Defect engineering could provide rich active sites, optimized electronic structure and intimate anchoring of active species, displaying multiple roles in promoting the electrocatalytic hydrogen evolution reaction.

The transformation of PVDF from α-phase to β-phase makes PVDF more polar and decreases the crystallinity of PVDF.

Low-cost and efficient catalytic electrode toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is strongly attractive for overall water splitting. Herein, a 3D bifunctional electrode of FeNi phosphide nanosheets with a thin amorphous layer on Nickel foam (FeNi-P/NF) is designed via phosphorizing NiFe-layered double hydroxide-coated nickel foam (FeNi LDH/NF) in red phosphorus vapor at 500 °C. Benefiting from the unique architecture with increased exposure and accessibility of active sites, the electrode exhibits excellent electrocatalytic performance toward both HER and OER in 1.0 M NaOH with 102 and 224 mV low overpotentials to achieve a catalytic current density of 10 mA cm −2 , respectively. As a bifunctional electrode, the FeNi-P/NF can release a current density of 10 mA cm −2 at a low cell voltage of 1.57 V and 100 mA cm −2 at 1.82 V in an alkali electrolyzer, possessing significant durability over 100 h electrolysis at high current density of 100 mA cm −2 .