Non-aqueous Electrolyte Research Articles

Influence of Electrolyte Choice on Zinc Electrodeposition.

Zinc electrodeposition serves as a crucial electrochemical process widely employed in various industries, particularly in automotive manufacturing, owing to its cost effectiveness compared to traditional methods. However, traditional zinc electrodeposition using aqueous solutions faces challenges related to toxicity and hydrogen gas generation. Non-aqueous electrolytes such as ionic liquids (ILs) and deep eutectic solvents (DESs) have gained attention, with choline-chloride-based DESs showing promise despite raising environmental concerns. In this study, zinc electrodeposition on mild steel was investigated using three distinct electrolytes: (i) halide-free aqueous solutions, (ii) chloride-based DES, and (iii) halide-free acetate-based organic solutions. The study examined the influence of deposition time on the growth of Zn on mild steel substrates from these electrolytes using physical characterization techniques, including scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicate that glycol + acetate-based non-aqueous organic solutions provide an eco-friendly alternative, exhibiting comparable efficiency, enhanced crystalline growth, and promising corrosion resistance. This research contributes valuable insights into the impact of electrolyte choice on zinc electrodeposition, offering a pathway towards more sustainable and efficient processes. Through a comprehensive comparison and analysis of these methods, it advances our understanding of the practical applications of zinc electrodeposition technology.

A Comparative Study of Degradation Behaviors of LiFePO4, LiMn2O4, and LiNi0.8Mn0.1Co0.1O2 in Different Aqueous Electrolytes

Aqueous Li-ion batteries (ALIBs) are an important class of battery chemistries owing to the intrinsic non-flammability of aqueous electrolytes. However, water is detrimental to most cathode materials and could result in rapid cell failure. Identifying the degradation mechanisms and evaluating the pros and cons of different cathode materials are crucial to guide the materials selection and maximize their electrochemical performance in ALIBs. In this study, we investigate the stability of LiFePO4 (LFP), LiMn2O4 (LMO) and LiNi0.8Mn0.1Co0.1O2 (NMC) cathodes, without protective coating, in three different aqueous electrolytes, i.e., salt-in-water, water-in-salt, and molecular crowding electrolytes. The latter two are the widely reported “water-deficient electrolytes.” LFP cycled in the molecular crowding electrolyte exhibits the best cycle life in both symmetric and full cells owing to the stable crystal structure. Mn dissolution and surface reduction accelerate the capacity decay of LMO in water-rich electrolyte. On the other hand, the bulk structural collapse leads to the degradation of NMC cathodes. LMO demonstrates better full-cell performance than NMC in water-deficient aqueous electrolytes. LFP is shown to be more promising than LMO and NMC for long-cycle-life ALIB full cells, especially in the molecular crowding electrolyte. However, none of the aqueous electrolytes studied here provide enough battery performance that can compete with conventional non-aqueous electrolytes. This work reveals the degradation mechanisms of olivine, spinel, and layered cathodes in different aqueous electrolytes and yields insights into improving electrode materials and electrolytes for ALIBs.

An All-Climate Nonaqueous Hydrogen Gas-Proton Battery.

Rechargeable hydrogen gas batteries, driven by hydrogen evolution and oxidation reactions (HER/HOR), are emerging grid-scale energy storage technologies owing to their low cost and superb cycle life. However, compared with aqueous electrolytes, the HER/HOR activities in nonaqueous electrolytes have rarely been studied. Here, for the first time, we develop a nonaqueous proton electrolyte (NAPE) for a high-performance hydrogen gas-proton battery for all-climate energy storage applications. The advanced nonaqueous hydrogen gas-proton battery (NAHPB) assembled with a representative V2(PO4)3 cathode and H2 anode in a NAPE exhibits a high discharge capacity of 165 mAh g-1 at 1 C at room temperature. It also efficiently operates under all-climate conditions (from -30 to +70 °C) with an excellent electrochemical performance. Our findings offer a new direction for designing nonaqueous proton batteries in a wide temperature range.

