Flower‐Like Nickel Phosphide Microballs Assembled by Nanoplates with Exposed High‐Energy (0 0 1) Facets: Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Abstract

The fabrication of low-cost and earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) over a broad pH range is attractive. In this work, a facile precursor route is developed to synthesize flower-like nickel phosphide microballs with a diameter of approximately 12 μm. With a controlled phosphorization temperature, flower-like nickel phosphide microballs with different crystalline structures (Ni P and Ni P) were obtained easily. Flower-like Ni P microballs possessed two advantageous features for enhanced HER: fast vectorial electron transfer path along the building block nanoplates and enhanced inherent catalytic activity of each active site for high-energy (0 0 1) facets. The flower-like Ni P microballs electrocatalyst thus displayed excellent activity for the HER with a low overpotential (η) of 35.4 mV to reach current densities of 10 mA cm and a small Tafel slope of 48 mV dec in acid solution. In addition, it showed excellent activity in 1 m KOH with η=47 mV at 10 mA cm . DFT studies indicated that the free energy of hydrogen adsorbed on the Ni site of Ni P was 0.152 eV, which is smaller than that of the Ni site of Ni P (0.182 eV). Therefore, flower-like Ni P microballs exhibited better HER activity than Ni P, which is consistent with our HER data. This hierarchical structure with exposed high-energy (0 0 1) facets paves the way to design and synthesize low-cost, high-performance catalysts for the HER.

Phase Diversity of Nickel Phosphides in Oxygen Reduction Catalysis

“…[60,66,67] The NiPÀC-900 and NiPÀC-1000 catalysts have also show the Ni 2p 3/2 and Ni 2p 1/2 energy levels similar to those of NiPÀC-800. [66][67][68][69][70][71][72][73] As shown in Figure 5, the oxidized metal (Ni) species at~856 and~874 eV and oxidized P species at~132 eV start slightly decreasing with increasing the carbonization temperature, which can be due to the reduction of phosphate species to lower oxidation state at higher temperature, which is in agreement with XRD results. The greater shift of Ni 2p 3/2 toward high energy suggests more positively charged Ni centers (d +) in the series of Ni x P y /C samples, as illustrated in NiPÀC-800 obtained at lower temperature, which contains more Ni 2 P.Therefore, the value of d + is in the order for the obtained catalysts: d NiPÀC-800 > d NiPÀC-900 > d NiPÀC-1000.…”

Phase‐Controlled Synthesis of Nickel Phosphide Nanocrystals and Their Electrocatalytic Performance for the Hydrogen Evolution Reaction

“…In these works, trioctylphosphine oxide, NaH 2 PO 2 , or elemental phosphorus were employed as the phosphorus source, and they reacted with nickel salt, nickel hydroxide, or nickel metal to fabricate Ni 5 P 4 nanomaterials. Pure‐phase Ni 5 P 4 thin films, flower‐like microballs and spherical particles with a diameter of 500 nm, and mixed‐phase nanosheets were obtained. However, these Ni 5 P 4 nanomaterials are still large in size, which is an adversity for catalytic applications.…”

“…[8] Liu et al realized the phase-controlled synthesis of nickel phosphide nanocrystals by changing the molar ratio of the P/Ni precursor. [9] Small size Ni 12 P 5 and Ni 2 Pn anocrystals were successfully synthesized, but they only formedn anocrystal aggregates of hundreds of nanometers in size for Ni 5 P 4 .T od ate, there are only af ew reports with respect to the controlled synthesis of Ni 5 P 4 nanocrystals.I nt hesew orks, trioctylphosphine oxide, [10] NaH 2 PO 2 , [11] or elemental phosphorus [12] were employed as the phosphorus source, and they reacted with nickel salt, [10] nickel hydroxide, [11] or nickel metal [12] to fabricateN i 5 P 4 nanomaterials. Pure-phase Ni 5 P 4 thin films, [12a] flower-like microballs [11b] and spherical parti- cles with ad iameter of 500 nm, [10] and mixed-phase nanosheets [11a, 12b] were obtained.…”

Graphene‐Like Multilayered CuS Nanosheets Assembled into Flower‐Like Microspheres and Their Electrocatalytic Oxygen Evolution Properties

“…At present, the design of efficient oxygen evolution reaction (OER) catalytic has attracted great attention, because the OER plays an important role in many electrochemical reaction and large‐scale storage of intermittent energy . However, the OER suffers from sluggish kinetics and high overpotential, so that the efficient OER catalysts are still desired . Although RuO 2 and IrO 2 are the most effective catalysts in OER, their high cost, low abundance, and instability hinder their large‐scale applications .…”

“…[11] However, the OER suffers from sluggish kinetics and high overpotential, [11b] so that the efficient OER catalysts are still desired. [12] Although RuO 2 and IrO 2 are the most effective catalysts in OER, their high cost, low abundance, and instability hinder their large-scale applications. [11b, 10, 13] Therefore, new catalysts made of earth-abundant elements have attracted increasing attention in OER.…”