiCo-LDH nanosheets (H-NiCo-LDH) decorated N-doped graphene quantum dots (N-GQDs) is constructed using zeolitic imidazolate framework-67 (ZIF-67) as self-sacrificed template. The hollow nanocage structure suppresses the agglomeration of nanosheets and enlarges the electrochemical interface, while the decoration of N-GQDs effectively improves electrical conductivity and provides more abundant active sites. More importantly, HRTEM characterization shows the construction of heterojunctions between H-NiCo-LDH and N-GQDs, and the interfacial charge redistribution through p-n heterojunction promotes interfacial electron transfer and enhances redox activity. Consequently, the N-GQD/H-NiCo-LDH electrode delivers a high specific capacitance of 2347 F g−1 (326 mA h g−1) at 1 A g−1 with excellent rate performance (82% capacitance retention at 10 A g−1). The assembled asymmetric supercapacitor by N-GQD/H-NiCo-LDH and active carbon exhibits an energy density of 52.1 W h kg−1 at a power density of 770 W kg−1 with remarkable cycling stability (80.5% capacitance retention after 5000 cycles). The hollow nanocage structure and enhanced electrical conductivity of N-GQDs make the N-GQD/H-NiCo-LDH a highly promising material for electrochemical energy storage applications.

A Happy Get-Together - Probing Electrochemical Interfaces by Non-Linear Vibrational Spectroscopy.

Electrochemical interfaces are key structures in energy storage and catalysis. Hence, a molecular understanding of the active sites at these interfaces, their solvation, the structure of adsorbates, and the formation of solid-electrolyte interfaces are crucial for an in-depth mechanistic understanding of their function. Vibrational sum-frequency generation (VSFG) spectroscopy has emerged as an operando spectroscopic technique to monitor complex electrochemical interfaces due to its intrinsic interface sensitivity and chemical specificity. Thus, this review discusses the happy get-together between VSFG spectroscopy and electrochemical interfaces. Methodological approaches for answering core issues associated with the behavior of adsorbates on electrodes, the structure of solvent adlayers, the transient formation of reaction intermediates, and the emergence of solid electrolyte interphase in battery research are assessed to provide a critical inventory of highly promising avenues to bring optical spectroscopy to use in modern material research in energy conversion and storage.

Manipulating Interfacial Dissolution–Redeposition Dynamics to Resynthesize Electrode Surface Chemistry

The solid–liquid electrochemical interface offers a reactive environment for interfacial reactions to tailor electrode surface chemistry under operating conditions. Herein, we demonstrate that the dissolution and redeposition kinetics of transition metal cations, a ubiquitous phenomenon at the electrochemical interface, can be manipulated to regulate the chemical composition and crystal structure of the electrode surface, as well as the overall electrochemical performance. Foreign cations (e.g., Ti4+), either added as electrolyte additives or dissolved from surface coatings, can rapidly participate in the electrode dissolution–redeposition process and facilitate the establishment of the dissolution–redeposition equilibrium. Our work expands the control over the electrochemical reactions at the solid–liquid interface and provides new insights into interfacial studies in electrochemistry and surface science.

Gaining Insight into the Electrochemical Interface Dynamics in an Organic Redox Flow Battery with a Kinetic Monte Carlo Approach.

Finding low-cost and nontoxic redox couples for organic redox flow batteries is challenging due to unrevealed reaction mechanisms and side reactions. In this study, a 3D kinetic Monte Carlo model to study the electrode-anolyte interface of a methyl viologen-based organic redox flow battery is presented. This model captures various electrode processes, such as ionic displacement and degradation of active materials. The workflow consists of input parameters obtained from density functional theory calculations, a kinetic Monte Carlo algorithm to simulate the discharging process, and an electric double layer model to account for the electric field distribution near the electrode surface. Galvanostatic discharge is simulated at different anolyte concentrations and input current densities, which demonstrate that the model captured the formation of the electrical double layer due to ionic transport. The simulated electrochemical kinetics (potential, charge density) are found to be in agreement with the Nernst equation and the obtained EDL structure corresponded with published molecular dynamics results. The model's flexibility allows further applications of simulating the behavior of different redox couples and makes it possible to consider other molecular-scale phenomena. This study paves the way for computational screening of active species by assessing their potential kinetics in electrochemical environments.

