Iron-embedded hollow-out nitrogen-doped carbon nanoboxes catalyst with enhanced oxygen transport for improved ORR performance

Constructing iron-nitrogen-carbon (Fe- N -C) catalysts with high intrinsic activity for the oxygen reduction reaction (ORR) remains challenging. Meanwhile, additional structural optimization is necessary to improve mass transport and attain higher power density for practical applications. Herein, using silicalite-1 zeolite as a template, we employed a region-selective strategy to construct iron-embedded hollow-out nitrogen-doped carbon nanoboxes (Fe- N -HOCNs) catalyst with coexisted Fe-N x and Fe nanoclusters, and as an efficient ORR electrocatalyst for the zinc-air batteries (ZABs). Despite the Fe content of 4.73 wt% in Fe- N -HOCNs, it exhibits a high half-wave potential ( E 1/2  = 0.87 V), excellent mass activity ( j m , 658.17 mA mg −1 ), and turnover frequency (TOF, 0.3808 e − site −1 s −1 ), with ORR performance surpassing that of commercial Pt/C. This is attributed to the synergistic effect of coexisting Fe-N x and Fe nanoclusters, which effectively lower the energy barrier of the ORR, optimizes the adsorption of reaction intermediates, and enhances electronic conductivity. Moreover, the abundant short-range, penetrable microporous/mesoporous channels overcome the diffusion limitations of O 2 , significantly improving electrochemical wettability, accessibility, and utilization efficiency of the limited catalytic active sites, facilitating the exposure of active sites at the three-phase boundary. Finite element simulations reveal that the multidirectional hollow-out structure of Fe- N -HOCNs functions as interconnected pathways, substantially reducing O 2 transport resistance within the cathode catalyst layer. In ZABs, Fe- N -HOCNs enable the device to achieve a power density of 164 mW cm −2 and a specific capacity of 776 mA h g −1 , along with excellent rate performance.