Achieving One Part Per Billion Hydrogen Sulfide (H2S) Level Detection through Optimizing Composition and Crystallinity of Gold-Decorated Tungsten Trioxide (Au-WO3) Nanofibers.

As a common environmental pollutant and an important breath biomarker for several diseases, it is essential to develop a hydrogen sulfide gas sensor with a low-ppb level detection limit to prevent harmful gas exposure and allow early diagnoses of diseases in low-resource settings. Gold doped/decorated tungsten trioxide (Au-WO3) nanofibers with various compositions and crystallinities were synthesized to optimize H2S-sensing performance. Systematically experimental results demonstrated the ability to detect 1 ppb H2S with a response value (Rair/Rgas) of 2.01 using a 5 at % Au-WO3 nanofibers with average grain sizes of around 15 nm. Additionally, energy barrier difference of sensing materials in air and nitrogen (ΔEb) and power law exponent (n) were determined to be 0.36 eV and 0.7, respectively, at 450 °C indicating that O- is predominately ionic oxygen species and adsorption of O- significantly altered the Schottky barrier between the grain. Such quantitative analysis provides a comprehensive understanding of H2S detection mechanism.

Simple fabrication of an electrospun polystyrene microfiber filter that meets N95 filtering facepiece respirator filtration and breathability standards.

During the global spread of COVID-19, high demand and limited availability of melt-blown filtration material led to a manufacturing backlog of N95 Filtering Facepiece Respirators (FFRs). This shortfall prompted the search for alternative filter materials that could be quickly mass produced while meeting N95 FFR filtration and breathability performance standards. Here, an unsupported, nonwoven layer of uncharged polystyrene (PS) microfibers was produced via electrospinning that achieves N95 performance standards based on physical parameters (e.g., filter thickness) alone. PS microfibers 3-6 µm in diameter and deposited in an ~5 mm thick filter layer are favorable for use in FFRs, achieving high filtration efficiencies (≥97.5%) and low pressure drops (≤15 mm H2O). The PS microfiber filter demonstrates durability upon disinfection with hydroxyl radicals (•OH), maintaining high filtration efficiencies and low pressure drops over six rounds of disinfection. Additionally, the PS microfibers exhibit antibacterial activity (1-log removal of E. coli) and can be modified readily through integration of silver nanoparticles (AgNPs) during electrospinning to enhance their activity (≥3-log removal at 25 wt% AgNP integration). Because of their tunable performance, potential reusability with disinfection, and antimicrobial properties, these electrospun PS microfibers may represent a suitable, alternative filter material for use in N95 FFRs.

Nitrous Oxide Is No Laughing Matter: A Historical Review of Nitrous Oxide Gas-Sensing Capabilities Highlighting the Need for Further Exploration.

Nitrous oxide (N2O), also known as laughing gas, is arguably one of the most detrimental greenhouse gases while concurrently being overlooked by the public. Specifically, N2O is ∼300 times more damaging than its better-known counterpart carbon dioxide (CO2) and has a longer-lived lifetime in the atmosphere than CO2. There exist both natural and anthropogenic sources of N2O, and thus, for a better understanding of sources, capture, and decomposition, it is pivotal to identify N2O within the nitrogen biosphere. This review covers the past and current low-cost N2O gas-sensing technologies, focusing specifically on low-cost metal oxide semiconductors (MOSs), chemiresistive and electrochemical sensors that can provide spatial and temporal monitoring of N2O emissions from various sources. Additionally, compositional modifications to MOsS using metal-organic frameworks (MOFs) are discussed, potentially facilitating new awareness and efforts for increased sensing performance and functionality in N2O detection.

Effect of solution pH, precursor ratio, agitation and temperature on Ni-Mo and Ni-Mo-O electrodeposits from ammonium citrate baths.

The induced co-electrodeposition of Ni and Mo is a complex process, where metallic Ni-Mo alloys and Ni-Mo-O composites can originate from the complete and partial reduction of Mo respectively. By adjusting electrolyte compositions and electrodeposition parameters, various metallic, metal/oxide composite, and oxide thin films of Ni-Mo and Ni-Mo-O were electrodeposited from ammonium citrate baths. Ni-ammonia complexes, which play a critical role in promoting the deposition of metallic Ni-Mo alloys, were enhanced at alkaline pH (i.e., 8-10) and lower temperature (i.e., 25-45°C). Moreover, the electrochemical reduction of Ni is under mass transfer limitation, so the deposited Mo content decreased with increasing agitation. On the other hand, higher Mo content can be achieved by relatively higher citrate concentration and larger Mo-to-Ni precursor molar ratio. However, a critical molar ratio of metal precursor resulted in transition from alloy to composite due to Ni inducing the reduction of Mo.

