Influence of the Fe : Ni Ratio in Fe x Ni 9‐x S 8 (x=3–6) on the CO 2 Electroreduction

The electrochemical CO 2 reduction (CO 2 R) is a promising approach to decrease the amount of CO 2 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 CO 2 R to industrial scales. Transition metal chalcogenides of the pentlandite structure (M 9 X 8 ) have emerged as promising electrocatalysts to produce syngas. In this line, we present the electrochemical CO 2 R of Fe x Ni 9‐x S 8 (x=3–6) with variable Fe : Ni ratios. All materials can reduce H 2 O/CO 2 mixtures to CO or H 2 respectively with varying efficiency depending on the Fe : Ni ratio and the water content. While CO 2 R in proton‐rich organic electrolytes was mainly accompanied by hydrogen evolution, the CO 2 R activity climaxed with F.E. of 3.6 % for CO and 0.3 % for methane using Fe 3 Ni 6 S 8 . 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 CO 2 R 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 CO 2 R activity opening the path towards the development of more active and robust CO 2 R electrocatalysts.