Co@Co Cages Engineered from Hollowing MOFs for Enhanced Hydrogen Evolution Reaction Performance.

Advances in hollow engineering of metal-organic frameworks (MOFs) have enabled a variety of applications in catalysts, sensors, and batteries, but the hollow derivatives are often limited to hydroxides, oxides, selenides, and sulfides with the presence of additional elements from the environment. Here we have successfully synthesized hollow metallic Co@Co cages through a facile two-step strategy. Interestingly, the Co@Co(C) cages with a small amount of residual carbon show excellent catalytic performance due to the abundant exposed active sites and fast charge transfer. During the hydrogen evolution reaction, the overpotential of Co@Co(C) is as low as ∼54 mV at the current density of 10 mA cm, which is close to that of ∼38 mV for the Pt/C electrodes. The two-step synthesis strategy opens up opportunities for increasing the number of catalytic active sites and rates of charge/mass transfer while pushing the limits of materials utilization beyond that achieved in existing MOF-based nanostructures.