Influence of the Fe. Ni Ratio in FexNi9-xS8 (x=3-6) on the CO2 Electroreduction

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.