Isostructural ATMP-based phosphonates: A versatile platform for monometallic and Fe-doped Co/Ni electrocatalysts towards alkaline water electrolysis

Abstract

Metal tetraphosphates and phosphides were obtained by pyrolysis of isostructural transition-metal aminotris (methylenephosphonates) (M′xM1-xATMP; M and M′ = Mn2+, Fe2+, Co2+, Ni2+) under N2 or 5% H2–Ar atmo- spheres, respectively. Co-based tetraphosphates evolved from ~7 Å nanoclusters (500 ◦C) to crystalline m- Co2P4O12 (800 ◦C), as revealed by pair distribution function (PDF). Cobalt phosphides exhibited the highest OER and HER activity. Fe doping further enhances OER performance, reaching a η50 of 278 mV in 1.0 M KOH on carbon fiber paper (CFP), associated with the in-situ formation of nanometric CoO(OH) (~25 Å). The best alkaline HER performance was achieved for a CFP-supported CoP catalyst (η10 = 97 mV). When the Fe0.3Co0⋅7O (OH) catalyst, derived from the corresponding metal phosphide solid solution (Fe0.3Co0.7@750-H2), was used as the anode with a Pt/C cathode in alkaline water electrolysis (AWE), a cell voltage of 1.50 V at 10 mA cm 2 was achieved, with remarkable long-term stability.