Electrochemical lithium capture using titanate materials: mechanistic insights and proposed advances

Abstract

The rising demand for lithium in energy storage technologies requires the development of sustainable and selective recovery methods from unconventional, earth-abundant brine resources. Moving beyond traditional lithium mining and pH-swing-driven ion exchange, electrochemical pathways offer a promising, environmentally friendly alternative for lithium capture. In this perspective, we explore the potential of H₂TiO₃ (HTO) ion-sieve materials, widely known for their pH-driven lithium selectivity, in a membrane-free, single-cell electrochemical system. This approach leverages an applied voltage bias (−1.2 V vs. Ag/AgCl) to enhance lithium concentration at the electrode surface, driving the H⁺-Li⁺ exchange without external pH adjustment. Under these conditions, lithium adsorption capacity reached 9.61 ± 0.2 mg/g, over six times higher than in the physisorption control. The system also demonstrated superior lithium selectivity over competing cations in complex brine, with separation factors of 32.41 for Li⁺/Na⁺, 43.5 for Li⁺/K⁺ and 7.6 for Li⁺/Mg²⁺. By eliminating the need for chemical pH swings and enabling electricity-driven lithium enrichment at the electrode interface, this approach highlights the potential of electrochemical pathways for sustainable, selective lithium recovery from complex brine feedstocks. Future directions for advancing material design, selectivity mechanisms, and process-level optimization are discussed to guide further research in this emerging field.

Motivation and background

The rapid growth of renewable energy and storage technologies relies on developing sustainable and cost-effective methods to recover critical metals. These metals are essential for tackling the challenges posed by the inconsistent availability and scaling of solar and wind power¹. To unlock the full potential of these intermittent power sources, advanced storage solutions, particularly batteries, are vital for delivering reliable, dispatchable power. Such energy storage technologies play a crucial role in enhancing energy security and enabling the large-scale integration of renewable power into the grid². Among electrochemical energy storage technologies, lithium ion batteries are growing rapidly due to their versatility for applications ranging from grid-scale storage to electric vehicles (EVs)³. In 2023, global lithium demand surged to 165,000 tons, with batteries accounting for 85% of this demand, representing 30% increase from 2022⁴. Global lithium demand is expected to reach 0.7 million tons in 2030 and double to 1.4 million tons in 2040, due to growing energy storage needs^1,5. Over 70% of global lithium is currently sourced from salt lake brines, but rising demand is accelerating interest in extraction from abundant, lower-concentration sources such as geothermal, oilfield brines, and seawater^3,6.

Since most lithium is currently obtained through economical but slow and environmentally challenging solar evaporation processes from brine sources, there is a need for more sustainable pathways to recover lithium^7,8 Geothermal and Salt Lake brines pose an even greater challenge, as they contain significantly lower Li⁺ concentration compared to other competing cations (Na⁺ and Mg²⁺) further complicating selective extraction. To address this challenge, direct lithium extraction techniques such as ion exchange^9,10, solvent extraction¹¹, nanofiltration, and electrochemical separations¹² have emerged as promising alternatives. Nevertheless, these pathways involve significant use of chemicals for pH adjustment or solvents for ion separation, posing challenges related to cost, scalability, and environmental sustainability. Therefore, novel economical, energy–efficient, and environmentally benign routes are needed for the selective separation of lithium from complex brines to advance sustainable solutions.

Electrochemical approaches for selective lithium recovery from brines remain underexplored, yet they offer a sustainable alternative to conventional chemical extraction methods. By minimizing the use of acids, bases, and organic solvents, and leveraging renewable electricity, these approaches have the potential for lower environmental and energy footprints. However, several critical challenges such as (a) low Li selectivity, (b) poor electrode stability under highly saline conditions, and (c) energy inefficiencies, demand further research. Use of membrane-assisted electrochemical systems improve selectivity but introduce additional issues including increased electrical resistance, fouling, and added system complexity and cost. Addressing these challenges is essential for realizing practical, scalable, and economically viable electrochemical lithium recovery technologies.

