Using transition metal tetraphosphonates as precursor of phosphorus-containing electrocatalysts

Abstract

Coordination polymers (CPs) are widely studied due to their applicability in many fields. Among them, metal phosphonates (MPs) are attractive materials due to their versatile structural diversity and functionality, with interesting properties as proton conductors and electrocatalyst precursors. In this work, we report the synthesis and crystal structures of several MPs derived from the combination of hexamethylenediamine-N,N,N’,N’-tetrakis(methylenephosphonic acid) (HDTMP) with different transition metals (M2+= Mn, Fe, Co, and Ni). The resulting solids, M[(HO3PCH2)2N(CH2)6N(CH2PO3H)2]·2H2O, show pillared-layered structures with capabilities of ammonia adsorption (Co2+ and Ni2+ derivatives). The ammonia-containing solids are crystalline, with a composition M[(HO3PCH2)2N(CH2)6N(CH2PO3H)2(H2O)2](NH3)4(H2O)12. The catalytic activities toward Oxygen Evolution Reaction (OER), Oxygen Reduction Reaction (ORR) and Hydrogen Evolution Reaction (HER) of the corresponding (5% H2-Ar)-pyrolyzed materials, as well as the crystal structure of non-pyrolyzed precursor solids, will be discussed.