Interconnecting 3D Conductive Networks with Nanostructured Iron/Iron Oxide Enables a High-Performance Flexible Battery

MnS-BaS Heterostructures as Effective Catalysts for Oxygen Reduction Reaction

The inadequate electrical conductivity of metal sulfides, along with their tendency to agglomerate, has hindered their use in energy storage and catalysis. The construction of a heterojunction can ameliorate these deficiencies to some extent. In this paper, MnS-BaS heterojunction catalysts were prepared by a hydrothermal method, which is a simple and inexpensive process. The MnS-BaS heterojunction catalysts exhibited superior performance owing to the strong synergistic interaction between MnS and BaS. Density functional theory (DFT) calculations reveal strong interactions at the heterojunction interface and significant electron transfer between MnS and BaS, which further modulates the electronic structure of Mn. The elevation of the center of the d-band enhances the adsorption of oxygen and oxygen-containing intermediates on the catalyst, thus promoting the oxygen reduction reaction (ORR). The practical application of MnS-BaS catalysts was tested by assembling zinc-air batteries. This study provides a rational strategy for designing transition metal catalysts that are efficient and low cost.

Defect-stabilized and oxygen-coordinated iron single-atom sites facilitate hydrogen peroxide electrosynthesis

The selective two-electron electrochemical oxygen reduction reaction (ORR) for hydrogen peroxide (H2O2) production is a promising and green alternative method to the current energy-intensive anthraquinone process used in industry. In this study, we develop a single-atom catalyst (CNT-D-O-Fe) by anchoring defect-stabilized and oxygen-coordinated iron atomic sites (Fe-O4) onto porous carbon nanotubes using a local etching strategy. Compared to O-doped CNTs with vacancy defects (CNT-D-O) and oxygen-coordinated Fe single-atom site modifying CNTs without a porous structure (CNT-O-Fe), CNT-D-O-Fe exhibits the highest H2O2 selectivity of 94.4% with a kinetic current density of 13.4 mA cm-2. Fe-O4 single-atom sites in the catalyst probably contribute to the intrinsic reactivity for the two-electron transfer process while vacancy defects greatly enhance the electrocatalytic stability. Theoretical calculations further support that the coordinated environment and defective moiety in CNT-D-O-Fe could efficiently optimize the adsorption strength of the *OOH intermediate over the Fe single atomic active sites. This contribution sheds light on the potential of defect-stabilized and oxygen-coordinated single-atom metal sites as a promising avenue for the rational design of highly efficient and selective catalysts towards various electrocatalytic reactions.

Coating CoFe2O4 shell on Fe particles to increase the utilization efficiencies of Fe and peroxymonosulfate for low-cost Fenton-like reactions

Bimetallic composites (Fe@CoFe2O4) with zero-valent Fe as the core encapsulated by CoFe2O4 layers are synthesized by a coprecipitation-calcination method, which are applied to activate PMS for the degradation of bisphenol A (BPA). Enhanced activity of Fe@CoFe2O4 is achieved with very fast degradation rate (kobs = 0.5737 min-1). In the fixed-bed reactor, the catalyst lifetime (tul) of Fe@CoFe2O4 is determined to be 22 h compared to 11 h of Fe, and the deactivation rate constant (kd) for Fe@CoFe2O4 is 0.0083 mg·L-1·h-1, only ∼1/10 of Fe (0.0731). The XPS results indicate that the core-shell structure of Fe@CoFe2O4 could promote the redox cycles of Co3+/Co2+ and Fe3+/Fe2+. It is proved that the coating of CoFe2O4 shell on Fe0 can protect the Fe0 core from being oxidized by PMS to form passivation layer. The electrons of Fe0 can therefore be used effectively for activating PMS to produce ROSs via the CoFe2O4 shell. This modification method of Fe0 would decrease the cost of PMS based wastewater remediation greatly, thus should have great potential on an industrial scale.

Uniform Fe2 O3 Nanospheres Anchored on Multilayer Graphene as Anode Materials for High-Rate Ni-Fe Batteries

Ni-Fe battery is one of prospective aqueous alkaline batteries due to its high safety, eco-friendliness and cost-effectiveness. However, the electrochemical performance of Fe-based anodes is limited due to the particle aggregation and low electric conductivity. In this work, iron powder is used as a precursor in a chemical bath deposition method. By optimizing the concentration of HNO3 , a balanced dissolution-crystallization process is achieved to obtain uniform Fe2 O3 nanospheres in size between 60 and 90 nm, which are separately anchored on ultrasonically prepared multilayer graphene (MLG). This composite delivers specific discharge capacities of 191.1 and 160.8 mAh g-1 at the current densities of 2 and 10 A g-1 , respectively. A Ni-Fe battery with the as-prepared Fe2 O3 /MLG as anode and Ni(OH)2 /MLG as cathode exhibits an energy density of 69.5 Wh kg-1 at a high power density of 3931.6 W kg-1 .

High-Performance Biscrolled Ni-Fe Yarn Battery with Outer Buffer Layer

The increasing demand for portable and wearable electronics has promoted the development of safe and flexible yarn-based batteries with outstanding electrochemical properties. However, achieving superior energy storage performance with a high active material (AM) load and long cycle life with this device format remains a challenge. In this study, a stable and rechargeable high-performance aqueous Ni-Fe yarn battery was constructed via biscrolling to embed AMs within helical carbon nanotube (CNT) yarn corridors. Owing to the high load of charge storage nanoparticles (NPs; above 97 wt%) and the outer neat CNT layer, the buffered biscrolled Ni-Fe yarn battery demonstrates excellent linear capacity (0.053 mAh/cm) and cycling stability (60.1% retention after 300 charge/discharge cycles) in an aqueous electrolyte. Moreover, our flexible yarn battery exhibits maximum energy/power densities of 422 mWh/cm³ and 7535 mW/cm³ based on the total volume of the cathode and anode, respectively, which exceed those reported for many flexible Ni-Fe batteries. Thus, biscrolled Ni-Fe yarn batteries are promising candidates for next-generation conformal energy solutions.

Material design and surface chemistry for advanced rechargeable zinc-air batteries

Zinc–air batteries (ZABs) have been considered as a next-generation battery system with high energy density and abundant resources. However, the sluggish multi-step reaction of the oxygen is the main obstacle for the practical application of ZABs. Therefore, bifunctional electrocatalysts with high stability and activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are greatly required to promote the catalytic reaction. In this review, we first explain the reaction mechanism of the ZABs, mainly focusing on multiple oxygen intermediates. Then, the latest studies on bifunctional electrocatalysts for the air cathodes and their progress of the ZABs are discussed with following aspects: platinum group metal, metal-free, transition metal, and metal compound-derived electrocatalysts. Finally, we highlight the advanced ZAB systems with the design of the full-temperature range operation, the all-solid-state, and the newly reported non-alkaline electrolyte, summarizing the remaining challenges and requirements of the future research directions.

This work reviews latest research on the bifunctional electrocatalysts for air cathodes, introducing the advanced zinc–air batteries with the full-temperature range operation, all-solid-states, and newly reported non-alkaline electrolytes.

Phytic acid assisted ultra-fast in-situ constructing Ni foam-supported amorphous Ni-Fe phytates to enhance catalytic performance for oxygen evolution reaction

It is important for the efficient and low-cost utilization of the clean energies to prepare robust catalytic electrodes for oxygen evolution reaction (OER, the key half-reaction in new energy conversion...