Co₇Se₈ Nanostructures as Catalysts for Oxygen Reduction Reaction with High Methanol Tolerance

Co₇Se₈ nanostructures electrodeposited on glassy carbon (GC) electrodes show high efficiency for oxygen reduction reaction (ORR) with high methanol tolerance as compared to Pt electrocatalysts. In the presence of methanol, the onset potential for the ORR at Pt/GC is shifted from 0.931 V (vs reversible hydrogen electrode (RHE)) to 0.801 V (vs RHE), whereas it remains the same (0.811 V vs RHE) at Co₇Se₈/GC in the presence and absence of methanol in 0.5 M H₂SO₄ solution. The Co₇Se₈/GC electrodes also showed high cyclability in the presence of methanol, with no degradation of catalytic performance. It is also noteworthy that the Co₇Se₈/GC exhibited exclusively a four-electron reduction pathway for ORR and very low H₂O₂ yield in acidic electrolyte. The admirable performance of Co₇Se₈/GC catalyst along with its cost-effective nature holds great potential for application in direct methanol fuel cells

Superconducting MgB₂ Nanohelices Grown on Various Substrates

Masses of superconducting MgB2 nanohelices and nanowires were grown on various substrates by reaction of Mg metal with diborane (B2H6). The growth occurs via a self-catalyzed vapor−liquid−solid (VLS) mechanism. It is postulated that strain in the wires due to the presence of screw dislocations is responsible for the helical morphology. The several hundred micrometer long helices have a range of diameters and pitch and are made up of wires from 50 to 200 nm in diameter. Magnetic measurements indicate that the helices superconduct below ∼32 K. These nanohelices could be used to manufacture highly flexible superconducting cables or “nanosolenoids.

Synthesis of Superconducting Nanocables of FeSe Encapsulated in Carbonaceous Shell

The recent discovery of superconductivity in iron selenide has attracted considerable attention due to the simplicity of composition, unconventional nature of superconductivity, and ease of synthesis. We have synthesized superconducting FeSe nanowires with a simple catalyst-aided vapor transport reaction at 800 °C in an inert atmosphere. The precursors were chosen to be elemental Se and iron acetylacetonate [Fe^III(C₅H₈O₂)₃]. These vaporized very easily, thereby facilitating transport, and also contributed to the formation of a carbonaceous shell encapsulating the FeSe nanowires. The superconductivity of these nanocables was confirmed through magnetic measurements and a <i>T</i>_c of ≈8 K was obtained for an ensemble of nanocables. The length of FeSe filling inside the carbon nanofibers could be varied by controlling the reaction conditions while the diameter of nanowires was dependent on the thickness of Au–Pd coating used as a catalyst. Extensive analysis through high-resolution microscopy revealed that there was considerable lattice contraction of FeSe in the nanocable up to about 3.6% along the <i>c</i>-direction leading to a reduced spacing between the (001) lattice planes. Interestingly, this compression was more pronounced near the catalyst-FeSe interface and was reduced further along the length of the nanocable. The presence of carbon nanofibers as a shell around the FeSe protected the FeSe nanowires from both atmospheric O₂ and moisture attack, as was evident from the very long ambient condition shelf life of these nanocables, and also makes them more stable under e-beam irradiation

Copper Cobalt Selenide as a Bifunctional Electrocatalyst for the Selective Reduction of CO₂ to Carbon-Rich Products and Alcohol Oxidation

