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With the increasing demand for green and efficient energy storage devices， advanced technologies for clean energy conversion have attracted close attention from researchers. Fuel cells with environmental friendliness and high energy conversion efficiency are promising alternatives to traditional energy sources. However， Pt catalysts with high commercialization degrees in the industrial catalysis field have some problems， such as high cost， poor stability and weak anti-toxicity ability， which limits the further development of fuel cells. The development of non-Pt oxygen reduction reaction （ORR） catalysts with abundant reserves， low cost and excellent performance is an effective way to improve the efficiency of fuel cells. In this paper， based on the research results at home and abroad in recent years， various types of non-Pt system ORR catalysts， including non-precious metal and non-metal catalysts， are systematically introduced. The advantages， disadvantages and modification strategies of various catalysts are summarized， and challenges and prospects for the development of ORR electrocatalysts are put forward. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction （ORR） is an important cathode reaction for metal-air batteries and proton exchange membrane fuel cells （PEMFCs）. It is of great significance to study non-noble metal catalysts with high activity and stability. In this paper， MIL-101（- Al-Fe） with hierarchical porous structure is innovatively used as the metal precursor template， and Fe-N-C catalysts with rich mesoporous structure are successfully prepared. Electrochemical test results show that Fe-N-C-MIL-900 shows the best ORR activity with half-wave potential of 0. 905 V in 0. 1 mol/L KOH electrolyte. The ORR electron transfer number of Fe-N-C-MIL-900 catalyst is 3. 98， and the H2O2 yield is less than 3%， demonstrating an obvious 4-electron ORR pathway. This work provides a new way to prepare hierarchically porous Fe-N-C catalysts with high ORR activity. [ABSTRACT FROM AUTHOR]