Construction of the Embedded Li4Ti5O12-MWCNTs Nanocomposite Electrode for Diverse Applications in Electrochemical Sensing and Rechargeable Battery

Here, a facile and cost-effective hydrothermal method was used to synthesize lithium titanate (Li4Ti5O12, (LTO))-multiwalled carbon nanotubes (MWCNTs) nanocomposite for the bifunctional property of sensing and energy storage applications. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to confirm the formation of LTO-MWCNTs nanocomposite. The electrochemical sensing of Dopamine (DA) at LTO-MWCNTs modified glassy carbon electrode (GCE) was studied. The modified electrode demonstrated remarkable sensitivity, with a detection limit of 1.54 µM of DA. Moreover, the modified electrode was used for the selective measurement of DA in presence of 5-hydroxytryptamine (5-HT) and folic acid (FA) without interfering with their respective potentials. The modified electrode was used to quantify the DA in commercial DA injection sample with satisfactory recoveries. The modified LTO-MWCNTs/GCE electrode showed acceptable reproducibility and excellent stability. In addition, LTO-MWCNTs nanocomposite electrode delivered a high initial discharge capacity of 176 mAh g− 1 at a charge-discharge rate of 1 C in a constant-current charge-discharge experiment, which proved its efficacy as a rechargeable battery anode material.

