Influence of the Fe : Ni Ratio in Fe_xNi_9‐xS₈ (x=3–6) on the CO₂ Electroreduction

Abstract

The electrochemical CO2 reduction (CO2R) is a promising approach to decrease the amount of CO2 in the atmosphere by producing commodity chemicals or fuels using renewable energies. Herein, the development of non‐noble metal electrocatalysts is regarded as a key point for achieving the transition of CO2R to industrial scales. Transition metal chalcogenides of the pentlandite structure (M9X8) have emerged as promising electrocatalysts to produce syngas. In this line, we present the electrochemical CO2R of FexNi9‐xS8 (x=3–6) with variable Fe : Ni ratios. All materials can reduce H2O/CO2 mixtures to CO or H2 respectively with varying efficiency depending on the Fe : Ni ratio and the water content. While CO2R in proton‐rich organic electrolytes was mainly accompanied by hydrogen evolution, the CO2R activity climaxed with F.E. of 3.6 % for CO and 0.3 % for methane using Fe3Ni6S8. Using electrolytes with low water content, CO production with F.E. close to 90 % was demonstrated. Counterintuitively, the variation of the Fe : Ni ratio led only to small alterations in the CO2R activity. Quantum mechanical studies were performed to get further information on the observed trends and provide further insight into structure/activity relationships for the Fe/Ni pentlandite system and its CO2R activity opening the path towards the development of more active and robust CO2R electrocatalysts.

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

“…This class of catalysts allows us to vary the metal centres without leading to any significant structural changes of the crystal lattice. 22 Following reported synthetic procedures for pentlandite materials, we prepared a series of Fe 9− x Ni x S 8 ( x = 3–6, herein denoted as Ni x ) catalysts, with different Ni/Fe ratios, via mechanochemical methods (Fig. S1†).…”

“…This class of catalysts allows us to vary the metal centres without leading to any significant structural changes of the crystal lattice. 22 Following reported synthetic procedures for pentlandite materials, we prepared a series of Fe9-xNixS8 (x=3-6, herein denoted as Nix) catalysts, with different Ni/Fe ratios, via mechanochemical methods (Figure S1). 21 Subsequently, aiming to investigate the intrinsic activity of the (Fe,Ni)9S8, the obtained powders were pressed into pellets and mounted into electrodes with the help of a conductive non-catalytically active carbon glue.…”

“…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.…”

“…[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.…”

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

“…Along this line, transition metal-rich inorganic materials have recently emerged as vital and important alternatives to precious metal electrocatalysts because of their rich stoichiometric flexibility, high stability, achievable pseudo-metallic conductivity as well as the ease of preparation from cheap and readily available starting materials ( Dou et al., 2019 ; Siegmund et al., 2020 ). Within this family of metal-rich inorganic materials, the transition metals are commonly accompanied by a variety of main group elements forming, e.g., oxides ( Simon et al., 2021 ; Zakaria et al., 2015 ), sulfides ( Bentley et al., 2018 ; Smialkowski et al., 2021 ; Tetzlaff et al., 2021 ), carbides ( Zakaria et al., 2016 , 2017 ), borides ( Yao et al., 2021 ), phosphides ( Pu et al., 2020 ), selenides ( Desalegn et al, 2022 ; Feng et al., 2019 ; Xia et al., 2020 ), and double layered hydroxides ( Sun et al., 2020 ). Despite the almost infinite number of conceivable materials, there is still no real competitor to replace current electrocatalysts in AEL and PEM technologies and achieve the efficiency and stability needed for large-scale practical applications to date ( Grigoriev et al., 2020 ; Siegmund et al., 2021 ).…”