Enhancing electrocatalytic reforming of CO2/CH4 with in situ exsolved metal-oxide interfaces in a solid oxide electrolysis cell

Solid oxide electrolysis cells (SOECs) can convert the electric energy into chemical energy, which is convenient for energy storage and transportation. Meanwhile, it can reduce the CO2 and CH4 in the atmosphere, thus reduce the greenhouse effect. In this paper, we demonstrate the high-efficiency electrochemical reforming of CO2/CH4 into syngas (CO and H2) in a SOEC in which we in situ construct active metal-oxide interface in perovskite cathodes to improve the coking resistance and catalyst stability. XRD, XPS, SEM and TEM analysis together confirm that the exsolution of metal-oxide interfaces on the surface of LSCM creates the active electrochemical interface to enhance the activity as well as the stability with the durable operation of CO2 and CH4 to syngas for more than 70 h and 7 redox cycles. The exsolved metal-oxide interface could also be applied for other metal-oxide catalyst for improving catalytic activity and stability.

Microenvironment Alters the Oxygen Reduction Activity of Metal/N/C Catalysts at the Triple-Phase Boundary

Metal- and nitrogen-doped carbon (M/N/C) catalysts are promising catalysts that may replace platinum in the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells. At the triple-phase boundary, the complex electrochemical interface of M/N/C catalysts involves the water film between highly dispersed active sites and aggregated ionomers, and the electrochemical behavior is different from that at the double-phase boundary, where a rotating disk electrode (RDE) is directly submerged in the aqueous solution. In this work, the ORR kinetics of the same Fe/N/C catalyst at the double-phase boundary at the RDE and the triple-phase boundary at the gas diffusion electrode (GDE) were compared to determine the microenvironmental factors that can tune the ORR activity. A model was created based on the reaction mechanism, microkinetic analysis, and local proton transport in the pores. The model fitting identified the accessible active sites and the water activity as the factors influencing the different ORR kinetics of the RDE and GDE. The surface charge and functional groups were proposed to tune the proton transport in the pores, resulting in a loss of accessible active sites when E > EQ/HQ at the GDE. Low water activity in the GDE was predicted by the model fitting. This low activity triggered a low OH* coverage and facilitated the reaction kinetics, but it limited the proton transport at the GDE. Strategies for improving proton transport are suggested for the future design of catalysts and ionomers. This study quantitatively demonstrates how the microenvironment alters the ORR kinetics of Fe/N/C catalysts.

Cation Size Effect on Oxygen Reduction Reaction in Aprotic Electrolytes

The most important cathodic process in alkali metal-air (M-O2) batteries is the electrocatalytic oxygen reduction reaction (ORR) typically forming superoxide (MO2), and peroxide (M2O2).1 Cation size in aqueous solvents have been demonstrated to affect the ORR activity due to the cation hydration energy.2 However, within aprotic electrolytes, the reaction mechanisms and the activity of ORR with respect to cation size remains undetermined.Traditionally, electrochemistry has been involved in the analysis of the reaction mechanisms of ORR. Nonetheless, this technique by itself is not suitable to identify intermediaries and products of the redox reactions taking place at the electrochemical interface. The combination of cyclic voltammetry with in situ Raman spectroscopy provide the opportunity to study and develop a fundamental understanding of the ORR under potential control, accessing reaction pathways and relating them directly to surface structure.3 In this sense, the breakthrough of Shell-Isolated Nanoparticles for Enhanced Raman Spectroscopy (SHINERS)4,5 is noteworthy. SHINERS is a non-destructive, powerful technique for surface analysis that has been demonstrated to provide SERS effect even in the absence of intrinsic roughness and without requiring Au, Ag or Cu to be used as working electrodes.3,5 In this work, electrochemical measurements and SHINERS are utilised to study the effect of cation upon electrified interfaces during ORR. Zhang, J., Zhang, X.-G., Dong, J.-C., Radjenovic, P. M., Young, D. J., Yao, J.-L., Yuan, Y.-X., Tian, Z.-Q. & Li, J.-F. Real-Time Monitoring of Surface Effects on the Oxygen Reduction Reaction Mechanism for Aprotic Na–O2 Batteries. J. Am. Chem. Soc. 143, 20049–20054 (2021).Kumeda, T., Tajiri, H., Sakata, O., Hoshi, N. & Nakamura, M. Effect of hydrophobic cations on the oxygen reduction reaction on single‒crystal platinum electrodes. Nat. Commun. 9, 1–7 (2018).Guan, S., Attard, G. A. & Wain, A. J. Observation of Substituent Effects in the Electrochemical Adsorption and Hydrogenation of Alkynes on Pt{hkl} Using SHINERS. ACS Catal. 10, 10999–11010 (2020).Li, J. F., Huang, Y. F., Ding, Y., Yang, Z. L., Li, S. B., Zhou, X. S., Fan, F. R., Zhang, W., Zhou, Z. Y., Wu, D. Y., Ren, B., Wang, Z. L. & Tian, Z. Q. Shell-isolated nanoparticle-enhanced Raman spectroscopy. Nature 464, 392–395 (2010).Galloway, T. A., Dong, J.-C., Li, J.-F., Attard, G. & Hardwick, L. J. Oxygen reactions on Pt{hkl} in a non-aqueous Na+ electrolyte: site selective stabilisation of a sodium peroxy species. Chem. Sci. 10, 2956–2964 (2019).

