Crystalline cages held together by hydrogen bonds can trap a wide range of molecules based on their size.

The research of high efficiency water splitting catalyst is important for the development of renewable energy economy. Here, the progress in the preparation of high efficiency hydrogen evolution reaction (HER) catalyst is reported. The support material is based on a polyhexaphenylbenzene material with intrinsic holes, which heals into carbon materials upon heating. The healing process is found to be useful for anchoring various transition metal atoms, among which the supported Ir Single‐atom catalyst (SAC) catalyst shows much higher electrocatalytic activity and stability than the commercial Pt/C and Ir/C in HER. There is only 17 mV overpotential at 10 mA cm^–2, which is significantly lower than that of commercial Pt/C and Ir/C catalysts respectively by 26 and 3 mV, and the catalyst has an ultra‐high mass activity (MA) of 51.6 at 70 mV potential and turn over frequencies (TOF) of 171.61 s^–1 at the potential of 100 mV. The density functional theory (DFT) calculation reveals the significant role of carbon coordination around the Ir center. A series of monatomic PBN‐300‐M are synthesized by using of designed carbon materials. The findings provide an enabling and versatile platform for facile accessing SACs toward many industrial important reactions.