Controlling the Product Syngas H2:CO Ratio through Pulsed-Bias Electrochemical Reduction of CO2 on Copper

The electrochemical reduction of CO2 is a promising method for sustainable, carbon-neutral chemical synthesis as well as the storage of intermittent renewable energy in the form of energy-dense fuels compatible with existing infrastructure. In this work, we investigated a pulsed-bias technique for CO2 reduction on Cu, which led to a major shift in the product selectivity relative to potentiostatic electrolysis conditions. With applied voltage pulses in the millisecond time regime, syngas (CO + H-2) became the only product and had a pulse-time-dependent H-2:CO molar ratio, ranging from similar to 32:1 to 9:16 for pulse times between 10 and 80 ms, respectively, at the same applied working potential. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) data suggested that in situ oxidation and reduction of the Cu partially caused the preference for CO formation over other carbon products on polycrystalline Cu. Significant nonfaradaic current arising from electrical double layer charging and discharging was also suspected to contribute to the desorption of key reaction intermediates and further promote CO. The results provide an electronic technique for the electrochemical production of a controllable syngas feedstock for utilization in numerous industrial applications (e.g., Fischer Tropsch process and hydroformylation of alkenes to aldehydes).