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Chromium–iridium oxide (CrxIr1−xO2) alloys with a wire-in-tube morphology were primally prepared as highly efficient electrocatalysts for the oxygen evolution reaction (OER) via a simple electrospinning method.

Single-phase Co3V2O8 with the structural integrity of nanofiber exhibits high electrocatalytic activity for the oxidation of ascorbic acid (AA).

We report the direct growth of highly single crystalline rhenium trioxide (ReO3) nanorods on a tungsten (W) microwire electrode via the physical vapor transport process without any catalyst. In our growth mode, ReO3 nanocubes were initially formed on the surface of a tungsten (W) microwire electrode and further they were anisotropically grown along the [001] crystallographic direction. Furthermore, we performed the fundamental electrochemical experiments so that from cyclic voltammetric measurements, ReO3 nanorods on a W microwire exhibit a good capacitance and Nernstian behavior for a Fe(CN)63−/Fe(CN)64− redox couple in 1 M KNO3 aqueous solution, indicating a promising electrode material for electrochemical applications.

Effects of the B←N unit on the energy level of conjugated small molecule were investigated by synthesizing a new small molecule BPDPP (3,8-bis(5-(2,5-dioctyl-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-thiophen-2-yl)-6,6-dioctyl-6H-benzo[3,4] [1,2]azaborolo[1,5-a]pyridin-5-ium-6-uide) via Suzuki coupling. For comparison, CPDPP (6,6′-(5,5′-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(thiophene-5,2-diyl))bis(2,5-dioctyl-3-(thiophen-2-yl)pyrrolo[3,4-c] pyrrole-1,4(2H,5H)-dione)) having the same chemical structure with BPDPP except the B←N unit is synthesized through the same coupling reaction. Absorption spectra and cyclovoltammetry analysis for these small molecules revealed that the B←N unit reduces the band gap of BPDPP by maintaining large oxidation potential. As a result, the blend film of BPDPP and PC71BM maintained 87.4% of the initial absorption intensity after 1sun light soaking test for 315 h. The photo stability of the BPDPP is significantly higher than the blend film of P3HT: PC71BM, which maintained only 19.8% of the initial absorption intensity only after light soaking for 23 h.

A variety of binary Ru–Co mixed oxide nanotubes (RuxCo1−xOy with x = 0.19, 0.33, 0.47, 0.64 and 0.77) were readily synthesized via electrospinning and subsequent calcination. RuxCo1−xOy nanotubes (0 < x < 0.77) were composed of both rutile (Ru in RuO2 is replaced with Co) and spinel (Co in Co3O4 is replaced with Ru) structures. This elemental substitution created oxygen vacancies in the rutile structure and also resulted in the incorporation of Ru3+ in the octahedral sites of the spinel structure. The as-prepared RuxCo1−xOy nanotubes were investigated for oxygen evolution reaction (OER) electrocatalytic activity in 1.0 M HClO4 aqueous solution. RuxCo1−xOy nanotubes with x ≥ 0.47 presented an excellent OER activity comparable to pure RuO2, known to be the best OER catalyst. Even after more than half of the noble/active Ru content was replaced with cheap/less-active Co, Ru0.47Co0.53Oy showed a good OER activity and a greatly improved stability compared to RuO2 under the continuous OER. These attractive catalytic properties of RuxCo1−xOy can be attributed to the relatively large surface area of the tubular morphology and the substituted structures, presenting feasibility as a practical and economical OER catalyst.

A series of gold (Au) nanostructures, having different morphologies, were fabricated for amperometric selective detection of carbon monoxide (CO), a biologically important signaling molecule. Au layers were electrodeposited from a precursor solution of 7 mM HAuCl4 with a constant deposition charge (0.04 C) at various deposition potentials. The obtained Au nanostructures became rougher and spikier as the deposition potential lowered from 0.45 V to 0.05 V (vs. Ag/AgCl). As prepared Au layers showed different hydrophobicity: The sharper morphology, the greater hydrophobicity. The Au deposit formed at 0.05 V had the sharpest shape and the greatest surface hydrophobicity. The sensitivity of an Au deposit for amperometric CO sensing was enhanced as the Au surface exhibits higher hydrophobicity. In fact, CO selectivity over common electroactive biological interferents (L-ascorbic acid, 4-acetamidophenol, 4-aminobutyric acid and nitrite) was improved eminently once the Au deposit became more hydrophobic. The most hydrophobic Au was also confirmed to sense CO exclusively without responding to nitric oxide, another similar gas signaling molecule, in contrast to a hydrophobic platinum (Pt) counterpart. This study presents a feasible strategy to enhance the sensitivity and selectivity for amperometric CO sensing via the fine control of Au electrode nanostructures.

