Indium Tin Oxide Glass Electrode Research Articles

Polymer Dots for Photoelectrochemical Bioanalysis.

Different from the most extensively used inorganic quantum dots (Qdots) for the current state-of-the-art photoelectrochemical (PEC) bioanalysis, this work reports the first demonstration of polymer dots (Pdots) for novel PEC bioanalysis. The semiconducting Pdots were prepared via the reprecipitation method and then immobilized onto the transparent indium tin oxide glass electrode for PEC biodetection of the model molecule l-cysteine. The experimental results revealed that the as-fabricated Pdots exhibited excellent and interesting PEC activity and good analytical performance of rapid response, high stability, wide linear range, and excellent selectivity. In particular, the PEC sensor could easily discriminate l-cysteine from reduced l-glutathione (l-GSH). This work manifested the great promise of Pdots in the field of PEC bioanalysis, and it is believed that our work could inspire the development of numerous functional Pdots with unique properties for innovative PEC bioanalytical purposes in the future.

A Urea Potentiometric Biosensor Based on a Thiophene Copolymer

A potentiometric enzyme biosensor is a convenient detector for quantification of urea concentrations in industrial processes, or for monitoring patients with diabetes, kidney damage or liver malfunction. In this work, poly(3-hexylthiophene-co-3-thiopheneacetic acid) (P(3HT-co-3TAA)) was chemically synthesized, characterized and spin-coated onto conductive indium tin oxide (ITO) glass electrodes. Urease (Urs) was covalently attached to the smooth surface of this copolymer via carbodiimide coupling. The electrochemical behavior and stability of the modified Urs/P(3HT-co-3TAA)/ITO glass electrode were investigated by cyclic voltammetry, and the bound enzyme activity was confirmed by spectrophotometry. Potentiometric response studies indicated that this electrode could determine the concentration of urea in aqueous solutions, with a quasi-Nernstian response up to about 5 mM. No attempt was made to optimize the response speed; full equilibration occurred after 10 min, but the half-time for response was typically <1 min.

Synthesis and electrochemical properties of potassium 5-trifluoromethyl-1,3,4-thiadiazole-2-thiolate/disulfide redox couple

A new redox couple, composed of the reduced species potassium 5-trifluoromethyl-1,3,4-thiadiazole-2-thiolate 2 and the oxidized species 5,5′-bis (2-trifluoromethyl-1,3,4-thidiazole) disulfide 3, was synthesized and characterized chemically and electrochemically when dissolved in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMITFSI). Platinum (Pt), glassy carbon (GC) and cobalt sulfide-coated indium tin oxide glass (ITO-CoS) electrodes were used. The diffusion-controlled redox processes were shown to be electrochemically irreversible. At higher electrolyte temperature, the current densities are enhanced, and the potential difference between the anodic and cathodic peaks is decreased, in conjunction with a decrease in the viscosity of the electrolytic medium. The best electrocatalytic performance was obtained with the ITO-CoS electrode, followed by GC and Pt electrodes. A greater thiolate/disulfide ratio favors larger anodic current densities, whereas a smaller ratio leads to higher cathodic current densities. Preliminary stability studies of the ITO-CoS electrode confirmed the very good electrochemical and mechanical stability of this electrode considered as a serious candidate to replace platinum as the counter electrode in dye-sensitized solar cells (DSSCs). The electrolytic media studied in this work exhibits a very low absorption of visible light, contrarily to the conventional I3−/I− mediator, offering the possibility of illumination of the device via the counter electrode.

Cu and Ni Nanoparticles Deposited on ITO Electrode for Nonenzymatic Electrochemical Carbohydrates Sensor Applications

