Self-supported CuS nanowire array: an efficient hydrogen-evolving electrode in neutral media

Effect of urea and ammonium fluoride ratio on CuCo2S4/NF as a highly efficient HER catalyst

CuCo2S4 as a spinel-structured transition metal sulfide is a highly effective HER catalyst due to its excellent endurance, low overpotential, and low Tafel slope. In this work, the CuCo2S4/Ni foam (NF) catalysts with various morphologies have been successfully synthesized by controlling the ratio of urea and ammonium fluoride (NH4F) based on the hydrothermal method. Urea and NH4F ratio exhibit a great influence on the microstructure and the HER catalytic performance of CuCo2S4/NF catalysts is discussed in detail.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Two-dimensional covalent organic framework films prepared on various substrates through vapor induced conversion

Covalent organic frameworks (COFs) can exhibit high specific surface area and catalytic activity, but traditional solution-based synthesis methods often lead to insoluble and infusible powders or fragile films on solution surface. Herein we report large-area –C=N– linked two-dimensional (2D) COF films with controllable thicknesses via vapor induced conversion in a chemical vapor deposition (CVD) system. The assembly process is achieved by reversible Schiff base polycondensation between PyTTA film and TPA vapor, which results in a uniform organic framework film directly on growth substrate, and is driven by π‐π stacking interactions with the aid of water and acetic acid. Wafer-scale 2D COF films with different structures have been successfully synthesized by adjusting their building blocks, suggesting its generic applicability. The carrier mobility of PyTTA-TPA COF films can reach 1.89 × 10⁻³ cm² V⁻¹ s⁻¹. When employed as catalysts in hydrogen evolution reaction (HER), they show high electrocatalytic activity compared with metal-free COFs or even some metallic catalysts. Our results represent a versatile route for the direct construction of large-area uniform 2D COF films on substrates towards multi-functional applications of 2D π‐conjugated systems.

Solution-based synthesis of covalent organic frameworks (COFs) often leads to insoluble powders or fragile films on solution surfaces. Here, the authors report large-area two-dimensional (2D) COF films with controllable thicknesses via vapour induced conversion.

Electrochemically Derived Crystalline CuO from Covellite CuS Nanoplates: A Multifunctional Anode Material

In the present era, electrochemical water splitting has been showcased as a reliable solution for alternative and sustainable energy development. The development of a cheap, albeit active, catalyst to split water at a substantial overpotential with long durability is a perdurable challenge. Moreover, understanding the nature of surface-active species under electrochemical conditions remains fundamentally important. A facile hydrothermal approach is herein adapted to prepare covellite (hexagonal) phase CuS nanoplates. In the covellite CuS lattice, copper is present in a mixed-valent state, supported by two different binding energy values (932.10 eV for Cu^I and 933.65 eV for Cu^II) found in X-ray photoelectron spectroscopy analysis, and adopted two different geometries, that is, trigonal planar preferably for Cu^I and tetrahedral preferably for Cu^II. The as-synthesized covellite CuS behaves as an efficient electro(pre)catalyst for alkaline water oxidation while deposited on a glassy carbon and nickel foam (NF) electrodes. Under cyclic voltammetry cycles, covellite CuS electrochemically and irreversibly oxidized to CuO, indicated by a redox feature at 1.2 V (vs the reversible hydrogen electrode) and an ex situ Raman study. Electrochemically activated covellite CuS to the CuO phase (termed as CuS_EA) behaves as a pure copper-based catalyst showing an overpotential (η) of only 349 (±5) mV at a current density of 20 mA cm^-2, and the TOF value obtained at η₃₄₉ (at 349 mV) is 1.1 × 10^-3 s^-1. A low R_ct of 5.90 Ω and a moderate Tafel slope of 82 mV dec^-1 confirm the fair activity of the CuS_EA catalyst compared to the CuS precatalyst, reference CuO, and other reported copper catalysts. Notably, the CuS_EA/NF anode can deliver a constant current of ca. 15 mA cm^-2 over a period of 10 h and even a high current density of 100 mA cm^-2 for 1 h. Post-oxygen evolution reaction (OER)-chronoamperometric characterization of the anode via several spectroscopic and microscopic tools firmly establishes the formation of crystalline CuO as the active material along with some amorphous Cu(OH)₂ via bulk reconstruction of the covellite CuS under electrochemical conditions. Given the promising OER activity, the CuS_EA/NF anode can be fabricated as a water electrolyzer, Pt(-)//(+)CuS_EA/NF, that delivers a j of 10 mA cm^-2 at a cell potential of 1.58 V. The same electrolyzer can further be used for electrochemical transformation of organic feedstocks like ethanol, furfural, and 5-hydroxymethylfurfural to their respective acids. The present study showcases that a highly active CuO/Cu(OH)₂ heterostructure can be constructed in situ on NF from the covellite CuS nanoplate, which is not only a superior pure copper-based electrocatalyst active for OER and overall water splitting but also for the electro-oxidation of industrial feedstocks.

