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DOE OSTI2020

Materials Data on Co2P by Materials Project

Co2P crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are two inequivalent Co+1.50+ sites. In the first Co+1.50+ site, Co+1.50+ is bonded to five P3- atoms to form distorted CoP5 trigonal bipyramids that share corners with six equivalent CoP4 tetrahedra, corners with ten equivalent CoP5 trigonal bipyramids, edges with six equivalent CoP4 tetrahedra, and edges with six equivalent CoP5 trigonal bipyramids. There are one shorter (2.28 Å) and four longer (2.44 Å) Co–P bond lengths. In the second Co+1.50+ site, Co+1.50+ is bonded to four P3- atoms to form CoP4 tetrahedra that share corners with ten equivalent CoP4 tetrahedra, corners with six equivalent CoP5 trigonal bipyramids, edges with two equivalent CoP4 tetrahedra, and edges with six equivalent CoP5 trigonal bipyramids. There are two shorter (2.15 Å) and two longer (2.26 Å) Co–P bond lengths. There are two inequivalent P3- sites. In the first P3- site, P3- is bonded in a 9-coordinate geometry to nine Co+1.50+ atoms. In the second P3- site, P3- is bonded in a 9-coordinate geometry to nine Co+1.50+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Co2P by Materials Project

Co2P is Cotunnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Co+1.50+ sites. In the first Co+1.50+ site, Co+1.50+ is bonded in a 5-coordinate geometry to five equivalent P3- atoms. There are a spread of Co–P bond distances ranging from 2.26–2.54 Å. In the second Co+1.50+ site, Co+1.50+ is bonded to four equivalent P3- atoms to form a mixture of edge and corner-sharing CoP4 tetrahedra. There are a spread of Co–P bond distances ranging from 2.15–2.22 Å. P3- is bonded in a 9-coordinate geometry to nine Co+1.50+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

High-performance light-driven heterogeneous CO 2 catalysis with near-unity selectivity on metal phosphides

Akin to single-site homogeneous catalysis, a long sought-after goal is to achieve reaction site precision in heterogeneous catalysis for chemical control over patterns of activity, selectivity and stability. Herein, we report on metal phosphides as a class of material capable of realizing these attributes and unlock their potential in solar-driven CO 2 hydrogenation. Selected as an archetype, Ni 12 P 5 affords a structure based upon highly dispersed nickel nanoclusters integrated into a phosphorus lattice that harvest light intensely across the entire solar spectral range. Motivated by its panchromatic absorption and unique linearly bonded nickel-carbonyl-dominated reaction route, Ni 12 P 5 is found to be a photothermal catalyst for the reverse water gas shift reaction, offering a CO production rate of 960 ± 12 mmol g cat –1 h –1 , near 100% selectivity and long-term stability. Successful extension of this idea to Co2P analogs implies that metal phosphide materials are poised as a universal platform for high-rate and highly selective photothermal CO 2 catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Facet-Dependent Hydrogen Evolution Reaction on M 2 P (M = Ni, Co, Fe) Single Crystals

Transition-metal phosphides (MPs) are promising earth-abundant catalysts for hydrogen evolution reactions (HERs) due to their remarkable activity and stability. To further improve their properties, facet control is a key strategy. The growth of shape-selected nanoparticles may substantially enhance electrocatalytic activity, but this approach requires fundamental studies of facet-specific catalytic properties. There are only a few reports on the facet effects of MPs, which leads to a limited understanding of the activity of each facet and hampers catalyst design. Here, in this study, we grew large hexagonal-prism-shaped single crystals of three representative M 2 P (M = Ni, Co, and Fe) catalysts using metal flux routes. Two facets of M 2 P single crystals were tested to study facet-dependent HER activities, and it was consistently demonstrated that for all M 2 P crystals, a tip facet [(0001) for Ni 2 P/Fe 2 P and (010) for Co 2 P] had a higher activity than the side facet [(101̅0) for Ni 2 P/Fe 2 P and (100) for Co 2 P]. HER activity between the same facet elucidated the activity ordered between different transition metals as Fe 2 P > Co 2 P > Ni 2 P under low-potential regions. At high applied potentials, this trend is reversed due to the differences in Tafel slopes, with Ni 2 P becoming the most active catalyst, such that the activity of the (0001) facet of Ni 2 P approaches that of Pt. The calculated surface density of states (DOS) of each facet and its local curvature were found to be a useful descriptor for the activity trends among different transition metals of the same facets.

Co2P↗