Towards the Use of Low‐Concentration CO2 Sources by Direct Selective Electrocatalytic Reduction

Abstract The direct CO 2 reduction reaction (CO 2 RR) from simulated flue gas of various CO 2 concentrations could minimize extra energy for pre‐concentration processes to highly concentrated CO 2 as a feedstock. We investigate the challenges for CO 2 RR caused by low CO 2 concentrations and provide strategies concerning the impact of the chosen electrocatalyst material and the selection of the electrolyte to attain high CO selectivity. We continuously feed CO 2 mixed with N 2 (the typical dilutant in flue gas) in various ratios to gas diffusion electrodes in a model flow‐through electrolyzer. Operating the CO 2 RR at lower CO 2 concentrations results in an overpotential shift to more cathodic values. We show that higher active catalysts can maintain high CO selectivity down to 5 % CO 2 by using NiCu‐based catalysts. NiCu reached its limit when the CO 2 concentration was lowered to 2 %, due to low CO 2 availability and competition of carbonate formation. Employing near‐neutral electrolytes with buffering capacity, we maintained high Faradaic efficiency at low overpotentials and higher CO 2 utilization at low CO 2 concentration.