Facile synthesis of Mn 3 O 4 -rGO hybrid materials for the high-performance electrocatalytic reduction of oxygen

Achieving Solar-Thermal-Electro Integration Evaporator Nine-Grid Array with Asymmetric Strategy for Simultaneous Harvesting Clean Water and Electricity

Water evaporation is a ubiquitous and spontaneous phase transition process. The utilization of solar-driven interface water evaporation that simultaneously obtains clean water and power generation can effectively alleviate people's concerns about fresh water and energy shortages. However, it remains a great challenge to efficiently integrate the required functions into the same device to reduce the complexity of the system and alleviate its dependence on solar energy to achieve full-time operation. In this work, a multifunctional device based on reduced graphene oxide (RGO)/Mn3 O4 /Al2 O3 composite nanomaterials is realized by an asymmetric strategy for effective solar-thermal-electro integration that can induce power generation by water evaporation in the presence/absence of light. Under one sun irradiation, the solar-driven evaporation rate and output voltage are 1.74 kg m-2  h-1 and 0.778 V, respectively. More strikingly, the nine-grid evaporation/power generation array integrated with multiple devices in series has the advantages of small volume, large evaporation area, and high power generation, and can light up light-emitting diodes (LEDs), providing the possibility for large-scale production and application. Based on the high photothermal conversion efficiency and power production capacity of the RGO/Mn3 O4 /Al2 O3 composite evaporation/generator, it will be a promising energy conversion device for future sustainable energy development and applications.

Boosting the Capacitive Performance of Supercapacitors by Hybridizing N, P-Codoped Carbon Polycrystalline with Mn3O4-Based Flexible Electrodes

Chitosan, a biomass raw material, was utilized as a carbon skeleton source and served as a nitrogen (N) atom dopant in this study. By co-doping phosphorus (P) atoms from H3PO4 and nitrogen (N) atoms with a carbon (C) skeleton and hybridizing them with Mn3O4 on a carbon fiber cloth (CC), an Mn3O4@NPC/CC electrode was fabricated, which exhibited an excellent capacitive performance. The N, P-codoped carbon polycrystalline material was hybridized with Mn3O4 during the chitosan carbonization process. This carbon polycrystalline structure exhibited an enhanced conductivity and increased mesopore content, thereby optimizing the micropore/mesopore ratio in the electrode material. This optimization contributed to the improved storage, transmission, and diffusion of electrolyte ions within the Mn3O4@NPC electrode. The electrochemical behavior was evaluated via cyclic voltammetry and galvanostatic charge-discharge tests using a 1 M Na2SO4 electrolyte. The capacitance significantly increased to 256.8 F g-1 at 1 A g-1, and the capacitance retention rate reached 97.3% after 5000 charge/discharge cycles, owing to the higher concentration of the P-dopant in the Mn3O4@NPC/CC electrode. These findings highlight the tremendous potential of flexible supercapacitor electrodes in various applications.

Microwave assisted synthesis of Mn3O4 nanograins intercalated into reduced graphene oxide layers as cathode material for alternative clean power generation energy device

Mn₃O₄ nanograins incorporated into reduced graphene oxide as a nanocomposite electrocatalyst have been synthesized via one-step, facile, and single-pot microwave-assisted hydrothermal technique. The nanocomposites were employed as cathode material of fuel cells for oxygen reduction reaction (ORR). The synthesized product was thoroughly studied by using important characterization, such as XRD for the structure analysis and FESEM and TEM analyses to assess the morphological structures of the material. Raman spectra were employed to study the GO, rGO bands and formation of Mn₃O₄@rGO nanocomposite. FTIR and UV–Vis spectroscopic analysis were used to verify the effective synthesis of the desired electrocatalyst. The Mn₃O₄@rGO-10% nanocomposite with 10 wt% of graphene oxide was used to alter the shiny surface of the working electrode and applied for ORR in O₂ purged 0.5 M KOH electrolyte solution. The Mn₃O₄@rGO-10% nanocomposite electrocatalyst exhibited outstanding performance with an improved current of − 0.738 mA/cm² and shifted overpotential values of − 0.345 V when compared to other controlled electrodes, including the conventionally used Pt/C catalyst generally used for ORR activity. The tolerance of Mn₃O₄@rGO-10% nanocomposite was tested by injecting a higher concentration of methanol, i.e., 0.5 M, and found unsusceptible by methanol crossover. The stability test of the synthesized electrocatalyst after 3000 s was also considered, and it demonstrated excellent current retention of 98% compared to commercially available Pt/C electrocatalyst. The synthesized nanocomposite material could be regarded as an effective and Pt-free electrocatalyst for practical ORR that meets the requirement of low cost, facile fabrication, and adequate stability.

Transition metal oxides with perovskite and spinel structures for electrochemical energy production applications

Transition metal oxide-based materials are an interesting alternative to substitute noble-metal based catalyst in energy conversion devices designed for oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evolution reactions (HER). Perovskite (ABO₃) and spinel (AB₂O₄) oxides stand out against other structures due to the possibility of tailoring their chemical composition and, consequently, their properties. Particularly, the electrocatalytic performance of these materials depends on features such as chemical composition, crystal structure, nanostructure, cation substitution level, e_g orbital filling or oxygen vacancies. However, they suffer from low electrical conductivity and surface area, which affects the catalytic response. To mitigate these drawbacks, they have been combined with carbon materials (e.g. carbon black, carbon nanotubes, activated carbon, and graphene) that positively influence the overall catalytic activity. This review provides an overview on tunable perovskites (mainly lanthanum-based) and spinels featuring 3d metal cations such as Mn, Fe, Co, Ni and Cu on octahedral sites, which are known to be active for the electrochemical energy conversion.

