Recent Progress in Non-Precious and Carbon-Based Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Media

The oxygen reduction reaction (ORR) is a key process in electrochemical energy conversion technologies such as fuel cells and metal–air batteries; however, its sluggish kinetics and reliance on precious metal catalysts limit large-scale application. This review provides a comprehensive overview of recent advances in non-precious nanoscale electrocatalysts for ORR in alkaline media. Particular emphasis is placed on reaction mechanisms, including dominant pathways, kinetics, and key intermediates, as well as the advantages of alkaline electrolytes over acidic systems. The performance of various catalyst classes is systematically discussed, including transition metal-based materials (Fe, Co, Zn, Cu, and bimetallic systems) and metal-free carbon-based electrocatalysts. Special attention is given to heteroatom-doped carbon materials, carbon nanostructures, and emerging hybrid systems such as MXene-based composites. Comparative analysis highlights the relationship between catalyst composition, structure, and electrochemical performance metrics, including half-wave potential, onset potential, Tafel slope, number of electron transfer, and operational stability. Overall, non-precious catalysts demonstrate promising activity and durability, approaching that of noble metals under alkaline conditions. The insights summarized in this review guide the rational design of efficient, cost-effective ORR electrocatalysts and support the development of sustainable energy technologies.