Electrochemical lithium capture pathways

Proposed electrochemical lithium pathways in literature can be broadly categorized into electromembrane/electrodialysis processes and electrochemical ion pumping/electrosorption¹. Electrodialysis (ED) uses an applied electric field and ion-exchange membranes to drive the migration of dissolved ions, enabling their selective removal from saline streams. For lithium recovery from brines, ED offers a promising, energy-efficient alternative to conventional evaporation and precipitation methods, which are slow and resource-intensive. The effectiveness of ED depends critically on the properties of the membranes, which must deliver high selectivity, low resistance, and long-term chemical and mechanical stability in highly saline, multicomponent environments^13,14. Fig. 1A is a schematic representation of selective electrodialysis for lithium extraction from brine. A major advantage of ED over traditional processes is its ability to directly produce lithium hydroxide (LiOH) which is a preferred precursor for lithium-ion batteries, without first forming lithium carbonate (Li₂CO₃), thereby minimizing CO₂ emissions associated with intermediate conversion steps^15,16. Recent progress in membrane materials and system design has advanced ED toward industrial viability¹⁵, indicating their technological readiness and commercial viability.

Fig. 1: Summary of electrochemical lithium capture approaches.

A electro membrane or electrodialysis or B Electrosorption or electrochemical ion pumping. CEM and AEM represent cation exchange membrane and anion exchange membrane, respectively.

Electrochemical ion pumping is another approach to selectively capture lithium^17,18. Fig. 1B represents the steps involved in electrochemical ion-pumping route: (1) intercalation of lithium ions onto electrode materials at negative bias, (2) replacement of the lithium source solution with a recovery solution, (3) application of positive bias to the electrode to release and recover lithium, and (4) replacement of the recovery solution with the source solution to reinitiate this cycle¹⁹. In contrast to the ED, electrodes in electrosorption processes are directly involved in the selective capture of lithium ions. Lithium-ion battery cathode and anode materials are often explored for this application, owing to the lithium intercalation mechanism which enables lithium extraction²⁰. The absence of a membrane, ion pumping methods can operate in harsh geothermal brine conditions such as high salinity, pressure, and temperature^21,22. Moreover, the operational voltage required for electrosorption is generally less than 2.0 V²³, in contrast to electromembrane that can operates at voltage range from 5 to 30 V²⁴. However, a primary challenge in the electrochemical ion pumping process is identifying selective electrode materials capable of efficiently capturing lithium with high-selectivity. Examples of such electrode materials^{25,26,27,28,29} are presented in Table 1. Electrosorption-based lithium recovery is primarily constrained by low ion selectivity, as competing cations such as magnesium and sodium co-adsorb with lithium, and by the inherently limited sorption capacity of available electrode materials. For example, materials like LiB₂O₄ show less than 0.5% lithium uptake experimentally. These factors, along with electrode stability and durability, directly influence the efficiency, cost-effectiveness, and long-term sustainability of the process³⁰.

Table 1 Comparison of electro-sorption lithium capture studies

Electrosorption materials and their lithium capture mechanism

Lithium capture materials and mechanisms are inspired by battery electrodes due to their similar charge-discharge behavior. Figure 2A illustrates the two primary electrochemical lithium capture mechanisms: capacitive response (Fig. 2A right), where lithium ions accumulate in the electrical double layer, and Faradaic intercalation (Fig. 2A left), where lithium ions insert into the electrode lattice via redox reactions. In Faradaic intercalation, the lithium capture occurs through redox reactions and intercalation into the electrode lattice, which offers higher selectivity due to the crystal structure’s inherent preference for Li⁺ over other cations. This structural selectivity arises from factors such as ionic size compatibility and lattice binding energies. In contrast, capacitive systems rely on the accumulation of Li⁺ in the Helmholtz double layer at the electrode-electrolyte interface, which is a non-Faradaic and surface-limited process. While capacitive capture enables faster kinetics and lower energy consumption, the lithium selectivity arises from a combination of field-enhanced Li⁺ concentration near the surface and the favorable interaction of Li⁺ with the electrode surface. Amongst various Li capture materials, lithium iron phosphate (LFP, LiFePO₄), lithium manganese oxide (LMO, LiMn₂O₄), and lithium nickel cobalt manganese oxide (NCM, LiNi_1/3Co_1/3Mn_1/3O₂) have been broadly proposed and studied for the lithium recovery^31,32. The Faradaic current response in these materials arises from electrochemical redox reactions at the electrode- electrolyte interface³³, followed by lithium capture through the intercalation of lithium into the material, (Fig. 2B), as illustrated by a few example reactions below:

$${{Li}}_{1-x}{{Fe}}_{1-x}^{{II}}{{Fe}}_{x}^{{III}}{{PO}}_{4(s)}+{{{xLi}}^{+}}_{({aq})}+{{xe}}^{-}\to {Li}{{Fe}}^{{II}}{{PO}}_{4(s)}$$