In this paper, LTO was first described as an electrochemical sensor on the surface of a glassy carbon electrode (GCE) for the electrochemical detection of dopamine (DA) and as an anode material for LIBs. Unfortunately, the inherent poor electronic conductivity of LTO particles (10 − 9 − 10 − 13 S/ cm) and moderate lithium-ion diffusion coefficient (10 − 8 cm 2 s − 1 ) still have an impact on their ability to perform electrochemical performance in sensing and energy storage applications [25]. Several effective methods have been used to overcome the above problems, such as doping metals and metal oxides [26,27], reducing the particle size to nanosize [28], and coating with conductive materials [29]. The disadvantage of atom doping is that the number of active Ti + 4 ions are reduced, which ultimately reduces the capacity of LTO anode [16]. Therefore, another way to increase the conductivity of LTO is by reducing its particle size to nano-size. It is anticipated that shrinking the LTO particle to the nanoscale range will improve the capacity and rate capabilities [30]. However, the aggregation of primary particles prevents the uniform dispersion of these nanoscale LTO particles over the electrode surface. To counteract the aforementioned concern, we have decided to distribute LTO with conductive material made of carbon, which prevents particle agglomeration and provides a reliable and effective framework throughout the electrochemical process. In order to build an effective conductive network among various carbonaceous materials, carbon nanotubes (CNTs) are interesting and belong to a new member of the carbon family. CNTs can be considered as special candidates for the construction of composites in electrochemical sensing applications because they have not only a high surface area and mechanical stability but also good electrical conductivity, resulting in excellent conductive nanocomposites [31]. Several carbon-based nanomaterials have been developed for electrochemical sensing applications [32][33][34][35][36]. Due to the unique properties of CNTs, many researchers have shown that it has been used as electrode material with the combination of metal oxides in LIBs. According to prior research, sol-gel synthesis method was utilized to develop Li 4 Ti 5 O 12 / carbon nanotube composite with a discharge capacity of 145 mAh g − 1 at the charge/discharge rate of 5 C [37]. The solidstate method was utilized to synthesize Li 4 Ti 5 O 12 /carbon/ carbon nano-tubes composite, which had discharge capacities of 163, 148, and 143 mAh g − 1 at charge/discharge rates of 0.5 C, 5.0 and 10.0 C, respectively [38]. The Li 4 Ti 5 O 12 / MWCNT composite was produced by π-π interaction strategy, and its discharge capacity was 132 mAh g − 1 at the charge/discharge rate of 50 C [39]. The Li 4 Ti 5 O 12 /AB/ MWCNTs composite was synthesised by solid-state reaction with its discharge capacity of 163 mAh g − 1 at the charge/ discharge rate of 2 C [40].
Neurotransmitters transmit information in the form of brain impulses in the human body [41]. One of the most crucial neurotransmitters in the human body is DA, a member of the catecholamine family [42]. It is produced in multiple regions of the adrenal glands and brain. It also affects the renal and cardiovascular systems. DA also performs biochemical precursors of other neurotransmitters such as epinephrine and norepinephrine belonging to the catecholamine family [43]. Any deviation from normal DA levels in the body might result in some neurological illnesses including Parkinson's disease and schizophrenia [44]. Therefore, it is crucial to create an easy, affordable, and accurate method for the electrochemical detection of DA. However, DA tends to coexist with the oxidation potentials of 5-HT and FA, resulting in the overlapping of voltammetric responses and may strongly affect the sensitivity and selectivity of the method. Several techniques, including mass spectrometry, liquid chromatography, and capillary electrophoresis, have been reported for the selective detection of DA [45][46][47][48][49]. 5-hydroxytryptamine (5-HT), often known as serotonin, is a biological monoamine neurotransmitter produced by serotonergic neurons in the human brain's central nervous system [50,51]. It modulates the activity of neurons in the central or peripheral nervous systems of mammals [52]. It controls and regulates some physiological processes such as mood, muscle contraction, sleep, food intake and depression [53]. Abnormal levels of 5-HT lead to the various neurological disorders such as Down syndrome, Alzheimer's disease etc. [54]. Therefore, the recognizing of 5-HT in biological samples is an important task for the researchers. Numerous techniques, such as mass spectrometry, chemiluminescence, and fluorescence detection, have been reported for the selective measurement of 5-HT [55][56][57]. Folic acid (FA) or folate has been considered as a part of water-soluble Vitamin B-complex and it is also called as Vitamin B 9 [58]. It is naturally occurred in vegetables, meat (such as liver and kidney), beans and bananas. It is more important for cell growth and differentiation. FA is essential for pregnant women to prevent miscarriages and megaloblastic anaemia. Normal levels of FA in serum are usually 7 to 42 nM [59]. FA deficiency leads to neural tube defects, heart attacks, fetal developmental defects, leucopoenia, and anaemia [60]. Therefore, recognizing FA levels is more important for the researchers. Numerous techniques, such as capillary electrophoresis and high-performance liquid chromatography, have been reported for the selective measurement of FA [61,62]. The above methods suffer from time-consuming operation, laboriousness, and more expensive equipment. However, the electrochemical methods are of low cost, simple to operate and exhibited good sensitivity, selectivity, and accuracy [63,64]. Chemically modified electrodes (CMEs) often have advantages over conventional electrodes such as reducing the potential required for the easy occurrence of electrochemical reactions and also by improving the sensitivity through electrocatalytic activity [65]. CMEs are an approach to electrode system design that is used in a wide range of basic electrochemical investigations, such as the relationship of heterogeneous electron transfer and chemical reactivity of electrode surface chemistry, electrostatic phenomena at the electrode surface, electron and ionic transport phenomena in polymers, and the design of electrochemical devices and systems for chemical applications. Due to the aforementioned rationale, it is crucial for the researchers to determine the modifier that makes the analyte detection process the easiest. For example, the CMEs such as MWC-NTs/CuFe 2 O 4 nanocomposite, MWCNTs/Fe 3 O 4 -SH/Au and SBA-15-Met/Au/Apt modified GCEs was developed for the detection of bisphenol A [66][67][68], nanocrystalline Fe 50 Ni 50 alloys modified carbon paste electrode (CPE) was developed for the detection of tiopronin [69], CPE was modified with Nano-TiO 2 /ferrocene carboxylic acid for the detection of captopril [70], Nickel disc electrode modified by N,Nbis(salicylidene)phenylenediamine (salophen) used as catalyst for methanol oxidation [71], Ag@Fe 3 O 4 -CH modified GCE was developed for the hydrogen peroxide sensing [72] and electro-magnetic polyfuran/Fe 3 O 4 nanocomposite for biosensing application [73].
Herein, we report the fabrication of LTO-MWCNTs nanocomposite using a simple hydrothermal method. The synthesized LTO-MWCNTs nanocomposite material has been drop-casted onto the GCE surface (named, LTO-MWCNTs/ GCE) and was successfully utilized for dual applications. Here, we found that a composite of LTO-MWCNTs had better electrochemical performance than that of pristine LTO. We strongly believed that it is because of MWCNTs, they can act as bridges connecting to LTO nanoparticles, resulting enhanced electronic conductivity than pristine LTO. It was discovered that the LTO-MWCNTs/GCE sensor has a good conductivity, sensitivity, and selectivity with respect to the electrochemical detection of DA using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The high-rate performance of LTO-MWCNTs/GCE was further investigated using electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD) experiments.