Effects of NH4 +/citrate complexing agent ratio on Ni-Mo and Ni-Mo-O electrodeposits from ammonium citrate baths.

To understand the effect of complexing agents (i.e., ammonium and citrate) in nickel-molybdenum electrodeposition, calculation of the concentration of various Ni and Mo species as a function of pH and initial concentration of metal ions and complexing agents was performed. In addition, linear sweep voltammetry and Hull cell experiments were systematically investigated to understand the effect of current density and ammonium-to-citrate ratio to film compositions, morphology, and crystallinity. The results indicated that Ni(NH3)3 2+ played a critical role in induced co-deposition mechanism of Ni-Mo alloys, which involved the reduced Ni and absorbed H atoms. Microstructure analysis of deposits indicated that the transition from smooth laminarly grown amorphous Ni-Mo-O composites to columnar and nanocrystalline metallic Ni-Mo alloys with a globular structure as the ammonium-to-citrate molar ratio increases. The highest Mo content of alloys was as high as 19 at%, and up to 70 at% O was present in the composites.

Non-destructive characterization of bone mineral content by machine learning-assisted electrochemical impedance spectroscopy.

Continuous quantitative monitoring of the change in mineral content during the bone healing process is crucial for efficient clinical treatment. Current radiography-based modalities, however, pose various technological, medical, and economical challenges such as low sensitivity, radiation exposure risk, and high cost/instrument accessibility. In this regard, an analytical approach utilizing electrochemical impedance spectroscopy (EIS) assisted by machine learning algorithms is developed to quantitatively characterize the physico-electrochemical properties of the bone, in response to the changes in the bone mineral contents. The system is designed and validated following the process of impedance data measurement, equivalent circuit model designing, machine learning algorithm optimization, and data training and testing. Overall, the systematic machine learning-based classification utilizing the combination of EIS measurements and electrical circuit modeling offers a means to accurately monitor the status of the bone healing process.

Multiplexed Anodic Stripping Voltammetry Detection of Heavy Metals in Water Using Nanocomposites Modified Screen-Printed Electrodes Integrated With a 3D-Printed Flow Cell.

In this study, we present multiplexed anodic stripping voltammetry (ASV) detection of heavy metal ions (HMIs)-As(III), Cd(II), and Pb(II)-using a homemade electrochemical cell consisting of dual working, reference and counter screen-printed electrodes (SPE) on polyimide substrate integrated with a 3D-printed flow cell. Working and counter electrodes were fabricated by the screen-printing of graphite paste while the Ag/AgCl paste was screen-printed as a reference electrode (Ag/AgCl quasi-reference electrode). The working electrodes were modified with (BiO)2CO3-reduced graphene oxide (rGO)-Nafion [(BiO)2CO3-rGO-Nafion] and Fe3O4 magnetic nanoparticles (Fe3O4MNPs) decorated Au nanoparticles (AuNPs)-ionic liquid (IL) (Fe3O4-Au-IL) nanocomposites separately to enhance HMIs sensing. Electrochemical detection was achieved using square wave ASV technique. The desired structure of the flow electrochemical cell was optimized by the computational fluid dynamic (CFD). Different experimental parameters for stripping analysis of HMIs were optimized including deposition time, deposition potential and flow rate. The linear range of calibration curves with the sensing nanocomposites modified SPE for the three metal ions was from 0-50 µg/L. The limits of detection (S/N = 3) were estimated to be 2.4 µg/L for As(III), 1.2 µg/L for Pb(II) and 0.8 µg/L for Cd(II). Furthermore, the homemade flow anodic stripping sensor platform was used to detect HMIs in simulated river water with a 95-101% recovery, indicating high selectivity and accuracy and great potential for applicability even in complex matrices.

Recent advances and remaining barriers to the development of electrospun nanofiber and nanofiber composites for point-of-use and point-of-entry water treatment systems.