(1)

$${{Li}}_{1-x}{{Mn}}_{1-x}^{{III}}{{Mn}}^{{IV}}{O}_{4(s)}+{{{xLi}}^{+}}_{({aq})}+{{xe}}^{-}\to {Li}{{Mn}}^{{III}}{{Mn}}^{{IV}}{O}_{4(s)}$$

(2)

Fig. 2: Mechanisms of electro sorption lithium capture.

A Faradaic response and Capacitive response. Examples of electrode materials associated with faradaic responses and capacitive responses are shown in (B, C). Note: yellow and black balls in (C) are H⁺ and Li⁺ ions, respectively^10,31.

The LFP system demonstrates excellent long-term stability, making it attractive for lithium capture applications. However, LFP suffers from co-intercalation of competing cations, which reduces insertion capacity and selectivity³⁴. In contrast, LMO is favored for its high Li⁺ selectivity and considerable insertion capacity^12,31 attributed to its spinel structure that promotes high ion-conductivity. However, LMO suffers from structural instability due to the Jahn-Taller effect of the manganese during charge and discharge cycling, causing manganese species leaching into the electrolyte affecting the long-term electrode stability⁹. Another promising approach for lithium capture leverages electrochemical capacitive desalination (CDI), which operates on the principle of electrostatic adsorption of ions into the electrical double layers formed at the surface of porous, conductive electrodes³⁵. Compared to conventional desalination technologies, CDI demonstrates significantly lower specific energy consumption, making it an increasingly attractive solution for water purification^35,36. While conventional capacitive deionization (CDI) typically exhibits limited ion selectivity, recent advances have demonstrated the feasibility of targeted separation of specific ions, such as phosphate, nitrate, and lithium. Integrating ion-exchange membranes into CDI systems, known as membrane capacitive deionization, has been shown to significantly enhance ion removal efficiency, charge utilization, and selectivity compared to conventional CDI³⁷. Another promising strategy for selective lithium recovery involves incorporating lithium-ion sieve (LIS) materials into the CDI electrodes. For example, layered hydrated titanates, such as H₂TiO₃ (Fig. 2C), have been widely studied as lithium-selective materials, traditionally applied in pH-driven ion exchange processes, and are now being explored for electrochemical lithium capture^10,38,39,40. In this class of material, lithium capture is achieved in a similar mechanism as occurs in pH driven approach via ion exchange reaction as represented below:

$${{MO}-H}_{(s)}+{{{Li}}^{+}}_{\left({aq}\right)}\leftrightarrow {{MO}-{Li}}_{(s)}+{{H}^{+}}_{({aq})}$$

(3)

The capacitive response caused by the voltage application across the electrodes results in increased lithium surface concentration in contrast with pH - driven approaches via breaking of Li–O bonds by electrons. This results in a more effective lithium capture without the need for chemically intensive pH adjustment processes.