(Invited) Tailored Electrochemical Interfaces for the Production of Renewable Fuels

Tailoring the structure of the electrochemical interface at the atomic level is key to design new electrocatalysts for renewable energy conversion and storage. This talk will focus on novel catalyst materials and engineered interfaces for electrochemical energy conversion. In particular, I will discuss structure sensitivity and electrolyte effects for oxygen and carbon dioxide/carbon monoxide electrocatalysis.First, I will present our work toward understanding the structure-activity-stability relations on high surface area nanostructured Ir-based materials for oxygen evolution. Then, I will highlight the importance of carrying out model studies on Cu-based surfaces to understand the structure-properties relations for CO2 and CO reduction. We have investigated the effect of pH, specific anion adsorption and potential dependence for CO reduction on Cu single-crystalline electrodes. We show how well defined studies are essential to design efficient electrocatalysts for the production of renewable fuels.

Investigation of Hydrogen Electrode Formation on the Surface of Noble Metals (Pd, Ir, Au) Exposed to Nitrogen Atmosphere: A Comprehensive Study Using Scanning Kelvin Probe

The importance of hydrogen evolution reaction (HER) in engineering and energy conversion related applications grows stronger and it is important to develop better catalysts to enhance the efficiency of the catalytic process. The introduction of computational chemistry (e.g., DFT) into the field of electrochemistry allows general prediction and understanding of activity trends. Great progress is made in modelling the electrochemical double layer under potentiostatic control [1]. However, a reliable and feasible experimental methodology providing in-depth experimental data for improving the theoretical model is lacking, as the electrochemical interface is usually buried under bulk electrolyte, which prevents most important surface analytical techniques to be applied for its investigation. However, it could be recently shown that a hydrogen electrode forms on a palladium surface even in nitrogen atmosphere, even at very low humidity [2] . The electrochemical double layer of this “hydrogen electrode in the dry” is confined just 1-2 monolayers of adsorbed water. However, it is still fully polarizable by adjusting the hydrogen activity from the backside of the electrode and it is even possible to measure full current-potential dependencies for reactions such as e.g. oxygen reduction [3]. Hence, this could be revolutionary new approach for investigating electrochemical electrodes in operando by standard surface analytical techniques. For this however, it needs to be investigated in how far this approach can be also applied beyond palladium. Since the potential of such “electrodes in the dry” cannot be measured with standard reference electrode a Kelvin probe is used instead [2,3]. Basically, the Kelvin probe measures the Volta potential difference between sample and probe (ψ KP - ψ S), and upon suitable calibration such measurement provides the electrode potential of the sample.Evers et.al has proposed the “Hydrogen electrode in dry” concept based on adjusting the hydrogen activity (cathodic charging) from one side of a palladium sample and measuring the work function on the other side using Kelvin probe [2]. In this work, the hydrogen electrode formation in dry (<0.1% R.H) as well as humid condition (>95% R.H) for Palladium (Pd), iridium (Ir) and gold (Au) was carried out using scanning Kelvin probe method by electrochemical charging of hydrogen from entry side and subsequently measuring the Volta potential on exit side (see fig.1). The measured potential on the exit side can be related to electrode potential. Palladium showed a 1:1 correlation between applied potential and measured potential at higher hydrogen activities (between 0 to 300 mVSHE) by establishing electrochemical equilibrium in both conditions, in accordance with [1]. Though the partial pressure of water is very low (0.23mbar) in dry condition, still the hydrogen electrode formation occurred on the palladium. In the case of Ir, it shows 1:1 correlation only in humid condition and not in dry condition. Further, the hydrogen electrode formation on Ir at different partial pressures of water was investigated by controlling the humidity on the exit side of the sample and the obtained results can be attributed to slight differences of thickness of the water layer in the monolayer and even sub-monolayer range. A linear decrease in the potential was observed when increasing the humidity from low to high humidity and the correlation between potential applied from the back and potential measure in the “dry” shows a decrease in responsiveness with decreasing humidity. No correlation was observed for iridium in dry conditions and it can be attributed to presence of insufficient amount of adsorbed water. For gold no correlation was observed in both the conditions. However, a slight behavior was observed at very high activities of hydrogen. This may be due to the initial hydrophobicity of gold, which has first to overcome by a formation of a double layer. On the whole, the effect of water layer adsorption on different metals and its influence on the establishment of a hydrogen electrode at a dry surface was studied.

