Deep reconstruction of crystalline–amorphous heterojunction electrocatalysts for efficient and stable water and methanol electrolysis

Abstract

During electrocatalytic water splitting, surface reconstruction often occurs to generate truly active species for catalytic reactions, but the stability and mass activity of the catalysts is a huge challenge. A method that combines cation doping with morphology control strategies and constructs an amorphous–crystalline heterostructure is proposed to achieve deep reconstruction of the catalyst during the electrochemical activation process, thereby significantly improving catalytic activity and stability. Amorphous iron borate (FeBO) is deposited on cobalt-doped nickel sulfide (Co-Ni₃S₂) crystals to form ultrathin nanosheet heterostructures (FeBO/Co-Ni₃S₂) as bifunctional electrocatalysts for the OER and methanol oxidation reaction (MOR). During the OER process, FeBO/Co-Ni₃S₂ is deeply reconstructed to form a NiFeOOH/Co-Ni₃S₂ composite structure with ultrathin nanosheets with abundant amorphous–crystalline interfaces to ensure structural stability. Furthermore, Co-Ni₃S₂ electrocatalysts were synthesized via nickel foam (NF) self-derivation, which resulted in strong adhesion between the catalyst and substrate and formed a hierarchical structure consisting of interconnected nanosheets with excellent mass transfer and abundant active sites to increase the activity and stability of the electrocatalyst. The dual-electrode electrolyzer requires cell voltages of 1.58 and 1.44 V to achieve water and methanol overall electrolysis at a current density of 10 mA cm⁻² and keep working over 100 and 25 h, respectively. This strategy provides a new way to promote reconstruction to construct excellent bifunctional electrocatalysts.