AbstractA novel non‐enzymatic carbohydrates sensor which was an indium tin oxide (ITO) glass electrode modified by nickel and copper nanoparticles (Cu/Ni/ITO) was developed by an electrochemical method. The crystallinity, morphology, electrochemical measurements and amperometric response of the as‐prepared ITO modified electrode were examined by the X‐ray diffraction (XRD), scanning electron microscopic (SEM), cyclic voltammetry (CV) and chronoamperometry, respectively. The Cu/Ni/ITO electrode had better electroactivity for glucose oxidation than that obtained using Cu/ITO, Ni/ITO, and Ni/Cu/ITO. The logistic regression equation, Ipa = (A1 – A2)/[1 + (Cglucose/x0)p] + A2, was used to fit the calibration curves of glucose aqueous solution concentrations and responsive current intensity. In research of other saccharides, such as fructose, lactose, sucrose, and maltose, which were detected by the Cu/Ni/ITO electrode, it was obvious that the Cu/Ni/ITO electrode was more sensitive to monosaccharides than disaccharides. Monosaccharides and disaccharides can be detected because the saccharides themselves had aldehyde group or be isomerized to an isomer having an aldehyde group in alkaline environment, and then aldehyde group produced carboxylic acid in the catalytic oxidation of the electrode, which lead to the change of electrode surface conductivity and the appearance of oxidation peak, and the alkaline environment further promotes the above reaction.

Surface Characterization and Morphology of Conducting Polypyrrole Thin Films during Polymer Growth on ITO Glass Electrode

Statistical, morphological, and fractal analyses of the conducting polypyrrole (PPy) thin films during polymer growth on the indium tin oxide (ITO) glass electrode were investigated. Cyclic voltammetry (CV) was used to synthesize polymer thin films with different thicknesses and for calculation of fractal dimensions (Df). Atomic force microscopy (AFM) as a powerful technique was employed to statistically study and analyze the morphology of different types of thin film surfaces with parameters such as root mean square (RMS), kurtosis (Ku), skewness (Sk), and Df. In calculating the fractal dimensions from AFM images of different thin films, power spectral density, perimeter–area, and box-counting methods were used. The results show that the fractal dimensions increased with increasing thicknesses of the films. RMS, Ku, and Sk parameters of the films were changed with increasing film thicknesses. Moreover, X-ray diffraction (XRD) analysis technique confirmed the process of growing polymers on polycrystalline...

Silver nanostructures synthesis via optically induced electrochemical deposition.

We present a new digitally controlled, optically induced electrochemical deposition (OED) method for fabricating silver nanostructures. Projected light patterns were used to induce an electrochemical reaction in a specialized sandwich-like microfluidic device composed of one indium tin oxide (ITO) glass electrode and an optically sensitive-layer-covered ITO electrode. Silver polyhedral nanoparticles, triangular and hexagonal nanoplates, and nanobelts were controllably synthesized in specific positions at which projected light was illuminated. The silver nanobelts had rectangular cross-sections with an average width of 300 nm and an average thickness of 100 nm. By controlling the applied voltage, frequency, and time, different silver nanostructure morphologies were obtained. Based on the classic electric double-layer theory, a dynamic process of reduction and crystallization can be described in terms of three phases. Because it is template- and surfactant-free, the digitally controlled OED method facilitates the easy, low cost, efficient, and flexible synthesis of functional silver nanostructures, especially quasi-one-dimensional nanobelts.

Study of ITO Glass Electrode Modified with Iron Oxide Nanoparticles and Nafion for Glucose Biosensor Application

In this study, we report the fabrication of the indium tin oxide (ITO) glass electrode modified with iron oxide nanoparticles (IONPs) and nafion for glucose biosensor applications. The IONPs was synthesized using the precipitation method and functionalized with citric acid (CA) to provide hydrophilic surface and functional group for glucose oxidase (GOx) enzyme immobilization. The structural and morphological studies of CA-IONPs were characterized using X-ray diffractometer (XRD) and transmission electron microscope (TEM). The size of the IONPs measured from TEM image was ∼17nm. The bioelectrode designated as Nafion/GOx/CA-IONPs/ITO was developed by drop casting of the CA-IONPs, GOx and nafion on the ITO glass. The Nafion/GOx/CA-IONPs/ITO bioelectrode showed good electrochemical performance for glucose detection. The functionalized CA-IONPs acted as the catalyst and help to improve the electron transfer rate between GOx and ITO electrode. In addition, thin nafion film was coated on the electrode to prevent interference and improve chemical stability. The Nafion/GOx/CA-IONPs/ITO bioelectrode showed high sensitivity of 70.1μAmM-1cm-2 for the linear range of 1.0-8.0mM glucose concentrations.

