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Fuel cells are considered renewable and clean energy sources to replace the dwindling fossil fuel resources. However, the sluggish reaction kinetics of the anodic fuel oxidation and cathodic oxygen reduction reactions hinder the wide commercialization of fuel cells. The Pt/C material is still the most efficient electrocatalyst; however, its high price and poor stability severely impede its large-scale application. Recently, transition metal nitrides (TMNs) have been regarded as promising electrocatalyst materials owing to their unique physical, chemical, and electronic properties, e.g., thermal stability, metallic conductivity, great hardness, and corrosion resistance. Herein, the advances pertaining to TMN-based catalyst materials for fuel cells are reviewed, ranging from their structures, properties, and synthesis to their applications. TMNs can act as catalysts or supports in electrocatalytic processes. Briefly, as catalysts, TMNs are grouped into free-standing TMNs (including binary and ternary TMNs) and TMN/carbon composites. Moreover, as supports, TMNs can be categorized as pure TMNs supports and hybrid supports to anchor noble metals. Finally, the challenges and perspectives of TMN-based catalyst materials for high-performance fuel cell systems are discussed.

Magnesium hydroxide (MH) has attracted much attention as an environmentally friendly flame retardant. In this paper, high throughput preparation of high-grade MH flame retardant was successfully achieved via microreaction technology and hydrothermal treatment. The results indicated that the reactant molar ratio and reactant concentration had a significant effect on the properties of MH including the morphology, average particle size and BET specific surface area, while the flow velocity and reaction temperature had little effect. To obtain MH with desirable properties, a highly concentrated NaOH solution was added into the hydrothermal slurry. The properties of MH were remarkably influenced by hydrothermal parameters such as NaOH concentration, time, temperature and solid content. High-grade MH flame retardant can be obtained with a NaOH concentration ≥2.4 M, hydrothermal time ≥3 h, hydrothermal temperature ≥170 °C and solid content ≤6.0 wt%. On the basis of laboratory work, a microreaction system based on a stacked plate microchannel reactor with an external volume of 7 L was developed for the pilot scale preparation of MH. The production capacity of MH slurry was up to 12.6 m3 h−1, and the pressure drop of the microreaction system was kept at 1.1 bar. The average particle size and BET specific surface area of as-prepared MH were 1.0 μm and 3.4 m2 g−1, respectively, which met the requirement of high-grade flame retardant.