CrN-encapsulated hollow Cr-N-C capsules boosting oxygen reduction catalysis in PEMFC

Understanding the origin of the catalytic activity for the development of efficient catalysts is critical yet challenging. Herein, we report a simple strategy for the synthesis of chromium nitride nanoparticles (CrNNPs) encapsulated into hollow chromium-nitrogen-carbon capsules (CrN@H-Cr-N_x-C). The CrN@H-Cr-N_x-C demonstrated excellent electrocatalytic activity for the oxygen reduction reaction (ORR) in acidic solutions. When applied as a cathode material in a proton-exchange membrane fuel cell (PEMFC), the CrN@H-Cr-N_x-C achieved outstanding initial performance, which is better than that of the PEMFC with H-Cr-N_x-C cathode material. The CrN@H-Cr-N_x-C cathode also showed good stability over 110 h of operation. These results demonstrated that the coexistence of atomically dispersed CrN_x sites and sufficient CrNNPs is essential for excellent PEMFC performances. Density functional theory (DFT) studies further corroborated that CrNNPs can boost the ORR activity of H-Cr-N_x-C. This finding opens a new avenue for the fabrication of low-cost, highly active, and durable ORR catalysts for PEMFC and other applications.