Neural depolarization triggers Mg2+ influx in rat hippocampal neurons

Homeostasis of magnesium ion (Mg2+) plays key roles in healthy neuronal functions, and deficiency of Mg2+ is involved in various neuronal diseases. In neurons, we have reported that excitotoxicity induced by excitatory neurotransmitter glutamate increases intracellular Mg2+ concentration ([Mg2+]i). However, it has not been revealed whether neuronal activity under physiological condition modulates [Mg2+]i. The aim of this study is to explore the direct relationship between neural activity and [Mg2+]i dynamics. In rat primary-dissociated hippocampal neurons, the [Mg2+]i and [Ca2+]i dynamics were simultaneously visualized with a highly selective fluorescent Mg2+ probe, KMG-104, and a fluorescent Ca2+ probe, Fura Red, respectively. [Mg2+]i increase concomitant with neural activity by direct current stimulation was observed in neurons plated on an indium-tin oxide (ITO) glass electrode, which enables fluorescent imaging during neural stimulation. The neural activity-dependent [Mg2+]i increase was also detected in neurons whose excitability was enhanced by the treatment of a voltage-gated K+ channel blocker, tetraethylammonium (TEA) at the timings of spontaneous Ca2+ increase. Furthermore, the [Mg2+]i increase was abolished in Mg2+-free extracellular medium, indicating [Mg2+]i increase is due to Mg2+ influx induced by neural activity. The direct neuronal depolarization by veratridine, a Na+ channel opener, induced [Mg2+]i increase, and this [Mg2+]i increase was suppressed by the pretreatment of a non-specific Mg2+ channel inhibitor, 2-aminoethoxydiphenyl borate (2-APB). Overall, activity-dependent [Mg2+]i increase results from Mg2+ influx through 2-APB-sensitive channels in rat hippocampal neurons.

Involvement of flocculin in negative potential-applied ITO electrode adhesion of yeast cells.

The purpose of this study was to develop novel methods for attachment and cultivation of specifically positioned single yeast cells on a microelectrode surface with the application of a weak electrical potential. Saccharomyces cerevisiae diploid strains attached to an indium tin oxide/glass (ITO) electrode to which a negative potential between −0.2 and −0.4 V vs. Ag/AgCl was applied, while they did not adhere to a gallium-doped zinc oxide/glass electrode surface. The yeast cells attached to the negative potential-applied ITO electrodes showed normal cell proliferation. We found that the flocculin FLO10 gene-disrupted diploid BY4743 mutant strain (flo10Δ /flo10Δ) almost completely lost the ability to adhere to the negative potential-applied ITO electrode. Our results indicate that the mechanisms of diploid BY4743 S. cerevisiae adhesion involve interaction between the negative potential-applied ITO electrode and the Flo10 protein on the cell wall surface. A combination of micropatterning techniques of living single yeast cell on the ITO electrode and omics technologies holds potential of novel, highly parallelized, microchip-based single-cell analysis that will contribute to new screening concepts and applications.

Electrochemically Tunable Cell Adsorption on a Transparent and Adhesion-Switchable Superhydrophobic Polythiophene Film.

A superhydrophobic polythiophene film (SSPTH) is prepared by double-layer electrodeposition on an indium tin oxide (ITO) glass electrode. This film shows not only electroresponsive superhydrophobic features, but also high transparency compared with the usual polythiophene film. The water-droplet adhesion on the SSPTH film can be switched between sliding and pinned states under the applied potential. More intresetingly, the change in water-droplet adhesion results in a change in cell adsorption on the SSPTH film. The low-adhesion (dedoped) SSPTH films can prevent Hela cell adhesion, whereas high-adhesion (doped) SSPTH films can promote Hela cell adsorption. This controllable cell adhesion on a SSPTH film may be developed as a smart biointerface material.

