In-situ construction of N-doped carbon nanosnakes encapsulated FeCoSe nanoparticles as efficient bifunctional electrocatalyst for overall water splitting

The NCNSs encapsulated Fe-doped CoSe NPs have been synthesized by polymerization–pyrolysis–selenization strategy. The FeCoSe@NCNSs shows excellent electrocatalytic HER and OER performance. The development of bifunctional electrocatalysts with high activity and stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial for efficient overall water splitting but still challenging. Herein, we propose a facile and effective polymerization–pyrolysis–selenization (PPS) strategy for in-situ synthesis of N-doped carbon nanosnakes (NCNSs) encapsulated Fe-doped CoSe nanoparticles (NPs) derived from predesigned trimetallic Zn/Fe/Co polyphthalocyanine conjugated polymer networks. Benefiting from the synergistic effect between the regulation of Fe atoms and CoSe NPs as well as the confinement effect of in situ formed porous conductive carbon nanosnakes, the FeCoSe@NCNSs catalyst exhibited the excellent electrocatalytic activity for HER with small overpotentials (142 and 99 mV in 0.5 M H 2 SO 4 and 1 M KOH) and OER (320 mV in 1 M KOH) at the current density of 10 mA cm −2 . Particularly, it also can be used as an efficient bifunctional electrocatalyst with a cell voltage of 1.66 V to achieve a current density of 10 mA cm −2 and superior stability for overall water splitting. Density functional theory study reveals that the doping of Fe atoms on CoSe enhanced the splitting and delocalization of metal- d orbitals close Fermi level, and modifies the distribution of Se- p orbitals close Fermi level, which improved the flexibility of electron donor-acceptor system and the hydrogen adsorption free energy change on metal-metal bridge sites in FeCoSe@NCNSs. Additionally, beneficial from the accepting of Fe-Se bridge site, the overpotential of OER which following intramolecular oxygen coupling mechanism is also decreased, thus accelerating the electrocatalytic performance. This work presents a novel strategy to regulate the activity and stability of transition metal selenides and facilitating the rational design of bifunctional electrocatalysts for overall water splitting applications.