Oxygen-coordinated Cu single atoms enable unconventional inverse size-effect in Cu nanoparticles for superior...

The size effect has a significant impact on the catalytic performance of metal nanostructures, where smaller sizes often correspond to higher specific surface area and specific activity. This study investigates the pyrolysis-temperature-dependent evolution of Cu-MOFs and reveals an anomalous size effect of Cu nanoparticles in glucose electrooxidation. Although low-temperature pyrolysis produces small Cu nanoparticles, the high-temperature pyrolysis product demonstrates exceptional performance despite the larger size of its Cu nanoparticles. The sensor based on larger Cu nanoparticles exhibits 24-fold higher sensitivity‌ compared to small Cu nanoparticles. In-depth study reveals that high-temperature pyrolysis not only produces large-sized Cu nanoparticles but also induces and promotes the formation of oxygen-coordinated Cu single atoms. The coexistence of oxygen-coordinated Cu single atoms electronically modulates adjacent Cu nanoparticles via charge transfer, which accelerates the electron transfer rate and promots the generation of highly active sites at lower operating potentials, thereby overriding conventional size-activity constraints. This study not only highlights the non-negligible role of oxygen-coordinated metal single atoms during high-temperature pyrolysis and provides a new perspective to explain the anomalous size effect, but also redefines sensing materials design principles through single atom-nanoparticle interactions.