Synthesis of LTO-MWCNTs Nanocomposite
The LTO-MWCNTs nanocomposite was synthesized using simple hydrothermal method. The LTO-MWCNTs nanocomposite was prepared using TiO 2 , LiOH.H 2 O and MWCNTs as precursors. In a typical synthesis, 0.4 g of AR grade TiO 2 powder was added to aqueous LiOH and stirred 30 min to form a suspension. 50 mg of commercially available MWCNTs were dissolved in 30 mL deionized water and subjected to sonication for 30 min. In order to achieve thorough binding between the metal oxide nanoparticles and MWCNTs, fully dispersed MWCNTs were added to the suspension obtained above. The combination was then stirred at 80 °C for 1 h. The resultant mixture was transferred into a 50 mL Teflon stainless steel autoclave and heated at 200 °C for 12 h, later cooled to the room temperature and centrifuged. It was then repeatedly cleaned with methanol and deionized water, dried for 12 h at 60 °C. Finally, the obtained powder was calcined at 600 °C for 3 h to improve the crystallinity of the LTO-MWCNTs nanocomposite. The graphical representation of synthesis of LTO-MWCNTs nanocomposite was showed in scheme 1. The similar synthesis procedure was also followed to obtain the pristine LTO nanoparticles with same conditions without adding MWCNTs.

Instrumentation
A model 3003 TT siefert computerized X-ray diffractometer equipped with a CuK radiation source (λ = 1.5406 A o ) was used for the X-ray diffraction (XRD) investigation to examine the structural characterisation of as-synthesized materials. Transmission electron microscopy (TEM) model-TALOS F200S G2 (200 kV, FEG, CMOS Camera 4k × 4k, in column EDS detector STEM) was used to analyze the detailed microstructure and selected area electron diffraction (SAED). Carl Zeiss EVO-MA15 scanning electron microscope (SEM) model was used to analyze the surface morphology. An electrochemical analyzer (model: CHI-660D, USA) was used to determine the electrochemical properties of the synthesized samples utilizing CV, DPV, EIS, and chronopotentiometry (CP). The working electrode in the three-electrode configuration was LTO-MWCNTs/GCE, the reference electrode was saturated calomel, and the counter electrode was 0.5 mm platinum wire. The pH electrode of CL51B was connected to an Elico U 120 pH meter, which was used to record the various pH values.

Construction of LTO-MWCNTs/GCE
The 3 mm-diameter GCE was hand-polished with alumina powder of several grades, including 1.0, 0.3, and 0.05 μm, before the working electrode was constructed. After being polished, the GCE was rinsed with ultra-pure water and sonicated for one minute in a 1: 1 solution of methanol and water. Thereafter, 5 µL of LTO-MWCNTs nanocomposite (which had been prepared in methanol at a ratio of 1 mg/1 mL) was drop-casted onto the cleaned mirror-like GCE surface and allowed for drying. As a result, an electrode known as LTO-MWCNTs/ GCE was constructed and served as a working electrode in this study. Similarly, modified electrodes like LTO/GCE and MWCNTs/GCE were also constructed using the same method. respectively, corresponding to the cubic structure of LTO with Fd3m space group (JCPDS-49-0207). Both spectral lines showed no additional distinctive peaks, indicating the formation of phase-pure materials. The LTO-MWCNTs composite displays sharp and intense peaks, which denote the presence of MWCNTs and suggest that the addition of MWCNTs to the precursor has no effect on the synthesis of phase-pure LTO after heat treatment. The same tendency in the formation of composite and intensity in the peaks were observed in the case of Li 2 TiO 3 /CNTs composite and consistence with the literature [74,75]. The average particle size of pristine LTO and LTO-MWCNTs nanocomposite was calculated from the Bragg's peaks using well-known Scherrer's formula Eq. 1.