Towards Highly Efficient Chalcopyrite Photocathodes for Water Splitting: The Use of Cocatalysts beyond Pt

Solar radiation is a renewable and clean energy source used in photoelectrochemical cells (PEC) to produce hydrogen gas as a powerful alternative to carbon-based fuels. Semiconductors play a vital role in this approach, absorbing the incident solar photons and converting them into electrons and holes. The hydrogen evolution reaction (HER) occurs in the interface of the p-type semiconductor that works as a photocathode in the PEC. Cu-chalcopyrites such as Cu(In, Ga)(Se,S)₂ (CIGS) and CuIn(Se,S)₂ (CIS) present excellent semiconductor characteristics for this purpose, but drawbacks as charge recombination, deficient chemical stability, and slow charge transfer kinetics, demanding improvements like the use of n-type buffer layer, a protective layer, and a cocatalyst material. Concerning the last one, platinum (Pt) is the most efficient and stable material, but the high price due to its scarcity imposes the search for inexpensive and abundant alternative cocatalyst. The present Minireview highlighted the use of metal alloys, transition metal chalcogenides, and inorganic carbon-based nanostructures as efficient alternative cocatalysts for HER in PEC.

Optimal control of the compositions, interfaces, and defects of hollow sulfide for electromagnetic wave absorption

The aimlessness in the selection of dielectric absorbing materials and the regulation of complex permittivity consumes time and resources. It is an effective way to construct electromagnetic wave (EMW)-absorbing materials dominated by dielectric loss to select materials and adjust complex permittivity based on theory. With sulfide as an example, a hollow ZnO/ZnS composite was constructed using ZnO as a hard template. Subsequently, based on the diverse binding ability of Cu and Zn ions to S ions, the compositions, interfaces, and defects of the sample were simultaneously regulated. There was competition and synergy between the relaxation process caused by the defects and interfaces and the conductivity loss, resulting in the regulation of complex permittivity. Furthermore, the hollow structure effectively reduced the density of the material and improved the impedance matching ability of the sample. As a result, the effective absorption bandwidth (EAB) of the hollow nanoflower ZnO/ZnS/CuS composite reached 5.2 GHz (from 12.8 to 18 GHz) with a matching thickness of 1.59 mm. This method provides a direction for ameliorating the complex permittivity of EMW-absorbing materials dominated by dielectric loss to realize broadband absorption.

In situ confined vertical growth of a 1D-CuCo2S4 nanoarray on Ni foam covered by a 3D-PANI mesh layer to form a self-supporting hierarchical structure for high-efficiency oxygen evolution catalysis

