Evolution of Carbonate‐Intercalated γ‐NiOOH from a Molecularly Derived Nickel Sulfide (Pre)Catalyst for Efficient Water and Selective Organic Oxidation

Abstract

The development of a competent (pre)catalyst for the oxygen evolution reaction (OER) to produce green hydrogen is critical for a carbon‐neutral economy. In this aspect, the low‐temperature, single‐source precursor (SSP) method allows the formation of highly efficient OER electrocatalysts, with better control over their structural and electronic properties. Herein, a transition metal (TM) based chalcogenide material, nickel sulfide (NiS), is prepared from a novel molecular complex [NiII(PyHS)4][OTf]2 (1) and utilized as a (pre)catalyst for OER. The NiS (pre)catalyst requires an overpotential of only 255 mV to reach the benchmark current density of 10 mA cm−2 and shows 63 h of chronopotentiometry (CP) stability along with over 95% Faradaic efficiency in 1 m KOH. Several ex situ measurements and quasi in situ Raman spectroscopy uncover that NiS irreversibly transformed to a carbonate‐intercalated γ−NiOOH phase under the alkaline OER conditions, which serves as the actual active structure for the OER. Additionally, this in situ formed active phase successfully catalyzes the selective oxidation of alcohol, aldehyde, and amine‐based organic substrates to value‐added chemicals, with high efficiencies.

New Avenues to Chemical Space for Energy Materials by the Molecular Precursor Approach

“…[ 14 ] Most recently, we designed a nickel (II) complex, [Ni II (PyHS) 4 ][Otf] 2 with a square‐planar {Ni II S 4 } core. [ 46 ] Following a simple, single‐step synthetic protocol, the novel Ni II ‐SSP could be easily transformed into nanostructured NiS using the hot‐injection method at relatively mild conditions. The SSP‐derived NiS proved to be a highly active (pre)catalyst for OER with low overpotential, and charge‐transfer resistance, smaller Tafel slope value, as well as better intrinsic properties when compared to reference materials.…”

“…[ 45 ] Long‐term OER stabilities were also exhibited by Mn 3 N 2 for 180 h at 10 mA cm −2 , [ 44 ] CuCo 2 S 4 for 40 h at 1.53 V, [ 126 ] Co‐substituted ZnO for 6 h at 0.8 V Ag/AgCl. [ 77 ] Moreover, NiS exhibited stable performance under a high OER current density of 500 mA cm −2 for 10 h. [ 46 ] Several SSP‐derived materials also showed long‐term stability for HER such as Mo 3+2 x Si 3 C 0.6 for 35 h at −10 mA cm −2 , [ 114 ] NiPt 3 @NiS for 8 days at −0.012 V [ 28 ] and NiSe for 60 h at −100 mA cm −2 . [ 99 ] In addition, NiSe displayed long‐term stability for OER and OWS for 60 h (at 100 mA cm −2 ) and for 12 h (at 50 mA cm −2 ), respectively.…”

“…As discussed earlier, most of these SSP‐derived intermetallic, pnictide, and chalcogenide materials behave as (pre)catalysts for the electrochemical processes (OER, HER, OWS) under applied potentials and reconstruct into the actual active catalysts. [ 21,45,46,77,88,100 ] As shown in Figure , the possible pathways for electrocatalyst reconstructions have already been discussed earlier, which lead to the formation of amorphous or crystalline, high surface area, and metal‐rich active structures. [ 52,61 ] Nevertheless, a detailed analysis of post‐electrochemical measurements of materials is required to obtain an in‐depth understanding of the reconstruction process, and their chemical composition, phase, morphology, and structural and electronic properties of the real active sites for catalysis.…”

“…Reproduced with permission. [ 46 ] Copyright 2023, Wiley‐VCH. d) Crystal structure of molecular‐derived NiGe and electrochemically generated active phase ( γ‐ NiOOH) with ionic intercalation of OH − /CO 3 2− during OER in an alkaline KOH.…”

“…[ 14 ] Similarly, the Ni III peaks in the Ni 2p spectrum of the NiS (pre)catalyst after OER corresponds to the γ ‐Ni III OOH‐active structure. [ 46 ] Therefore, XPS is a highly efficient technique to reveal the active species involved in catalysis, when supported by other advanced in situ techniques such as Raman spectroscopy and X‐ray absorption spectroscopy (XAS). [ 21 ] In addition to that, Fourier‐transform infrared spectroscopy (FTIR) is also an effective tool to reveal some information about the surface composition of the transformed phase.…”