Structural and Morphological Analysis
Where 'Lc' denotes the crystallite size, 'K' is the Scherrer's constant (0.94), 'λ' denotes the X-ray radiation wavelength, 'β' is the full width at half maximum, and 'θ' denotes the diffraction angle. The typical crystallite size of pure LTO and LTO-MWCNTs nanocomposite is around 75 nm and 60 nm, respectively.
The surface morphology of pristine LTO and LTO-MWC-NTs nanocomposite was studied using SEM and HRTEM analysis. Figure 2A  it demonstrates the small size of the LTO particles grown in the presence of carbon nanotubes. The MWCNTs were wrapped around the LTO particles as shown in Fig. 2c, indicating that the well-connected MWCNTs are in intimate contact with the LTO particles and produced conductive network. This network enhances quick electron transport and enables strong binding between LTO nanoparticles, considerably improving the electrochemical performance of the electrode surface. Figure 2b and d show the EDX spectra of pure LTO and LTO-MWCNTs nanocomposite, respectively, which demonstrate the presence of Ti, C, and O elements in varying molar ratios. SEM micrographs of cable-like sheeted MWCNTs at various magnifications are shown in Fig. 2E,F.
The detailed microstructure of LTO-MWCNTs nanocomposite is shown in Fig. 3A-E observed in TEM, HRTEM and SAED micrographs. As shown in Fig. 3a-c (TEM images with different magnifications), MWCNTs are in intimate contact with LTO nanoparticles, which may enhance the electron transport pathway between adjacent LTO particles. The particle size range distribution of ~ 50-100 nm and this observation were in good agreement with the data of crystallites from XRD. HRTEM and SAED patterns provide more detailed structural information (Fig. 3d and e). As can be seen from Fig. 3D, the unique lattice edge distance in the range of approximately d = 0.28 nm corresponds to the (400) plane of the pristine LTO. The clear bright spots and diffuse diffraction rings can be seen in the SAED (Fig. 3e) image, which is further evidence, that the LTO-MWCNTs was made up of extremely crystalline, nanoscale particles. Figure 3f shows the EDX pattern of the LTO-MWCNTs with various Ti, O, and C element ratios.

Electrochemical Evaluation of Modified Electrodes
The kinetic barrier of the electrode and solution interface of the electroactive species can be evaluated using the CV approach [76].  Here, Ip = peak current, n = number of electrons, A = active surface area and υ = scan rate, respectively. The other terms such as F, R, and T stand for the temperature, gas constant, and faraday constant, respectively. According to the results, the estimated 'Γ' values for LTO-MWCNTs, MWCNTs, pristine LTO, and bare GCE electrodes were 5.12 × 10 − 8 mol cm − 3 , 3.98 × 10 − 8 mol cm − 3 , 2.72 × 10 − 8 mol cm − 3 , and 1.42 × 10 − 8 mol cm − 3 respectively. Higher 'Γ', maximum peak current and lowest peak separation potential was due to the faster electron transfer kinetics of LTO-MWCNTs/GCE. In order to evidence it, the fabricated electrodes were further subjected to EIS tests.
EIS technique is a powerful, non-destructive, and very useful technique for detecting molecules on the surface of the electrodes. It provides important information on the phenomenon of charge transfer through the properties of the electrode/electrolyte interface [79]. The EIS spectrum for bare (a), pristine LTO (b), pristine MWCNTs (c) and LTO-MWCNTs (d) modified electrodes in 0.1 M KCl/1mM [Fe(CN) 6 ] 3−/4− was displayed in Fig. 5. In general, the (2) Ip = n 2 F 2 A Γ∕4RT, semicircular diameter at high frequencies in the EIS spectrum shows the electron transfer resistance (R ct ) on the electrode surface [80]. As shown in Fig. 5, the indented semicircular diameter for LTO-MWCNTs/GCE was 35 Ω, which was smaller than the bare GCE (70 Ω), LTO/GCE (52 Ω) and MWCNTs/GCE (44 Ω). The electrode made of LTO-MWCNTs have the lowest Rct value, indicating that a strong electron conduction route has formed between the electrode surface and the electrolyte. Furthermore, the synergistic interaction between MWCNTs and nanoscale LTO was also responsible for the lowest R ct value LTO-MWC-NTs/GCE. Additionally, the amalgamation of MWCNTs and LTO provided a high electronic conductivity and high active surface area. As can be seen in the inset of Fig. 5, the impedance spectrum was fitted using the Randles equivalent circuit. The circuit has four separate parameters: Z w , CPE, R ct , and R s , which stand for Warburg impedance, constant phase element, charge transfer resistance, and solution resistance. According to the findings of CV and EIS, we conclude that the LTO-MWCNTs/GCE nanocomposite electrode has excellent conductivity in comparison with all fabricated electrodes. 29 mV) and the higher peak currents with respect to LTO-MWCNTs/GCE towards DA detection can be explained by the high electrocatalytic activity of LTO-MWCNTs composite, which acted as highly conductive wires that contributed to the fast charge transfer kinetics. Additionally, LTO particle agglomeration was effectively reduced by MWCNTs, leading to an increase in the electrochemically active surface area, resulting in an improvement in redox peak currents [81]. However, compared to LTO-MWCNTs/GCE, the LTO/ GCE (curve c) displayed reduced peak currents (I pa /I pc = 6.82 × 10 − 6 /-5.13 × 10 − 6 A) and a change in peak potentials towards a higher value (ΔE p = 45 mV). The significant agglomeration of LTO particles was the cause of the poor electrocatalytic activity of LTO/GCE. The MWCNTs/ GCE (curve d) showed increased peak currents (I pa /I pc = 8.32 × 10 − 6 /-6.34 × 10 − 6 A) and a shift in peak potentials towards the lower value (ΔE p = 36 mV) when compared with LTO/GCE. This was due to the fact that the highly conductive cable-like structures of MWCNTs provided large surface area for the electrode, thereby attracting more analyte particles on the surface. Very weak peak currents (I pa / I pc = 3.54 × 10 − 6 /-3.03 × 10 − 6 A) and a shift of peak potentials towards a higher value (ΔE p = 93 mV) was seen in the case of bare GCE (peak b) compared with all the fabricated electrodes (peaks c, d and e). This was owing to GCE's low conductivity and tiny active surface area. Based on the foregoing findings, a synergistic effect of both LTO and MWC-NTs in the composite was proposed to be considered. As a

