Tailoring the Electrocatalytic Activity of Pentlandite Fe_xNi_9‐XS₈ Nanoparticles via Variation of the Fe : Ni Ratio for Enhanced Water Oxidation

Abstract

The development of efficient and cost-effective electrocatalytic materials is an important part in scaling up sustainable electrochemical energy devices such as electrolyzers and fuel cells. In particular, the sluggish kinetics of the oxygen evolution reaction (OER) during water splitting renders the need of a catalyst indispensable. However, the development of catalysts is often based on laboratorial trial-and-error approaches and complex synthetic routes. Herein, the facile and systematic synthesis of pentlandite-like Fe x Ni 9-x S 8 (x = 0-9) nanosized particles from its elements with distinct Fe: Ni ratios was achieved using a mechanochemical method. The OER performance is optimized through tailoring the surface properties via altering the catalyst composition. The catalytic activity increases with higher nickel content in the structure, accomplishing an overpotential of 354 and 420 mV for 'Ni 9 S 8 ' to drive 10 and 100 mA cm À 2 , respectively, with high stability. The in-situ formed nickel oxide/ hydroxide species concurrent with sulphur depletion from the pentlandite structure upon OER are more active than NiS, inferring the crucial role of the pentlandite structure in activity. The herein reported simple synthetic approach could bring significant progress in the catalyst material development via rationally screening pentlandites with desired properties for modern energy systems.

Boosting the overall electrochemical water splitting performance of pentlandites through non-metallic heteroatom incorporation

“…Moreover, FCNSNP on GCE undergoes an activation in the first 15 h and then shows a steady performance for the next 5 h as revealed by the chronoamperometry responses recorded at a fixed potential of 1.558 V versus RHE ( Figure S16 B). This enhancement in OER performance and stability can be explained by the electrochemical activation of the electrode during electrocatalytic OER because of formation of thermodynamically stable oxyhydroxide phases on the surface, which was intensively studied previously ( Amin et al., 2021 ; Jin, 2017 ; Xu, 2019 ; Yang et al., 2020a ).…”

“…Most importantly, powder XRD patterns reflect the formation the metal oxide shell because of surface oxidation during OER ( Figure 5 B) as was forecasted by DFT calculations in this work ( Figure S25 ). Thus, the studies show that pentlandites readily convert into the thermodynamically more stable oxide and/or oxyhydroxide phases during OER which contribute to the high activity of the materials ( Amin et al., 2021 ).

Figure 5 Studying morphlogy, composition, and crystal structure using scanning electron microscope attached to energy dispersive X-ray spectroscopy (SEM/EDX) and wide-angle X-ray diffraction (XRD) (A) SEM and Fe, Co, Ni, S, N, P, and O atoms mapping images of FCNSNP on CPE after chronopotentiometry test for 24 h at 100mAcm −2 .

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Sulfur incorporation into NiFe oxygen evolution electrocatalysts for improved high current density operation

“…47 The O 1s peak at 529.9 eV can be assigned to the lattice oxygen incorporated into the structure. 50 .…”

Repurposing metal containing wastes and mass-produced materials as electrocatalysts for water electrolysis

“…This indicates that ores/synthetic versions of this type are not only suitable for alkaline water electrolysis but could have applications for proton exchange membrane water splitting. Recently Hatem et al 119 also chemically synthesized pentlandite-like Fe x Ni 9− x S 8 ( x = 0–9) nanoparticles with distinct Fe : Ni ratios using a mechanochemical method. The OER performance was optimized through tailoring the surface properties resulting in an overpotential of 354 mV to achieve 10 mA cm −2 for the OER with a Tafel slope of 56 mV dec −1 .…”