Solution-phase phosphorus substitution for enhanced oxygen evolution reaction in Cu2WS4

Biomineralization of Sulfate-Reducing Bacteria In Situ-Induced Preparation of Nano Fe2O3-Fe(Ni)S/C as High-Efficiency Oxygen Evolution Electrocatalyst

Transition metal-based catalysts possess high catalytic activity for oxygen evolution reaction (OER). However, the preparation of high-performance OER electrocatalysts using simple strategies with a low cost still faces a major challenge. Herein, this work presents an innovative, in situ-induced preparation of the Fe2O3, FeS, and NiS nanoparticles, supported on carbon blacks (CBs) (denoted as Fe2O3-Fe(Ni)S/C) as a high-efficiency oxygen evolution electrocatalyst by employing biomineralization. Biomineralization, a simple synthesis strategy, demonstrates a huge advantage in controlling the size of the Fe2O3 and Fe(Ni)S nanoparticles, as well as achieving uniform nanoparticle distribution on carbon blacks. It is found that the electrocatalyst Fe2O3-Fe(Ni)S/C-200 shows a good OER electrocatalytic activity with a small loading capacity, and it has a small overpotential and Tafel slope in 1 m KOH solution with values of 264 mV and 42 mV dec-1, respectively, at a current density of 10 mA cm-2. Additionally, it presents good electrochemical stability for over 24 h. The remarkable and robust electrocatalytic performance of Fe2O3-Fe(Ni)S/C-200 is attributed to the synergistic effect of Fe2O3, FeS, and doped-Ni species as well as its distinct 3D spherical structure. This approach indicates the promising applications of biomineralization for the bio-preparation of functional materials and energy conversion.

Understanding the charge transfer dynamics of the Cu2WS4-CNT-FeOOH ternary composite for photo-electrochemical studies

Ternary transition metal chalcogenide (Cu2WS4) is a semiconductor with a band gap of 2.1 eV and could be a promising candidate for photoelectrochemical water splitting and solar energy conversion applications. Despite numerous reports on ternary transition metal chalcogenides, this semiconductor's ultrafast charge transfer dynamics remain unknown. Here, we report on charge carrier dynamics in a pristine Cu2WS4 system with the aid of ultrafast transient (TA) pump-probe spectroscopy and a hot carrier transfer process from Cu2WS4 to multi-walled carbon nanotubes (CNTs) and FeOOH has been observed. Furthermore, we have explored Cu2WS4-FeOOH having a type-II composite for photo-electrochemical (PEC) water oxidation and modified this with the addition of multi-walled carbon nanotubes to expedite the charge-transfer processes and photo-anodic performance. The photo-electrochemical studies demonstrate that the Cu2WS4-CNT, Cu2WS4-FeOOH, and Cu2WS4-CNT-FeOOH provide nearly 3-, 8- and 12-fold enhancement in photocurrent density relative to the bare Cu2WS4 photo-anode at 1.23 V vs. RHE. These photo-electrochemical studies support the results obtained from the TA investigation and further prove the higher charge separation in the ternary composite system. These studies probe the excited states and provide evidence of longer charge separation in the binary and ternary composites, responsible for their remarkable photo-electrochemical performance.

Ternary Copper Tungsten Sulfide (Cu2WS4) Nanoparticles Obtained through a Solvothermal Approach: A Bi-Functional Electrocatalyst for the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER)

In this work, Cu2WS4 nanoparticles have been synthesized via a solvothermal decomposition approach using a heterobimetallic single source precursor, WCu2S4(PPh3)3. The single source precursor, WCu2S4(PPh3)3, has been characterized using multinuclear NMR spectroscopy, while Cu2WS4 nanoparticles have been characterized by powder X-ray diffraction (PXRD) for which Rietveld refinement has been performed to authenticate the lattice structure of the decomposed product, Cu2WS4. Furthermore, FESEM and EDAX analyses have been performed to assess the morphology and composition of Cu2WS4. An electrochemical study in acidic as well as basic media suggested that Cu2WS4 nanoparticles possess efficient bifunctional activity towards electrochemical hydrogen as well as oxygen evolution reactions. Linear sweep voltammetry (LSV) performed in 0.5 N H2SO4 indicates an onset potential for the HER of 462 mV and a Tafel slope of 140 mV dec-1. While LSV performed in 0.1 M KOH indicates an onset potential for the OER of 190 mV and a Tafel Slope of 117 mV dec-1.

2D and 3D nanostructuring strategies for thermoelectric materials

Thermoelectric materials have attracted increased research attention as the implementation of various nanostructures has potential to improve both their performance and applicability. A traditional limitation of thermoelectric performance in bulk materials is the interconnected nature of the individual parameters (for example, it is difficult to decrease thermal conductivity while maintaining electrical conductivity), but through the rational design of nanoscale structures, it is possible to decouple these relationships and greatly enhance the performance. For 2D strategies, newly investigated materials such as graphene, transition metal dichalcogenides, black phosphorus, etc. are attractive thanks to not only their unique thermoelectric properties, but also potential advantages in ease of processing, flexibility, and lack of rare or toxic constituent elements. For 3D strategies, the use of induced porosity, assembly of various nanostructures, and nanoscale lithography all offer specific advantages over bulk materials of the same chemical composition, most notably decreased thermal conductivity due to phonon scattering and enhanced Seebeck coefficient due to energy filtering. In this review, a general summary of the popular techniques and strategies for 2D and 3D thermoelectric materials will be provided, along with suggestions for future research directions based on the observed trends.

Spinel oxide CoFe2O4 grown on Ni foam as an efficient electrocatalyst for oxygen evolution reaction

The effect of the oxygen evolution reaction (OER) is important in water splitting. In this work, we develop sphere-like morphology spinel oxide CoFe2O4/NF by hydrothermal reaction and calcination, and the diameter of the spheres is about 111.1 nm. The CoFe2O4/NF catalyst exhibits excellent electrocatalytic performance with an overpotential of 273 mV at a current density of 10 mA cm-2 and a Tafel slope of 78 mV dec-1. The cycling stability of CoFe2O4/NF is remarkable, and it only increased by 5 mV at a current density of 100 mA cm-2 after 3000 cycles. Therefore, this simple method to prepare CoFe2O4/NF can enhance the OER properties of electrocatalysts, which makes CoFe2O4/NF a promising material to replace noble metal-based catalysts for the oxygen evolution reaction.