Influence of pH Buffer
CV was utilized to investigate the impact of pH on the redox behavior of DA in the presence of varying pH of the electrolytes at LTO-MWCNTs/GCE. In Fig. 7a, CVs with varying pHs (5.0-9.0) were produced at LTO-MWC-NTs/GCE containing 1 mM DA. As shown in Fig. 7a, the pH of the buffer solution had an impact on the I pa /I pc and their ΔE p of DA. With an increase in pH, the peak potentials were linearly moved towards negative potentials, confirming the involvement of protons in the redox reaction, which suggests that the electrooxidation reaction of DA includes an electron transfer reaction followed by a proton transfer process [82]. The oxidation peak currents of DA steadily rose between pH 5.0 and pH 7.0. This came about because of the electrostatic interaction between the electrode surface and the charged DA molecules. At the same time, due to a deficiency in protons in the basic natured PBS, peak currents of DA progressively decreased from pH 7.0-9.0. Figure 7b exemplifies the effect of pH on the oxidation peak potential (E pa ) and its peak current. The pH dependency vs. E pa relationship was expressed as E pa (V) = 0.3607 − 0.0539 pH (R 2 = 0.9952) with a slope value Fig. 7 a CVs of LTO-MWC-NTs/GCE in 1 mM DA at varying pH of the electrolytes. b Relationship of the peak potentials and oxidation peak currents of DA against different pH values of 0.053 V/pH for DA. The observed slope value nearly fits the theoretical Nernst value of -0.059 V/pH for two electrons and two protons participating in the oxidation process, which is in good accord with the reported literature [83,84]. Based on the findings of the pH investigation, a higher peak current was observed at pH 7.0, thus pH 7.0 was chosen as the optimal pH value for further research.