Pd-H as an irreplaceable model system for the study of hydrogen electrosorption in aqueous and non-aqueous electrolytes

Even though Pd-H system has been known since the nineteenth century, it is still of interest to scientists. Pd thin film electrode (called as a Limited Volume Electrode – LVE) is able to electrosorb hydrogen form aqueous (acid, base) and non-aqueous electrolytes (e.g. ionic liquids). Therefore Pd-H is an irreplaceable model system for the study of hydrogen electrosorption in different media. The paper presents: (1) short overview of the study of hydrogen sorption in Pd, (2) the detailed description of the electrochemical measurement methods and (3) the equations for the determination of hydrogen electrosorption charges needed to hydrogen electrosorption isotherms creation. The presented approach can be applied for laboratory work. The results show that Pd-LVE can be effectively used as a model system before the studies of multicomponent hydrogen storage alloys (e.g. AB5 alloys).Graphical abstract

Precise analyses of photoelectrochemical reactions on particulate Zn0.25Cd0.75Se photoanodes in nonaqueous electrolytes using Ru bipyridyl complexes as a probe.

Recombination of photoexcited carriers at interface states is generally believed to strongly govern the photoelectrochemical (PEC) performance of semiconductors in electrolytes. Sacrificial reagents (e.g., methanol or Na2SO3) are often used to assess the ideal PEC performance of photoanodes in cases of minimised interfacial recombination kinetics as well as accelerated surface reaction kinetics. However, varying the sacrificial reagents in the electrolyte means simultaneously changing the equilibrium potential and the number of electrons required to perform the sacrificial reaction, and thus the thermodynamic and kinetic aspects of the PEC reactions cannot be distinguished. In the present study, we propose an alternative methodology to experimentally evaluate the energy levels of interfacial recombination centres that can reduce PEC performance. We prepare nonaqueous electrolytes containing three different Ru complexes with different bipyridyl ligands; redox reactions of Ru complexes represent one-electron processes with similar charge transfer rates and diffusion coefficients. Therefore, the Ru complexes can serve as a probe to isolate and evaluate only the thermodynamic aspects of PEC reactions. Recombination centres at the interface between a nonaqueous electrolyte and a Zn0.25Cd0.75Se particulate photoanode are elucidated using this method as a model case. The energy level at which photocorrosion proceeds is also determined.

Spectroelectrochemical determination of thiolate self-assembled monolayer adsorptive stability in aqueous and non-aqueous electrolytes.

Self-assembled monolayers (SAM) are ubiquitous in studies of modified electrodes for sensing, electrocatalysis, and environmental and energy applications. However, determining their adsorptive stability is crucial to ensure robust experiments. In this work, the stable potential window (SPW) in which a SAM-covered electrode can function without inducing SAM desorption was determined for aromatic SAMs on gold electrodes in aqueous and non-aqueous solvents. The SPWs were determined by employing cyclic voltammetry, attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), and surface plasmon resonance (SPR). The electrochemical and spectroscopic findings concluded that all the aromatic SAMs used displayed similar trends and SPWs. In aqueous systems, the SPW lies between the reductive desorption and oxidative desorption, with pH being the decisive factor affecting the range of the SPW, with the widest SPW observed at pH 1. In the non-aqueous electrolytes, the desorption of SAMs was observed to be slow and progressive. The polarity of the solvent was the main factor in determining the SPW. The lower the polarity of the solvent, the larger the SPW, with 1-butanol displaying the widest SPW. This work showcases the power of spectroelectrochemical analysis and provides ample future directions for the use of non-polar solvents to increase SAM stability in electrochemical applications.

Mechanism of ORR and OER in non-aqueous electrolytes: general discussion.

Mechanism of ORR and OER in non-aqueous electrolytes: general discussion.

Effect of alkali-metal cation on oxygen adsorption at Pt single-crystal electrodes in non-aqueous electrolytes.

