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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ni5P4 by Materials Project

Ni5P4 crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. there are four inequivalent Ni2+ sites. In the first Ni2+ site, Ni2+ is bonded to five P+2.50- atoms to form distorted NiP5 trigonal bipyramids that share corners with two equivalent PNiP3 tetrahedra, corners with five equivalent NiP4 tetrahedra, corners with eight NiP5 trigonal bipyramids, corners with two equivalent NiP4 trigonal pyramids, edges with two equivalent NiP4 tetrahedra, edges with three NiP5 trigonal bipyramids, and a faceface with one NiP5 trigonal bipyramid. There are a spread of Ni–P bond distances ranging from 2.29–2.46 Å. In the second Ni2+ site, Ni2+ is bonded to four P+2.50- atoms to form NiP4 trigonal pyramids that share corners with twelve NiP5 trigonal bipyramids and edges with three equivalent NiP4 tetrahedra. There are three shorter (2.16 Å) and one longer (2.19 Å) Ni–P bond lengths. In the third Ni2+ site, Ni2+ is bonded to four P+2.50- atoms to form distorted NiP4 tetrahedra that share a cornercorner with one PNiP3 tetrahedra, corners with four equivalent NiP4 tetrahedra, corners with ten NiP5 trigonal bipyramids, edges with four NiP5 trigonal bipyramids, and an edgeedge with one NiP4 trigonal pyramid. There are a spread of Ni–P bond distances ranging from 2.27–2.46 Å. In the fourth Ni2+ site, Ni2+ is bonded to five P+2.50- atoms to form distorted NiP5 trigonal bipyramids that share corners with two equivalent PNiP3 tetrahedra, corners with five equivalent NiP4 tetrahedra, corners with eight NiP5 trigonal bipyramids, corners with two equivalent NiP4 trigonal pyramids, edges with two equivalent NiP4 tetrahedra, edges with three NiP5 trigonal bipyramids, and a faceface with one NiP5 trigonal bipyramid. There are a spread of Ni–P bond distances ranging from 2.28–2.41 Å. There are four inequivalent P+2.50- sites. In the first P+2.50- site, P+2.50- is bonded in a q6 geometry to nine Ni2+ atoms. In the second P+2.50- site, P+2.50- is bonded to one Ni2+ and three equivalent P+2.50- atoms to form PNiP3 tetrahedra that share corners with three equivalent NiP4 tetrahedra and corners with twelve NiP5 trigonal bipyramids. All P–P bond lengths are 2.20 Å. In the third P+2.50- site, P+2.50- is bonded in a 6-coordinate geometry to five Ni2+ and one P+2.50- atom. In the fourth P+2.50- site, P+2.50- is bonded in a 7-coordinate geometry to seven Ni2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni5P4(O8F)2 by Materials Project

Ni5P4(O8F)2 crystallizes in the orthorhombic Aea2 space group. The structure is three-dimensional. there are three inequivalent Ni+2.80+ sites. In the first Ni+2.80+ site, Ni+2.80+ is bonded to five O2- and one F1- atom to form NiO5F octahedra that share corners with two NiO4F2 octahedra, corners with three equivalent PO4 tetrahedra, and edges with two equivalent NiO5F octahedra. The corner-sharing octahedra tilt angles range from 56–69°. There are a spread of Ni–O bond distances ranging from 1.96–2.18 Å. The Ni–F bond length is 2.11 Å. In the second Ni+2.80+ site, Ni+2.80+ is bonded to four O2- and two equivalent F1- atoms to form corner-sharing NiO4F2 octahedra. The corner-sharing octahedra tilt angles range from 46–56°. There are two shorter (2.00 Å) and two longer (2.01 Å) Ni–O bond lengths. Both Ni–F bond lengths are 2.04 Å. In the third Ni+2.80+ site, Ni+2.80+ is bonded to five O2- and one F1- atom to form distorted NiO5F octahedra that share corners with two NiO5F octahedra, corners with two equivalent PO4 tetrahedra, edges with two equivalent NiO5F octahedra, and an edgeedge with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 46–69°. There are a spread of Ni–O bond distances ranging from 2.03–2.31 Å. The Ni–F bond length is 2.04 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.48 Å) and one longer (1.50 Å) P–O bond length. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with five NiO5F octahedra and an edgeedge with one NiO5F octahedra. The corner-sharing octahedra tilt angles range from 53–67°. There are a spread of P–O bond distances ranging from 1.55–1.57 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two Ni+2.80+ and one P5+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one Ni+2.80+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one Ni+2.80+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two Ni+2.80+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one Ni+2.80+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ni+2.80+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ni+2.80+ and one P5+ atom. In the eighth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ni+2.80+ and one P5+ atom. F1- is bonded in a distorted trigonal planar geometry to three Ni+2.80+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing of the Noninnocent Role of P in Transition-Metal Phosphide Hydrogen Evolution Reaction Electrocatalysts via Replacement with Electropositive Si

Transition-metal phosphides (TMP) have been identified as promising electrocatalysts for the hydrogen evolution reaction (HER). Despite recent computational investigations identifying P sites as being crucial for hydrogen adsorption, the main mode of optimization for TMPs has been focused on changing the metal sites. Here, to experimentally verify computational hypotheses and provide a route for HER electrocatalyst optimization via ternary compounds, we performed systematic experimental studies of structurally related NiSi 1–x P x phases, namely, Ni 2 SiP, Ni 5 Si 2 P 3 , Ni 3 SiP 2 , and Ni 7 Si 2 P 5 , which are ordered derivatives of the NiSi structure (Pnma, oP-8, MnP structure type). We found that P played a significant role in modulating HER activity in an acidic electrolyte because the incorporation of P in NiSi reduced the overpotential at current density j = 10 mA/cm 2 from η 10 = 529 mV (NiSi) to η 10 = 97 mV (Ni 2 SiP). Ni 2 SiP outperformed the current state-of-the-art Ni5P4 electrocatalyst prepared and studied in identical conditions both in terms of activity and stability, which is attributed to the presence of covalent Ni–Si bonding in the structure. Within the family of ternary Ni–Si–P compounds, electrocatalytic activity correlates with the number of Ni-3d states at the Fermi energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