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

The electrochemical reduction of CO₂ 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_4.5Ni_4.5S₈ (pentlandite) was recently reported as a cheap and robust catalyst for electrochemical water splitting, as well as for CO₂ reduction with a solvent-dependent product selectivity. Inspired by numerous reports on monometallic sulfoselenides and selenides revealing higher catalytic activity for the CO₂ reduction reaction (CO₂RR) than their sulfide counterparts, the authors investigated the influence of stepwise S/Se exchange in seleno-pentlandites Fe_4.5Ni_4.5S_8-YSe_Y (Y=1–5) and their ability to act as CO₂ reducing catalysts. It is demonstrated that the incorporation of higher equivalents of selenium favors the CO₂RR with Fe_4.5Ni_4.5S₄Se₄ revealing the highest activity for CO formation. Under galvanostatic conditions in acetonitrile, Fe_4.5Ni_4.5S₄Se₄ generates CO with a Faradaic Efficiency close to 100 % at applied current densities of −50 mA cm⁻² and −100 mA cm⁻². This work offers insight into the tunability of the pentlandite based electrocatalysts for the CO₂ reduction reaction.     

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

In recent years, metal-rich sulfides of the pentlandite type (M₉S₈) have attracted considerable attention for energy storage applications. However, common synthetic routes towards pentlandites either involve energy intensive high temperature procedures or solvothermal methods with specialized precursors and non-sustainable organic solvents. Herein, we demonstrate that ball milling is a simple and efficient method to synthesize nanosized bimetallic pentlandite particles (Fe_4.5Ni_4.5S₈, Pn) with an average size of ca. 250 nm in a single synthetic step from elemental- or sulfidic mixtures. We herein highlight the effects of the milling ball quantity, precursor types and milling time on the product quality. Along this line, Raman spectroscopy as well as temperature/pressure monitoring during the milling processes provide valuable insights into mechanistic differences between the mechanochemical Pn-formation. By employing the obtained Pn-nanosized particles as cathodic electrocatalysts for water splitting in a zero-gap PEM electrolyzer we provide a comprehensive path for a potential sustainable future process involving non-noble metal catalysts.

A sustainable and rapid mechanochemical method for the preparation of bimetallic nanosized pentlandite particles as cathode material is developed and tested within zero-gap PEM cells.