The effect of Group 1 alkali-metal cations (Na+, K+, and Cs+) on the oxygen reduction and evolution reactions (ORR and OER) using dimethyl sulfoxide (DMSO)-based electrolytes was investigated. Cyclic voltammetry (CV) utilising different Pt-electrode surfaces (polycrystalline Pt, Pt(111) and Pt(100)) was undertaken to investigate the influence of surface structure upon the ORR and OER. For K+ and Cs+, negligible variation in the CV response (in contrast to Na+) was observed using Pt(111), Pt(100) and Pt(poly) electrodes, consistent with a weak surface-metal/superoxide complex interaction. Indeed, changes in the half-wave potentials (E1/2) and relative intensities of the redox peaks corresponding to superoxy (O2-) and peroxy (O22-) ion formation were consistent with a solution-mediated mechanism for larger cations, such as Cs+. Support for this finding was obtained via in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). During the ORR and in the presence of Cs+, O2- and weakly adsorbed caesium superoxide (CsO2) species were detected. Because DMSO was found to strongly interact with the surface at potentials associated with the ORR, CsO2 was readily displaced at more negative potentials via increased solvent adsorption at the surface. This finding highlights the important impact of the solvent during ORR/OER reactions.

Improvements in the evaluation of electrocatalytic ammonia oxidation reactions.

For a reliable evaluation of the electrocatalytic ammonia oxidation reaction (EAOR), we revised the standard electrode potentials in both aqueous and nonaqueous electrolytes using the solvation energies of ammonia. Moreover, we developed an improved assessment protocol for EAOR systems, particularly for those employing nonaqueous electrolytes and/or nitrogen-containing materials.

Inert is not inactive: origin of carbon dioxide electroreduction activity over a carbon current collector-based electrode

Commercial carbon paper (CP), a classical current collector, does not remain inert when subjected to CO2 electroreduction in a non-aqueous electrolyte.

Concluding remarks: a summary of the Faraday Discussion on rechargeable non-aqueous metal-oxygen batteries.

The Faraday Discussion on rechargeable non-aqueous metal-oxygen batteries is summarised. The remarks paper highlights the specific science contributions made in the vital areas of oxygen reduction and evolution reaction mechanisms in non-aqueous electrolytes; material developments for stable metal-oxygen battery cathodes; achieving stable metal anodes and protected interfaces; and, finally, contributions concerning the progress towards practical metal-oxygen batteries. Key conclusions associated with these papers will be highlighted in an order such that readers can identify papers that they would like to explore in more detail.

Engineering a zinc anode interphasial chemistry for acidic, alkaline and non-aqueous electrolytes

By employing 3,5-bis(trifluoromethyl) pyrazole (TFMP) as an electrolyte additive in both aqueous and non-aqueous mediums, a versatile interphase strategy is achieved. This facilitates stable Zn anodes with improved efficiency and longer cycling life.

Non-aqueous battery electrolytes: high-throughput experimentation and machine learning-aided optimization of ionic conductivity

We study the ionic conductivity of a bi-salt (LiPF6, LiFSI) and ternary solvent (EC, EMC, PC) liquid battery electrolyte with high throughput experimentation and the open source Liquid Electrolyte Composition Analysis (LECA) Machine-Learning library.

Design of sulfonimide anions for rechargeable lithium batteries.

Sulfonimide salts are considered as promising electrolyte materials in the construction of high-performant rechargeable lithium-ion batteries (LIBs) and lithium metal batteries (LMBs), owing to their delocalized negative charges, superior structural flexibility, and decent thermal/chemical stability. In this work, a historical overview of the development of sulfonimide anions in the field of electrolyte materials is presented, and the unique features of sulfonimide anions are discussed, in comparison with some popular anions [e.g., hexafluorophosphate anion (PF6-)] being employed for batteries. The key advances in the design of sulfonimide salts as electrolyte materials are scrutinized, encompassing their use in nonaqueous liquid electrolytes, ionic liquid electrolytes, and solid polymer electrolytes. Based on the existing reports and our experiences in this domain, possible research directions related to further improvement of sulfonimide-based electrolytes are highlighted. Besides demonstrating the status quo and research progress, this work also expands the structural design toolkit of sulfonimide-based electrolytes, which may accelerate the development and realization of sulfonimide anion-based electrolytes in practical LIBs/LMBs and simultaneously give new impetus to other kinds of rechargeable battery technologies (e.g., sodium and potassium batteries).