NixRh1–x alloy nanofibers were synthesized by the thermal reduction of single-phase spinel NiRh2O4 nanofibers under a hydrogen gas flow. First, single-phase NiRh2O4 nanofibers were prepared via calcination preceded by electrospinning. The synthetic conditions including the metal precursor ratio in electrospinning solution and calcination temperature were finely optimized to produce single-phase NiRh2O4. Then, the thermal treatment at a temperature ≥200 °C under a H2 gas flow converted NiRh2O4 to NixRh1–x alloy nanofibers. Their electrocatalytic activity for the hydrogen evolution reaction (HER) was examined with voltammetry in alkaline, neutral and acidic media. NixRh1–x alloy nanofibers showed the lowest overpotentials at −10 mA cm−2 and the smallest Tafel slopes in all media, indicating a HER activity superior to those of commercial Pt, pure Rh metal, and Rh-/Ni-based electrocatalysts found in the literature. The reason for the superb activity of NixRh1–x alloys is ascribed to the synergistic effect of the facilitated hydrogen adsorption on alloyed Rh and Ni atoms and the enlarged electroactive areas from the porous uneven nanofiber structure. Considering that only a few pH-universal HER catalysts have been reported, NixRh1–x alloy nanofibers, where expensive Rh is diluted with cheap Ni, present excellent feasibility as a practical and cost-effective HER catalyst.

The nanotubular structures of IrO2 and Ir metal were successfully synthesized without any template. First, IrO2 nanotubes were prepared by electrospinning and post-calcination, where a fine control of synthetic conditions (e.g., precursor concentration and solvent composition in electrospinning solution, temperature increasing rate for calcination) was required. Then, a further thermal treatment of IrO2 nanotubes under hydrogen gas atmosphere produced Ir metal nanotubes. The electroactivity of the resultant Ir metal nanotubes was investigated toward carbon monoxide (CO) oxidation using linear sweep voltammetry (LSV) and amperometry. The anodic current response of Ir metal nanotubes was linearly proportional to CO concentration change, with a high sensitivity and a short response time. The amperometric sensitivity of Ir metal nanotubes for CO sensing was greater than a nanofibrous counterpart (i.e., Ir metal nanofibers) and commercial Pt (20 wt% Pt loading on carbon). Density functional theory calculations support stronger CO adsorption on Ir(111) than Pt(111). This study demonstrates that metallic Ir in a nanotubular structure is a good electrode material for the amperometric sensing of CO.

We report the effective crystal growth for a unique single phase of spinel cobalt rhodium oxide (Co2RhO4) nanotubes via the electrospinning process combined with the thermal annealing process. In the spinel structure of the electrospun Co2RhO4 nanotubes, Co3+ cations and Rh3+ cations randomly occupy the octahedral sites, while the remaining half of the Co2+ cations occupy the centres of the tetrahedral sites as proved by microscopic and spectroscopic observations. Furthermore, electrospun spinel Co2RhO4 nanotubes exhibit excellent catalytic performances with the least positive onset potential, greatest current density, and low Tafel slope which are even better than those of the commercial Ir/C electrocatalyst for the oxygen evolution reaction (OER) in alkaline solution. Our demonstration of significantly enhanced OER activity with a single phase of electrospun spinel Co2RhO4 nanotubes thus opens up the broad applicability of our synthetic methodology for accessing new OER catalysis.

Nanocomposites of gold (Au) and iridium (Ir) oxide with various compositions (denoted as AuxIr1–xOy, x = 0.05, 0.10, or 0.33, Au precursor molar ratio to Ir precursor) were synthesized via electrospinning and subsequent calcination method with two different solvent composition ratios of ethanol to N,N-dimethylformamide (DMF) in the electrospinning solution (ethanol/DMF = 70:30 or 50:50% v/v). Simple single-step electrospinning successfully fabricated a hierarchical nanostructure having Au nanoparticles formed on fibrous main frames of Ir/IrO2. Different solvent composition in the electrospinning solution induced the formation of main frames with distinct nanostructures; nanoribbons (AuxIr1–xOy-70) with ethanol/DMF = 70:30; and nanofibers (AuxIr1–xOy-50) with ethanol/DMF = 50:50. The pure Ir or Au counterparts (IrOy and Au) were also prepared by the same synthetic procedure as AuxIr1–xOy. Oxygen evolution reaction (OER) activities of as-synthesized AuxIr1–xOy were investigated in 0.5 M H2SO4 and compared t...

Oxygen reduction reaction (ORR) is of great interest in various areas, including energy conversion. This paper presents the simple synthesis and characterization of one-dimensional silver halides nanowires (AgClNW and AgBrNW) as an electrocatalyst for ORR in alkaline media, as well as an investigation of the ORR pathway at AgCl. AgClNW and AgBrNW were prepared via a galvanic replacement reaction (GRR) between silver nanowires (AgNW) and a halide precursor. AgClNW exhibited excellent ORR catalytic activity that was comparable to or better than that for commercial Pt (20 wt% Pt loading on Vulcan carbon), demonstrating potential to replace Pt-based catalysts. A scanning electrochemical microscopy (SECM) analysis supports the existence of an associative ORR pathway at AgCl, and first-principles density functional theory (DFT) calculations suggest that the high ORR activity of AgCl is possibly attributed to the up-shifted Ag d-band center energy in AgCl as well as the assistance of adsorbed water molecules.