Electrocatalytic activity of calcined manganese ferrite solid nanospheres in the oxygen reduction reaction

In this study, we synthesized MnFe₂O₄ solid nanospheres (MSN) calcined at different temperatures (200-500 °C) and MSN-based materials mixed with carbon black, for their use as electrocatalysts in the oxygen reduction reaction (ORR) in alkaline medium (0.1 M KOH). It was demonstrated that the calcination temperature of MSN material determined its chemical surface composition and microstructure and it had an important effect on the electrocatalytic properties for ORR, which in turn was reflected in the performance of MSN/CB-based electrocatalysts. The study revealed that the presence of Mn species plays a key role in the ORR activity. Among tested, MSN200/CB and MSN350/CB exhibited the best electrochemical performances together with outstanding stability.

Fabrication of polyoxometalate-modified palladium–nickel/reduced graphene oxide alloy catalysts for enhanced oxygen reduction reaction activity

A novel nanocatalyst, polyoxometalate-modified palladium–nickel/reduced graphene oxide (Pd8Ni2/rGO-POM), is prepared and served as an effective ORR nanomaterial in alkaline media.

Development of Nanosized Mn3O4-Co3O4 on Multiwalled Carbon Nanotubes for Cathode Catalyst in Urea Fuel Cell

Double-oxide Mn3O4-Co3O4 nanoparticles were synthesized and anchored on multiwalled carbon nanotubes (MWCNTs) via a single-step solvothermal method. The largest specific area (99.82 m2g−1) of the catalyst was confirmed via a nitrogen adsorption isotherm. Furthermore, the uniform coating of the Mn3O4-Co3O4 nanoparticles on the surface of the MWCNTs was observed via scanning electron microscopy and transmission electron microscopy; the uniform coating provided an effective transport pathway during the electrocatalytic activities. The rotating disk electrode and rotating ring disk electrode measurements indicated that the electron transfer number was 3.96 and the evolution of H2O2 was 2%. In addition, the Mn3O4-Co3O4/MWCNT catalyst did not undergo urea poisoning and remained stable in an alkaline solution. Conversely, commercial Pt/C could not withstand urea poisoning for long. The performance cell achieved a power density of 0.4226 mW cm−2 at 50 °C. Therefore, Mn3O4-Co3O4/MWCNT is an efficient and inexpensive noble-metal-free cathodic catalyst for direct urea fuel cells.

Recent developments of nano-structured materials as the catalysts for oxygen reduction reaction

Developments of high efficient materials for electrocatalyst are significant topics of numerous researches since a few decades. Recent global interests related with energy conversion and storage lead to the expansion of efforts to find cost-effective catalysts that can substitute conventional catalytic materials. Especially, in the field of fuel cell, novel materials for oxygen reduction reaction (ORR) have been noticed to overcome disadvantages of conventional platinum-based catalysts. Various approaching methods have been attempted to achieve low cost and high electrochemical activity comparable with Pt-based catalysts, including reducing Pt consumption by the formation of hybrid materials, Pt-based alloys, and not-Pt metal or carbon based materials. To enhance catalytic performance and stability, numerous methods such as structural modifications and complex formations with other functional materials are proposed, and they are basically based on well-defined and well-ordered catalytic active sites by exquisite control at nanoscale. In this review, we highlight the development of nano-structured catalytic materials for ORR based on recent findings, and discuss about an outlook for the direction of future researches.

Synthesis of TiO2/rGO composites with different morphologies and their electrocatalysis for the oxygen reduction reaction

An octahedral TiO₂/rGO composite shows the best catalytic activity for the ORR.

Fabrication and high ORR performance of MnOx nanopyramid layers with enriched oxygen vacancies

MnO_x nanopyramids with enriched OVs vertically grown on nitrogen doped carbon microlaminate arrays with narrow spacing yield a high ORR performance.

Reduced graphene oxide-mediated synthesis of Mn3O4 nanomaterials for an asymmetric supercapacitor cell

Herein, Mn₃O₄/reduced graphene oxide composites are prepared via a facile solution-phase method for supercapacitor application. Transmission electron microscopy results reveal the uniform distribution of Mn₃O₄ nanoparticles on graphene layers. The morphology of the Mn₃O₄ nanomaterial is changed by introducing the reduced graphene oxide during the preparation process. An asymmetric supercapacitor cell based on the Mn₃O₄/reduced graphene oxide composite with the weight ratio of 1 : 1 exhibits relatively superior charge storage properties with higher specific capacitance and larger energy density compared with those of pure reduced graphene oxide or Mn₃O₄. More importantly, the long-term stability of the composite with more than 90.3% capacitance retention after 10 000 cycles can ensure that the product is widely applied in energy storage devices.

The existence presence of rGO can affect the morphology of an Mn₃O₄/rGO composite, and the asymmetric supercapacitor cell created with this composite exhibits good capacitive performance.