Trimetallic Pentlandites (Fe,Co,Ni)₉S₈ for the Electrocatalytical HER in Acidic Media

Abstract

Recently, pentlandite materials have been shown to exhibit promising properties with respect to the hydrogen evolution reaction (HER). A whole series of trimetallic FeCoNi-pentlandite materials and composites have been synthesized from the elements using high-temperature synthesis and categorized in terms of purity. Furthermore, the electrocatalytic properties regarding the HER were determined and correlated to hydrogen adsorption energies, which were determined by means of density functional theory (DFT) calculations. The relationships between activity and its origin generated in this way help to better understand the pentlandite system and provide meaningful approaches for catalyst synthesis.

Tailoring the electrocatalytic activity of multicomponent (Co,Fe,Ni)9S8−xSex pentlandite solid electrodes

“…4d) is high (217 mV dec −1 ) and indicated a mixed Volmer-Heyrovsky reaction path, with the Volmer (proton adsorption) step being the limiting one, which conrms This journal is © The Royal Society of Chemistry 2023 that the sulfur depletion in this material is somehow hindered, worsening at the same time the entire HER process. The Tafel slope of the trimetallic ingot with only sulfur anions (125 mV dec −1 ) is at a level comparable to the one presented recently by Smialkowski et al, 18 indicating a similar mechanism with an improved ratio of two absorbed protons (Tafel step) compared to the selenium-rich sample.…”

“…The deconvoluted spectra indicated the presence of each TM mainly in the second oxidation state, typical for pentlandite-oriented studies. 17–19 For all TM, small amounts of metallic sites (at about 7, 16, and 2 molar% of total Co, Fe, and Ni content respectively) were also identified, as well as oxidized Co 3+ /Fe 3+ (23/44 molar%) cations, whose occurrence in tetrahedral sites (coordinated by S/Se at 8c Wyckoff sites) should positively influence catalytic activity. 21 The slightly shifted binding energies of TM towards higher values compared to mono- and bimetallic chalcogenides, as well as the position of the S 2p and Se 3d peaks, agree well with various non-stoichiometric chalcogenides, indicating the half-metallic character of the sample and the strong hybridization between TMs and Chs.…”

“…23 Since the previous work did not address the catalytic properties, here, the sintering procedure was repeated for all single-phase compositions and their electrochemical performances were tested. Since the densities of the materials pressed at 400 °C were not ideal and the thermal stability of the pentlandite phase was estimated up to 600 °C, 18 the sintering procedures were also performed for the final temperature set at 450 and 500 °C (above the boiling point of sulfur). Hot pressing is one of the basic techniques used to consolidate polycrystalline powder materials into highly densified solids and is widely used in thermoelectric, fuel cell or metallurgical processes.…”

“…23 On the other hand, similar effects may be reached by tailoring the anionic sublattices, a relatively new concept, untouched for the rst high-entropy materials based on oxide compounds, and expanded for non-oxide materials. 23,26,29,30 Thus, the two possible approaches, namely tailoring the cationic (Co/Fe/Ni) ratio in 4-component (TM 9 S 8 ) and 5-component (TM 9 S 4 Se 4 ), or tailoring the S/Se ratio in 5component (TM 9 Ch 8 ) pentlandites, should be considered as extremely promising methods aimed at improving their catalytic performances Although detailed studies on tailoring the Co/Fe/Ni in trimetallic pentlandites have already been described, 18 the effects of selenium concentration on the catalytic performance in 5-component pentlandites remain an open issue.…”

Opening the pathway towards a scalable electrochemical semi-hydrogenation of alkynolsviaearth-abundant metal chalcogenides

“…Most signicantly, a crucial advantage of the pentlandite structure over other transition metal chalcogenides is the ability to ne-tune structural and electronic properties of the employed catalysts via a plethora of metal (Fe/Co/Ni) and chalcogenide (S/Se) variations. [22][23][24][25] Consequently, utilising this stoichiometric exibility more active pentlandite catalysts for the hydrogen evolution reaction (HER), CO 2 reduction and oxygen evolution (OER) reaction could be developed in recent years. [21][22][23]25,26 Overall, this interesting subgroup of multi-functional electrocatalysts demonstrates a combination of ideal properties towards the application in the eld of ECH.…”