Near-100% site utilization of single atoms for efficient electrocatalysis

Despite that enhancing site utilization (U_site) of single atoms (SAs) is crucial in electrocatalysis beyond increasing intrinsic activity and site density, numerous SAs are inaccessible during reaction due to the dense micropores and disordered stacking of carbon particles. Here, the enhancement for U_site of SAs is achieved through a surfactant-assis'ted freeze-casting (SAFC) strategy. The sodium dodecyl sulfate (SDS)-modified Fe-doped zeolitic imidazolate framework-8 (Fe/ZIF-8) particles assemble into single-layer two-dimensional (2D) superstructures along the ice-crystal. During pyrolysis, the dual-stress effect derived from SDS shell and tight alignment of particles induces Fe/ZIF-8 to transform into concave and mesopore-rich carbon. 2D FeNC with optimized structures at both macro- and micro-scales exhibits enhanced electron/mass transport capabilities, achieving near-100% U_site of SAs and a half-wave potential of 0.958 V for oxygen reduction in alkali. This SAFC strategy demonstrates its universality in improving the catalytic performance of various 2D MNCs across different electrocatalytic reactions.