The effective management of oxygen transport resistance (OTR) within the cathode catalyst layer (CCL) is crucial for achieving a high catalyst performance at low platinum (Pt) loading. Over the past two decades, significant advancements have been made in the development of various high active platinum-based catalysts, aiming at enhancing oxygen mass transport and the oxygen reduction reaction (ORR). However, experimental investigations of transport processes in porous media are often computational costs and restrained by limitations in in-situ measurement capabilities, as well as spatial and temporal resolution. Fortunately, numerical simulation provides a valuable alternative for unveiling the intricate relationship between local transport properties and overall cell performance that remain unresolved or uncoupled through experimental approach. In this review, we elucidate the primary experimental and numerical efforts undertaken to improve OTR. We consolidate the available literature on OTR values and perform a quantitative comparison of the effectiveness of different strategies in mitigating OTR. Furthermore, we analyze the intrinsic limitations and challenges associated with current experimental and numerical methods. Finally, we outline future prospect for advancements in both experimental techniques and modelling methods.

Metal-organic frameworks (MOFs), which are constructed by metal ions or clusters with organic ligands, have shown great potential in gas storage and separation, luminescence, catalysis, drug delivery, sensing, and so on. More than 20,000 MOFs have been reported by adjusting the composition and reaction conditions, and most of them were synthesized by hydrothermal or solvothermal methods. The conventional solvothermal methods are favorable for the slow crystallization of MOFs to obtain single crystals or highly crystalline powders, which are suitable for the structure analysis. However, their harsh synthesis conditions, long reaction time, and difficulty in continuous synthesis limit their scale-up in industrial production and application. Meanwhile, shaping or processing is also required to bring MOF crystals and powders into the market. Therefore, this review demonstrates the crystallization mechanisms of MOFs to understand how the synthetic parameters affect the final products. Additionally, a variety of promising synthetic routes which can be used for large scale synthesis were reviewed in details. Lastly, the prospects of MOF shaping and processing are provided to promote their industrial application.