N-doped LaPO4: An effective Pt-free catalyst for electrocatalytic oxygen reduction

This work provides a novel rare-earth-based catalyst of N-regulated lanthanum phosphate (N-LaPO4/C) and the corresponding rational measurement of catalytic activity for the oxygen reduction reaction (ORR). Developed N-LaPO4/C displays more positive half-wave potential (0.88 V) and onset potential (1.02 V) for the ORR, surpassing commercial Pt/C (0.96 and 0.85 V) and most reported research works. The robust stability of N-LaPO4/C for the ORR is also demonstrated. Comprehensive analyses through X-ray absorption spectroscopy, surface Pourbaix diagram, microkinetic modeling, and data mining based on an advanced explainable machine learning demonstrate a self-oxidation process on LaPO4 during the alkaline ORR and identify the key role of N in LaPO4 in promoting ORR. N-doped LaPO4 in N-LaPO4/C is found to be an active center. Further findings show that N-LaPO4/C + RuO2 can be applied in rechargeable Zn-air batteries as an air cathode, showing a good power density and a long cycle life.