Nanoporous ruthenium dioxide (RuO2) was simply prepared by electrodeposition with potential cycling in RuCl3 solution in the presence of reverse micelles of Triton X-100. The electrodeposited RuO2 on Au substrate electrode showed high electroactivity for the oxidations of L-ascorbic acid (AA) and uric acid (UA), while AA oxidation started from a less positive potential compared to UA oxidation. Simultaneous quantitative analysis of AA and UA was successfully carried out via chronoamperometric measurements at two different applied potentials using RuO2 deposited electrode. Due to the oxidation potential difference between AA and UA at RuO2 electrode, only AA was oxidized at an applied potential of 0.20 V vs. SCE and both AA and UA were oxidized at 0.32 V vs. SCE. AA concentration was determined from the current measured at 0.20 V; and then UA concentration was estimated from the current measured at 0.32 V using the predetermined AA concentration. Electrodeposited nanoporous RuO2 electrode exhibited current responses linearly proportional to AA and UA concentrations in a wide concentration range (0–1 mM) and fast response time (≤1 s). The current sensitivities were 342.8 ± 26.3 μA mM−1 cm−2 for AA at 0.20 V; 377.8 ± 18.4 μA mM−1 cm−2 for AA at 0.32 V; and 344.2 ± 11.6 μA mM−1 cm−2 for UA at 0.32 V. In addition, RuO2 electrode showed a high selectivity over interferents such as 4-acetamidophenol (AP), dopamine (DA), and glucose. Reasonable stability and repeatability of RuO2 electrode were also confirmed. Selective quantification of AA and UA in an arbitrary mixture and a human urine sample demonstrated that RuO2 electrode has practical utility in real sample analysis with satisfactory results.

New small molecular semiconductors with small band gap and low-lying highest occupied molecular orbital (EHOMO), namely TBDPPOT, TBDPPEH, and TBDPPEHT4 were synthesized by incorporating the B←N bridged thienylthiazole and diketopyrrolopyrrole (DPP) derivatives. TBDPPOT and TBDPPEH were prepared, respectively, using two different DPPs having 1-octyl and 2-ethylhexyl moiety as the solubilizing group. In addition, the band gap of the TBDPPEH is further reduced by introducing planar thienothiophene unit, which was used for the preparation of TBDPPEHT4. These synthesized SMs are blended with fullerene derivative to construct a photo-active layer for organic photovoltaics. Among OPVs utilizing those SMs, the TBDPPEH exhibits highest power conversion efficiency of 3.21% with an exceptionally high VOC of 0.92 V, which is ascribed to low-lying HOMO energy level of −5.62 eV. It is expected that the utilization of TBDPPEH as a photo-active layer for OPVs would enhance the oxidation stability of the OPVs.

Bimetallic AuRu alloy nanofibers (NFs) with Au:Ru atomic ratios of 7.5:92.5 are constructed and characterized as a bifunctional electrocatalyst for electrochemical overall water splitting (OWS) of both oxygen (OER) and hydrogen evolution reaction (HER). First, composite NFs consisting of RuO2 fibrous mainframes adorned with tiny Au nanoparticles are synthesized by electrospinning and calcination. The following heat treatment of these composite NFs under H2 gas flowing induces the reduction of RuO2 mainframes to metallic Ru within which Au atoms are dispersed to form homogeneous AuRu alloy NFs regardless of their immiscibility. The OWS activities of prepared AuRu alloy NFs are investigated in 0.5 M H2SO4 aqueous solution; and compared to those of RuO2, Ru, Au, and commercial catalysts, M/C (20 wt% metal loading on Vulcan XC-72 with M = Pt, Ru and Ir). In particular, AuRu alloy NFs show outstanding activity for OER: the lowest overpotential at 10 mA cm−2 and the smallest Tafel slope among the tested catalysts. Of great importance, AuRu alloy NFs also present an excellent long-term stability in a sharp contrast to easily deteriorated Ru-based catalysts (e.g., Ru NFs and Ru/C). AuRu alloy NFs also exhibit good HER activity and stability better than most of tested materials. In a two-electrode system, AuRu NFs ∣∣ AuRu NFs is confirmed to have a lower overpotential for OWS than Ir/C ∣∣ Pt/C, a commercial standard. The OWS performance of AuRu alloy NFs is superior to those of Ru-based bifunctional catalysts found in the literature. HER at AuRu alloy is further studied with density functional theory calculation. The current study reveals Ru alloyed with a small amount of Au having a robust nanofibrous morphology improves the electroactivity and stability for both OER and HER in acidic environments. Given that stable bifunctional catalysts for acidic water splitting have been rarely reported, AuRu alloy NFs exhibit an outstanding feasibility as a practical electrocatalyst for overall water splitting with the high activity and stability.

Here, we report the unique transformation of one-dimensional tubular mixed oxide nanocomposites of iridium (Ir) and cobalt (Co) denoted as IrxCo1–xOy, where x is the relative Ir atomic content to the overall metal content. The formation of a variety of IrxCo1–xOy (0 ≤ x ≤ 1) crystalline tubular nanocomposites was readily achieved by electrospinning and subsequent calcination process. Structural characterization clearly confirmed that IrxCo1–xOy polycrystalline nanocomposites had a tubular morphology consisting of Ir/IrO2 and Co3O4, where Ir, Co, and O were homogeneously distributed throughout the entire nanostructures. The facile formation of IrxCo1–xOy nanotubes was mainly ascribed to the inclination of Co3O4 to form the nanotubes during the calcination process, which could play a critical role in providing a template of tubular structure and facilitating the formation of IrO2 by being incorporated with Ir precursors. Furthermore, the electroactivity of obtained IrxCo1–xOy nanotubes was characterized for...