Valinomycin-induced pore formation in thin lipid film and its effect on splay and bend elastic constant

AbstractValinomycin-induced rapid changes in the orientation patterns of lipid molecules under an applied field were observed in 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) thin films, aligned on polyvinyl-alcohol-coated indium tin oxide (ITO) glass electrodes both below (Lβ) and above (Lα) phase transition temperatures of DPPC. With the increasing concentration of valinomycin, Freedericksz's transition patterns change significantly. The values of splay (κ11) and bend (κ33) elastic constant changed by several orders of magnitude depending upon the concentration of valinomycin in the DPPC thin films. From the micrographs of field emission scanning electron microscopy, it was clear that pore formation on DPPC thin films would be a reason behind the decay of elastic constant. The decay of elastic constant was described by an exponential decay formula, y = A1e−x/t1+y0. From this point of view, we propose that our system can be used as a biosensor to detect antibiotic-like valinomycin.Keywords: valinomycinFreedericksz's transitionbiosensorlipid aggregatesmembrane elasticity AcknowledgementsThe helpful discussion with Dr Ashesh Nandy and Dr Smarajit Manna, Centre for Interdisciplinary Research and Education, and Dr Suman Bhandary, Bose Institute, are acknowledged.Disclosure statementNo potential conflict of interest was reported by the authors.Additional informationFundingWe thank Defense Research and Development Organization (DRDO), Defense Ministry, India, for their financial support [grant number: ERIP/ER/1103954/M/01/1413].

Kinetic and In Situ Spectroelectrochemical Studies of Conducting Polypyrrole and Its Substituted Growth on Gold and ITO Glass Electrodes

In situ spectroelectrochemistry and electrochemical synthesis of conducting polypyrrole (PPy), poly(N-methylpyrrole) (PNMPy), polyindole (PIn) and poly(pyrrole-indole) P(Py-In) on gold and indium tin oxide (ITO) glass electrode have been investigated and compared. The growth rate of all samples has been compared and studied for the first time. Characterization of the films was performed by cyclic voltammetry (CV), in situ-UV-Vis spectroscopy, in situ resistance measurements and scanning electron microscopy (SEM). The polymerization reactions are 0.71, 0.76, 0.83 and 0.91 orders with respect to the pyrrole, pyrrole-indole, N-methylpyrrole, indole concentrations and 0.59, 0.62, 0.65 and 0.69 orders with respect to the amount of PPy, P(Py-In), PNMPy and PIn in acetonitrile (ACN) and tetrabutylammonium tetra fluoroborate (TBATFB). The kinetic results indicate that the polymerization growth rate of PPy and P(Py-In) are faster than PNMPy and PIn. The in situ resistivity results indicate that the resistivity of PPy and P(Py-In) polymers was higher by around 1–2.5 orders of magnitude than PNMPy and PIn. The in situ UV-visible spectroscopy of polymers on modified ITO/glass with respect to different potential and time indicate a characteristic absorption's bands. The morphology of the samples revealed that the polymers were different and well dispersed.

Post-polymerization functionalization of poly(3,4-propylenedioxythiophene) (PProDOT) via thiol-ene "click" chemistry.

The surface functionalization of conjugated polymers such as the poly(alkoxythiophenes) poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-propylenedioxythiophene) (PProDOT) provides a potential means for systematically tailoring their physical properties. We previously reported the synthesis of an alkene-functionalized 3,4-propylenedioxy-thiophene (ProDOT) derivative that could be readily modified through thiol-ene "click" chemistry. Here, we investigated the post-polymerization modification of PProDOT surfaces by using a dialkene functionalized variant (ProDOT-diene). The chemical structure of the ProDOT-diene monomer was confirmed by Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared spectroscopy (FTIR). The ProDOT-diene monomer was either chemically or electrochemically polymerized into the PProDOT-diene polymer, and then subsequently modified with alkyl, PEG, or ferrocene moieties via radical-based thiol-ene chemistry. We found that the normally insoluble PProDOT-diene could be converted into a soluble derivative by grafting alkyl groups onto the polymer chains after chemical polymerization. When electrochemically deposited on indium-tin oxide (ITO) glass electrodes, the conductivity, electroactivity and contact angles of the modified PProDOT-diene films could be tuned over a broad range. Scanning Electron Microscopy (SEM) revealed that post-polymerization modification did not significantly alter the surface morphology of the PProDOT-diene films. Overall, this method allows for efficient, facile tuning of the surface chemistry of poly(alkylthiophene) films, making it possible to tailor properties such as conductivity and wettability for different applications.

