Enhancing the CO₂ Electroreduction of Fe/Ni‐Pentlandite Catalysts by S/Se Exchange

Abstract

The electrochemical reduction of CO 2 is an attractive strategy towards the mitigation of environmental pollution and production of bulk chemicals as well as fuels by renewables. The bimetallic sulfide Fe 4.5 Ni 4.5 S 8 (pentlandite) was recently reported as ac heap and robust catalyst for electrochemical water splitting, asw ell as for CO 2 reduction with a solvent-dependent product selectivity.I nspired by numerous reports on monometallic sulfoselenides and selenides revealing higher catalytic activity for the CO 2 reduction reaction (CO 2 RR) than their sulfide counterparts, the authors investigated the influence of stepwise S/Se exchange in seleno-pentlanditesF e 4.5 Ni 4.5 S 8-Y Se Y (Y = 1-5) and their ability to act as CO 2 reducingc atalysts. It is demonstrated that the incorporationo fh ighere quivalents of seleniumf avors the CO 2 RR with Fe 4.5 Ni 4.5 S 4 Se 4 revealingt he highest activity for CO formation. Under galvanostaticc onditions in acetonitrile, Fe 4.5 Ni 4.5 S 4 Se 4 generates CO with aF aradaic Efficiency close to 100 %a ta pplied current densities of À50 mA cm À2 and À100 mA cm À2 .T his work offers insight into the tunability of the pentlandite based electrocatalysts for the CO 2 reduction reaction.

Sustainable and rapid preparation of nanosized Fe/Ni-pentlandite particles by mechanochemistry

“…M ¼ Fe, Co, Ni], recently emerged as promising materials for catalytic purposes 1,2 (e.g. for CO 2 reduction 3,4 and water splitting [5][6][7][8][9][10][11][12] ), energy storage applications 13,14 as well as magnetic devices. 15 This widespread interest can be attributed to the chemically robust nature of pentlandites, its pseudo-metallic conductivity as well as their large exibility of stoichiometric compositions.…”

A surface oxidised Fe–S catalyst for the liquid phase hydrogenation of CO2

“…[1][2][3][4][5][6][7] Fe-S phases have been hypothesised as potential membrane catalysts produced at hydrothermal vents, which reduce aqueous carbon dioxide (CO 2 ) in the formation of prebiotic molecules on the pathway to the emergence of life on early Earth, [8][9][10] owing to their unique similarities to iron and sulfur clusters within enzyme active sites. Following this lead, bio-inspired Fe-S catalysts such as FeS 2 11 , Fe 3 S 4 1 and Fe 4.5 Ni 4.5 S 8 12,13 have been reported for the electrochemical reduction of CO 2 . However, in these systems the reduction potential of the H 2 /2H + couple is not sufficiently low to reduce CO 2 to formate (HCOO − ), formaldehyde (HCHO) or similar oxygenates, 14 resulting in poor activity and low product yields.…”

Influence of the Fe : Ni Ratio in FexNi9‐xS8 (x=3–6) on the CO2 Electroreduction

“…Under proton deficient conditions, the previously described activation effect of Fe‐X catalysts [16] , in water‐rich electrolytes, is also supported by a stark decrease of the observed overpotentials after two hours of electrolysis at −1.8 V for most catalysts (Figure 1e, Table S2). Under these conditions, the LSV curves of the tested electrocatalysts show small differences for the different Fe‐X catalysts reaching −4 mA cm ‐2 at approximately −1.50 V. Fe‐4 and Fe‐6 show the highest anodic shift of 0.15 V and 0.14 V, respectively, followed by Fe‐5 (0.12 V), whereas Fe‐3 shows a slight cathodic shift of 0.04 V. Interestingly, under the same conditions sulfoselenide‐based pentlandites, Fe 4.5 Ni 4.5 (S,Se) 8 showed a notable deactivation, hinting at how electronic and structural changes can lead to significantly different electrochemical behaviors between catalysts of the same material class [9,21] …”

“…All the investigated catalysts exhibit comparable behaviors reaching similar current densities of −15 mA cm −2 at the end of electrolysis at −1.8 V vs. NHE (Figure 2c). This is an interesting difference between the varied Fe‐X pentlandites and its sulfoselenide counterparts, where the S : Se ratio massively influences the observed CO 2 R selectivity as well as current density under similar conditions [9] . In addition, we tested the long‐term stability of the best performing Pn ‐catalyst (in terms of FE for CO), Fe‐3 , at −1.8 V vs. NHE in an electrolyte containing 24 ppm of water (Figure S6).…”

“…Notably, Pn systems are compatible with several first row transition metals as well as chalcogenides [10,11] and thus allows to establish a broad variety of mutlimetallic or multichalcogenide Pn species, each providing a different catalytic activity for CO 2 R as well as for the hydrogen evolution reaction (HER) [11–13] . We recently demonstrated that a sequential exchange of sulfur in Fe 4.5 Ni 4.5 S 8 with selenium favors the formation of CO over H 2 under otherwise identical conditions [9] . Due to the involvement of the reactive metal sites in the electrocatalytic conversion of CO 2 [7,14] , we expected similar effects upon variation of the metal content.…”