Influence of scan rate
The electrocatalytic reaction of LTO-MWCNTs/GCE on the redox behavior of DA was investigated at various scan rates using CV. The CVs at various scan speeds over the range of 10 to 500 mV s − 1 (a-y) in 1 mM DA containing PBS with a pH of 7.0 at LTO-MWCNTs/GCE was shown in Fig. 8a. As can be seen in Fig. 8a, all the redox peaks of DA showed small and gradual shifts as the scan rate increased, and the peak current intensity gradually increased. This result confirms that the mechanism of electrochemical Fig. 8 a CVs at different scan rates from 10-500 mV s -1 (peak a-y) in1 mM DA at LTO-MWC-NTs/GCE. b Plot of DA redox peak currents versus different scan rates 1 3 reaction is highly dependent on changes in scan speed. The relationship between the redox peak currents (I pa /I pc ) and various scan speeds in a range of 10-500 mV s − 1 was represented in Fig. 8b. The relationship can be expressed as I pa (A) = 0.2667 + 0.0162 v (mV s − 1 ) (R 2 = 0.9972) and I pc (A) = 0.0753-0.0161 v (mV s − 1 ) (R 2 = 0.9946), respectively. This result confirms an adsorption-controlled mechanism at the modified electrode [85]. The electrochemical kinetic parameters (such as the heterogeneous rate constant (k s ), electron transfer coefficient (α), and the number of electrons (n)) were also determined using the following Eqs. (3-4) [86].
The term 'n' was estimated using Eq. 4 and the plot of E p vs. ln, which found out to be 2.21. The plot of ln Ip vs. E p -E o was used to estimate the value of 'α' to be 0.513. With the help of Eq. 3, the 'k s ' at LTO-MWCNTs/GCE was determined to be 2.78 s − 1 , which was a greater value than that of the previously reported literatures [87,88]. These results demonstrate that the electrode modified with LTO-MWC-NTs exhibits good electrocatalytic activity in enhancing the detection of DA electron transfer during the electrochemical oxidation process. (3) m = RT∕ nF.

Sensitive Determination of DA at LTO-MWCNTs/ GCE Sensor
Under optimum experimental conditions, the modified LTO-MWCNTs/GCE electrode was used for the sensitive determination of various concentrations of DA in aqueous PBS using highly sensitive DPV technique. The DPV response at various DA concentrations over the range of 5-260 µM (a-t) at LTO-MWCNTs/GCE in PBS (pH 7.0) was depicted in Fig. 9. As we expected, as DA concentration increased over the range of 5-260 µM, the oxidation peak currents gradually increased. The plot of I pa vs. various concentrations (Inset Fig. 9) revealed the corresponding linear equation, which is I pa (µA) = -0.6292 + 0.0609 [DA] (µM) (R 2 = 0.9979). Using Eqs. (5) and (6), the detection and quantification limits of DA were computed and determined to be as 1.54 µM and 5.16 µM, respectively. In addition, the electrochemical characteristics of LTO-MWCNTs/GCE with respect to the detection of DA compared to other published literature were listed in Table 1 [89][90][91][92][93][94][95][96][97].
Where 'M' represents the slope value determined from the calibration graph and 'SD' represents the standard deviation of peak currents.

Selectivity Study
The selective DA detection in the existence of 5-HT, and FA was examined at LTO-MWCNTs/GCE. The selectivity investigation involved changing the concentration of one species while keeping the concentrations of the other two species constant. As seen in Fig. 10a, the concentrations of DA were changed from 10 to 70 µM while the concentrations of the other two species remained constant. The concentrations of 5-HT (20-400 µM) and FA (20-310 µM) were adjusted in a similar manner, but the concentrations of the other two species remained constant ( Fig. 10b and c). As shown in Fig. 10a-c, the peak currents of DA, 5-HT, and FA were proportionate to the different amounts of each substance. The peak potentials and peak currents of DA, 5-HT, and FA did not alter during the investigation. Hence, these findings suggest that the proposed LTO-MWCNTs/GCE method has good selectivity. The peak currents showed a strong linear relationship with different concentrations of DA, 5-HT, and FA (Insets Fig. 10a-c). The corresponding three linear equations were found as (7), (8), and (9) respectively.

