Amorphous-crystalline cobalt phosphide hollow nanocubes induced by dual ligand environment for highly efficient hydrogen evolution.

ABSTRACT

CoP is one of the most promising catalysts for catalyzing hydrogen evolution reaction. The foremost issue is how to improve intrinsic activity by regulating electronic structure at the molecular level. Herein, utilizing selective combination of EDTA and Co2+, an amorphous-crystalline CoP with lower valence cobalt and hollow porous structure which induced by dual ligand environment is successfully synthesized via microwave heating and following phosphating process. Synthesize CoPBA from EDTA3+ and Co3+ in a ratio of 11 and followed by phosphating (ECP-1) exhibits excellent performance for HER in alkaline media, requiring 173 mV to achieve 10 mA cm-2. The enhanced catalytic activity may be ascribed to the amorphous-crystalline crystal structure with enlarged exposure of active sites and the hollow porous framework induced by EDTA, as well as the homogeneously distribution of (111) plane, on which the change of free energy on both Co bridge sites and P top sites is close to zero when adsorbing hydrogen. Besides, its great catalytic stability has been evaluated via 1000 cycles of CV measurement. The possible mechanism of valence state regulation of cobalt ions in CoP is discussed in detail. Furthermore, the optimal ratio of EDTA to Co2+ and different precursor states are explored reasonably.