Size-dependent selectivity of Cu2O nanocube catalysts for CO2 reduction at industrial current densities

The electrochemical reduction of CO₂ (CO₂RR) to value-added chemicals offers a promising route for carbon recycling and renewable energy storage. Cu-based catalysts are uniquely capable of producing multi-carbon products such as ethylene, but their selectivity is highly sensitive to their morphology. In this work, we systematically investigate the impact of Cu₂O nanocube size (45–600 nm) on CO₂RR performance in both alkaline flow cell and zero-gap electrolyzer, both operating at industrially-relevant current densities. The catalysts were synthesized with well-controlled geometries and edge lengths. In the flow-cell, smaller nanocubes (45–75 nm) exhibited superior selectivity toward ethylene and liquid C2 products, achieving Faradaic efficiencies toward C2 products (FEC2) of up to 50%, attributed to an optimal balance between edge and facet sites. In contrast, in the zero-gap cell, although 45 nm cubes were the most ethylene-selective, overall FEC2 was reduced and strongly influenced by operational parameters, such as anolyte composition. Long-term tests revealed a trade-off between catalyst durability and ethylene selectivity. These findings demonstrate the critical interplay between nanostructure, testing configuration, and electrolyte, and emphasize the need to assess catalyst performance under industrially-relevant conditions.