Reproducibility, Stability, and Analytical Utilization of the Fabricated Sensor
Newly produced LTO-MWCNTs/GCE (ten times) were utilized to investigate the reproducibility of the method with the help of CV in 0.1 M PBS (pH 7.0) containing 1 mM DA (Fig. 11). The findings showed that the peak currents of the DA had a relative standard deviation (RSD) of about 3.5%, indicating that the established method's reproducibility was satisfactory. Additionally, the CV responses of DA over a seven-day period were examined in order to assess the stability of the LTO-MWCNTs/GCE electrode (the CV response was measured on each day). According to these findings, the peak CV currents at the LTO-MWCNTs/GCE electrode were unaffected, indicating that the modified electrode has a high degree of stability [98]. To further investigate the applicability of LTO-MWCNTs/GCE, the DPV method was used to determine DA content in the injection sample. Before analysis, the commercial dopamine hydrochloride injection (40.0 mg/mL) sample was diluted in 0.1 M PBS (pH 7.0) and storing it in a refrigerator. The recoveries of DA were analyzed using the standard addition method and found to be 99.86%, 98.88%, 99.78%, and 97.92%, respectively. From these results, satisfactory recoveries were noticed. Hence, the suggested LTO-MWCNTs/GCE sensor demonstrated good electrocatalytic activity and sensitivity for DA assay in a pharmaceutical sample.

Galvanostatic Charge-Discharge (GCD) Tests
As synthesized samples were characterized by chargedischarge experiments in an aqueous cell at a rate of 1 C between the potential window of -0.4 to + 0.4 V. (vs.    Fig. 12a. All the electrodes have flat plateaus in their charge/discharge curves, as shown in Fig. 12a, which agrees well with the CV data. The estimated initial discharge capacities of electrodes a, b, c, and d were 176 mAh g − 1 , 158 mAh g − 1 , 142 mAh g − 1 , and 132 mAh g − 1 , respectively. These results showed that the initial discharge capacity at the LTO-MWCNTs (a) nanocomposite electrode was greater than the initial discharge capacities at the other three electrodes (b, c, and d), as well as good comparable with the previously published literatures [37][38][39][40]. The high initial discharge capacity at LTO-MWCNTs electrode can be explained by the fact that (i) The LTO spinal structure's ionic intercalation and de-intercalation are correlated with the redox behavior of Ti + 4 /Ti + 3 [99]. (ii) A conductive network is created when well-bonded MWCNTs cling firmly to the surface of LTO nanoparticles. This network offers LTO nanoparticles robust binding, which improves initial discharge capacity to a higher degree. (iii) In addition, the increased active surface area and improved electrochemical activity of LTO-MWCNTs/GCE were achieved in comparison to the above electrodes.  Figure 12(B-E) present the cyclability curves and the coulombic efficiency vs. cycle number of electrodes tested at 1 C rate over 30 cycles for LTO-MWCNTs (B), MWCNTs (C), and pristine LTO (D) and bare GCE (E), respectively. The obtained discharge capacities were 167 mAh g − 1 , 148 mAh g − 1 , 130 mAh g − 1 , and 118 mAh g − 1 for LTO-MWC-NTs (B), MWCNTs (C), and pristine LTO (D) and bare GCE (E), respectively with the capacity retention 95%, 94%, 92%, and 90%, respectively, after 30 discharge cycles. The calculated average coulombic efficiencies were 99.37%, 98.52%, 96.67% and 93.74% respectively for electrodes B, C, D and E, respectively. The obtained efficiency for LTO-MWCNTs showed the excellent electrochemical reversibility of the electrode over other electrodes. These findings support the LTO-MWCNTs nanocomposite as a superior anode material for LIBs with high-coulombic efficiency.

Conclusion
In the current study, the LTO-MWCNTs nanocomposite material was successfully made using a simple hydrothermal approach. It was then used as an efficacious anode material in the LIBs as well as an electrochemical sensor for detecting DA. The phase purity and crystallite size were confirmed by XRD analysis. SEM and HRTEM images were acquired to confirm the integration of LTO nanoparticles and MWCNTs. LTO-MWCNTs/GCE nanocomposite electrode exhibited good electrochemical properties such as good sensitivity, selectivity, reproducibility, stability, discharge capacity and cyclic stability when compared to MWCNTs, pristine LTO and bare GCE. According to experiments performed on simultaneous determination, the LTO-MWCNTs/ GCE sensor exhibited DA detection even in the presence of interfering species including 5-HT and FA. Furthermore, the proposed sensor demonstrated acceptable recoveries in real-time DA sensing in commercial injection sample analysis. Finally, the GCD test revealed that the suggested LTO-MWCNTs nanocomposite functions as an anode material, with a high initial discharge capacity of 176 mAh g − 1 and acceptable cycle stability.