Copper cobalt selenide, CuCo2Se4, has been identified as an efficient catalyst for electrocatalytic CO2 reduction, exhibiting high selectivity for carbon-rich and value-added products. Achieving product selectivity is one of the primary challenges for CO2 reduction reactions, and the catalyst surface plays a pivotal role in determining the reaction pathway and, more importantly, the intermediate adsorption kinetics leading to C1- or C2+-based products. In this research, the catalyst surface was designed to optimize the adsorption of the intermediate CO (carbonyl) group on the catalytic site such that its dwell time on the surface was long enough for further reduction to carbon-rich products but not strong enough for surface passivation and poisoning. CuCo2Se4 was synthesized through hydrothermal method, and the assembled electrode showed the electrocatalytic reduction of CO2 at various applied potentials ranging from −0.1 to −0.9 V vs RHE. More importantly, it was observed that the CuCo2Se4-modified electrode could produce exclusive C2 products such as acetic acid and ethanol with 100% faradaic efficiency at a lower applied potential (−0.1 to −0.3 V), while C1 products such as formic acid and methanol were obtained at higher applied potentials (−0.9 V). Such high selectivity and preference for acetic acid and ethanol formation highlight the novelty of this catalyst. The catalyst surface was also probed through density functional theory (DFT) calculations, and the high selectivity for C2 product formation could be attributed to the optimal CO adsorption energy on the catalytic site. It was further estimated that the Cu site showed a better catalytic activity than Co; however, the presence of neighboring Co atoms with the residual magnetic moment on the surface and subsurface layers influenced the charge density redistribution on the catalytic site after intermediate CO adsorption. In addition to CO2 reduction, this catalytic site was also active for alcohol oxidation producing formic or acetic acid from methanol or ethanol, respectively, in the anodic chamber. This report not only illustrates the highly efficient catalytic activity of CuCo2Se4 for CO2 reduction with high product selectivity but also offers a proper insight of the catalyst surface design and how to obtain such high selectivity, thereby providing knowledge that can be transformative for the field

Enhancement of Superconducting <i>T</i>_c (33 K) by Entrapment of FeSe in Carbon Coated Au–Pd₁₇Se₁₅ Nanoparticles

FeSe has been an interesting member of the Fe-based superconductor family ever since the discovery of superconductivity in this simple binary chalcogenide. Simplicity of composition and ease of synthesis has made FeSe, in particular, very lucrative as a test system to understand the unconventional nature of superconductivity, especially in low-dimensional models. In this article we report the synthesis of composite nanoparticles containing FeSe nanoislands entrapped within an <i>ent</i>-FeSe-Pd₁₆Se₁₅–Au nanoparticle and sharing an interface with Pd₁₇Se₁₅. This assembly exhibits a significant enhancement in the superconducting <i>T</i>_<i>c</i> (onset at 33 K) accompanied by a noticeable lattice compression of FeSe along the ⟨001⟩ and ⟨101⟩ directions. The <i>T</i>_<i>c</i> in FeSe is very sensitive to application of pressure and it has been shown that with increasing external pressure <i>T</i>_<i>c</i> can be increased almost 4-fold. In these composite nanoparticles reported here, immobilization of FeSe on the Pd₁₇Se₁₅ surface contributes to increasing the effect of interfacial pressure, thereby enhancing the <i>T</i>_<i>c</i>. The effect of interfacial pressure is also manifested in the contraction of the FeSe lattice (up to 3.8% in ⟨001⟩ direction) as observed through extensive high-resolution TEM imaging. The confined FeSe in these nanoparticles occupied a region of approximately 15–25 nm, where lattice compression was uniform over the entire FeSe region, thereby maximizing its effect in enhancing the <i>T</i>_<i>c</i>. The nanoparticles have been synthesized by a simple catalyst-aided vapor transport reaction at 800 °C where iron acetylacetonate and Se were used as precursors. Morphology and composition of these nanoparticles have been studied in details through extensive electron microscopy

Excellent Bifunctional Oxygen Evolution and Reduction Electrocatalysts (5A_1/5)Co₂O₄ and Their Tunability