Reconciling electrolyte donicity and polarity for lithium carbon fluoride batteries

For nonaqueous electrolytes designed for carbon fluoride batteries, a higher donicity is beneficial for stabilizing positively charged carbon atoms, while a moderate polarity is favorable for detaching negatively charged fluorine atoms.

Anodic dissolution of aluminum in non-aqueous electrolyte solutions for sodium-ion batteries

The respective impact of the electrolyte and solvent, during anodic dissolution or passivation of aluminum was investigated in electrolyte solutions developed for sodium-ion batteries.

Interlayer Confined Water Enabled Pseudocapacitive Sodium-Ion Storage in Nonaqueous Electrolyte.

Electrochemical capacitors have faced the limitations of low energy density for decades, owing to the low capacity of electric double-layer capacitance (EDLC)-type positive electrodes. In this work, we reveal the functions of interlayer confined water in iron vanadate (FeV3O8.7·nH2O) for sodium-ion storage in nonaqueous electrolyte. Using an electrochemical quartz crystal microbalance, in situ Raman, and ex situ X-ray diffraction and X-ray photoelectron spectroscopy, we demonstrate that both nonfaradaic (surficial EDLC) and faradaic (pseudocapacitance-dominated Na+ intercalation) processes are involved in the charge storages. The interlayer confined water is able to accelerate the fast Na+ intercalations and is highly stable (without the removal of water or co-intercalation of [Na-diglyme]+) in the nonaqueous environment. Furthermore, coupling the pseudocapacitive FeV3O8.7·nH2O with EDLC-type activated carbon (FeVO-AC) as the positive electrode brings comprehensive enhancements, displaying the enlarged compaction density of ∼2 times, specific capacity of ∼1.5 times, and volumetric capacity of ∼3 times compared to the AC electrode. Furthermore, the as-assembled hybrid sodium-ion capacitor, consisting of an FeVO-AC positive electrode and a mesocarbon microbeads negative electrode, shows a high energy density of 108 Wh kg-1 at 108 W kg-1 and 15.3 Wh kg-1 at 8.3 kW kg-1. Our results offer an emerging route for improving both specific and volumetric energy densities of electrochemical capacitors.

Thin Reinforced Anion-Exchange Membranes for Non-Aqueous Redox Flow Battery Employing Fe/Co-Metal Complex Redox Species

Non-aqueous redox flow batteries (NARFBs) have been attracting much attention because they can significantly increase power and energy density compared to conventional RFBs. In this study, novel pore-filled anion-exchange membranes (PFAEMs) for application to a NAPFB employing metal polypyridyl complexes (i.e., Fe(bpy)32+/Fe(bpy)33+ and Co(bpy)32+/Co(bpy)33+) as the redox species are successfully developed. A porous polyethylene support with excellent solvent resistance and mechanical strength is used for membrane fabrication. The PFAEMs are prepared by filling an ionic liquid monomer containing an imidazolium group and a crosslinking agent into the pores of the support film and then performing in situ photopolymerization. As a result, the prepared membranes exhibit excellent mechanical strength and stability in a non-aqueous medium as well as high ion conductivity. In addition, a low crossover rate for redox ion species is observed for the prepared membranes because they have relatively low swelling characteristics in non-aqueous electrolyte solutions and low affinity for the metal-complex redox species compared to a commercial membrane. Consequently, the PFAEM is revealed to possess superior battery performance than a commercial membrane in the NARFB tests, showing high energy efficiency of about 85% and stable operation for 100 cycles.

Ruthenium Electrodeposition from Non-Aqueous Electrolytes Containing Divalent Ions