(Invited) Gold Electrodes Emersed from Aqueous Electrolytes: A Kelvin Probe and Infrared Spectroscopy Approach

The study of the electric double layer (solid/liquid interface) is of crucial importance for an in-depth understanding electrochemical processes. However, the electrochemical interface (or interphase) is usually buried under a barrier of bulk water which is blocking direct access for most analytical tools. One way to enable direct access is e.g. the emersed electrode concept. For this, electrodes are emersed under potential control from the electrolyte into an inert atmosphere. It was shown in prior works for emersion into UHV [1] and into humid nitrogen [2] that the electrochemical double layer seems to be kept more or less intact during this process. However, thus an electrochemical double layer is obtained that is vertically confined to just one or two monolayers, depending on the humidity of the environment. The Kelvin probe technique can be employed for measuring the resulting electrode potential of such emersed electrodes [3], often providing a linear correlation between applied potentials during the electrochemical polarization and the potentials determined after emersing the sample from the electrolyte [2]. An open question is the role of the amount of water molecules in the double layer on the electrode potential [1,2]. A powerful technique for the investigation of the structure of the water molecules in the double layer region is infrared spectroscopy. Since infrared spectroscopy techniques (using an ATR set-up) can also be applied for characterization of the electrode immersed bulk electrolyte [4], a direct comparison between these two cases is possible.For this work, NaClO4 and H2SO4 diluted aqueous solutions were used as electrolytes, which both present anions with similar specific adsorption [5]. The Kelvin probe tip was calibrated against an Ag/AgCl/KCl homemade reference electrode [6]. Different atmosphere conditions (relative humidity) were used and their effect on the emersed electrode was investigated by Kelvin probe and IR spectroscopy. Furthermore, studies employing Near Ambient Pressure X-Ray Photoelectron Spectroscopy (NAP-XPS) technique have been conducted in order to detect the presence of anions and cations in the electrochemical double-layer and also for in operando studies with different atmosphere conditions.Literature:[1] H. Neff, R. Kötz, J. Electroanal. Chem. 1983, 151, 305.[2] Z. Samec, B. W. Johnson, K. Doblhofer, Surf. Sci. 1992, 264, 440.[3] M. Rohwerder, F. Turcu, Electrochim. Acta 2007, 53, 290.[4] K. Ataka, T. Yotsuyanagi, M. Osawa, J. Phys. Chem. 1996, 100, 10664.[5] D. D. Bodé Jr., T. N. Andersen, H. Eyring, J. Phys. Chem. 1967, 71, 792.[6] M. Uebel, A. Vimalanandan, A. Laaboudi, S. Evers, M. Stratmann, D. Diesing, M. Rohwerder, Langmuir 2017, 33, 10807.

Investigation and Design of Soybean-Derived Carbon Anode Materials for Potassium-Ion Battery Applications

Lithium-ion battery (LIBs) system is one the most widely used energy storage systems in today’s renewable energy field. However, with the dramatically increased demand over the past decades and limited core material storage, concerns arise regarding its sustainability and large-scale applications. While trying to make more efficient LIBs, the studies of alternative battery systems also appear to be more and more critical. Among many newly studied battery systems, Potassium-ion batteries (PIBs) have caught our attention. With the advantage of high abundance of Potassium (K) and low redox potential of K/K+ (2.93 V vs. standard hydrogen electrode), it appears to be a perfect candidate for substituting many of the current LIBs applications. However, the absence of a suitable carbon anode has hindered the development of PIBs. Herein, we used low-cost and abundant soybean as base material and developed a high-performance hard carbon anode for PIBs. Hard carbon, produced with 500 degrees process, exhibited the highest discharge capacity of 225 mA h g-1, long lifetime of 900 cycles, and good rate capability. Benefited from low activation temperature, the soybean-derived carbon has a medium surface area, large interplanar spacing graphene layers and low degree of graphitization, which are favored by the adsorption-dominated K-ion storage mechanism. To further improve the anode efficiency, a thin layer of Al2O3 coating (~ 2 nm) was applied on the hard carbon by Atomic Layer Deposition (ALD) to function as artificial solid electrolyte interphase and increased the Coulombic efficiency from 99.0% to 99.6%. After investigating the relationship among electrochemical performance, material interface, structural design, and mechanism of potassium-ion storage, we provided new insights for the design and synthesis of carbonaceous materials with improved storage capacity and efficiency for future developments of PIBs.