In this study, we have carried out electrodeposition of tantalum (Ta) nanostructures on pencil lead electrode in non-aqueous media at room temperature by applying a constant potential. The deposited Ta on pencil lead was examined for the catalytic effect regarding hydrogen peroxide (H2O2) reduction with voltammetry and amperometry. Ta/pencil lead electrode exhibited amperometric sensitivity of 0.317 μA mM−1 cm−2 and fast response time of 0.75 s, where selective detection of H2O2 was fulfilled without interruption from common electroactive biomaterials such as O2, uric acid, ascorbic acid, dopamine, acetamidophenol, and glucose. For practical applications, the dynamic concentration changes of H2O2 during catalase and glucose oxidase-involved reactions, either eliminating or producing H2O2, were successfully traced in real time with as-prepared electrode. From the kinetics study for catalase and glucose oxidase, we evaluated Michaelis constants (Kmapp) as 7.8 mM for catalase and 37 mM for glucose oxidase, respectively.

RhCo alloy nanotubes were synthesized via the reduction of single-phase Co2RhO4 nanotubes. The reduction was conducted by thermal annealing of the Co2RhO4 nanotubes under hydrogen gas flow. The crystallinity of the prepared RhCo alloy nanotubes depended on the reduction temperature: amorphous phase (200 °C reduction) and the crystalline phase (300 °C reduction). The hydrogen evolution reaction (HER) on RhCo alloys was investigated with voltammetry in 1.0 M HClO4 solution. Amorphous RhCo alloys provided lower overpotential than the crystalline counterpart despite their similar morphology and composition. Of great interest, amorphous RhCo alloy nanotubes exhibited an outstanding HER electroactivity verified with a low overpotential at -10 mA cm-2 (-22 mV) and a small Tafel slope (-24.1 mV dec-1), outperforming commercial Pt, pure Rh metal, and the other previously reported Rh-based catalysts. This excellent HER activity of amorphous RhCo nanotubes was attributed to the amorphous structure having a large electrochemical surface area and maximized Rh-Co interfaces in the alloy facilitating HER. Active but expensive Rh alloyed with less active but cheap Co was successfully demonstrated as a potential cost-effective HER catalyst.

Correction for 'Single phase of spinel Co

We report the effective crystal growth for a unique single phase of spinel cobalt rhodium oxide (Co2RhO4) nanotubes via the electrospinning process combined with the thermal annealing process. In the spinel structure of the electrospun Co2RhO4 nanotubes, Co3+ cations and Rh3+ cations randomly occupy the octahedral sites, while the remaining half of the Co2+ cations occupy the centres of the tetrahedral sites as proved by microscopic and spectroscopic observations. Furthermore, electrospun spinel Co2RhO4 nanotubes exhibit excellent catalytic performances with the least positive onset potential, greatest current density, and low Tafel slope which are even better than those of the commercial Ir/C electrocatalyst for the oxygen evolution reaction (OER) in alkaline solution. Our demonstration of significantly enhanced OER activity with a single phase of electrospun spinel Co2RhO4 nanotubes thus opens up the broad applicability of our synthetic methodology for accessing new OER catalysis.

Two distinct crystalline phases of bimetallic CoxRh1−x alloy nanofibers were synthesized through the thermal H2-reduction of single-phase CoRh2O4 nanofibers that were prepared via calcination preceded by electrospinning. By varying the reduction temperature (T) and retention time (t), it was confirmed that the formation of a fully reduced crystalline metallic alloy required T ≥ 250 °C for t ≥ 2 h. During the reduction process, the single phase of CoRh2O4 was first transformed to an intermediate face centered cubic (fcc) phase where Rh element was principally reduce to Rh(0) and Co element was present as the oxide form. Then, a fully reduced CoxRh1−x alloy was obtained in hexagonal close-packed (hcp) phase. In particular, the hcp structured CoxRh1−x showed a fascinating hydrogen evolution reaction (HER) activity (e.g., the lowest overpotential at 10 mA cm−2 and the smallest Tafel slope) pH independently that was superior to those of commercial Pt and the pure single metal (Co and Rh) nanofibers. CoxRh1−x alloy also showed a robust stability during 10 000-s continuous HER and 1000-repetitive potential sweeps in alkaline (1.0 M NaOH), neutral (1.0 M PBS, pH 7.2) and acidic (0.5 M H2SO4) media. The pH-universal HER activity was ascribed to alloying effect: Co atoms in the alloy interact O atoms in H2O molecules and therefore assist neighboring Rh atoms in adsorbing H atoms readily in alkaline and neutral condition.

In this paper, we demonstrate a simple fabrication of bimetallic silver (Ag) and cobalt (Co) nanostructures (AgCo) with various Ag to Co relative contents via electrochemical co-deposition. A series of AgCo catalysts was electrodeposited on glassy carbon (GC) electrodes at −0.57 V vs. SCE in the deposition solutions, containing Ag precursor, Co precursor, Triton X-100, and 0.3 M KNO3 aqueous solution, with various Ag to Co precursor concentration ratios (1:x, x was varied from 3 to 11). The films, deposited with the total deposition charge of 0.042C, were denoted as Ag1Cox. SEM and TEM analyses showed that Ag1Cox formed a structure consisted of flower-like Co grown on tree-like Ag backbones while it had more Co flowers with a greater x. The ORR activities were examined in 0.1 M NaOH solution with rotating disk electrode (RDE) voltammetry and Ag1Co7 showed the best catalytic activity. The co-deposition mechanism was further investigated by varying the deposition time of Ag1Co7. At the early stage of deposition, Ag-tree branches were formed predominantly, followed by the growth of flower-like Co nanostructures on the Ag nanotrees: More Co flowers were produced on Ag backbones with longer deposition time, being attributed to both a less negative reduction potential of Ag+ to Ag than Co2+ to Co and promoted Co2+ reduction on the initially formed Ag surface. Ag1Co7 electrodeposited for 200 s, consisted of ∼14% Co, showed the greatest ORR catalytic activity which was better or comparable to noble metal Pt.

