Defect-rich Nanosheets Research Articles

Superfast hydrous-molten salt erosion to fabricate large-size self-supported electrodes for industrial-level current OER

Durable, active, and cheap oxygen evolution reaction (OER) electrocatalyst to replace the noble metal-based ones is appealing but challenging in energy storage fields. Here, we devise a one-pot low-temperature hydrous molten salt erosion strategy to vertically root the thin and dense bimetal hydroxide (NiFeOxHy) nanosheet on commercial nickel foam in 1 min. The defect-rich nanosheets are interdigitated together to yield a highly porous array, which offers affluent exposed electroactive centers, decreased charge/mass transfer, and augmented mechanical stability, while a strong Ni-Fe synergy elicits the signal redox reactivity of both metal and nonmetal lattice oxygen. Due to such effects, the typical NiFeOxHy electrode accesses a catalytic current of 10 mA cm−2 at a low overpotential 216 mV for freshwater electrolyte and 232 mV for saline one both with a small Tafel slope of 53 mV dec−1, while stably working for 1000 h at 0.1 A cm−2 in freshwater electrolyte and over 550 h at 1 A cm−2 in saline one. This evidences efficient and stable large-current–density OER performance, particularly a strong Cl− anti-erosion. The large-scale NiFeOxHy electrode materials (81 cm2) with a commensurate performance are fabricated on nickel foam, heralding the enormous prospect for practical usage. This exceedingly procedure-, energy- and time-saving erosion tactic can be generalized to common metal foam substrates and hydrous metal molten salts, accenting a momentous stepping stone for integral construction of self-supported and large-size electrodes towards commercially-met OER application and beyond.

Engineering Vacancies at the 2D Nanocrystals for Robust Bifunctional Electrocatalysts.

Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through water decomposition are feasible methods to produce green and clean energy. Herein, we report a facile two-step strategy for the preparation of non-noble metal defect-rich nanosheets by an electrochemical process at room temperature. First-principle calculations are used to study the bifunctional catalytic reaction mechanism of defect engineering in transition-metal dichalcogenides (TMDs); from the first-principle calculations, we predicted that the rich S vacancies on the nanosheet promoted electron transfer and reduced the energy barrier of electrocatalysis. As a substantiation, we conducted HER/OER electrochemical characterizations and found that the defect-rich atomic-thick tantalum sulfide is a kind of dual-function electrocatalyst with enhanced comprehensive properties of Tafel slope (39 mV/dec for HER, 38 mV/dec for OER) and low overpotential (0.099 V for HER, 0.153 V for OER) in acidic and alkaline environments, respectively. Likewise, the defect-rich catalysts exhibit high stability in acidic and alkaline solutions, which have potential applications as electrocatalysts for the large-scale production of hydrogen and oxygen.

An electrocatalytically active pine cone like NixCoyP for high efficiency over water splitting

Synthesis of bimetallic phosphide like Pine cone efficient electrocatalyst for the development of water electrolyzers is of significant interest. Herein, NixCoyP catalyst was synthesized via Condensation reflux and phosphating process, and it has a defect rich nanosheet like morphology. The special morphology provided more active toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). NiCoP delivers the current density of 10 mA/cm2 for HER at an overpotential of 226 mV in alkaline. NiCo2P is also highly active toward OER and requires 154 mV to attain 10 mA/cm2. The NiCo2P delivers 10 mA/cm2 current density at a cell voltage of 1.49 V and retains 75% of its initial current density even after 12 h of continuous electrolysis.

Influence of extensive disorder on the first order phase transformation and its implications on the rate capability and cycling stability of MoS2 nanosheets in intercalation regime

Continuous capacity loss or gain in electrodes during extended cycling is very intriguing. We investigate influence of nanosheet thickness and defects on charge storage properties of MoS2 nanosheets in intercalation regime. Strong correlation with irreversible lithium intake during first cycle is observed. Defect-rich nanosheets (MoS2−5L; with an average 5-layer thickness) show sloping potential indicating single-phase lithium intercalation during first lithiation, with unprecedentedly large Li+-intake (x~1.9) of which only half is extractable. Defect-suppressed nanosheets (MoS2−15L; 15 layers thick) exhibit flat potential characteristics of a first-order phase transformation with Li+-intake of x~1.22 and a capacity loss x~0.3. MoS2−15L nanosheets have larger charge storage at high current rates. MoS2−5L nanosheets show an increase in charge storage fraction upon cycling at high current rates. Similar results are seen for crystallites of intermediate layer thickness. EIS studies suggest reorganization of excess lithium in electrodes during high current cycling. Irreversible lithium trapped in the MoS2−5L nanosheets during the first cycle is contemplated to shuttle around activating the electrode and enhancing the charge storage properties. Optimum performance with large charge storage and extended cycling stability at high C-rates are seen in MoS2 nanosheets with a mix of certain degree of disorder and crystallinity.