In this review, we focus on electrospun nanofibers as a promising material alternative for the niche application of decentralized, point-of-use (POU) and point-of-entry (POE) water treatment systems. We focus our review on prior work with various formulations of electrospun materials, including nanofibers of carbon, pure metal oxides, functionalized polymers, and polymer-metal oxide composites, that exhibit analogous performance to media (e.g., activated carbon, ion exchange resins) commonly used in commercially available, certified POU/POE devices for contaminants including organic pollutants, metals (e.g., lead) and persistent oxyanions (e.g., nitrate). We then analyze the relevant strengths and remaining research and development opportunities of the relevant literature based on an evaluation framework that considers (i) performance comparison to commercial analogs; (ii) appropriate pollutant targets for POU/POE applications; (iii) testing in flow-through systems consistent with POU/POE applications; (iv) consideration of water quality effects; and (v) evaluation of material strength and longevity. We also identify several emerging issues in decentralized water treatment where nanofiber-based POU/POE devices could help meet existing needs including their use for treatment of uranium, disinfection, and in electrochemical treatment systems. To date, research has demonstrated promising material performance toward relevant targets for POU/POE applications, using appropriate aquatic matrices and considering material stability. To fully realize their promise as an emerging treatment technology, our analysis of the available literature reveals the need for more work that benchmarks nanofiber performance against established commercial analogs, as well as fabrication and performance validation at scales and under conditions simulating POU/POE water treatment.

Magneto- and opto-stimuli responsive nanofibers as a controlled drug delivery system.

The drawbacks of conventional drug administration include repeated administration, non-specific biodistribution in the body's systems, the long-term unsustainability of drug molecules, and high global cytotoxicity, posing a challenge for the efficient treatment of chronic diseases that require varying drug dosages over time for optimal therapeutic efficacy. Most controlled-release methods encapsulate drug molecules in biodegradable materials that dissolve over time to release the drug, making it difficult to deliver drugs on a schedule. To address these limitations, we developed a magneto-, opto-stimuli responsive drug delivery system based on functionalized electrospun nanofibers loaded with superparamagnetic iron oxide nanoparticles (SPIONs). We exploited the Néel relaxation effect of SPIONs, where heat generated from vibrating SPIONs under exogenously applied magnetic fields or laser illumination induced structural changes of the thermo-sensitive nanofibers that encapsulate the particles. We showed that this structural change of nanofibers is the governing factor in controlling the release of dye molecules, used as a model drug and co-encapsulated within the nanofibers. We also showed that the degree of nanofiber structural change depends on SPION loading and duration of stimulation, demonstrating the tunability of the drug release profile. Overall, we demonstrated the potential of SPION-embedded thermoplastic nanofibers as an attractive platform for on-demand drug delivery.

Aqueous Electrodeposition of SmCo Alloys: II. Direct Current Studies.

Previously, we reported the aqueous electrodeposition of rare earth - iron group alloys. A key factor was the complexation of the metal ions with various coordination compounds (e.g., aminoacetic acids), without which only the ferrous metal and rare earth hydroxides/oxides are deposited. In this work, samarium cobalt (SmCo) alloys were synthesized using direct current (DC) aqueous electrodeposition. The basic electrolyte solution consisted of 1 M samarium sulfamate, 0.05 M cobalt sulfate, and 0.15 M glycine, resulting in deposits containing >30 at% Sm at 60°C with current density of 500 mA/cm2. Supporting electrolytes (i.e., ammonium salts) decreased the Sm content in the deposit. Crystallinity of deposited films altered from nanocrystalline to amorphous as the Sm content increased. Deposits with high Sm content (32 at%) became isotropic with reduction in magnetic saturation (Ms) and coercivity (Hc). A deposition mechanism involving stepwise reduction of the complexed Sm-Co ions by depositing hydrogen atoms was proposed.

Formation of 3D Self-Organized Neuron-Glial Interface Derived from Neural Stem Cells via Mechano-Electrical Stimulation.

Due to dissimilarities in genetics and metabolism, current animal models cannot accurately depict human neurological diseases. To develop patient-specific in vitro neural models, a functional material-based technology that offers multi-potent stimuli for enhanced neural tissue development is devised. An electrospun piezoelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) nanofibrous scaffold is systematically optimized to maximize its piezoelectric properties while accommodating the cellular behaviors of neural stem cells. Hydro-acoustic actuation is elegantly utilized to remotely activate the piezoelectric effect of P(VDF-TrFE) scaffolds in a physiologically-safe manner for the generation of cell-relevant electric potentials. This mechano-electrical stimulation, which arose from the deflection of the scaffold and its consequent generation of electric charges on the scaffold surface under hydro-acoustic actuation, induces the multi-phenotypic differentiation of neural stem cells simultaneously toward neuronal, oligodendrocytic, and astrocytic phenotypes. As compared to the traditional biochemically-mediated differentiation, the 3D neuron-glial interface induced by the mechano-electrical stimulation results in enhanced interactions among cellular components, leading to superior neural connectivity and functionality. These results demonstrate the potential of piezoelectric material-based technology for developing functional neural tissues in vitro via effective neural stem cell modulation with multi-faceted regenerative stimuli.

