Interfacial Electron Transfer of Ni₂P–NiP₂ Polymorphs Inducing Enhanced Electrochemical Properties

Abstract

Heterointerface engineering can be used to develop excellent catalysts through electronic coupling effects between different components or phases. As one kind of promising Pt‐free electrocatalysts for hydrogen evolution reaction (HER), pure‐phased metal phosphide exhibits the unfavorable factor of strong or weak H*‐adsorption performance. Here, 6 nm wall‐thick Ni2P–NiP2 hollow nanoparticle polymorphs combining metallic Ni2P and metalloid NiP2 with observable heterointerfaces are synthesized. It shows excellent catalytic performance toward the HER, requiring an overpotential of 59.7 mV to achieve 10 mA cm−2 with a Tafel slope of 58.8 mV dec−1. Density functional theory calculations verify electrons' transfer from P to Ni at the heterointerfaces, which decreases the absolute value of H* adsorption energy and simultaneously enhance electronic conductivity. That is, the heterojunctions balance the metallic Ni2P and the metalloid NiP2 to form an optimized phosphide polymorph catalyst for the HER. Furthermore, this polymorph combination is used with NiFe‐LDH nanosheets to form an alkaline electrolyzer. It shows highly desirable electrochemical properties, which can reach 10 mA cm−2 in 1 m KOH at 1.48 V and be driven by an AAA battery with a nominal voltage of 1.5 V. The work about interfacial charge transfer might provide an insight into designing excellent polymorph catalysts.

Mo‐Doped Cu/Co Hybrid Oxide Nanoarrays: An Enhanced Electrocatalytic Performance for the Hydrogen Evolution Reaction

“…These distances can be indexed to the (111), (200), (111), (111) planes of CoO, Cu 2 O, CuO, Cu, respectively ,,. Polycrystal structures were inevitable to produce abundant subsequent interfacial structure and bestow the so‐called hetero‐interface effect, which could optimize the valence electron state of active sites and enhance the electronic conductivity of catalyst . The interfacial or grain boundaries, with energy similar to the surface energy, are more chemically reactive .…”

“…Furthermore, doping of heteroatoms tends to contribute valence electrons from itself to neighboring atoms, favoring electron migration from valence electron to conduction electron, achieving the reduced electric resistance . As well, polycrystalline materials possess more interfaces, which can optimize the valence electron state of active sites and enhance the electronic conductivity of catalyst . Amorphous materials were generally considered to show superior catalytic activity when compared to the crystalline analogue, due to the lower energy barrier for reactant absorption, originating from its greater density of surface‐unsaturated sites ,.…”

Interfacial Engineering of MoO2‐FeP Heterojunction for Highly Efficient Hydrogen Evolution Coupled with Biomass Electrooxidation

“…[ 47 ] A good HER catalyst should have a moderate Δ G H* (|Δ G H* | = 0). [ 48 ] The |Δ G H* | on MoO 2 ‐FeP is merely 0.21 eV (Figure 5e; Table S7, Supporting Information), which is much smaller than that on FeP (0.74 eV) and MoO 2 (0.85 eV). These results prove that the H* adsorption kinetics on MoO 2 ‐FeP is preferable for the HER.…”

Multifunctional Transition Metal‐Based Phosphides in Energy‐Related Electrocatalysis

“…As a consequence, the interfacial electronic structure would be tuned, giving rise to the enhanced electron conductivity and optimized adsorption energy toward intermediates. In this regard, a representative work has been done by Guo and co‐workers . They constructed the hollow Ni 2 P–NiP 2 polymorphs heterointerface by the phosphidation of NiS 2 single‐crystal precursor.…”

“…c) Diagram of Δ G H* for pure NiP 2 , Ni 2 P and Ni 2 P–NiP 2 (inserted plot: distribution of electron charge density at the interface of Ni 2 P–NiP 2 ). Reproduced with permission . Copyright 2018, John Wiley and Sons.…”