Inspired by the patchwork of artificial turf, where planting in a smaller area can result in a more uniform lawn that grows in one direction, here, we defined the growth position and orientation of a CuCo₂S₄ nanoarray for the first time by electroplating a PANI mesh layer onto a Ni foam to obtain a self-supporting hierarchical electrode material. The nitrogen species derived from the PANI building blocks act as bridging sites to bind with metal ions, which provides a strong coupling effect for the in situ growth of CuCo₂S₄. At the same time, the mesh structure of PANI divides the growable location into smaller blocks. Compared with a mesh plane with uniformly distributed nitrogen sites, only a small portion of the nitrogen sites are located on the narrow-width fence structure, which may make it difficult for CuCo₂S₄ to grow onto the fence structure, thereby limiting the self-growth space and confining CuCo₂S₄. The uniformly distributed growth sites direct CuCo₂S₄ to grow perpendicular to the plane while limiting their growth size. The excellent structural features further enhance the electrochemical oxygen evolution activity, and the oxygen evolution overpotential at a current density of 100 mA cm^-2 is only 291 mV, which is superior to that of the currently known cobalt-copper-based catalyst materials. In addition, the stable structure provides excellent electrode cyclic stability. The preparation of hierarchical self-supporting cobalt-copper bimetallic sulfide nanoarrays provided a reference direction for other transition metal catalytic materials and provided a basis for industrial applications.

Highly sensitive determination of L-tyrosine in pig serum based on ultrathin CuS nanosheets composite electrode

Nanometer-sized copper sulfide has remarkable properties such as metal like electrical conductivity and electrocatalytic activity. In this work, ultrathin copper sulfide nanosheets (CuS NS) were synthesized and employed to modify on surface of glassy carbon electrode (GCE) combining with chitosan (CS) and acidified multi-walled carbon nanotubes (F-MWCNTs). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the shape of CuS NS was hexagon with side length of 13.33 ± 0.67 nm and thickness of 4.50 ± 0.58 nm. The electrochemical characteristics of different nanocomposite modified electrodes were examined by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), indicating that the modified electrode of CuS NS-CS/F-MWCNTs/GCE possessed good electrocatalytic activity towards oxidation of L-tyrosine (L-Tyr). Under the optimal condition, the modified electrode exhibited a wide linear response range for L-Tyr (0.08-1.0 μM) with a detection limit of 4.9 nM. No obvious interferences from coexisted two-fold of L-tryptophan and 50-fold of other amino acids could be observed, indicating its relatively good selectivity. The electrode also had good repeatability, reproducibility and stability. Compared with a commercial instrument analytical method, HPLC, the electrode can be successfully applied to the determination of L-Tyr in pig serums with a recovery rate of 95.7%-102.6%, and its test results are in good agreement with that of HPLC, showing its promising application value.

A Novel Bimetallic Nickel-Molybdenum Carbide Nanowire Array for Efficient Hydrogen Evolution

The design and fabrication of noble-metal-free hydrogenevolution electrocatalysts with high activity is significant to future renewable energy systems. In this work, self-supported NiMo carbide nanowires on carbon cloth (Ni₃ Mo₃ C@NPC NWs/CC; NPC=N,P-doped carbon) were developed through an electropolymerization-assisted procedure. During the synthesis process, NiMoO₄ nanowires were first grown on CC through a hydrothermal reaction that was free of any polymer binder such as Nafion. By use of electropolymerization, the as-prepared NiMoO₄ NWs/CC sample was then coated by a layer of polypyrole (PPy) that served as the carbon source for subsequent conversion into Ni₃ Mo₃ C@NPC NWs/CC by carbothermal reduction. The experimental results indicated that judicious choices of the amount of coated PPy and the pyrolysis temperature were essential for obtaining the pure-phase, nanowire array structure of Ni₃ Mo₃ C@NPC NWs/CC. Benefitting from the pure phase of the bimetallic carbide, the unique architecture of the nanowire array, and its self-supported nature, the optimized Ni₃ Mo₃ C@NPC NWs/CC electrode exhibited excellent performance in the hydrogen evolution reaction (HER) in both acidic and alkaline media. Low overpotentials of 161 and 215 mV were required to afford a high current density of 100 mA cm^-2 toward the HER in acidic and alkaline media, respectively, and the catalytic activity was maintained for at least 48 h, which puts Ni₃ Mo₃ C@NPC NWs/CC among the best HER electrocatalysts based on metallic carbides yet reported.