Hastening the progress of rechargeable metal–air batteries and hydrogen fuel cells necessitates the advancement of economically feasible, earth-abundant, inexpensive, and efficient electrocatalysts facilitating both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a recently reported family of nano (5A1/5)Co2O4 (A = combinations of transition metals, Mg, Mn, Fe, Ni, Cu, and Zn) compositionally complex oxides (CCOs) [Wang et al., Chemistry of Materials, 2023, 35 (17), 7283–7291.] are studied as bifunctional OER and ORR electrocatalysts. Among the different low-temperature soft-templating samples, those subjected to 600 °C postannealing heat treatment exhibit superior performance in alkaline media. One specific composition (Mn0.2Fe0.2Ni0.2Cu0.2Zn0.2)Co2O4 exhibited an exceptional overpotential (260 mV at 10 mA cm–2) for the OER, a favorable Tafel slope of 68 mV dec–1, excellent onset potential (0.9 V) for the ORR, and lower than 6% H2O2 yields over a potential range of 0.2 to 0.8 V vs the reversible hydrogen electrode. Furthermore, this catalyst displayed stability over a 22 h chronoamperometry measurement, as confirmed by X-ray photoelectron spectroscopy analysis. Considering the outstanding performance, the low cost and scalability of the synthesis method, and the demonstrated tunability through chemical substitutions and processing variables, CCO ACo2O4 spinel oxides are highly promising candidates for future sustainable electrocatalytic applications

Soft-Chemical Synthetic Route to Superparamagnetic FeAs@C Core–Shell Nanoparticles Exhibiting High Blocking Temperature

Superparamagnetic FeAs nanoparticles with a fairly high blocking temperature (<i>T</i>_B) have been synthesized through a hot injection precipitation technique. The synthesis involved usage of triphenylarsine (TPA) as the As precursor, which reacts with Fe­(CO)₅ by ligand displacement at moderate temperatures (300 °C). Addition of a surfactant, hexadecylamine (HDA), assists in the formation of the nanoparticles, due to its coordinating ability and low melting point which provides a molten flux like condition making this synthesis a solventless method. Decomposition of the carbonaceous precursors, HDA, TPA and Fe­(CO)₅, also produces the carbonaceous shell coating the FeAs nanoparticles. Magnetic characterization of these nanoparticles revealed the superparamagnetic nature of these nanoparticles with a perfect anhysteretic nature of the isothermal magnetization above <i>T</i>_B. The <i>T</i>_B observed in this system was indeed high (240 K) when compared with other superparamagnetic systems conventionally utilized for magnetic storage devices. It could be further increased by decreasing the strength of the applied magnetic field. The narrow hysteresis with low magnitude of coercivity at 5 K suggested soft ferromagnetic ordering in these nanoparticle ensembles. Mössbauer and XPS studies indicated that the Fe was present in +3 oxidation state and there was no signature of Fe(0) that could have been responsible for the increased magnetic moment and superparamagnetism. Typically for superparamagnetic nanoparticle ensemble, the need for isolation of the superparamagnetic domains (thereby inhibiting particle aggregation and enhancing the <i>T</i>_B) has been in constant limelight. Carbonaceous coating on these as-synthesized nanoparticles formed <i>in situ</i> provided the physical nonmagnetic barrier needed for such isolation. The high <i>T</i>_B and room temperature magnetic moment of these FeAs@C nanoparticles also make them potentially useful for applications in ferrofluids and magnetic refrigeration. In principle this method can be used as a general route toward synthesis of other arsenide nanostructures including the transition metal arsenide which show interesting magnetic and electronic properties (e.g., CoAs, MnAs) with finer control over morphology, composition and structure

DataSheet1_Solar enhanced oxygen evolution reaction with transition metal telluride.PDF