Electrochemical lithium capture with layered titanate material

Prior advances suggested that H₂TiO₃ is promising material due to its theoretical lithium adsorption capacity of ~128 mg/g, which is significantly higher than alternative widely used but less stable materials such as λ-MnO₂ that has a theoretical capacity of ~60 mg/g^10,41. Li and co-workers showed that titania dissolution in H₂TiO₃ is 0.31% per adsorption and desorption cycle^41,42, which is more than an order of magnitude lower than Li₂MnO₄. Despite the favorable characteristics of H₂TiO₃ as an active material for electrochemical lithium capture, there remains a limited number of studies that explore its use for electrochemical lithium capture. Bhaskaran et al.²⁸, developed a membrane capacitive desalination approach utilizing H₂TiO_3. Lithium insertion capacity as high as 13.67 mg/g was demonstrated in the optimal condition utilizing 60% reduced graphene oxide additive. However, investigation into the selectivity of the material is limited, focusing mainly on comparisons with pure sodium chloride and lacking experiments with complex brine solutions²⁸. Zhang et al.²⁹, explored ways to enhance H₂TiO₃ based electrode performance through tannic acid treatment in addition to the use of reduced graphene oxide as the conducting agent. Acid treatment enhanced the electrode’s hydrophilicity, improving lithium adsorption with a demonstrated capacity of up to 25.2 mg/g in the optimal configuration. The process is also shown to have a high separation factor over sodium and magnesium. However, the feed brine utilized for the study has a high lithium concentration of 1412 mg/L and a pH of 10.98²⁹. These conditions are quite favorable for extraction, but most deposits have lithium concentration less than 400 mg/L⁸. These challenges motivate innovative advances in electrochemical capture of lithium selectively by harnessing synthetic brines over H₂TiO₃ layered electrodes.

In this perspective, we investigate the potential of H₂TiO₃ (HTO)-based electrodes for electrochemical lithium recovery from brines using a membrane-free system, offering a promising alternative to conventional chemical ion-exchange processes, which are inherently slow. By applying an electric field, the local cation concentration at the electrode surface is enhanced, accelerating the lithium exchange kinetics. However, this approach also introduces challenges related to differences in hydration radius, ion mobility, ion-exchange selectivity, and hydration energy among competing ions present in complex brines. Here, we systematically examine the influence of solution pH on lithium selectivity and uptake, assess the energy efficiency of the process, and critically discuss the limitations and research needs for advancing HTO-based electrochemical capture systems toward practical, competitive lithium recovery technologies.

Materials and methods

Synthesis of H₂TiO₃ (HTO) powder

Li₂TiO₃ (LTO) is synthesized through a solid-state reaction¹, by mixing Li₂CO₃ (Sigma Aldrich) and anatase TiO₂ (Thermo Fischer) in 2: 1 molar ratio of Li/Ti with a mortar and pestle for 20 min. Furthermore, as synthesized LTO was annealed at 700 °C for 4 h (ramp rate = 6 °C/min) in a muffle furnace. Moreover, to remove any unreacted lithium carbonate, the annealed LTO powder was washed thoroughly with deionized water (DI) water and dried overnight in an oven at 80 °C. Subsequently, HTO powder is synthesized by magnetically stirring the LTO powder at 800 rpm in 0.2 M hydrochloric acid (HCl) with a solid to liquid ratio of 1:200 for 24 h. Finally, HTO powder was obtained with repeated washing and centrifugation followed by overnight drying at 80 °C in vacuum oven.

Preparation of electrode

To prepare electrodes for lithium capture, a carbon cloth was used as conductive support. Prior to the coating process, carbon cloth (Fuel Cell Store, 360 µm) was cut into 3 × 3 cm² and sonicated in a 1:1:1 volumetric ratio of acetone, ethanol, DI water solutions for 10 min and dried at 80 °C for 15 min. Further, as synthesized HTO powder, C65 (Timcal), and PVDF (Sigma Aldrich) were mixed in NMP (Thermo Fischer) using mortar pestle with a mass ratio of 8:1:1, respectively. The as-prepared slurry was uniformly coated on the surface of carbon cloth with the help of glass slides. Furthermore, resultant electrodes were dried in a vacuum oven at 60 °C for 12 h, to evaporate the volatile solvent and fixation of the coatings (Fig. S1). The difference of mass between the electrode and plain carbon cloth is measured and is used to calculate the active mass loading of the electrode.

Electrochemical lithium adsorption study

Electrochemical lithium adsorption was conducted in a three-electrode system electrolytic cell, where the prepared HTO electrode was used as working electrode, platinum mesh as counter electrode, and Ag/AgCl in saturated KCl was used as reference electrode. The working HTO electrode was suspended in the electrolyte by a PTFE holder with platinum contact. The distance between the working and counter electrode was approximately 2 cm. The synthesized brine solution was used as feed, prepared from chloride salts by mimicking Atacama brine^2,3 and the composition is presented in Table S1. In a typical electrochemical lithium capture process, the electrodes were immersed in 35 mL (dipped area 3 × 2 cm²) of the feed solution. Lithium capture experiments in this study are conducted in batch mode with applied potential of −1.2 vs Ag/AgCl while magnetically stirred at 50 rpm for 2 h. The influence of pH on the Li capture process was studied by varying the pH from 5.8, 7.0, and 9.0 using 0.1 M ammonium hydroxide. A set of lithium physisorption experiments were also conducted for comparison in the similar configuration in absence of electrical potential.