Ruthenium as a metal is characterized by interesting technological and aesthetic properties, which make it an ideal choice for many applications. Ruthenium is dark grey in appearance, it presents a reduced tendency to corrode, low contact resistance and high hardness. When applied in the form of thin films, it can be used in jewels production, protection of electrical contacts, deposition of barrier layers in microelectronics and manufacturing of interconnects in integrated circuits [1].Ruthenium layers can be advantageously deposited exploiting electrodeposition, typically from aqueous sulfamate based electrolytes containing the metal in the form of a complex known as μ-nitridobisaquatetrachlororuthenate [Ru2(μ-N)(H2O)2Cl8]3-. These baths are routinely used at the industrial level and provide good coatings at acceptable cathodic efficiencies. However, ruthenium tends to oxidize in aqueous environment and the resulting deposits can contain impurities or oxides. In addition, the electrodeposition of ruthenium in water-based electrolytes presents difficulties when thick and crack-free coatings are required.In an attempt to solve these limitations, the use of non-aqueous electrolytes for the deposition of ruthenium coatings has been proposed. The substitution of water with alternative solvents can potentially relieve the problem of ruthenium oxidation. Moreover, non-aqueous electrolytes are characterized by wide potential windows, which translate into a reduction in the entity of parasitic hydrogen evolution reactions. Consequently, the properties of the deposit obtained can be potentially improved. In the context of non-aqueous electrolytes, ruthenium has been deposited from water and air stable ionic liquids [2, 3] and from deep eutectic solvents [4].With respect to our previous paper on the deposition of ruthenium [4], where the metal was deposited from the (IV) oxidation state, the present work describes a diametrically different approach. Indeed, we investigate the electrodeposition of ruthenium layers from a non-aqueous electrolyte based on ethylene glycol and containing the metal in its divalent state. The (II) oxidation state is obtained by reducing trivalent RuCl3 with ascorbic acid. A complete physical and electrochemical characterization of the resulting electrolytes is performed, demonstrating the reduction of Ru(III) to Ru(II). The deposition of thin and thick layers is attempted and the resulting coatings are characterized to exclude the possible presence of oxides or other secondary phases. Finally, the possible application of ruthenium layers for electrical contacts protection is evaluated.[1] R. Bernasconi and L. Magagnin, J. Electrochem. Soc. 166(1), D3219-D3225 (2019)[2] O. Raz, G. Cohn, W. Freyland, O. Mann and Y. Ein-Eli, Electrochim. Acta 54, 6042 (2009)[3] O. Mann, W. Freyland, O. Raz and Y. Ein-Eli, Chem. Phys. Lett. 460, 178 (2008)[4] R. Bernasconi, A. Lucotti, L. Nobili and L. Magagnin, J. Electrochem. Soc. 165(13), D620-D627 (2018)

(Invited) Electrodeposition of In and Ga from Non-Aqueous Electrolytes

Indium and gallium are metals whose applications have increased during the last decades. Both metals are primarily used in the form of binary, tertiary or quaternary (semi)conductor compounds in integrated circuits, photovoltaics, liquid crystal display devices, lasers and light-emitting diodes.In the past, the electrodeposition of indium and gallium has been investigated from both aqueous and non-aqueous electrolytes. Due to the negative standard reduction potentials of the two metals (E°In(III)/In(0) = −0.34 V and E°Ga(III)/Ga(0) = −0.53 V), their electrodeposition from aqueous electrolytes is hampered. This is especially true for gallium. In this talk, the electrodeposition of indium and gallium was investigated from several organic solvents. The investigated electrolytes are 1,2-dimethoxyethane (DME), polyethylene glycol (PEG), dimethyl sulfoxide (DMSO), and acetonitrile, containing chloride, bistriflimide, or methanesulfonate-based indium or gallium precursors.The electrochemistry and the electrodeposition of indium and gallium was studied using various electrochemical methods in combination with quartz crystal microbalance (QCM) and rotating (ring) disk electrodes. DMSO-based electrolytes enabled the electrodeposition of indium at room temperature and above its melting point (159.6 °C), while DME electrolytes gave rise to gallium electrodeposits composed of small liquid gallium spheres (Fig 1). In all the investigated electrolytes, the formation of intermediate monovalent indium(I) or gallium(I) species during reduction and oxidation was demonstrated. These species are unstable and react away via disproportionation reactions. Yet, it was found that the extent of their formation and their stability depends on the nature of the electrolyte. In addition, the electrodeposition of indium antimonide (InSb) films and eutectic gallium indium (EGaIn) liquid metal lines and patterns will be discussed, as well as the electrochemical synthesis of spherical indium nanoparticles.