We introduce a facile growth process for mixed metal oxide nanorods of Ir1−xVxO2 in the broad range of metal contents between iridium and vanadium via a vapor phase transport process and their electrochemical performance. The growth process of Ir1−xVxO2 nanorods was performed by modulating the ratios of two precursors of VO2 and IrO2, the growth temperature, the position of metal oxide precursors in a furnace, and the flow rate of carrier gases. The results indicated that quasi one-dimensional nanostructures of Ir1−xVxO2 can be obtained of a single crystalline nature with the tetragonal rutile crystal structure by randomly incorporating Ir4+ and V4+ metal ions into the same lattice unit of the tetragonal structure owing to similar ionic sizes. In addition, the fundamental electrochemical performances for Ir1−xVxO2 nanorods grown directly on an Au microelectrode of 25 μm in diameter were carefully tested in order to explore the nonenzymatic amperometric sensing capacity of ascorbic acid as a biologically important molecule.

In this work, we synthesized tantalum (Ta) nanoclusters on carbon black (Ta/CB) via simple electrodeposition in non-aqueous solvent, acetonitrile (ACN) at ambient temperature. Transmission electron microscopy (TEM) images showed that the electrodeposited Ta nanoclusters consisted of tiny Ta nanoparticles. X-ray photoelectron spectroscopy (XPS) result represented that the outermost Ta formed the native oxide on Ta/CB due to its ambient exposure to air. Electrochemical catalytic properties of prepared Ta/CB on glassy carbon electrode (Ta/CB/GC) were investigated toward reductions of oxygen and hydrogen peroxide, and oxidations of ascorbic acid and dopamine. For oxygen reduction reaction (ORR) in acid, Ta/CB/GC represented a decent electrocatalytic performance which was better or comparable to bare Pt. The operational stability in acidic condition was maintained up to 500 repetitive potential cycles presumably due to the protective native Ta oxide layer. Ta/CB/GC also showed high amperometric sensitivity (4.5 (±0.16) mA mM(-1) cm(-2), n = 5) for reduction of hydrogen peroxide in 0.1 M phosphate buffer solution (PBS, pH 7.4). In addition, Ta/CB/GC was demonstrated for the possibility of simultaneous detection of ascorbic acid and dopamine using differential pulse voltammetry (DPV).

Li 2 S with theoretical capacity of 1166 mAh g −1 has been considered as a promising candidate for Li-S cathode as it could be paired with safer Li-free electrodes to resolve safety issues. However, the success is hindered by the nature of Li 2 S and corresponding reduction species, including low conductivity and the shuttling phenomenon. Herein, we simply coat graphene films directly onto the Li 2 S cathode, which can suppress polysulfides dissolution effectively. The electrochemical performance of the cathode depending on graphene interlayer thickness (0, 20, 45, 54, 77 and 88 μm) has been investigated. Li 2 S cathode with the 45 μm thick interlayer exhibits initial discharge capacity of 1029.21 mAh g −1 and 779.74 mAh g −1 at 0.05C and 0.1C, respectively, and capacity retention of above 60% with coulombic efficiency of around 90% over 300 cycles at high C rates. The results are discussed in terms of the graphene film thickness and the conductivity of the film as well as Li ion diffusivity.

Electroactivity of nanoporous Pt (npPt) depending on the pore characteristics was studied for various electrode reactions having a range of electrode reaction kinetics: ferrocene oxidation, l -ascorbic acid (AA) oxidation, oxygen reduction reaction (ORR), H2O2 reduction, and glucose oxidation. npPts with two different degrees of the porosities (npPt-1 and npPt-2) were electrodeposited on recessed Pt microdisk electrodes (100-μm diameter), employing deposition solutions in which the composition ratios of Pt precursor, Triton X-100, and lead acetate were varied. npPt-1 has smaller microscale pores than npPt-2. The electroactivities of npPts were analyzed using amperometric sensitivities at mass-transfer-controlled and kinetic-controlled potential regions. Both npPt-1 and npPt-2 increased the sensitivities for all the reactions but reversible ferrocene oxidation remarkably compared to bare Pt. In the kinetic-controlled region, npPt-1 showed more greatly enhanced sensitivity compared to npPt-2 due to the smaller pores exerting more efficient confinement of a reactant near the Pt surface. In mass-transfer controlled region, npPt-2 was beneficial for relatively fast reactions (AA oxidation, ORR); while npPt-1 was advantageous for slower reactions (H2O2 reduction, glucose oxidation). This suggests that the particle-to-particle distance of the npPt affects the electroactivity and an optimum degree of the porosity is different depending on the reaction kinetics.