Nanoengineering Approaches Toward Artificial Nose.

Significant scientific efforts have been made to mimic and potentially supersede the mammalian nose using artificial noses based on arrays of individual cross-sensitive gas sensors over the past couple decades. To this end, thousands of research articles have been published regarding the design of gas sensor arrays to function as artificial noses. Nanoengineered materials possessing high surface area for enhanced reaction kinetics and uniquely tunable optical, electronic, and optoelectronic properties have been extensively used as gas sensing materials in single gas sensors and sensor arrays. Therefore, nanoengineered materials address some of the shortcomings in sensitivity and selectivity inherent in microscale and macroscale materials for chemical sensors. In this article, the fundamental gas sensing mechanisms are briefly reviewed for each material class and sensing modality (electrical, optical, optoelectronic), followed by a survey and review of the various strategies for engineering or functionalizing these nanomaterials to improve their gas sensing selectivity, sensitivity and other measures of gas sensing performance. Specifically, one major focus of this review is on nanoscale materials and nanoengineering approaches for semiconducting metal oxides, transition metal dichalcogenides, carbonaceous nanomaterials, conducting polymers, and others as used in single gas sensors or sensor arrays for electrical sensing modality. Additionally, this review discusses the various nano-enabled techniques and materials of optical gas detection modality, including photonic crystals, surface plasmonic sensing, and nanoscale waveguides. Strategies for improving or tuning the sensitivity and selectivity of materials toward different gases are given priority due to the importance of having cross-sensitivity and selectivity toward various analytes in designing an effective artificial nose. Furthermore, optoelectrical sensing, which has to date not served as a common sensing modality, is also reviewed to highlight potential research directions. We close with some perspective on the future development of artificial noses which utilize optical and electrical sensing modalities, with additional focus on the less researched optoelectronic sensing modality.

Phosphate removal using surface enriched hematite and tetra-n-butylammonium bromide incorporated polyacrylonitrile composite nanofibers.

The nanosized iron oxides-based adsorbent has been widely used to alleviate water eutrophication. However, it is challenging to industrialize the application of nanosized iron oxides-based adsorbent due to their poor stability, difficult separation and recovery. Herein, hematite and tetra-n-butylammonium bromide incorporated polyacrylonitrile (PAN/Fe2O3/TBAB) composite nanofibers with a controlled diameter (i.e., 66 to 305 nm) and composition were systematically synthesized as an adsorbent for phosphate removal from water using surfactant-mediated electrospinning. During the electrospinning process, polar TBAB surfactant enhanced the migration of Fe2O3 nanoparticles toward the surface of nanofibers resulting in Fe2O3 nanoparticles/TBAB surface enriched nanofibers. The synthesized nanofiber membranes were used for phosphate removal, and their adsorption kinetics, adsorption mechanism, and reusability were investigated. Data showed that adsorption kinetic followed the pseudo-second-order model whereas the adsorption mechanism follows the Langmuir model. The phosphate removal was mainly derived from the chemisorption of surface-enriched α-Fe2O3 nanoparticles at acidic and circumneutral pH values, with a small contribution from anion exchange at TBAB sites. The maximum phosphate removal capacity was approx. 8.76 mg/g (i.e., 23.1 mg/g, P/active materials) at pH 3. Additionally, the synthesized nanofiber membrane also shows excellent reusability.

Sandwich-type electrochemical immunosensor for CEA detection using magnetic hollow Ni/C@SiO2 nanomatrix and boronic acid functionalized CPS@PANI@Au probe.

A sandwich-type electrochemical immunosensor was developed for the detection of CEA where hollow magnetic silica coated nickel/carbon (Ni/C@SiO2) nanocomposites was used as an immobilized carrier and gold nanoparticle-coated PANI microsphere (CPS@PANI@Au) as electrochemical transducer. Magnetic assembly of Ni/C@SiO2 nanocomposites allow easy separation and assembly which eliminates the further modification process. In addition, the prepared CPS@PANI@Au possess good biocompatibility, and electrical conductivity. The fabricated immunosensor show excellent sensing performance including a wide dynamic range from 0.006 to 12.00 ng mL-1 and low detection limit at 1.56 pg mL-1. Moreover, this sensor shows superior selectivity with excellent reliability and reproducibility which might lead into easier implementation in clinical setting.

