Boron pretreatment promotes phosphorization of FeNi catalysts for oxygen evolution

Oxygen evolution reaction (OER) is a crucial half-reaction for many energy conversion technologies, which requires efficient catalysts to boost its sluggish kinetics. Herein, the FeNi catalyst with a high phosphating level (HP-FexNi2−xP) is constructed by a three-step synthetic route: (i) hydrothermal deposition of lamellar sheets, (ii) NaBH4 pretreatment, and (iii) in situ phosphorization. FeNi layered double lamellar hydroxides were synthesized as the pre-catalysts. Then NaBH4 pretreatment was used to remove the oxide impurities and introduce oxygen vacancies to promote phosphorization in the subsequent process. Finally, HP-FexNi2−xP nanosheets were achieved, with several advantages like abundant exposed active sites, high conductivity, and accessible mass transport channels. During the OER process, FeNiOOH/HP-FexNi2−xP interfaces are formed through spontaneous electrochemical activation and surface reconstruction. Benefitting from the synergistic interfacial effect and abundant exposed active sites, the NiFe based catalysts show an overpotential of ≈ 208 mV to reach 10 mA cm−2 in 1 M KOH, and a stability of 200 h at 1 A cm−2. Overall, this work reports the rational design and preparation of a highly active OER catalyst, but also provides a general route through NaBH4 pretreatment, which can be usefully applied to promote phosphorization in other systems of interest for catalytic applications.