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_4.5 Ni_4.5 S₈ (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 (CO₂ RR) than their sulfide counterparts, the authors investigated the influence of stepwise S/Se exchange in seleno-pentlandites Fe_4.5 Ni_4.5 S_8-Y Se_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 CO₂ RR with Fe_4.5 Ni_4.5 S₄ Se₄ revealing the highest activity for CO formation. Under galvanostatic conditions in acetonitrile, Fe_4.5 Ni_4.5 S₄ Se₄ 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.