ZIF-67 Derived MnO2 Doped Electrocatalyst for Oxygen Reduction Reaction

Synthesis of a carbon-wrapped microsphere MoO2/Mo2C heterojunction as an efficient electrocatalyst for the oxygen reduction reaction and the hydrogen evolution reaction

The development of non-noble metal catalysts for the optimization of conversion and storage devices is an important research topic. Hence, the microsphere MoO2/Mo2C/C heterojunction composites, which play an important role in the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER), were synthesized using the solvothermal-sintering method. The results revealed that the as-prepared composite exhibited better ORR and HER catalytic performances than those of MoO2/Mo2C and Vulcan XC-72R (carbon black), and approaching that of commercial Pt/C. At the same time, it has a superior methanol tolerance and electrochemical stability than that of the commercial Pt/C. The excellent performance may be attributed to the synergistic effect of the MoO2/Mo2C heterostructure, highly conductive Vulcan XC-72R, and oxygen vacancies (Ov). This research offers new insights into the design and synthesis of cost-effective, environmentally friendly heterojunction composite catalysts used as a high-performance cathode material in fuel cells and water splitting.

MOF Derived Manganese Oxides Nanospheres Embedded in N-Doped Carbon for Oxygen Reduction Reaction

Manganese oxides (MnOx) have been regarded as promising catalyst candidates for oxygen reduction reaction (ORR) due to their natural abundance and extremely low toxicity. However, the intrinsic low conductivity of MnOx limits their application. In this work, Mn oxide embedded in N doped porous carbon (MnOx@C-N) electrocatalysts were prepared through a facile zeolitic imidazolate framework (ZIF-8) template method for ORR. The structure, morphology, and composition of the prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Electrocatalytic performances of the prepared materials were investigated by linear sweep voltammetry. Benefiting from the well-defined morphology, high surface area, and porous structure, the MnOx@C-N electrocatalyst showed the highest ORR activity among all investigated materials with the limiting current density of 5.38 mA/cm2 at a rotation speed of 1600 rpm, the positive half-wave potential of 0.645 V vs. RHE, and the electron transfer number of 3.90. This work showcases an effective strategy to enhance ORR activity of MnOx.

Advanced strategies in Metal-Organic Frameworks for CO2 Capture and Separation

The continuous carbon dioxide (CO₂ ) gas emissions associated with fossil fuel production, valorization, and utilization are serious challenges to the global environment. Therefore, several developments of CO₂ capture, separation, transportation, storage, and valorization have been explored. Consequently, we documented a comprehensive review of the most advanced strategies adopted in metal-organic frameworks (MOFs) for CO₂ capture and separation. The enhancements in CO₂ capture and separation are generally achieved due to the chemistry of MOFs by controlling pore window, pore size, open-metal sites, acidity, chemical doping, post or pre-synthetic modifications. The chemistry of defects engineering, breathing in MOFs, functionalization in MOFs, hydrophobicity, and topology are the salient advanced strategies, recently reported in MOFs for CO₂ capture and separation. Therefore, this review summarizes MOF materials' advancement explaining different strategies and their role in the CO₂ mitigations. The study also provided useful insights into key areas for further investigations.

Photocatalytic and Electrocatalytic Properties of Cu-Loaded ZIF-67-Derivatized Bean Sprout-Like Co-TiO2/Ti Nanostructures

ZIF-derivatized catalysts have shown high potential in catalysis. Herein, bean sprout-like Co-TiO2/Ti nanostructures were first synthesized by thermal treatment at 800 °C under Ar-flow conditions using sacrificial ZIF-67 templated on Ti sheets. It was observed that ZIF-67 on Ti sheets started to thermally decompose at around 350 °C and was converted to the cubic phase Co3O4. The head of the bean sprout structure was observed to be Co3O4, while the stem showed a crystal structure of rutile TiO2 grown from the metallic Ti support. Cu sputter-deposited Co-TiO2/Ti nanostructures were also prepared for photocatalytic and electrocatalytic CO2 reduction performances, as well as electrochemical oxygen reaction (OER). Gas chromatography results after photocatalytic CO2 reduction showed that CH3OH, CO and CH4 were produced as major products with the highest MeOH selectivity of 64% and minor C2 compounds of C2H2, C2H4 and C2H6. For electrocatalytic CO2 reduction, CO, CH4 and C2H4 were meaningfully detected, but H2 was dominantly produced. The amounts were observed to be dependent on the Cu deposition amount. Electrochemical OER performances in 0.1 M KOH electrolyte exhibited onset overpotentials of 330-430 mV (vs. RHE) and Tafel slopes of 117-134 mV/dec that were dependent on Cu-loading thickness. The present unique results provide useful information for synthesis of bean sprout-like Co-TiO2/Ti hybrid nanostructures and their applications to CO2 reduction and electrochemical water splitting in energy and environmental fields.

Metal Organic Frameworks for Advanced Applications

Metal organic frameworks (MOFs) are a class of porous materials with a modular structure [...]