Material characterizations

The crystal structures and crystallinity of the synthesized HTO powder and electrode samples were confirmed through X-Ray Diffraction (XRD, Bruker D8 Advance ECO powder diffractometer) with Cu K_α radiation at 40 kV, and 25 mA. Typical scan was done from a 2θ angle of 10° to 80° with and scan step size of 0.019°. Raman Spectroscopy (WITec Alpha300R) was used to determine the chemical bond formation in different states of the electrode. Raman Spectroscopy was carried out using 532 nm laser. The scanning electron microscopy (SEM) analysis was done on Zeiss Sigma 500 SEM. The electrolyte concentration was measured with Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES, Thermo Scientific, iCAP 7400). The elemental states of the elements were measured using X-ray photoelectron spectroscopy (XPS) on Thermo Fisher Scientific Nexsa G2 XPS instrument with monochromatic Al-K_α X-ray source.

Results and discussion

Electrode development for electrochemical lithium capture

The approach to synthesize and prepare HTO electrodes is shown in Fig. S1. The structural features of synthesized Li₂TiO₃ and H₂TiO₃ powder and electrode are investigated using X-Ray Diffractogram (XRD) and shown in Fig. 3A. Figure 3A(a, b) displays the XRD patterns of Li₂TiO₃ powder and electrode, respectively. The characteristic XRD peaks are located at 2θ values of 18.01 °, 43.45 °, 63.19 ° and are indexed to (002), (22-2) and (312) planes of monoclinic-structured Li₂TiO₃ (ICDD PDF 00-033-0831). The structure of Li₂TiO₃ powder and electrode are in agreement with the monoclinic phase of β-Li₂TiO₃^10,43. Fig. 3A(c, d) show the disappearance of the (111), (22-2) and (312) and (062) XRD peaks in the H₂TiO₃ powder and electrode demonstrating the structural disorders arising due to the delithiation process. The diffraction pattern of H₂TiO₃ powder and electrode is consistent with that of layered structure of H₂TiO₃¹⁰. To investigate the influence of acid delithiation on O-Li bonds in LTO, the characteristic features of the synthesized Li₂TiO₃ and H₂TiO₃ powder and electrode are investigated using Raman spectroscopy (Fig. 3B(a–d)). The Li-O stretching and O-Li-O bending vibration results in shifts in the Raman peaks at 293, 308, and 405 cm⁻¹⁵ on the LTO powder and electrode samples (Fig. 3B(a, b)). The intensity corresponding to these peaks is found to reduce or disappear after the acid delithiation (Fig. 3B(c, d)), further providing evidence of successful HTO synthesis. The peak at 663 cm⁻¹ is assigned to Ti-O bonds stretching, as the region between 550–700 cm⁻¹ is associated with TiO₆ octahedra in lithium titanate materials⁴⁴. This Ti–O stretching peak appears broadened after delithiation, suggesting the presence of hydrogen in different coordination states, which could correspond to hydrogen in H and HTi₂ layers. Both X-Ray Diffraction (XRD) patterns and Raman spectra show no notable differences between the powder and electrode form of the LTO and HTO, which indicate the successful preparation of the electrode that retains the characteristics of the LTO and HTO powders. The structural and morphological features of the H₂TiO₃ electrode were analyzed, SEM imaging revealed agglomerated particles with primary particle sizes in the range of 100–200 nm (Fig. S3), consistent with prior studies¹⁰. Literature reports further indicate that H₂TiO₃ exhibits a mesoporous structure, with BET surface area measurements showing type IV nitrogen adsorption–desorption isotherms and H1-type hysteresis, characteristic of uniform mesoporosity and cylindrical pores^36,45. This mesoporosity, together with the observed particle morphology, provides a high surface area and accessible pore network, facilitating lithium adsorption through enhanced ion accessibility and electric double-layer formation within the pores. Furthermore, XPS analyses were conducted on the H₂TiO₃ electrodes to examine the surface chemical valence states of the elements. Figure S4A presents the deconvoluted Ti 2p spectrum of HTO, showing binding energies at 458.08 and 456.50 eV for Ti 2p_3/2, and 463.97 and 461.58 eV for Ti 2p_1/2. This observation confirms the coexistence of Ti⁺⁴ and Ti⁺³ oxidation states, where the presence of Ti⁺³ enhances the electronic conductivity by introducing additional charge carriers. These results are consistent with previous reports^46,47. The O 1 s peak near 530 eV corresponds to lattice oxygen in the Ti-O framework (Fig. S4B). A second peak, centered around 531.5–532.5 eV, is commonly attributed to surface hydroxyl groups due to surface defects(Ti⁺³). Additionally, the appearance of a peak near 534 eV is typically associated with adsorbed water, which may be due to the material’s high surface area and strong affinity for moisture⁴⁸. The mixed-valence state is expected to facilitate charge transport within the electrode matrix for electrochemical application.

