Enhanced Heterogeneous Interfacial Coupling of NiCoS@NiCo(CH3COO)x as Efficient and Long-term Stable Electrocatalysts for Oxygen Evolution Reaction

Regulating the interfacial coupling of core–shell structured electrocatalysts is critical for enhancing the electrocatalytic performance toward oxygen evolution reaction (OER). In this work, 1D NiCo-LDH (layered double hydroxide) and NiCo oxides were selected as a model to study the effect of interlamellar bonding strength on the structure and performance of the as-synthesized 1D NiCoS@NiCo(CH₃COO)_x (NCS@COAC). It was revealed that the sulfides obtained from NiCo-LDH and NiCo oxide exhibit different crystallinities, which in turn diversifies the morphology of NCS@COAC and P-NCS@COAC. In particular, the low crystallinity of NCS results in the Kendall effect between CH₃COO^– and S^2–, leading to the formation of a hierarchical core–shell structure of NCS@COAC that is composed of nanorod and nanotube structures. The appearance of nanotubes increases the ratio of accessible active sites, facilitating the proceeding of the OER. In addition, the interaction between CH₃COO^– and S^2– regulates the local chemical environment of Co/Ni, increasing the density of high-valent Co, especially for NCS@COAC obtained from hydroxides. Moreover, the formation of a core–shell structure also inhibits the leaching of S^2– in the OER, which is beneficial for maintaining the 1D core–shell structure. As a result, NCS@COAC delivers a decreased overpotential of 23 mV lower than that of P-NCS@COAC at the current density of 20 mA cm^–2 and superior stability with retention of the original current after testing for 100 h.