Relationship between the Surface Reconstruction of Nickel Phosphides and Their Activity toward the Hydrogen Evolution Reaction

Abstract

Nickel phosphides (Ni x P y ) are a class of materials that are made out of earth abundant elements and have shown relatively high hydrogen evolution reaction (HER) activity. Here, we perform first-principles density functional theory (DFT) calculations to systematically investigate the stoichiometric and nonstoichiometric surface reconstructions of six different Ni x P y , i.e., Ni3P, Ni12P5, Ni2P, Ni5P4, NiP2, and NiP3, under electrochemical conditions and to illustrate the implications of such reconstructions for the catalytic activity toward HER. Our results can explain a broad range of experimental observations on the HER activity of Ni x P y in a unified framework. For the majority of cases, our protocol can closely reproduce the experimentally measured overpotential trends in the literature, which validates its usefulness in generating physical insight into the surface phenomena responsible for HER activity. We find that, among the Ni x P y studied here, Ni3P and Ni5P4 are the most active catalysts toward HER in acid, whereas Ni5P4 performs the best compared to other Ni x P y in base, in agreement with previous experimental reports. We show that P-vacancy formation in base renders the Ni-rich Ni x P y (Ni3P, Ni12P5, Ni2P, and Ni5P4) worse performers in base when compared to their activity in acid and hence propose that introducing nonmetals, which are less prone to dissolution, can improve their catalytic performance. In terms of active site design, we find Ni3 hollow sites bind H too strongly and surface P sites with P–Ni bonds bind H too weakly. On the other hand, we identify that surface P sites with P–P bonds offer the best catalytic performances, and therefore, we predict that active site engineering to maximize the abundance of such surface motifs can further improve the HER activity. Moreover, we unravel the nature of H binding across the material class for different binding motifs via electronic structure theory analysis. The chemical insight we provide in this work can help rationalize the search for materials composed of inexpensive earth abundant elements that provide improved HER catalytic activity.

Two-Legged Molecular Walker and Curvature: Mechanochemical Ring Migration on Graphene

“…We find that for a C–H bond formation on graphene, three different regions appear in the projected density of state (PDOS) plot (Figure A), bonding, nonbonding, and antibonding regions, in accordance with the previous observation . We calculate the center of the H band below the Fermi energy (red dotted lines in Figure A) and above the Fermi energy (blue dotted line in Figure A) and define it as the H band split ( in Figure A) . Hence …”

“…We find that for a C–H bond formation on graphene, three different regions appear in the projected density of state (PDOS) plot (Figure A), bonding, nonbonding, and antibonding regions, in accordance with the previous observation . We calculate the center of the H band below the Fermi energy (red dotted lines in Figure A) and above the Fermi energy (blue dotted line in Figure A) and define it as the H band split ( normalΔ E normals normalp normall normali normalt normalH .25em b a n d in Figure A) . Hence normalΔ E normals normalp normall normali normalt normalH .25em b a n d = ∫ E normalF ∞ ρ 1 normals ( E ) E d E ∫ E normalF ∞ ρ 1 normals ( E ) ⁣ d E − ∫ − ∞ E normalF ρ 1 normals ( E ) E d E ∫ − ∞ E normalF ρ 1 normals ( E ) ⁣ …”

“…73 We calculate the center of the H band below the Fermi energy (red dotted lines in Figure 2A) and above the Fermi energy (blue dotted line in Figure 2A) and define it as the H band split ( E split H band in Figure 2A). 74 Hence…”

An iron phosphate hydroxide hydrate electrocatalyst: synergistic effects of Fe2+ and Fe3+ for enhanced hydrogen evolution reaction stability

“…25–28 Among them, TMPs offer a number of active sites for catalytic processes and have many exposed crystalline surfaces despite lacking a layered structure. 29–32 The phosphate group has drawn attention since its P–O bond weakens the M–O bond, which is advantageous for an electrocatalyst. 33–36 On the other hand, the optimization of proton and hydroxide adsorption is the first step in the hydrogen evolution reaction.…”

Metal Ce-Leaching Induced Structural Optimization of Bismuth Electrocatalyst for Enhanced CO2 Electroreduction

“…Surface reconstruction of electrocatalysts is a common phenomenon during electrocatalytic process, especially for the electrocatalytic oxygen/hydrogen evolution reactions (OER/HER), which provides a crucial idea to understand the real active sites. , The metal leaching and redeposition are accompanied by the reconstitution process of surface layers. For example, the metal Mo will be leached from the Fe-NiMo-NH 3 /H 2 catalyst after the anodic activation, leading to the reconstitution of active iron–nickel oxyhydroxides for OER .…”