Phase Evolution, Polymorphism, and Catalytic Activity of Nickel Dichalcogenide Nanocrystals

Abstract

The nickel chalcogenide family contains multiple phases, each with varying properties that can be applied to an expansive range of industrially relevant processes. Specifically, pyrite-type NiS2 and NiSe2 have been used as electrocatalysts for oxygen or hydrogen evolution reactions. These pyrites have also been used in batteries and solar cells due to their optoelectronic and transport properties. The phase evolution of pyrite NiS2 and polymorphism of NiSe2 have briefly been studied in the literature, but there has been limited work focusing on the phase transformations within each of these two systems. Using experiments and calculations, we detail how pyrite NiS2 nanocrystals decompose into hexagonal α-NiS, and how the synthesis of pyrite NiSe2 nanocrystals is affected by the presence of two polymorphs, a metastable orthorhombic marcasite phase and a more stable cubic pyrite phase. Each reaction can be controlled by fine-tuning the reaction parameters, including temperature, time, and the precursor identity and concentration. Interestingly, both NiS2 and NiSe2 nanopyrites are active catalysts in the selective reduction of nitrobenzene to aniline, in agreement with other catalysts containing an fcc (sub) lattice. Our results demonstrate a feasible, logical process for synthesizing nanocrystalline pyrites without common byproducts or impurities. This work can help in solving a major problem suspected in preventing pyrite FeS2 and similar materials from large-scale use: the presence of small amounts of secondary phases and impurities.

Phase engineering of iron group transition metal selenides for water splitting

“…Briefly, two possible interpretations of the phase transition mechanism are as follows: (1) a seed phase that gradually transforms into another phase over time or (2) the initial generation of two phases in the reaction, with only one accumulating over time. 85 In conclusion, PE has been identified as a promising way for enhancing the performance of nanomaterials due to the following advantages: (i) Phase engineering could regulate the properties, functions, and applications of nanomaterials by rationally tuning their atomic arrangements. (ii) Phase engineering could construct nanocatalyts with unconventional phases by tuning the reaction kinetics and surface energy.…”

Halide-driven polymorph selectivity in the synthesis of MnX (X = S, Se) nanoparticles

“…Also favorable is the observation that at the nanoscale there can be a "polymorph inversion" where a bulk metastable phase becomes the more stable, lower energy phase. 14,15 Many research groups have exploited these factors to investigate polymorph selectivity in known systems as well as to access new metastable crystal structures in a range of materials, including Ni, 16 Co, 17,18 ZnS, 19 CdS, 20 CdSe, [21][22][23] GaP, 24 Cu 2 Se, [25][26][27] MnS, [28][29][30][31] CoO, 32 Ag 2 Se, 33,34 CuInS 2 , 35 CuInSe 2 , 36,37 CuSnSe 3 , 38 AgInSe 2 , 39 CuIn x Ga 1−x Se 2 , 40 Ni dichalcogenides, 41 and MnO. 42,43 Within the solution-based synthesis, several parameters can be varied to impart crystal structure control.…”

Role of carboxylates in the phase determination of metal sulfide nanoparticles

“…4 In the cobalt sulfide family, cattierite (CoS 2 ) has been used in lithium-sulfur battery cathodes to accelerate the redox reactions of polysulfides 5 while jaipurite (Co 9 S 8 ) has been used as a supercapacitor. 6 In the nickel sulfide family, vaesite (NiS 2 ) is an electrocatalyst for the hydrogen evolution reaction (HER) 7,8 while nickel sulfide (NiS) can be used as a supercapacitor. 9 Rationally synthesizing one phase over the other can be challenging when dealing with transition metal sulfides because of the multiple phases of varying stoichiometry and symmetry.…”