Hierarchical porous bimetal-sulfide bi-functional nanocatalysts for hydrogen production by overall water electrolysis

Electrocatalytic water splitting using bi-functional catalysts is one of the most promising approaches for clean hydrogen fuel production. To address shortcomings of the existing catalysts, here we develop a new bi-functional catalysts cobalt-based nano-architecture with ordered, Ni-doped two-dimensional (2D) defect-rich nanosheets. Innovative combination of doping, annealing, and sulfidation is developed to fabricate the hierarchical porous metal sulfide (denoted as Ni-Co-S) nanosheets arrays (HPNA) directly on conductive carbon cloth (CC). Owing to the unique architecture with the specific surface area and porous structure, short ion diffusion paths, the Ni-Co-S HPNA exhibits excellent electrocatalytic activitiy for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution, featuring low overpotentials of 110 and 270 mV at a current density of 10 mA cm−2, respectively. The excellent catalytic performance is attributed to the unique porous structure, abundant active sites and efficient mass transport. More importantly, when the Ni-Co-S HPNA serves as both the anode and cathode, it achieves a 1.62 V at 10 mA cm−2 and remains stable over 12 h of the overall water splitting process. This work opens new avenues for rational design of high-efficiency and stable bifunctional electrocatalysts for water electrolysis and a broader range of clean energy and sustainable chemistry applications.

Enhanced high rate capability of Li intercalation in planar and edge defect-rich MoS2 nanosheets.

(i) Edge and planar defect-rich and (ii) defect-suppressed MoS2 nanosheets are fabricated by controlled annealing of wet-chemically processed precursors. Wrinkles, folds, bends, and tears lead to the introduction of severe defects in MoS2 nanosheets. These defects are suppressed and highly crystalline MoS2 nanosheets are obtained upon high-temperature annealing. The influence of defects on the electrochemical properties, particularly rate capability and cycling stability, in the Li intercalation regime (1 V to 3 V vs. Li/Li+) and conversion regime (10 mV to 3 V vs. Li/Li+) are investigated. In the intercalation regime, the initial Li intake (x in LixMoS2) for defect-rich nanosheets is larger (x ≈ 1.6) as compared to that in defect-suppressed MoS2 (x ≈ 1.2). Although the reversible initial capacity of all the anodes is nearly the same (x ≈ 0.9) at 0.05C rate, defect-rich MoS2 exhibits high rate capability (>40 mA h g-1 at 40C or 26.8 A g-1). When cycled at 10C (6.7 A g-1) for 1000 cycles, 75% capacity retention is observed. High rate capability can be attributed to the defect-rich nature of MoS2, providing faster access to lithium intercalation by a shortened diffusion length facilitated by Li adsorption at the defect sites. The defect-rich nanosheets exhibit a power density of ∼20% more than that of defect-suppressed nanosheets. For the first time, MoS2/Li cells with a high power density of 10-40 kW kg-1 in the intercalation regime have been realized. In the conversion regime, defect-rich and defect-suppressed MoS2 exhibit initial lithiation capacities of ∼1000 and ∼840 mA h g-1, respectively. Defect-rich MoS2 had a capacity of ∼800 mA h g-1 at 0.1C (67 mA g-1), whereas defect-suppressed MoS2 had a capacity of only ∼80 mA h g-1 at the same current rate. Capacity retention of 78% was observed for defect-rich MoS2 with a reversible capacity of 591 mA h g-1 when cycled at 0.1C (67 mA g-1) for 100 cycles. Despite having a lower energy density in the intercalation regime, the power density of defect-rich MoS2 in the intercalation regime is significantly larger (by three orders of magnitude) as compared to that of defect-suppressed MoS2 in the conversion regime. Defect-rich MoS2 nanosheets are promising for high-rate-capability applications when operated in the intercalation regime.

Hierarchical ZnO Nanosheet-Nanorod Architectures for Fabrication of Poly(3-hexylthiophene)/ZnO Hybrid NO2 Sensor.

A facile one-step solution method has been developed here to fabricate hierarchical ZnO nanosheet-nanorod architectures for compositing with poly(3-hexylthiophene) (P3HT) for fabricating a hybrid NO2 sensor. The hierarchical ZnO nanosheet-nanorod architectures were controllably synthesized by aging the solutions containing 0.05 mol·L(-1) Zn(2+) and 0.33 mol·L(-1) OH(-) at 60 °C through a metastable phase-directed mechanism. The concentration of OH(-) played a huge role on the morphology evolution. When the [OH(-)] concentration was decreased from 0.5 to 0.3 mol·L(-1), the morphology of the ZnO nanostructures changed gradually from monodispersed nanorods (NR) to nanorod assemblies (NRA), and then to nanosheet-nanorod architectures (NS-NR) and nanosheet assemblies (NSA), depending on the formation of various metastable, intermediate phases. The formation of NS-NR included the initial formation of ZnO nanosheets/γ-Zn(OH)2 mixed intermediates, followed by the dissolution of Zn(OH)2, which served as soluble zinc source. Soluble Zn(OH)2 facilitated the dislocation-driven secondary growth of ZnO nanorod arrays on the primary defect-rich nanosheet substrates. Hybrid sensors based on composite films composed of P3HT and the as-prepared ZnO nanostructures were fabricated for the detection of NO2 at room temperature. The P3HT/ZnO NS-NR bilayer film exhibited not only the highest sensitivity but also good reproducibility and selectivity to NO2 at room temperature. The enhanced sensing performance was attributed to the formation of the P3HT/ZnO heterojunction in addition to the enhanced adsorption of NO2 by NS-NR ZnO rich in oxygen-vacancy defects.