CoMoP/NiFe-Layered Double-Hydroxide Hierarchical Nanosheet Arrays Standing on Ni Foam for Efficient Overall Water Splitting

For efficient water splitting and replacement of expensive Pt or Ir with the earth-abundant materials, we have designed a heterostructure based on the two-dimensional (2D) bimetallic phosphide and layered double hydroxide (LDH) to construct the electrode assembly (i.e., CoxMo1P/NiFe-LDH) and observed its catalytic activities for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. The optimized Co5.0Mo1P/NiFe-LDH hybrid obtained via the hydrothermal–phosphating–electrodeposition process consists of hierarchical nanosheet arrays including some silky and ultrathin NiFe-LDH nanosheets and numerous tiny and cross-linking Co5.0Mo1P nanoplates. Electrochemical tests display that Ni foam (NF)/Co5.0Mo1P/NiFe-LDH not only exhibits outstanding performance toward both HER and OER with an HER overpotential (η at 10 mA/cm2) of 98.9 mV and an OER overpotential (at 50 mA/cm2) of 225 mV outperforming NF/Co5.0Mo1P and NF/CoP but also presents superb stability in 1.0 M KOH. Moreover, it affords a cell voltage for water splitting of 1.68 V at 50 mA/cm2 with an excellent durability for more than 27 h. The abundant and intensive exposure of active sites provided by 2D porous and hierarchical nanosheet arrays and a strong electronic coupling and fast electronic transmission between various interfaces would explain the improved performance. In addition, the anchor effect between Co/Mo phosphides and NiFe-LDHs prevents corrosion of electrolyte solution and slows down the dissolution of the P element. This efficient and highly stable bifunctional electrode can serve as a practical electrode for electrochemical energy storage and conversion.