Mechano-Responsive Piezoelectric Nanofiber as an On-Demand Drug Delivery Vehicle.

The control over biodistribution and pharmacokinetics is critical to enhance the efficacy and minimize the side effects of therapeutic agents. To address the need for an on-demand drug delivery system for precise control over the release time and the quantity of drugs, we exploited the mechano-responsiveness of piezoelectric poly(vinylidene fluoride-trifluroethylene) (P(VDF-TrFE)) nanofibers for drug delivery applications. The large surface area-to-volume ratio inherent to nanomaterials, together with the transformative piezoelectric properties, allowed us to use the material as an ultrasensitive and mechano-responsive drug delivery platform driven by the direct piezoelectric effect. The intrinsic negative zeta potential of the nanofibers was utilized to electrostatically load cationic drug molecules, where surface potential changes by exogenous mechanical actuation trigger the release of drug molecules. We show that the drug release kinetics of the P(VDF-TrFE) nanofibers depends on the fiber diameter, thus piezoelectric properties. We further demonstrated that the drug release quantity can be tuned by the applied pressure or dose of physiologically safe corporeal shockwaves as a mechanical stimulus in in vitro and ex vivo models. Overall, we demonstrated the utility of piezoelectric electrospun nanofibers for mechano-responsive controlled drug release.

Comprehensive Review on Thermoelectric Electrodeposits: Enhancing Thermoelectric Performance Through Nanoengineering.

Thermoelectric devices based power generation and cooling systemsystem have lot of advantages over conventional refrigerator and power generators, becausebecause of solid-state devicesdevices, compact size, good scalability, nono-emissions and low maintenance requirement with long operating lifetime. However, the applications of thermoelectric devices have been limited owingowing to their low energy conversion efficiency. It has drawn tremendous attention in the field of thermoelectric materials and devices in the 21st century because of the need of sustainable energy harvesting technology and the ability to develop higher performance thermoelectric materials through nanoscale science and defect engineering. Among various fabrication methods, electrodeposition is one of the most promising synthesis methods to fabricate devices because of its ability to control morphology, composition, crystallinity, and crystal structure of materials through controlling electrodeposition parameters. Additionally, it is an additive manufacturing technique with minimum waste materials that operates at near room temperature. Furthermore, its growth rate is significantly higher (i.e., a few hundred microns per hour) than the vacuum processes, which allows device fabrication in cost effective matter. In this paper, the latest development of various electrodeposited thermoelectric materials (i.e., Te, PbTe, Bi2Te3 and their derivatives, BiSe, BiS, Sb2Te3) in different forms including thin films, nanowires, and nanocomposites were comprehensively reviewed. Additionally, their thermoelectric properties are correlated to the composition, morphology, and crystal structure.

Template-Free Electrochemical Deposition of t-Se Nano- and Sub-micro Structures With Controlled Morphology and Dimensions.

Selenium, depending on its crystal structure, can exhibit various properties and, as a result, be used in a wide range of applications. However, its exploitation has been limited due to the lack of understanding of its complex growth mechanism. In this work, template-free electrodeposition has been utilized for the first time to synthesize hexagonal-selenium (t-Se) microstructures of various morphologies at 80°C. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) revealed 5 reduction peaks, which were correlated with possible electrochemical or chemical reaction related to the formation of selenium. Potentiostatic electrodeposition using 100 mM SeO2 showed selenium nanorods formed at-0.389 V then increased in diameter up to -0.490 V, while more negative potentials (-0.594 V) induced formation of sub-micron wires with average diameter of 708 ± 116 nm. Submicron tubes of average diameter 744 ± 130 nm were deposited at -0.696 V. Finally, a mixture of tubes, wires, and particles was observed at more cathodic potential due to a combination of nucleation, growth, dissolution of structures as well as formation of amorphous selenium via comproportionation reaction. Texture coefficient as a function of applied potential described the preferred orientation of the sub-microstructures changed from (100) direction to more randomly oriented as more cathodic potentials were applied. Lower selenium precursor concentration lead to formation of nanowires only with smaller average diameters (124 ± 42 nm using 1 mM, 153 ± 46 nm using 10 mM SeO2 at -0.389 V). Time-dependent electrodeposition using 100 mM selenium precursor at -0.696 V explained selenium was formed first as amorphous, on top of which nucleation continued to form rods and wires, followed by preferential dissolution of the wire core to form tubes.