Fig. 3: Structural and vibrational characterization of electrode materials.

A X-ray diffraction patterns showing characteristic peaks of the synthesized materials at different synthesis stages: (a) Li₂TiO₃ powder, (b) Li₂TiO₃ electrode, (c) H₂TiO₃ powder, and (d) H₂TiO₃ electrodes. B Raman spectra of the same samples, showing Li-O stretching and O-Li-O bending vibrational modes at 293 cm⁻¹, 308 cm⁻¹, and 405 cm⁻¹ respectively. The series (a–d) correspond to the same samples as in (A), with light blue, blue, light green, and dark green traces respectively.

Lithium capture using HTO materials

The synthesized HTO electrodes are used to investigate physisorption and electrochemical lithium capture behavior. The feed for lithium uptake is the simulated Atacama brine with composition as outlined in Table S1. The lithium uptake of the HTO electrodes is investigated by varying the initial pH conditions of feed in three electrode setup (Fig. S2). Figure 4A shows that during physisorption, lithium uptake increases with a slight increase in the initial pH of the solution. In contrast, in the electrochemical capture mode, the amount of lithium captured decreases as the initial pH increases. However, the application of a −1.2 V potential to the working electrode in electrochemical lithium adsorption results in a significant improvement in lithium uptake, averaging more than six times the amount captured compared to the baseline physisorption process. During the electrochemical mode, lithium capture decreases with an increase in the initial pH, which is surprising since alkaline conditions are known to favor lithium uptake in wide-ranging materials including ion exchange resins¹⁰ and solvents¹¹. Typically, during the pH driven ion exchange adsorption mechanism, hydroxyl ions in solution assist weak acid dissociation in H₂TiO₃ thereby promoting Li-O bond formation¹⁰. The electrochemical lithium uptake indicates that the acid dissociation step is not essential for the adsorption process and electric double layer formation may facilitate a distinct favorable condition for the lithium uptake. This apparent contradiction can be attributed to the use of a NH₄Cl/NH₄OH buffer for pH adjustment, which introduces NH₄⁺ cations into the electrolyte. These NH₄⁺ ions compete with Li⁺ for adsorption sites within the Helmholtz layer at the negatively charged electrode surface. As the pH increases, the concentration of NH₄⁺ in the solution also increases, leading to a concentration-dependent suppression of Li-H exchange. This competitive effect of NH₄⁺ likely explains the observed decrease in lithium capture at higher pH in the electrochemical configuration. Interestingly, final pH of the brine in both electrochemical and physisorption modes decreases alongside the lithium adsorption process, as shown in Fig. 4 (B). Notably, the final pH in the electrochemical mode across all initial pH conditions converged to a similar value of 4.1. The drop in pH indicates that lithium adsorption is accompanied by the release of H⁺ ions, following an ion exchange reaction as shown below:

$${{MO}-H}_{\left(s\right)}+{{{Li}}^{+}}_{\left({aq}\right)}\,\leftrightarrow \,{{MO}-{Li}}_{\left(s\right)}+{{H}^{+}}_{\left({aq}\right)}$$

(4)

Fig. 4: Effect of sorption mechanisms and pH on lithium uptake and selectivity.