We report the synthesis and electrochemical performances of the hybrid architecture of rhodium oxide (Rh2O3) nanofibers (NF) and highly single crystalline RuO2 nanowires (NW) by combining the electrospinning process and a simple recrystallization process. The amorphous Ru(OH)3·xH2O precursors at relatively low temperature were efficiently transformed into highly single crystalline RuO2 nanowires with the tetragonal rutile structure on electrospun Rh2O3 nanofibers. Pure Rh2O3 NF and hybrid RuO2 NW–Rh2O3 NF exhibited different electroactivities toward H2O2 electrochemical reaction: Rh2O3 NF facilitates the H2O2 oxidation vs. hybrid RuO2 NW–Rh2O3 NF promotes H2O2 reduction more favorably. The H2O2 reduction free from O2 reduction interference at RuO2 NW–Rh2O3 NF is advantageous and finds the feasibility for selective H2O2 detection in various samples. Furthermore, RuO2 NW–Rh2O3 NF generated a greatly higher current induced by H2O2 reduction (i.e., enhanced sensitivity to H2O2) than bare Rh2O3 NF.

Metal oxide composite nanofibres consisting of Ni and Rh (denoted as NixRh1−xOy, 0

Proton exchange membrane (PEM) water electrolysis using acidic electrolytes has many positive aspects of high operating current densities, gases with high purity, and high efficiency. However, it has disadvantages such as noble electrocatalysts required. Metal oxides (RuO2, IrO2) known as efficient electrocatalysts for anodic oxygen evolution reaction (OER) are scarce and expensive. Therefore, a substantial research effort has been devoted to the development of economical electrocatalysts with high performance and durability. In this presentation, bimetallic RuCo mixed oxide nanotubes with various relative compositions are synthesized by electrospinning and calcination in expectation of the synergistic effect and cost cutting. The hollow morphologies, compositions and atomic distribution of the prepared RuCo mixed oxide nanotubes are characterized by field-emission scanning electron microscopy (FE-SEM) equipped with an energy disperse X-ray spectrometer (EDS) and transmission electron microscopy (TEM). Through X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis, the sizes of unit cell of RuO2 rutile structure and Co3O4 cubic structure are found to be changed due to the mutual substitution. Electrochemical acitivities of diverse RuCo mixed oxide nanotubes for OER are studied with rotating disk electrode (RDE) voltammetry in 1 M HClO4 aqueous solution. Tafel slopes are obtained from the corresponding voltammetric curves for OER to comprehensively elucidate the kinetics of OER. The onset potential of RuCo mixed oxide nanotubes is determined precisely using scanning electrochemical microscopy (SECM). This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science, ICT and Future Planning (NRF-2017R1A2A2A14001137).

Hydrogen is widely regarded as an environmentally-friendly and practical alternative energy to reduce reliance on fossil fuels. Also, hydrogen has the outstanding advantages of high energy storage density and sustainable reaction products. The most promising technology to produce hydrogen from abundant renewable sources is water electrolysis. Electrochemical water splitting involves two reaction systems, namely, an anodic oxygen evolution reaction (OER) and a cathodic hydrogen evolution reaction (HER). In general, typical HER catalysts with good activity in acidic solutions, such as Pt, exhibit poor activity in OER. Therefore, it is important to study bifunctional catalyst with high activity, efficiency and stability in acidic solutions. In this presentation, we demonstrate the synthesis of AuRu alloy nanofibers as bifunctional electrocatalysts for water splitting. The Au/RuO2 nanocomposites are synthesized via electrospinning and calcination. After the subsequent reduction process, the AuRu alloy nanofibers are formed. The reduction process of Au/RuO2 nanocomposites to AuRu alloy nanofibers are investigated and the physical properties of AuRu alloy nanofibers in comparison to those of pure Au and Ru are analyzed with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The morphologies of the Au/RuO2 nanocomposites and AuRu alloy nanofibers are confirmed with field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The electrocatalytic activity of AuRu alloy nanofibers are studied toward both OER and HER in Ar-saturated 0.5 M H2SO4 aqueous solution with rotating disk electrode (RDE) voltammetry. The Tafel slopes which represent kinetics of the reaction for OER and HER are obtained based on the corresponding RDE curves. In summary, this study presents the AuRu alloy nanofibers as a better bifunctional electrocatalyst for overall water splitting than Au/RuO2, RuO2, Ru, Pt/C, Ir/C, Au/C and Ru/C. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT& Future Planning (NRF-2017R1A2A2A14001137).

