Recent advances in electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) are reviewed. This comprehensive review focuses on low- and non-platinum electrocatalysts, including advanced platinum alloys, core–shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts, and metal-free catalysts. The review highlights the recent development of ORR electrocatalysts with novel structures and compositions, summarizes the understanding of the correlation between activity and shape, size, composition, and synthesis method, and documents the performance and stability of carbon-based materials in fuel cells compared to platinum. Research directions and perspectives on further development of more active and less expensive electrocatalysts are provided. The ORR activity screening technique based on rotating disk electrode (RDE) is discussed, emphasizing the importance of catalyst film quality, ink preparation, and measurement conditions. The Koutecky–Levich equation is used to derive the intrinsic activity of catalysts, and the effects of various factors such as electrolyte purity, potential scanning rate, and reference electrode position are analyzed. The review also addresses the challenges in calculating the electrochemical active area (ECA) of noble metal-based catalysts, noting that the ECA values derived from HUPD are often underestimated, especially for Pt alloys, and that more accurate methods such as CO stripping and Cu underpotential deposition (UPD) charges are recommended. The ORR behavior on pure Pt surfaces is discussed, highlighting the structural effects of high-index planes and the importance of stepped surfaces for enhanced activity. The particle size and shape effects on ORR activity are also analyzed, showing that smaller Pt nanoparticles exhibit lower activity due to increased oxygen binding energy. The review further explores the effects of Pt alloys, including Pt–late transition metal alloys, Pt–early transition metal alloys, ordered Pt alloys, and Pt alloys with NSTF structures. These alloys show improved ORR activity and stability compared to pure Pt, with the activity enhancement attributed to factors such as surface segregation, compressive strain, and the formation of ordered structures. The review also discusses the development of porous Pt alloys through dealloying, which provides more reaction sites and enhances activity via the nanoconfinement effect. The challenges and solutions for improving the performance of NSTF structures, such as flooding and poor proton conductivity, are addressed. Overall, the review provides a comprehensive overview of recent advances in ORR electrocatalysts, emphasizing the importance of structure, composition, and synthesis methods in achieving high activity and stability for PEMFCs.Recent advances in electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) are reviewed. This comprehensive review focuses on low- and non-platinum electrocatalysts, including advanced platinum alloys, core–shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts, and metal-free catalysts. The review highlights the recent development of ORR electrocatalysts with novel structures and compositions, summarizes the understanding of the correlation between activity and shape, size, composition, and synthesis method, and documents the performance and stability of carbon-based materials in fuel cells compared to platinum. Research directions and perspectives on further development of more active and less expensive electrocatalysts are provided. The ORR activity screening technique based on rotating disk electrode (RDE) is discussed, emphasizing the importance of catalyst film quality, ink preparation, and measurement conditions. The Koutecky–Levich equation is used to derive the intrinsic activity of catalysts, and the effects of various factors such as electrolyte purity, potential scanning rate, and reference electrode position are analyzed. The review also addresses the challenges in calculating the electrochemical active area (ECA) of noble metal-based catalysts, noting that the ECA values derived from HUPD are often underestimated, especially for Pt alloys, and that more accurate methods such as CO stripping and Cu underpotential deposition (UPD) charges are recommended. The ORR behavior on pure Pt surfaces is discussed, highlighting the structural effects of high-index planes and the importance of stepped surfaces for enhanced activity. The particle size and shape effects on ORR activity are also analyzed, showing that smaller Pt nanoparticles exhibit lower activity due to increased oxygen binding energy. The review further explores the effects of Pt alloys, including Pt–late transition metal alloys, Pt–early transition metal alloys, ordered Pt alloys, and Pt alloys with NSTF structures. These alloys show improved ORR activity and stability compared to pure Pt, with the activity enhancement attributed to factors such as surface segregation, compressive strain, and the formation of ordered structures. The review also discusses the development of porous Pt alloys through dealloying, which provides more reaction sites and enhances activity via the nanoconfinement effect. The challenges and solutions for improving the performance of NSTF structures, such as flooding and poor proton conductivity, are addressed. Overall, the review provides a comprehensive overview of recent advances in ORR electrocatalysts, emphasizing the importance of structure, composition, and synthesis methods in achieving high activity and stability for PEMFCs.