A Lithium uptake (mg/g) from Atacama brine after 2 h at 50 rpm under different pH conditions, comparing physisorption and electrochemical sorption. B pH of the solution before and after sorption under both conditions. C Selectivity coefficients of lithium over potassium (blue bars), sodium (red bars), and magnesium (gray bars) at different pH values during electrochemical sorption. D Schematic representation of ion distribution and sorption behavior at the electrode surface during electrochemical sorption.

In this reaction, MO-H refers to the metal oxide surface. The observed increase in lithium adsorption with higher initial pH in the physisorption mode (Fig. 4A) can be explained by the alkaline conditions depleting released H⁺ ions, thereby shifting the equilibrium to the right, favoring lithium adsorption. Conversely, the significant increase of lithium adsorption in the electrochemical mode (Fig. 4A) is attributed to the applied field increasing lithium concentration at the electrode surface by ~4-5x (complete description in Supplementary section), which accelerates H⁺-Li⁺ exchange. Lithium selectivity over other cations in the brine separation process is shown in Fig. 4C and Table S2. The observed selectivity stems from the H₂TiO₃’s mesoporosity and stronger O-Li bonding favoring lithium uptake over larger or more strongly hydrated cations. It is observed that lithium separation is generally most selective over potassium, followed by magnesium and sodium. Selectivity over potassium is expected to be high due to a significant difference in ionic radii compared to lithium⁴⁹. However, selectivity over sodium is found to be lower than magnesium despite sodium’s larger ionic radii, which can possibly be attributed to the large concentration of sodium in the initial brine solution (Table S1). Based on the results of lithium uptake and initial feed brine pH variation during the physisorption and electrochemical lithium uptake, the influence of charged surfaces on sorption behavior is proposed in Fig. 4D. As shown in Fig. 4D, in the absence of the external electric field, the cations in the brine can diffuse freely within the solution, whereas application of negative potential to working electrode leads to migration of the cations towards the electrode surface and specifically forms the layer of adsorbed cations⁵⁰. This phenomenon increases the surface lithium ion concentration, which shifts the equilibrium to the right (see Eq. 1), thereby increasing the lithium uptake. To assess the material’s stability in the electrochemical configuration, multiple cyclic voltammetry analysis was conducted at a slow scan rate for 100 cycles Fig. S5. SEM (Fig. S6) and XRD analyses (Fig. S7) after cycling confirmed no significant morphological degradation of the electrode, although additional phases corresponding to adsorbed cations such as Li⁺, Ca⁺², and Mg⁺² were detected after the adsorption process. These demonstrate the structural robustness of H₂TiO₃ under repeated electrochemical operation, underscoring its potential for sustainable and reusable lithium recovery from complex brines.

A preliminary estimate of the energy consumption for lithium recovery in this system was calculated as approximately 5.6 kWh per kilogram of lithium (complete description in Supplementary section). This compares favorably with conventional processes such as evaporation ponds (30–70 kWh/kg-Li) and electrodialysis or membrane-based methods (10–20 kWh/kg-Li)^37,51. Competitive energy efficiency, coupled with the elimination of harsh chemicals, large land requirements, and pH swings, highlights the potential of this approach as a sustainable alternative. However, lithium selectivity remains dependent on the composition of cations in the Stern layer, where the higher hydration enthalpy and larger hydration radius of Li⁺ limit its relative accumulation under an applied field, indicating a trade-off between energy input and selectivity that warrants further optimization.

Mechanistic insights into electrochemical lithium capture using HTO materials

To assess the efficacy of electrochemical separation, the cyclic voltammetry of HTO electrode is performed. The cyclic voltammetry curves of the electrode show largely capacitive behavior without any obvious faradaic peak (Fig. 5A). The peak current can also be correlated with scan rate variations to gain further insight into electrochemical behavior. A current response that is proportional to the square root of scan rate (v^1/2) is said to be limited by internal diffusion⁵², implying a fast faradaic electron transfer as well as a freely diffusing analyte⁵³ from the bulk to the surface and vice versa. The current of such a process is governed by the following expression⁵⁴:

$$i=C{v}^{1/2}$$

(5)

Fig. 5: Adsorption performance and mechanism.