Electrosynthesis and Electrochemical and Electrochromic Properties of Poly(aniline-co-N-methylthionine)

A novel conducting polymer, poly(aniline-co-N-methylthionine), is synthesized in a mildly acidic aqueous solution using cyclic voltammetry. The rate of copolymerization and the electrochemical properties of the obtained copolymers are substantially affected by pH, upper potential limit and comonomer concentration ratio. The copolymer possesses a high electrochemical activity in an aqueous solution up to pH 10.0. The copolymer formed on an indium-tin oxide glass electrode exhibits a black-to-transmissive electrochromism under relatively low potentials. The results from the Fourier transformed infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) of the copolymer show that NMTh units and Cl− ions were incorporated into the copolymer backbone during the electrosynthesis. The scanning electron microscopy (SEM) micrograph demonstrates that the copolymer film is composed of polymeric flower-like microparticles with an average diameter of 1μm.

Artificial photosynthesis by using chloroplasts from spinach adsorbed on a nanocrystalline TiO2 electrode for photovoltaic conversion

Photovoltaic conversion has been achieved by use of chloroplasts (photosynthetic organs) from spinach adsorbed on a nanocrystalline TiO2 film on an indium tin oxide (ITO) glass electrode (chloroplast/TiO2 electrode). The shape of the absorption spectrum of the chloroplast/TiO2 electrode is almost the same that of a dispersion of the chloroplasts. Absorption maxima of the chloroplast/TiO2 electrode observed at 430, 475, and 670 nm were attributed to carotenoid and chlorophyll molecules, suggesting that chloroplasts have been adsorbed by the nanocrystalline TiO2 film on the ITO electrode. The photocurrent responses of chloroplast/TiO2 electrodes were measured by using a solution of 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile as redox electrolyte in the presence or absence of water and 100 mW cm−2 irradiation. The photocurrent of the chloroplast/TiO2 electrode was increased by adding water to the redox electrolyte. The photocurrent responses of chloroplast/TiO2 electrodes irradiated with monochromatic light (680 nm, the absorption band of photosystem II complexed with evolved oxygen) were measured by use of a solution of 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile as redox electrolyte in the presence or absence of water. A chloroplast/TiO2 electrode photocurrent was observed only when the redox electrolyte containing water was used, indicating that the oxygen evolved from water by photosystem II in chloroplasts adsorbed by a nanocrystalline TiO2 film on an ITO electrode irradiated at 680 nm is reduced to water by the catalytic activity of the platinum electrode. The maximum incident photon-to-current conversion efficiency (IPCE) was 0.8 % on irradiation at 670 nm.

Electrodeposition of composites consisting of polypyrrole and microporous zeolites

Polypyrrole/zeolite composites were synthesized by electrochemical polymerization of pyrrole monomer at ambient temperature (22 ± 1 °C) in aqueous suspension of pure microporous zeolite particles. Electrodeposition was performed by using the method of constant potential. The proton form of Beta zeolites with SiO2/Al2O3 ratios of 25 and 300 and Y zeolites with SiO2/Al2O3 ratios of 12 and 80 was used in this work. The chemical compositions and the acidic properties of the zeolites were studied by inductively coupled plasma optical emission spectrometer and potentiometric acid–base titration. Polypyrrole/zeolite composite films deposited on platinum and indium tin oxide glass electrodes were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy with attenuated total reflectance, X-ray diffraction, and transmission electron micrographs, and their electrochemical behavior was studied by cyclic voltammetry. These measurements showed that polymerization of pyrrole took place on the outer surfaces of the host zeolite crystals. The oxidized cationic polypyrrole was charge-balanced by the anionic groups present in the zeolite framework. Content of the anionic groups in the zeolites was found to be important for the electrochemical behavior of the polypyrrole/zeolite composites.

Preparation of a lead sensor based on porous multiwalled carbon nanotubes/thiolated chitosan composite materials

Thiolated chitosan (CS--TGA) was prepared using chitosan (CS) and thioglycolic acid (TGA). Then MWCNTs were added to the mixture of CS--TGA and CS to prepare the CS/CS--TGA/MWCNs porous composite by freeze-drying method and this composite was used to modify an indium tin oxide glass electrode. The electrode was used as a sensor for Pb2+. The morphology and structure of the composite were characterized by infrared spectroscopy and scanning electron microscope, and their electrochemical behavior was also studied. Under the optimized experimental conditions, the sensor showed a linear range of 2.0 \times 10-9\sim 2.0 \times 10-8 mol L-1 for Pb2+ with a detection limit of 9.53 \times 10-10 mol L-1 according to the 3s rule. The prepared heavy ion sensor displayed excellent electrochemical response and high sensitivity.

