Phase Engineering of Iron-Cobalt Sulfides for Zn-Air and Na-Ion Batteries

Rechargeable batteries are promising platforms for sustainable development of energy conversion and storage technologies. Highly efficient multifunctional electrodes based on bimetallic sulfides for rechargeable batteries are extremely desirable but still challenging to tailor with controllable phase and structure. Here, we report a colloidal strategy to fabricate FeCo-based bimetallic sulfides on reduced graphene oxide (rGO), which are expected to display highly efficient oxygen electrocatalysis and sodium storage performances. Specifically, as-screened FeCo₈S₈ nanosheets (NSs) on rGO originating from suitable tailoring of the Co₉S₈ matrix with Fe at the atomic level exhibited a very low potential difference (0.77 V) at 10 mA cm^-2 and negligible voltage loss after 200 cycles as an air electrode for Zn-air batteries. For Na-ion batteries, FeCo₈S₈ NS/rGO demonstrated a superior high-rate capability (188 mAh g^-1 at 20 A g^-1) with long-term cycling stability. The bifunctional electrocatalytic property and sodium storage performance are attributed to not only the synergistic effect of Fe/Co but also the optimized catalytic activity and ion transport ability by the in situ rGO hybrid. This work demonstrates the potential applications of FeCo-based bimetallic sulfides as efficient electrode materials for both rechargeable Zn-air and Na-ion batteries.

A novel dual-tasking hollow cube NiFe2O4-NiCo-LDH@rGO hierarchical material for high preformance supercapacitor and glucose sensor

Binary transition metal oxides as electroactive materials have continuously aroused grumous attention due to their high theoretical specific capacitance, high valtage window, and multiple oxidation states. However, the tiny specific surface area, poor conductivity and unsatisfactory cycle stability limit their practical application. Hence, a synthetic strategy is designed to fabricate a dual-tasking hollow cube nickel ferrite (NiFe₂O₄) - based composite (NiFe₂O₄-NiCo-LDH@rGO) with hierarchical structure. The composite is constructed by firstly preparing hollow NiFe₂O₄ from cube-like Ni - Fe bimetallic organic framework (NiFe-MOF), and then integrating nickel cobalt layered double hydroxide (NiCo-LDH) nanowires, together with reduced graphene oxide (rGO) via pyrolysis in conjuction with hydrothermal method. The NiFe₂O₄ possessing cubic hollow structure contributes to a huge accessible surface area, meanwhile alleviates large volume expansion/contraction effect, which facilitates suffcient permeation of the electrolyte and rapid ion/charge transport, and results in high cycling stability. The introduction of layered NiCo-LDH results in hierarchical structure and thus offers maximum contact areas with electrolyte, which heightens the specific capacitance of obtained composite and enhances the electro-catlytic activity towards oxidation of glucose. Furthermore, rGO layer greatly improves the electrical conductivity and ion diffusion/transport capability of composite. Benefiting from the unique structure and individual components of NiFe₂O₄-NiCo-LDH@rGO composite, the electrode delivers a high specific capacitance (750 C g^-1) and superb durability. Simultaneously, the asymmetrical device based on NiFe₂O₄-NiCo-LDH@rGO as positive electrode delivers remarkable energy density (50 Wh kg^-1). Moreover, NiFe₂O₄-NiCo-LDH@rGO exhibits good sensing performance with a sensitivity of 111.86 µA/µM cm^-2, the wide linear range of 3.500 × 10^-5 - 4.525 × 10^-3 M, and the detection limit of 12.94 × 10^-6 M with a signal to noise ratio of 3. Consequently, the NiFe₂O₄-NiCo-LDH@rGO could provide a prospective notion constructing bifunctional materials with hollow-cube hierarchical structure in the field of supercapacitors and electrochemical sensors.

One-step fabrication of a self-supported Co@CoTe2 electrocatalyst for efficient and durable oxygen evolution reactions

The optimal hydrothermal synthesis of a Co@CoTe₂-240 electrode needs an overpotential of 286 mV to achieve a current density of 10 mA cm⁻² and is able to sustain galvanostatic OER electrolysis for 16 hours with little degradation of less than 20 mV.