Considering the growing attention to sustainable hydrogen production from water splitting, advanced materials for electrocatalytic water splitting are central to the area of renewable energy. Ideal water splitting catalysts should have not only low overpotential to produce hydrogen but also decent stability for a controlled period. While the previously reported water splitting catalysts have various compositions, the ones based on earth-abundant and non-precious metals are being studied extensively for hydrogen and oxygen production. However, noble metal oxides, in general, still exhibit superior electrocatalytic activity and enhanced stability under extreme environment compared with other cheap metals. Therefore, mixing non-precious transition metals (e.g. Ni, Co and Cu) with noble metals could be a possible strategy to utilize highly active but expensive noble metals providing economic feasibility. Here we present the synthetic processes and physical/electrochemical characterization of single-phase NiRh2O4 nanofibers (NFs) and their reduced form, RhNi NFs. Those NFs are synthesized through electrospinning, a simple way to facilitate 1D nanostructure, and post-thermal annealing process with and without hydrogen atmosphere. Under a certain optimized condition, single-phase NiRh2O4 NFs and single-phase alloy RhNi NFs are synthesized without and with hydrogen atmosphere, respectively. To find the proper synthetic conditions, NFs are electrospun with varying the precursor mixing ratios and calcined at different temperatures. The morphology and compositions of NiRh2O4 NFs and RhNi NFs were characterized by a field emission scanning electron microscope (FESEM) equipped with an energy dispersive X-ray spectrometer (EDS), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The crystalline structure of the prepared NFs are investigated through high-resolution X-ray diffraction (XRD). Electrochemical activities of NiRh2O4 NFs and RhNi NFs for hydrogen evolution reaction (HER) are studied with rotating disk electrode (RDE) voltammetry in N2-saturated 1.0 M NaOH, 1.0 M PBS and 1.0 M HClO4 aqueous solutions; and compared with those of pure metallic Rh, Ni counterparts in addition to commercial Pt/C. This work was financially supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF-2019R1F1A1059969 for CL) and Basic Science Research Program through the NRF funded by the Ministry of Education (NRF-2018R1A6A1A03025340 for YL and KMH).

This paper reports the facile formation of the alloy nanofibers of highly immiscible Au and Ir with diverse composition ratios (denoted as TH2_AuxIr1−x, x = 0.05, 0.10 or 0.33, relative molar content of Au precursor) and the application for direct glucose oxidation. First, the composite nanofibers consisting of Ir/IrO2 fibrous main frames decorated with Au nanoparticles (denoted as Pre_AuxIr1−xOy) were synthesized via electrospinning and calcination. Then, these composites were annealed under H2 gas flowing and successfully transformed to Au-Ir alloy nanofibers along with IrO2 reduction to Ir metal in the Ir/IrO2 fibrous frames. Thermal H2-treatments with varying temperatures and duration times confirmed that Au-Ir alloy production required an unusually low temperature ≥ 90 °C at which Au and Ir were completely alloyed within 1 min. This study suggests that the Au-Ir alloying and IrO2 reduction occur simultaneously and promote each other. TH2_Au0.33Ir0.67, with ∼50.4 % Au atomic %, was found to still have segregated Au phase, indicating the limited solubility (molar ratio of Au/Ir

Nitric oxide (NO) is a biologically multifunctional gaseous signaling molecule. For electrochemical NO detections, complex membranes are commonly adopted to acquire the selectivity for NO over other oxidizable biological species. In this study, we demonstrate the improved selectivity in amperometric NO measurements at nanostructured Pt. The Pt layers were electrodeposited on Au substrate electrodes at a constant potential (-0.2 V vs. Ag/AgCl) with a constant deposition charge (0.08 C). The various distinctive nanostructures of Pt deposits were obtained via either changing the precursor concentrations (from 5 to 75 mM K2PtCl4) or using a different precursor (75 mM H2PtCl6). With a higher K2PtCl4 concentration, the Pt deposition became less sharp and the smoothest Pt was deposited with 75 mM H2PtCl6. The most greatly sharp-pointed nanostructures were generated with the lowest precursor concentration (5 mM K2PtCl4) and exhibited the highest sensitivity, which was attributed to the hydrophobic property of sharply nanostructured Pt. A hydrophobic neutral gas molecule, NO, possibly has a more favorable access to the inner surface of more hydrophobic Pt deposition and eventually increases the oxidation current. NO current sensitivity was enhanced at the more hydrophobic Pt surface, whereas the oxidation currents of acetaminophen, l-ascorbic acid, nitrite and hydrogen peroxide, four oxidizable biological interfering species, were independent of the Pt nanostructure. Conclusively, the enhanced amperometric selectivity to NO was achieved by the simple electrodeposition method without any additional membranes.

In the current work, a new thiazolothiazole derivative Chol-TZTZ (1) was synthesized, in which a thiazolothiazole bearing aryl amine groups was linked with four cholesteryl units. Thiazolothiazole derivative 1 displayed a unique colorimetric change from green to blue upon the addition of Cu2+ via the formation of organic radicals. UV absorption maximum was changed from 395 nm to 700 nm when Cu2+ was added. Among the various solvents, cyclohexanone could induce gelation of compound 1. π–π interaction between the thiazolothiazole core and van der Waals forces between the cholesteryl group should be involved in the molecules self-assembly of the gelator chol-TZTZ into fibrous superstructures.

This paper reports the facile synthesis of highly single-crystalline IrO2 nanowires grown on an Au microwire (IrO2NW-Au) and its reduced form (Ir/IrO2NW-Au); and their electrocatalytic activity for oxygen reduction reaction, H2O2 reduction/oxidation, and dopamine (DA) oxidation. IrO2NW-Au, prepared by direct vapor transport process under atmospheric pressure, was reduced by H2 gas flowing at 200 °C. This additional modification resulted in the significant morphological changes from the smooth nanowire structures of IrO2NW-Au to substantially porous structures of Ir/IrO2NW-Au with sustaining the external nanowire frameworks. The compositions were also changed from mostly IrO2 in IrO2NW-Au to the mixture of IrO2 and Ir(0) metal in Ir/IrO2NW-Au. Ir/IrO2NW-Au showed highly enhanced and facilitated electrochemical reaction kinetics compared to IrO2NW-Au for ORR and H2O2 reduction/oxidation. The ORR limiting-like current at Ir/IrO2NW-Au was measured to be ∼19-fold greater than that of IrO2NW-Au. In addition, the amperometric responses to varying H2O2 concentration confirmed that Ir/IrO2NW-Au exhibited ∼8-fold (for H2O2 oxidation) and ∼750-fold (for H2O2 reduction) higher sensitivity than IrO2NW-Au. The observed enhanced activity of Ir/IrO2NW-Au could be attributed to the enlarged active surface area as well as the inherent electroactivity of Ir/IrO2NW material induced by co-existence of Ir oxide and metal. In contrast, more stable and decent anodic current responding to DA oxidation was measured at IrO2NW-Au than Ir/IrO2NW-Au, indicating IrO2 rather than Ir(0) has higher catalytic activity for DA oxidation.

