Mn3O4 Quantum Dots Supported on Nitrogen-Doped Partially Exfoliated Multiwall Carbon Nanotubes as Oxygen Reduction Electrocatalysts for High-Performance Zn-Air Batteries

Bimetal Oxides Anchored on Carbon Nanotubes/Nanosheets as High-Efficiency and Durable Bifunctional Oxygen Catalyst for Advanced Zn-Air Battery: Experiments and DFT Calculations

To meet increasing requirement for innovative energy storage and conversion technology, it is urgent to prepare effective, affordable, and long-term stable oxygen electrocatalysts to replace precious metal-based counterparts. Herein, a two-step pyrolysis strategy is developed for controlled synthesis of Fe2O3 and Mn3O4 anchored on carbon nanotubes/nanosheets (Fe2O3-Mn3O4-CNTs/NSs). The typical catalyst has a high half-wave potential (E1/2 = 0.87 V) for oxygen reduction reaction (ORR), accompanied with a smaller overpotential (η10 = 290 mV) for oxygen evolution reaction (OER), showing substantial improvement in the ORR and OER performances. As well, density functional theory calculations are performed to illustrate the catalytic mechanism, where the in situ generated Fe2O3 directly correlates to the reduced energy barrier, rather than Mn3O4. The Fe2O3-Mn3O4-CNTs/NSs-based Zn-air battery exhibits a high-power density (153 mW cm-2) and satisfyingly long durability (1650 charge/discharge cycles/550 h). This work provides a new reference for preparation of highly reversible oxygen conversion catalysts.

Recent Advancements in Chalcogenides for Electrochemical Energy Storage Applications

Energy storage has become increasingly important as a study area in recent decades. A growing number of academics are focusing their attention on developing and researching innovative materials for use in energy storage systems to promote sustainable development goals. This is due to the finite supply of traditional energy sources, such as oil, coal, and natural gas, and escalating regional tensions. Because of these issues, sustainable renewable energy sources have been touted as an alternative to nonrenewable fuels. Deployment of renewable energy sources requires efficient and reliable energy storage devices due to their intermittent nature. High-performance electrochemical energy storage technologies with high power and energy densities are heralded to be the next-generation storage devices. Transition metal chalcogenides (TMCs) have sparked interest among electrode materials because of their intriguing electrochemical properties. Researchers have revealed a variety of modifications to improve their electrochemical performance in energy storage. However, a stronger link between the type of change and the resulting electrochemical performance is still desired. This review examines the synthesis of chalcogenides for electrochemical energy storage devices, their limitations, and the importance of the modification method, followed by a detailed discussion of several modification procedures and how they have helped to improve their electrochemical performance. We also discussed chalcogenides and their composites in batteries and supercapacitors applications. Furthermore, this review discusses the subject’s current challenges as well as potential future opportunities.

In-situ growth of cobalt manganate spinel nanodots on carbon black toward high-performance zinc-air battery: Dual functions of 3-aminopropyltriethoxysilane

Developing cost-effective and stable non-noble electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is now the critical issue for large-scale application of zinc-air batteries. Here, we presented a simple method to synthesize highly dispersed cobalt manganate spinel nanodots in-situ embedded in amine-functionalized carbon black. Silane coupling agent 3-aminopropyltriethoxysilane (APTES) played dual roles in the preparation: (1) to achieve amine-functionalization of carbon support; (2) as weak alkali to precipitate metal hydroxides which were then converted to spinel nanodots after mild calcination. The hydrophilicity of the carbon substrate was enhanced by amine modification from APTES to disperse metal oxide evenly, and the electrochemical activity was promoted through the strong interface interaction between embedded spinel nanodots and carbon substrate during the calcination process. As expected, the CoMn₂O₄/C-NH₂-300 catalyst exhibited satisfactory bifunctional catalytic performance for both ORR and OER with an ΔE (E_1/2-E_j10) = 0.75 V, which was lower than most state-of-the-art catalysts. In addition, CoMn₂O₄/C-NH₂-300 as a cathode also exhibited remarkable zinc-air battery performance in alkaline solution. This strategy of APTES as a bifunctional coupling agent provided a novel way to design and explore highly active, durable, and cost-effective catalysts for renewable energy conversion and storage.

Tailoring the Co4+/Co3+ active sites in a single perovskite as a bifunctional catalyst for the oxygen electrode reactions

Developing a non-precious metal electrocatalyst for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is desirable for low-cost energy conversion devices. Herein, we designed and developed a new class of layered cation ordered single perovskite oxides (Pr0.9Ca0.1Co0.8Fe0.2O3-δ) with an optimum ratio of the Co4+/Co3+ oxidation state and oxygen vacancy for oxygen electrode reactions. Catalytic activities are investigated as a function of electronic structure and surface composition. A moderate amount of Ca and Fe dopants keeps the B-site Co cations at a higher oxidation state (Co4+) and generates a vast amount of an oxygen defect rich structure. The improved performance in the ORR and OER is explained by the increase in the sites of Co4+ cations, a state responsible for enhanced catalytic activity. A hypothesis for how doped Ca fraction affects the adsorbed oxygen species and contributes to catalytic activity is discussed. This work sheds light on the influence of crystal structure on the catalytic property and reports that ORR and OER activities are affected not only by oxygen vacancy concentration but also by the oxidation state of the transition metal in the perovskite oxide.