Synthesis of gold nanostructures using glycine as the reducing agent.

Biological synthesis of gold nanostructures could potentially offer an environmentally friendly alternative to traditional chemical synthetic methods. During the last decades, various biomolecules, including amino acids, have been successfully used as reducing and capping agents to synthesize multi-shaped gold nanostructures. A grand challenge in this field is to increase our ability to control the size and shape of gold nanostructures formed precisely by systematic synthetic approaches based on the understanding of the mechanism for structural determination. In this study, using glycine as the model amino acid and chloroaurate (AuCl4 -) ions as the precursor solution, we report the finding that the shape of the gold nanostructures synthesized showed a strong correlation with the speciation of gold complexes determined by the pH, precursor concentration and chloride concentration of the solvent system. The gold chloro-hydroxy speciation [AuClx(OH)4-x]- (with x = 0-4) influenced the shape of the gold nanostructures formed, with gold nanoplatelets, nanotriangles, nanokites and nanoribbons observed at x = 4, 3, 2 and 1, respectively, and spherical nanoparticles observed at x = 0. Glycine was found to play a role as a reducing agent, but no significant effect on the morphology was observed, indicating the dominance of gold chloro-hydroxy speciation in the structural formation. These results collectively provide synthetic considerations to systematically synthesize non-spherical to spherical biosynthesized gold nanostructures by controlling the speciation of [AuClx(OH)4-x]-.

Whispering gallery mode emission from dye-doped polymer fiber cross-sections fabricated by near-field electrospinning.

Whispering gallery mode (WGM) resonators demonstrate great potential for photonic and sensing applications. Yet, these devices are often disadvantaged by costly materials or complex fabrication approaches, in addition to lack of manufacturing scalability. Near-field electrospinning (NFES), a recently emerged facile fiber fabrication method, offers a solution. Here, WGM resonances are reported in Rhodamine 6G-doped poly(vinyl) alcohol (PVA) microfibers via NFES. Diameters are tuned over a range of more than 10 µm by varying substrate stage speed. Fibers display uniform distribution of dye, smooth surfaces, and circular cross-sections, all critical for supporting WGMs. High quality (Q) resonances are confirmed within fiber cross-sections through polarization experiments, free-spectral range analysis, and Mie-theory-derived mode assignment. In addition to WGMs, groups of associated spiral or conical modes are observed due to taper-induced weak optical confinement along the fiber axis. Crosslinked, dye-doped PVA fibers are utilized to sense the ethanol concentration in ethanol-water mixtures and actuation mechanisms are evaluated by comparison to theoretical spectra. The demonstration of high-Q resonances within NFES polymer microfibers is a critical step toward simple, cost effective, high-volume fabrication of WGM resonators for optoelectronics and biomedical devices.

Electrochemical Mechanism of Tellurium Reduction in Alkaline Medium.

A systematic electrochemical study was conducted to investigate the reduction of tellurium (Te) in alkaline solutions. The effect of various parameters, including tellurite ion concentration, applied potential, and pH was investigated by both linear sweep voltammograms (LSVs) and electrochemical quartz crystal microbalance (EQCM). EQCM was essential to understand the reduction of Te(0) to soluble Te 2 2 - (-I) or Te2-(-II). The Tafel slopes for two Te reduction reactions [i.e., Te(IV) to Te(0) and Te(0) to Te(-I)] indicated that the electrochemical reduction of Te is strongly dependent on solution pH, whereas it is independent of the concentration of TeO 3 2 - . At relatively weaker alkaline solutions (i.e., pH ≤ 12.5), the discharge of Te ( OH ) 3 + was determined to be the rate-limiting step during the reduction of Te(IV) to Te(0). For the reduction of Te(0) to Te(-I), the reaction follows a four-step reaction, which consisted of two discharge and two electrochemical reactions. The second discharge reaction was the rate-limiting step when pH ≤12.5 with the Tafel slope of 120 mV/decade. At a higher pH of 14.7, the Tafel slope was shifted to be 40 mV/decade, which indicated that the rate-limiting step was altered to the second electrochemical reaction. Te(0) deposits were found either on the surface of an electrode or in the solution depending on pH due to the different rate-limiting reactions, revealing that pH was a key parameter to dictate the morphology of the Te(0) deposits in alkaline media.