A Pacman-Like Titanium-Doped Cobalt Sulfide Hollow Superstructure for Electrocatalytic Oxygen Evolution

Transition-metal sulfides (TMSs) are attractive oxygen evolution reaction (OER) electrocatalysts. Developing new strategies to improve their electrochemical performance of TMSs is of great significance. Herein, a unique pacman-like titanium-doped cobalt sulfide hollow superstructure (Ti-CoSx HSS) is fabricated as an OER electrocatalyst. Using a prearranged metal-organic framework (MOF)-on-MOF heterostructure as a precursor treated by one-pot sulfidation, a sequential structural conversion process leads to the formation of Ti-CoSx HSS, which is assembled by interconnected Ti-doped CoSx nanocages around a cake-like cavity. Benefiting from the architecture and compositional advantages, Ti-CoSx HSS exhibits excellent OER performance with an overpotential of 249 mV at 10 mA cm^-2 and Tafel slope of 45.5 mV dec^-1 due to increased active site exposure, enhanced electron and mass transfer. This strategy enabled by MOF-on-MOF paves the way toward innovative MOF derivatives for various applications.