Bipolar membrane 3D microlattice electrode assembly design for zero-gap bicarbonate (CO2) electrolysis

The electrochemical reduction of CO₂ (eCO₂R) from carbon capture solutions, such as (bi)carbonate, offers a promising pathway for energy-efficient carbon recycling compared to traditional gas-phase approaches. However, the development of optimized membrane-electrode designs remains a critical challenge for advancing this technology toward commercial viability. In this study, we present a novel integration of 3D-printed microlattice carbon electrodes with bipolar membranes (BPMs) for bicarbonate electrolysis. We used projection micro-stereolithography (PμSL) to fabricate unique free-standing carbon electrodes with nature-inspired honeycomb architectures. Silver nanoparticles were deposited onto the electrodes via chronoamperometry under varying conditions of deposition potential (-0.1, -0.2, and -0.5 V vs Ag/AgCl), deposition time (0 to 1200 s), and catalyst loading (0 to 0.7 mg/cm²). The optimal BPM-3D electrode assembly significantly enhanced CO production efficiency, achieving a Faradaic efficiency for CO (FE_CO) of 38 % - a 22 times increase over uncoated electrodes (1.7 %) - at a current density of 12.5 mA/cm². This configuration, prepared at -0.2 V for 900 s with an Ag loading of 0.5 mg/cm², exhibited improved catalytic activity because of the formation of highly active Ag nanostructures. The electrode demonstrated an Integrated Catalytic Performance Index (ICPI) of approximately 150 mA/Vmg at 50 mA/cm². Stability tests revealed minimal degradation over 14 h of operation, affirming the durability of the Ag-coated 3D electrodes. A preliminary techno-economic analysis projects that CO production costs could be reduced by optimizing Faradaic efficiency (FE) and catalyst loading under scaled conditions. This work lays the foundation for integrating 3D printing and BPM technology for sustainable eCO₂R. However, achieving high selectivity and stability at >100 mA/cm² remains challenging, requiring optimized electrode design and interface engineering for commercial viability.