Ionic-Liquid-Assisted One-Step Synthesis of CoO Nanosheets as Electrocatalysts for Oxygen Evolution Reaction

The sluggish oxygen evolution reaction (OER) hinders the development of electrocatalytic water splitting for energy conversion and storage. Therefore, it is imperative to explore the cost-effective and highly efficient noble-metal-free electrocatalysts for OER. Herein, we are introducing such OER electrocatalyst based on Co, fabricated through an ionic-liquid-assisted one-step synthesis, where ionic liquid played a dual role as solvent cum structure-directing agent. Besides possessing large-accessible surface area and numerous active sites, the as-prepared stable CoO nanosheets exhibited excellent electrochemical activity through establishing an extensive contact with the electrolyte. Under alkaline conditions, the overpotential to achieve a current density of 10 mA cm^-2 is only 320 mV, and the Tafel slope is as small as 70 mV dec^-1. Thus, our work provides a new pathway for designing and engineering the highly efficient non-noble metal OER electrocatalysts by using ionic liquids.

Nano-Sized Inorganic Energy-Materials by the Low-Temperature Molecular Precursor Approach

The low-temperature synthesis of inorganic materials and their interfaces at the atomic and molecular level provides numerous opportunities for the design and improvement of inorganic materials in heterogeneous catalysis for sustainable chemical energy conversion or other energy-saving areas. Using suitable molecular precursors for functional inorganic nanomaterial synthesis allows for facile control over uniform particle size distribution, stoichiometry, and leads to desired chemical and physical properties. This Minireview outlines some advantages of the molecular precursor approach in light of selected recent developments of molecule-to-nanomaterials synthesis for renewable energy applications, relevant for the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water-splitting.

Three-Dimensionally Hierarchical Ni/Ni3S2/S Cathode for Lithium-Sulfur Battery

Lithium-sulfur (Li-S) batteries have attracted interest as a promising energy-storage technology due to their overwhelming advantages such as high energy density and low cost. However, their commercial success is impeded by deterioration of sulfur utilization, significant capacity fade, and poor cycle life, which are principally originated from the severe shuttle effect in relation to the dissolution and migration of lithium polysulfides. Herein, we proposed an effective and facile strategy to anchor the polysulfides and improve sulfur loading by constructing a three-dimensionally hierarchical Ni/Ni₃S₂/S cathode. This self-supported hybrid architecture is sequentially fabricated by the partial sulfurization of Ni foam by a mild hydrothermal process, followed by physical loading of elemental sulfur. The incorporation of Ni₃S₂, with high electronic conductivity and strong polysulfide adsorption capability, can not only empower the cathode to alleviate the shuttle effect, but also afford a favorable electrochemical environment with lower interfacial resistance, which could facilitate the redox kinetics of the anchored polysulfides. Consequently, the obtained Ni/Ni₃S₂/S cathode with a sulfur loading of ∼4.0 mg/cm² demonstrated excellent electrochemical characteristics. For example, at high current density of 4 mA/cm², this thick cathode demonstrated a discharge capacity of 441 mAh/g at the 150th cycle.

Atomic-layer-deposited ultrafine MoS2 nanocrystals on cobalt foam for efficient and stable electrochemical oxygen evolution

Ultrafine molybdenum sulfide (MoS₂) nanocrystals are grown on a porous cobalt (Co) foam current collector by atomic layer deposition (ALD) using molybdenum hexacarbonyl and hydrogen sulfide as precursors. When used to catalyze the oxygen evolution reaction (OER), the optimal Co@MoS₂ electrode, even with a MoS₂ loading as small as 0.06 mg cm^-2, exhibits a large cathodic shift of ca. 200 mV in the onset potential (the potential at which the current density is 5 mA cm^-2), a low overpotential of only 270 mV to attain an anodic current density of 10 mA cm^-2, much smaller charge transfer resistance and substantially improved long-term stability at both low and high current densities, with respect to the bare Co foam electrode, showing substantial promise for use as an efficient, low-cost and durable anode in water electrolyzers.

Co9S8 activated N/S co-doped carbon tubes in situ grown on carbon nanofibers for efficient oxygen reduction

Herein, we report a facile and environment-friendly route for the preparation of Co₉S₈ activated N/S co-doped carbon tubes (denoted as Co₉S₈@N/S–CT) in situ grown on a carbon nanofiber network derived from bacterial cellulose.