Slower Removing Ligands of Metal Organic Frameworks Enables Higher Electrocatalytic Performance of Derived Nanomaterials

The widely used route of high-temperature pyrolysis for transformation of Prussian blue analogs (PBAs) to functional nanomaterials leads to the fast removal of CN- ligands, and thus the formation of large metal aggregates and the loss of porous structures inside PBAs. Here, a controllable pyrolysis route at low temperature is reported for retaining the confined effect of CN- ligands to metal cations during the whole pyrolysis process, thereby preparing high-surface-area cubes comprising disordered bimetallic oxides (i.e., Co3O4 and Fe2O3) nanoparticles. The disordered structure of Co3O4 enables the exposure of abundant oxygen vacancies. Notably, for the first time, it is found that the in situ generated CoOOH during the oxygen evolution reaction (OER) can inherit the oxygen vacancies of pristine Co3O4 (i.e., before OER), and such CoOOH with abundant oxygen vacancies adsorbs two -OH in the following Co3+ to Co4+ for markedly promoting OER. However, during the similar step, the ordered Co3O4 with less oxygen vacancies only involves one -OH, resulting in the additional overpotentials for adsorbing -OH. Consequently, with high surface area and disordered Co3O4, the as-synthesized electrocatalysts have a low potential of 237 mV at 10 mA cm(-2), surpassing most of reported electrocatalysts.