Towards the use of low-concentration \(CO_{2}\) sources by direct selective electrocatalytic reduction

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.