Hydrogen energy is considered to be the most potential “ultimate energy source” due to its high combustion calorific value, cleanliness, and pollution-free characteristics. Furthermore, the production of hydrogen via the electrolysis of water has the advantages of simplicity, high efficiency, environmentally safe, and high-purity hydrogen. However, it is also associated with issues such as high-power consumption for the reaction and limited large-scale application of noble metal catalysts. Metal–organic frameworks (MOFs) are porous composite materials composed of metal ions and organic functional groups through orderly coordination with large specific surface areas and large porosity. Herein, we focus on the research status of MOFs and their transition metal derivatives for electrocatalytic water splitting to produce hydrogen and briefly describe the reaction mechanism and evaluation parameters of the electrocatalytic hydrogen evolution and oxygen evolution reactions. Furthermore, the relationship between the catalytic behavior and catalytic activity of different MOF-based catalysts and their morphology, elemental composition, and synthetic strategy is analyzed and discussed. The reasons for the excellent activity and poor stability of the original MOF materials for the electrolysis of water reaction are shown through analysis, and using various means to improve the catalytic activity by changing the electronic structure, active sites, and charge transfer rate, MOF-based catalysts were obtained. Finally, we present perspectives on the future development of MOFs for the electrocatalytic decomposition of water.

The nanocatalysts of Mn−Co/TiO₂ and Mn−Fe/TiO₂ were synthesized by hydrothermal method and comprehensively compared from nanostructures, catalytic performance, kinetics, and thermodynamics. The physicochemical properties of the nanocatalysts were analyzed by N₂ adsorption, transmission electron microscope (TEM), X-ray diffraction (XRD), H₂-temperature-programmed reduction (TPR), NH₃-temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Based on the multiple characterizations performed on Mn−Co/TiO₂ and Mn−Fe/TiO₂ nanocatalysts, it can be confirmed that the catalytic properties were decidedly dependent on the phase compositions of the nanocatalysts. The Mn−Co/TiO₂ sample presented superior structure characteristics than Mn−Fe/TiO₂, with the increased surface area, the promoted active components distribution, the diminished crystallinity, and the reduced nanoparticle size. Meanwhile, the Mn⁴⁺/Mnⁿ⁺ ratios in the Mn−Co/TiO₂ nanocatalyst were higher than Mn−Fe/TiO₂, which further confirmed the better oxidation ability and the larger amount of Lewis acid sites and Bronsted acid sites on the sample surface. Compared to Mn−Fe/TiO₂ nanocatalyst, Mn−Co/TiO₂ nanocatalyst displayed the preferable catalytic property with higher catalytic activity and stronger selectivity in the temperature range of 75–250 °C. The results of mechanism and kinetic study showed that both Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism reactions contributed to selective catalytic reduction of NO with NH₃ (NH₃-SCR) over Mn−Fe/TiO₂ and Mn−Co/TiO₂ nanocatalysts. In this test condition, the NO conversion rate of Mn−Co/TiO₂ nanocatalyst was always higher than that of Mn−Fe/TiO₂. Furthermore, comparing the reaction between doping transition metal oxides and NH₃, the order of temperature−Gibbs free energy under the same reaction temperature is as follows: Co₃O₄ < CoO < Fe₂O₃ < Fe₃O₄, which was exactly consistent with nanostructure characterization and NH₃-SCR performance. Meanwhile, the activity difference of MnO_x exhibited in reducibility properties and Ellingham Diagrams manifested the promotion effects of cobalt and iron dopings. Generally, it might offer a theoretical method to select superior doping metal oxides for NO conversion by comprehensive comparing the catalytic performance with the insight from nanostructure, catalytic performance, reaction kinetics, and thermodynamics.

As a typical carbon-based material, activated carbon (AC) has satisfied adsorption performance and is of great significance in the field of volatile organic compounds (VOCs) pollutants removal. In order to further reveal the optimization mechanism of AC adsorption performance, coconut shell-based AC was selected as the research object, and different concentrations of HNO ₃ coupled with microwave were used for rapid modification and activation. The characteristic changes of pore structure and surface chemical of AC before and after rapid modification were analyzed, and the performance changes of VOCs absorption were discussed from the perspective of reaction kinetics. The pore structure and surface chemical properties of before and after modification were analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Brunauer-Emmeta-Teller (BET) analysis, Fourier Transform Infrared Spectroscopy (FTIR), and Boehm titration. The results showed that HNO ₃ coupled with microwave could significantly eliminate impurities in the pores of AC. After impregnation in HNO ₃ at a concentration of 1.5 mol L ⁻¹ and under microwave irradiation of 900 W, the number of micropore on the surface of samples increased slightly. When the impregnation concentration of HNO ₃ continued to increase, the two adjacent pore structures of the samples merged, which lead to a large decrease in the number of micropore and a corresponding increase in the proportion of mesoporous. Meanwhile, the specific surface area S _BET of the modified NAC-6 sample increased to 1,140.40 m ² g ⁻¹ , and the total acidic oxygen-containing functional groups on the surface increased by 0.459 mmol g ⁻¹ compared to that of the unmodified raw carbon. Furthermore, by analyzing the experimental results of formaldehyde adsorption on AC samples, it was concluded that the saturated adsorption capacity of the modified NAC-6 sample was 43% higher than that of the raw carbon. This study provides a more convenient and faster modification method for AC in the field of gas phase pollutants purification, which is helpful to realize the practical engineering application of AC with high efficiency, energy saving and sustainable.

The cobalt/nitrogen-doped ZIF-67 derived carbon (CoN-ZIF-Cx) was constructed as the carrier material, and paraffin was used as the phase change core material to construct thermally enhanced shaped composite phase change materials.

A series of Mn−Fe−Ce−O_x/γ-Al₂O₃ nanocatalysts were synthesized with different Mn/Fe ratios for the catalytic oxidation of NO into NO₂ and the catalytic elimination of NO_x via fast selective catalytic reduction (SCR) reaction. The effects of Mn/Fe ratio on the physicochemical properties of the samples were analyzed by means of various techniques including N₂ adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂-temperature-programmed reduction (TPR), NH₃-temperature-programmed desorption (TPD) and NO-TPD, meanwhile, their catalytic performance was also evaluated and compared. Multiple characterizations revealed that the catalytic performance was highly dependent on the phase composition. The Mn15Fe15−Ce/Al sample with the Mn/Fe molar ratio of 1.0 presented the optimal structure characteristic among all tested samples, with the largest surface area, increased active components distributions, the reduced crystallinity and diminished particle sizes. In the meantime, the ratios of Mn⁴⁺/Mnⁿ⁺, Fe²⁺/Feⁿ⁺ and Ce³⁺/Ceⁿ⁺ in Mn15Fe15−Ce/Al samples were improved, which could enhance the redox capacity and increase the quantity of chemisorbed oxygen and oxygen vacancy, thus facilitating NO oxidation into NO₂ and eventually promoting the fast SCR reaction. In accord with the structure results, the Mn15Fe15−Ce/Al sample exhibited the highest NO oxidation rate of 64.2% at 350 °C and the broadest temperature window of 75–350 °C with the NO_x conversion >90%. Based on the structure–activity relationship discussion, the catalytic mechanism over the Mn−Fe−Ce ternary components supported by γ-Al₂O₃ were proposed. Overall, it was believed that the optimization of Mn/Fe ratio in Mn−Fe−Ce/Al nanocatalyst was an extremely effective method to improve the structure–activity relationships for NO pre-oxidation and the fast SCR reaction.