Concurrently Realizing Geometric Confined Growth and Doping of Transition Metals within Graphene Hosts for Bifunctional Electrocatalysts toward a Solid-State Rechargeable Micro-Zn-Air Battery

The simultaneous realization of confined growth and doping of transition metals within carbon hosts promises to deliver unusual bifunctional catalytic activity but still remains challenging due to the difficulty in achieving synchronous nucleation and diffusion of metallic ions in a single synthesis step. Herein, we present a simple synthesis strategy capable of concurrently realizing geometric confined growth and doping of transition metals within graphene hosts, demonstrated in Co,N-codoped graphene-confined FeNi nanoparticles (Co,N-GN-FeNi). The obtained Co,N-GN-FeNi can take full advantage of the hierarchy of interactions between the confined-grown FeNi nanoparticles (for high oxygen evolution reaction (OER) activity) and the Co,N-codoped graphene hosts (for high oxygen reduction reaction (ORR) activity). The overall structure is a rationally designed synergy that simultaneously realizes (i) adequate exposure of electroactive sites, (ii) effective protection against corrosion/aggregation of FeNi nanoparticles, and (iii) rapid transport of ions/electrons between the interfaces. As a result, Co,N-GN-FeNi exhibits excellent bifunctional electrocatalytic activity relying on a low ORR/OER subtraction (ΔE = 0.81 V). Subsequent combination with a planar electrode configuration and a solid polymer electrolyte further demonstrates the utilization of Co,N-GN-FeNi as air cathode bifunctional electrocatalysts in a solid-state rechargeable micro-Zn-air battery (SR-MZAB), which exhibits a large open-circuit voltage of 1.39 V, a high power density/specific capacity of 62.3 mW cm^-2/763 mAh g^-1, excellent durability (126 cycles/42 h), and mechanical flexibility. This work demonstrates an effective synthesis strategy for concurrently realizing geometric confined growth and doping of transition metals within carbon hosts, for enhanced bifunctional catalytic activity toward novel SR-MZABs with high energy efficiency, security, and flexibility for wearable micropower sources.

Fabrication of carbon cloth supporting MnO x and its application in Li-O2 batteries

High-efficiency and low-cost electrocatalysts are generally believed to be the critical factor and have been highly researched to catalyze the oxygen reduction reaction (ORR) during the operation of Li-O₂ battery (LOB). The catalysts with better ORR performance are essential for high-performance LOBs. Herein, a binder-free MnO _x @carbon cloth cathode composed of Mn₃O₄ nanoparticles and Mn₂O₃ nanosheets were directly synthesized on the carbon cloth by electrodeposition and subsequently heat treatment at different temperature (from 200 °C to 400 °C). With the increase of temperature, the Mn₃O₄ nanospheres gradually transformed into Mn₂O₃ nanosheets. The MnO _x obtained at 350 °C exhibited the best ORR performance. And MnO _x -350 °C could operate more than 80 cycles at 340 mA g^-1 with a limiting specific capacity of 1000 mAh g^-1, and its first discharge specific capacity could nearly achieve 8000 mAh g^-1 at 200 mA g^-1.

Boosting oxygen electrocatalytic reactions with Mn3O4/self-growth N-doped carbon nanotubes induced by transition metal cobalt

Oxygen electrocatalytic activities in transition-metal atoms and/or heteroatom-doped carbon nanostructures are strongly dependent on their conductivity and electron configurations.

Nanowire-Templated Synthesis of FeNx -Decorated Carbon Nanotubes as Highly Efficient, Universal-pH, Oxygen Reduction Reaction Catalysts

It is of increasing importance to develop highly active and economical oxygen reduction reaction (ORR) electrocatalysts, which have great significance for the large-scale implementation of various energy conversion systems, including metal-air batteries and fuel cells. Herein, a novel method to synthesize FeN_x -decorated carbon nanotubes as a high-efficiency ORR catalyst, by utilizing ZnO nanowires as a sacrificial template and a Fe-polydopamine complex as metal and carbon sources, is reported. The obtained catalyst shows great potential for replacing Pt/C as the ORR catalyst under various pH conditions, from alkaline to acidic electrolytes. The high conductivity, large surface area of the carbon nanotube, and highly active FeN_x species contributed greatly to the high performance of the catalyst. The work presented herein paves a new way for the synthesis of 1D porous nanomaterials for a broad range of energy-related applications.

Sn(OH)x-assisted synthesis of mesoporous Mn-porphyrinic frameworks and their carbon derivatives for electrocatalysis

5,10,15,20-Tetrakis (4-aminophenyl) Mn-porphyrin and 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde were combined into a new mesoporous organic framework by a Schiff-base-type reaction.