Hydorgen Peroxide Biosensor Based on Direct Electrochemistry of Hemin in Egg–Phosphatidylcholine Films

Abstract The mixture of egg-PC vesicles and hemin was casted onto indium-tin oxide glass (ITO) electrode. The hemin showed a direct electrochemical behavior on the modified electrode. A well-defined pair of redox peaks was obtained from the cyclic voltammograms at ITO electrode modified by the mixture of hemin and egg-phosphatidylcholine (egg-PC). The average value of the surface coverage of electroactive hemin, Γ, was 3.25 × 10 −12 mol cm −2 . The formal potential ( E o ') of hemin in the lipid film was linearly varied with the pH of phosphate buffer solution in the range from 4.0 to 9.0 with a slope of −43.7 mV/pH. The pH value of buffer solution for measuring hydrogen peroxide was decided to be 4.0. The linear range of the biosensor was from 10 μM to 200 μM with a detection limit of 5 μM. The modified electrode exhibited a good catalytic activity towards hydrogen peroxide. Therefore a third generation biosensor was developed.

Preparation of sulfonated poly(ether–ether–ketone) functionalized ternary graphene/AuNPs/chitosan nanocomposite for efficient glucose biosensor

A facile method of preparing water-dispersible sulfonated graphene (SPG) using sulfonated poly(ether–ether–ketone) organic polymer as a modifier was realized. A glucose biosensor was fabricated by immobilizing glucose oxidase (GOx) on the surface of AuNPs used to modify SPG and chitosan (CH) deposited on an indium tin-oxide (ITO) glass electrode by a solution casting method. Morphological and structural characterizations confirm that the AuNPs can be efficiently applied to the SPG–CH matrix. The amperometric response of the GOx/SPG–AuNPs–CH/ITO bioelectrode shows a broad linear range of 0.5 to 22.2mM, with a limit of detection of 0.13mM and a high sensitivity of 6.51μA/(mMcm2). The excellent performance of the constructed biosensor is attributed to the large surface-to-volume ratio and electron transfer ability of SPG, the high catalytic activity of the AuNPs, and the good biocompatibility of CH. In addition, the sensor has important advantages, such as its simple preparation, fast response time (10s), good stability (70 days), and high reproducibility. Favorable results upon examining the electrochemical response for the determination of glucose in human blood serum were obtained, without the assistance of a negligible effect of interfering bio-analytes. The results of studies show that the ternary SPG–AuNPs–CH nanocomposite may offer a new approach for developing novel types of highly sensitive and stable electrochemical biosensors.

Nanoparticle-Modified Electrode with Size- and Shape-Dependent Electrocatalytic Activities

The size, shape, composition, and crystalline structures of noble metal nanoparticles are the key parameters in determining their electrocatalytic performance. Here, we report on a robust chemical-tethering approach to immobilizing gold nanoparticles onto transparent indium tin oxide (ITO) glass electrode surfaces to systematically investigate their size- and shape-dependent electrocatalysis toward a methanol oxidation reaction (MOR) and an oxygen reduction reaction (ORR). Monodisperse 20 nm nanospheres (NS20s), 45 nm nanospheres (NS45s), and 20 nm × 63 nm nanorods (NRs), which could be chemically tethered to ITO-surface-forming submonolayers without any aggregation, were synthesized. These nanoparticle-modified ITO electrodes exhibited strong electrocatalytic activities toward MOR and ORR, but their mass current densities were highly dependent on the particle sizes and shapes. For particles with similar shapes, the size determined the mass current densities: smaller particle sizes led to greater catalytic current densities per unit mass because of the greater surface-to-volume ratio (NS20s > NS45s). For particles with comparable sizes, the shape or crystalline structure governed the selectivity of the electrocatalytic reactions: NS45 exhibited a higher mass current density in MOR than did NRs because its dominant (111) facets were exposed, whereas NRs exhibited a higher mass current density in ORR because its dominant (100) facets were exposed.