A Cyclic voltammograms recorded at scan rates ranging from 10 to 200 mV/s in 1 M LiCl electrolyte with platinum mesh counter electrode. B Peak current as a function of scan rate (ν) for oxidation (red circles) and reduction (black circles) processes. C Peak current as a function of square root of scan rate (ν^1/2) for oxidation (red circles) and reduction (black circles) indicating linear correlation between peak current and scan rate (ν), along with the deviation from linearity with (ν^1/2).

In this expression, i is current (A), C is capacitance (F), and $v$ is scan rate (mV/s). In contrast, a current response that is proportional to the scan rate ($v$) is said to be surface limited⁵², and the current arises from capacitive current due to the Helmholtz double layer formation. Formally, the current response can be described as follows⁵²:

$$i=\,v\,{C}_{d}A$$

(6)

In this expression, C_d is the capacitance of the electrode.

Figure 5 (B) and (C) show that both the oxidation and reduction current responses exhibit a better linear fit against the scan rate ($v$) rather than against the square root of the scan rate ($v$^1/2). The deviation from linearity with $v$^1/2, as described by Eq. (5) and the good linear fit with v as described by Eq. (6) indicates that the exchange process is dominated by surface-controlled kinetics (Fig. 2A). These results suggest that the observed current response from the cyclic voltammetry arises from capacitive current due to Helmholtz double layer formation, and the current response is due to an electrode-adsorbed species^52,55. This suggests that there is no electron transfer to the lithium in the process. Instead, the applied voltages enable the formation of inner Helmholtz plane consisting of lithium ion, which then further interacts with H₂TiO₃ active sites. In similar lithium capture experiments, Zhang and co-workers showed that there is no change on the oxidation state of titanium before and after lithium adsorption²⁹, which further supports the evidence of the absence of electron transfer in the lithium capture process.

Key conclusions, research directions, and opportunities

Electrochemical lithium extraction offers a promising pathway for industrial-scale production of lithium-based products such as LiOH.H₂O and Li₂CO₃, combining lower process complexity with the ability to utilize renewable electricity sources and tolerate diverse brine compositions. Its adaptability to varying feedstocks and operation across a wide pH range reduces the need for extensive pretreatment, and its faster kinetics compared to slow evaporation-based processes make it an attractive, sustainable alternative to conventional chemical and membrane-based methods for meeting the growing lithium demand.

While prior studies have largely focused on conventional battery materials and intercalation-based mechanisms, our findings show that ion-exchange materials such as H₂TiO₃ can also be effectively utilized in an electrochemical system. Although the lithium capture process is non-Faradaic, the application of an electric field enhances the local lithium concentration at the electrode surface, thereby accelerating the Li-H exchange. In this study, a lithium extraction capacity of 9.6 mg/g was achieved without pH adjustment, using a single-compartment, membrane-free system operated in batch mode.

Despite demonstrating the feasibility of H₂TiO₃-based electrochemical lithium recovery, several challenges remain. First, the observed lithium capture capacity of 9.6 mg/g is significantly lower than the theoretical capacity of ~128 mg/g, as the exchange primarily occurs at solvent-accessible surface sites. This highlights the need to synthesize highly porous materials with greater surface area and accessibility to active sites. Second, the separation factor of lithium over competing cations depends on the thermodynamics and kinetics of the cation-H⁺ exchange and the local cation concentrations in the Stern layer. This warrants further investigation using atomistic simulations, such as DFT or ab initio molecular dynamics, to elucidate these critical properties and their contributions to selectivity. Third, material modification strategies, such as metal doping and surface functionalization, should be explored computationally and experimentally to assess their effects on the thermodynamics and kinetics of Li-H exchange and suppression of competing reactions. Fourth, since the Stern layer cation composition can also be influenced by operational parameters, such as voltage pulsing and other potentiodynamic methods, systematic studies are needed to optimize operating conditions for improved selectivity and efficiency. Finally, comprehensive life cycle assessments and techno-economic analyses are crucial to evaluate the environmental and economic viability of this approach at scale. These findings provide a foundation for advancing H₂TiO₃-based electrochemical lithium recovery through material innovation, mechanistic understanding, and process optimization toward sustainable and scalable deployment.