Catalyst layer at the junction of a forward bias bipolar membrane for CO2 electrolysis

CO₂ reduction in an electrolysis cell with a forward bias bipolar membrane (BPM) ensures good selectivity and CO₂ utilization, but still suffers from large overvoltages. Recent studies have shown that integrating metal-oxide catalysts at the BPM junction in reverse bias significantly enhances the performance of water electrolyzers. It remains unclear if this method has the same positive effect on CO₂ electrolysis. We studied the performance of a specially designed zero-gap BPM CO₂ electrolyzer operating in forward bias mode, incorporating metal-oxide nanoparticles at the BPM interface. For TiO₂ catalyst, the optimal loading at the BPM junction was between 10 and 30 μg cm^-2, resulting in a 75% higher current density for the same iR-free overpotential. Physical characterization using scanning electron microscopy of the catalyst layers revealed that the optimum performance of the CO₂ electrolyzer correlates with a complete coverage. SiO₂ and IrO₂ metal-oxides were also tested at the BPM junction. SiO₂ showed comparable performance to TiO₂, whereas IrO₂ improved the current density by approximately 100% at an iR-free overpotential of 0.7 V compared to the pristine BPM.