西北化工研究院有限公司

Proton exchange membrane fuel cells(PEMFCs)have emerged as a revolutionary technology in the field of clean energy,enabling the direct conversion of chemical energy to electricity through hydrogen-oxygen electrochemical reactions.This technology fundamentally circumvents the limitations of conventional combustion-based power generation,achieving near-zero greenhouse gas emissions while presenting a critical solution for efficient and environmentally-benign utilization of chemical energy.As the critical component of PEMFCs,the proton exchange membrane(PEM)plays an essential role in determining device-level efficiency and long-term operational stability.The PEM is a proton conductive polymer membrane existing between the anode and cathode,enabling selective proton transport while blocking electrons and gases.The ideal PEM materials must concurrently satisfy two critical operational requirements:(1)establishing efficient proton conduction pathways from anode to cathode with directional specificity,while(2)exhibiting robust resistance to gas and electricity leakage.To address these competing demands,strategic innovations in nanostructured membrane architectures continue to drive progress in next-generation PEMs.Covalent organic frameworks(COFs),a novel class of porous organic crystalline materials,demonstrate exceptional potential as next-generation PEM candidates owing to their inherent advantages including precise structural tunability,periodic pore arrangements,customizable functionality,and remarkable chemical stability.The unique architectural features of COFs provide unprecedented opportunities for proton conduction engineering.Their molecu-lar-designed frameworks allow precise engineering of proton-conductive sites through strategic chemical modifications,while the well-defined nanochannels enable effective confinement of diverse proton carriers/vehicles.The periodic and topo-logical pore nanoarchitectures facilitate the establishment of hierarchical proton transport pathways.These characteristics demonstrate exceptional performances in either hydrated or anhydrous proton conduction systems.This review systematically examines recent advancements in the design and preparation of COF-based proton conducting materials.Beginning with a brief introduction to the PEMFCs and current PEM,the basic knowledge of COFs and their potential structural advantages for proton conduction are discussed.Subsequently,the preparation of COF-based membrane and the key performance evalua-tion of PEM are summarized.Particular emphasis is placed on design strategies to enhance proton conduction including:(1)Framework design with incorporation of proton-conducting functionalities,(2)Pore nanoconfinement of proton-conducting guest moieties and(3)Pore-structure engineering for building proton conducting superhighways.The proton conductivity under different temperatures and humidities are discussed,along with the correlations to their structures and proton conduc-tion mechanisms.Finally,the summary and perspective in this field are presented,underscoring challenges and opportunities in this burgeoning field.We hope this review would offer valuable insights into designing high-performance COF-based PEMs.

Medium-low temperature coal tar （LTCT） is a kind of heavy oil with high density and high viscosity. Hydrotreating is an important means for clean utilization of LTCT， which is mainly completed in trickle bed reactor （TBR）. As an important component of TBR， the gas-liquid distributor affects the performance of catalyst bed in the reactor. In this paper， a computational fluid dynamics （CFD） model based on Euler-Euler method was established， and the model was verified according to the cold model experiment results reported in the literature. The flow of LTCT and hydrogen in four kinds of distributors （bubble cap， multiport chimney， slot chimney and vapor-lift tube） was simulated. The liquid distribution， flow behavior and pressure drop of the distributors were compared and analyzed. In addition， the concept of liquid maldistribution factor (M f ) was introduced to quantitatively evaluate the gas-liquid distribution effect of four kinds of distributors. The results showed that the liquid phase coverage of LTCT was the widest after passing through the bubble cap. When the bubble cap was at y= -200 mm section， the M f value was 0.13， the distribution effect was the best， and the gas-liquid two-phase flow concentration phenomenon was not serious.