A ZnO-MnO composite was synthesized using a simple solvothermal method combined with a high-temperature treatment. To observe the phase change during the heating process, in situ high-temperature XRD analysis was performed under vacuum conditions. The results indicated that ZnMn2O4 transformed into the ZnO-MnO composite phase starting from 500 °C and that this composite structure was retained until 700 °C. The electrochemical performances of the ZnO-MnO composite electrode were evaluated through galvanostatic discharge-charge tests and cyclic voltammetry analysis. Its initial coulombic efficiency was significantly improved to 68.3% compared to that of ZnMn2O4 at 54.7%. Furthermore, the ZnO-MnO composite exhibited improved cycling performance and enhanced rate capability compared with untreated ZnMn2O4. To clarify the discharge-charge mechanism of the ZnO-MnO composite electrode, the structural changes during the charge and discharge processes were also investigated using ex situ XRD and TEM.

Electrochemical hydrogen evolution reaction (HER) has been an interesting research topic in terms of the increasing need of renewable and alternative energy conversion devices. In this article, IrxRu1–xOy (y = 0 or 2) nanofibers with diverse compositions of Ir/IrO2 and RuO2 are synthesized by electrospinning and calcination procedures. Their HER activities are measured in 1.0 M NaOH. Interestingly, the HER activities of IrxRu1–xOy nanofibers improve gradually during repetitive cathodic potential scans for HER, and then eventually reach the steady-state consistencies. This cathodic activation is attributed to the transformation of the nanofiber surface oxides to the metallic alloy. Among a series of IrxRu1–xOy nanofibers, the cathodically activated Ir0.80Ru0.20Oy shows the best HER activity and stability even compared with IrOy and RuOy, commercial Pt and commercial Ir (20 wt % each metal loading on Vulcan carbon), where a superior stability is possibly ascribed to the instant generation of active Ir and R...

We report the electrochemical activity of IrOx (0 < x ≤ 2) nanofibers prepared by electrospinning for the oxidations of biological species including L-ascorbic acid (AA), 4-acetamidophenol (AP), dopamine (DA), glucose, β-nicotinamide adenine dinucleotide (NADH), and uric acid (UA). Compared to bare glassy carbon electrode, IrOx nanofibers show high electroactivity for all the tested species and facilitate AA oxidation most significantly, shifting the oxidation potential to the less positive direction by ∼485 mV in linear sweep voltammetry while the oxidation of glucose is almost negligible at both electrodes. The amperometric response of IrOx nanofibers at the applied potential of −0.01 V (vs. SCE) is linearly proportional to the AA concentration, exhibiting high sensitivity (194.4 ± 6.8 μA mM−1 cm−2, n = 5), fast response time (t95% = 2.9 ± 1.2 s, n = 5), low detection limit (

We report a new nonenzymatic amperometric detection of ascorbic acid (AA) using a glassy carbon (GC) disk electrode modified with hollow gold/ruthenium (hAu-Ru) nanoshells, which exhibited decent sensing characteristics. The hAu-Ru nanoshells were prepared by the incorporation of Ru on hollow gold (hAu) nanoshells from Co nanoparticle templates, which enabled AA selectivity against glucose without aid of enzyme or membrane. The structure and electrocatalytic activities of the hAu-Ru catalysts were characterized by spectroscopic and electrochemical techniques. The hAu-Ru loaded on GC electrode (hAu-Ru/GC) showed sensitivity of 426 μA mM(-1) cm(-2) (normalized to the GC disk area) for the linear dynamic range of5 μM to 2 mM AA at physiological pH. The response time and detection limit were 1.6 s and 2.2 μM, respectively. Furthermore, the hAu-Ru/GC electrode displayed remarkable selectivity for ascorbic acid over all potential biological interferents, including glucose, uric acid (UA), dopamine (DA), 4-acetamidophenol (AP), and nicotinamide adenine dinucleotide (NADH), which could be especially good for biological sensing.

As a new approach to detect Cu 2+ , colorimetric detection of Cu 2+ via organo radical formation of thiazolothiazole is reported. Upon the addition of Cu 2+ , thiazolothiazole derivatives 1 and 2 form relatively stable organo radicals, resulting in a distinct colorimetric change from greenish yellow to blue. Among the various metal ions, only Cu 2+ showed a new peak appearance at 610 nm. In addition, a selective fluorescence quenching was also observed with Cu 2+ . To understand the origin of the Cu 2+ selectivity of 1 and 2, series of electrochemical data are reported. Finally, EPR (electron paramagnetic resonance) data clearly support the formation of this unique organic radical formation.