A Facile Molecular Approach to Amorphous Nickel Pnictides and Their Reconstruction to Crystalline Potassium‐Intercalated γ‐NiOOH_x Enabling High‐Performance Electrocatalytic Water Oxidation and Selective Oxidation of 5‐Hydroxymethylfurfural

Abstract

The low‐temperature molecular precursor approach can be beneficial to conventional solid‐state methods, which require high temperatures and lead to relatively large crystalline particles. Herein, a novel, single‐step, room‐temperature preparation of amorphous nickel pnictide (NiE; EP, As) nanomaterials is reported, starting from NaOCE(dioxane)n and NiBr2(thf)1.5. During application for the oxygen evolution reaction (OER), the pnictide anions leach, and both materials fully reconstruct into nickel(III/IV) oxide phases (similar to γ‐NiOOH) comprising edge‐sharing (NiO6) layers with intercalated potassium ions and a d‐spacing of 7.27 Å. Remarkably, the intercalated γ‐NiOOHx phases are nanocrystalline, unlike the amorphous nickel pnictide precatalysts. This unconventional reconstruction is fast and complete, which is ascribed to the amorphous nature of the nanostructured NiE precatalysts. The obtained γ‐NiOOHx can effectively catalyse the OER for 100 h at a high current density (400 mA cm−2) and achieves outstandingly high current densities (>600 mA cm−2) for the selective, value‐added oxidation of 5‐hydroxymethylfurfural (HMF). The NiP‐derived γ‐NiOOHx shows a higher activity for both processes due to more available active sites. It is anticipated that the herein developed, effective, room‐temperature molecular synthesis of amorphous nickel pnictide nanomaterials can be applied to other functional transition‐metal pnictides.

Water-soluble nickel and iron salts for hydroxymethylfurfural (HMF) and water oxidation: the simplest precatalysts?

“…The diffraction rings of the SAED are typical for transition metal oxyhydroxides formed during the OER. 12,53–56 The fast Fourier transforms of high-resolution TEM images confirm the lattice distances from the SAED, and the images show around 2 nm large crystallites, explaining the absence of diffraction in the PXRD. Thus, through the reconstruction of the water-soluble nitrates, porous, nanocrystalline, layered oxyhydroxides have formed.…”

“…As reported previously, the potassium is most likely intercalated into the oxyhydroxide structure. 12,23,29 For both compounds, transmission electron microscopy (TEM, Fig. 2c and f) shows porous, unordered, sheetlike morphologies.…”

“…The formation of such intercalated oxyhydroxides during OER has been widely reported in the literature. 12,23,29,51,52 For both phases, SEM-EDX mappings (Fig. 2a and b, for EDX spectra see Fig.…”

“…So far, a prerequisite for OER and OOR (pre)catalysts has been that they are non-water-soluble, as water is the main component of the electrolyte, leading to the potential loss of the electrodes’ catalyst coating. Therefore, various non-water-soluble compounds have been investigated, such as transition metal (oxy)hydroxide, 8–10 borides, 11 pnictides, 12 chalcogenides, 13,14 alloys, 15 or intermetallics. 16–20 These materials comprise an active site transition metal, such as iron, cobalt, or nickel, and additional constituting elements.…”

Two-dimensional nickel cyano-bridged coordination polymer thermally derived potent electrocatalysts for alkaline hydrogen evolution reaction

“…4). 47–49 Eventually, for Ni-Se, Ni displayed the energy levels of Ni 2p 3/2 , Ni 2p 1/2 , and satellite peaks. Also, the main peak of Se 3d existed at 55, with the Se oxide peak at 58.7 eV because of oxidized Se atoms on the sample surface (Fig.…”