The photo-enhanced electrocatalytic method of oxygen evolution reaction (OER) shows promise for enhancing the effectiveness of clear energy generation through water splitting by using renewable and sustainable source of energy. However, despite benefits of photoelectrocatalytic (PEC) water splitting, its uses are constrained by its low efficiency as a result of charge carrier recombination, a large overpotential, and sluggish reaction kinetics. Here, we illustrate that Nickel telluride (NiTe) synthesized by hydrothermal methods can function as an extremely effective photo-coupled electrochemical oxygen evolution reaction (POER) catalyst. In this study, NiTe was synthesized by hydrothermal method at 145°C within just an hour of reaction time. In dark conditions, the NiTe deposited on carbon cloth substrate shows a small oxygen evolution reaction overpotential (261 mV) at a current density of 10 mA cm–2, a reduced Tafel slope (65.4 mV dec−1), and negligible activity decay after 12 h of chronoamperometry. By virtue of its enhanced photo response, excellent light harvesting ability, and increased interfacial kinetics of charge separation, the NiTe electrode under simulated solar illumination displays exceptional photoelectrochemical performance exhibiting overpotential of 165 mV at current density of 10 mA cm-2, which is about 96 mV less than on dark conditions. In addition, Density Functional Theory investigations have been carried out on the NiTe surface, the results of which demonstrated a greater adsorption energy for intermediate -OH on the catalyst site. Since the -OH adsorption on the catalyst site correlates to catalyst activation, it indicates the facile electrocatalytic activity of NiTe owing to favorable catalyst activation. DFT calculations also revealed the facile charge density redistribution following intermediate -OH adsorption on the NiTe surface. This work demonstrates that arrays of NiTe elongated nanostructure are a promising option for both electrochemical and photoelectrocatalytic water oxidation and offers broad suggestions for developing effective PEC devices.</p

Highly Efficient Dopamine Sensing with a Carbon Nanotube-Encapsulated Metal Chalcogenide Nanostructure

Carbon nanotube-encapsulated nickel selenide composite nanostructures were used as nonenzymatic electrochemical sensors for dopamine detection. These composite nanostructures were synthesized through a simple, one-step, and environmentally friendly chemical vapor deposition method, wherein the CNTs were formed in situ from pyrolysis of a carbon-rich metallo-organic precursor. The composition and morphology of these hybrid NiSe2-filled carbon nanostructures were confirmed by powder X-ray diffraction, Raman, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy images. Electrochemical tests demonstrated that the as-synthesized hybrid nanostructures exhibited outstanding electrocatalytic performance toward dopamine oxidation, with a high sensitivity of 19.62 μA μM–1 cm–2, low detection limit, broad linear range of 5 nM–640 μM, and high selectivity. The synergistic effects of enhanced electrochemical activity of nickel selenide along with the enhanced conductivity of carbon nanotubes led to the high electrocatalytic efficiency for these nanostructured composites. The high sensitivity and selectivity of this nanostructured composite could be exploited to develop simple, selective, and sensitive electrochemical sensors to detect and quantify dopamine in human tear samples with high reliability. This nanotube-encapsulated sensor, hence, paves the way for discoveries in the development of dopamine sensors with low cost and high stability, which can be used for noninvasive dopamine detection in peripheral bodily fluids

Cobalt Selenide Nanostructures: An Efficient Bifunctional Catalyst with High Current Density at Low Coverage

Electrodeposited Co₇Se₈ nanostructures exhibiting flake-like morphology show bifunctional catalytic activity for oxygen evolution and hydrogen evolution reaction (OER and HER, respectively) in alkaline medium with long-term durability (>12 h) and high Faradaic efficiency (99.62%). In addition to low Tafel slope (32.6 mV per decade), the Co₇Se₈ OER electrocatalyst also exhibited very low overpotential to achieve 10 mA cm^–2 (0.26 V) which is lower than other transition metal chalcogenide based OER electrocatalysts reported in the literature and significantly lower than the state-of-the-art precious metal oxides. A low Tafel slope (59.1 mV per decade) was also obtained for the HER catalytic activity in alkaline electrolyte. The OER catalytic activity could be further improved by creating arrays of 3-dimensional rod-like and tubular structures of Co₇Se₈ through confined electrodeposition on lithographically patterned nanoelectrodes. Such arrays of patterned nanostructures produced exceptionally high mass activity and gravimetric current density (∼68 000 A g^–1) compared to the planar thin films (∼220 A g^–1). Such high mass activity of the catalysts underlines reduction in usage of the active material without compromising efficiency and their practical applicability. The catalyst layer could be electrodeposited on different substrates, and an effect of the substrate surface on the catalytic activity was also investigated. The Co₇Se₈ bifunctional catalyst enabled water electrolysis in alkaline solution at a cell voltage of 1.6 V. The electrodeposition works with exceptional reproducibility on any conducting substrate and shows unprecedented catalytic performance especially with the patterned growth of catalyst rods and tubes