A CO₂ electrolyzer tandem cell system for CO₂-CO co-feed valorization in a Ni-N-C/Cu-catalyzed reaction cascade

Coupled tandem electrolyzer concepts have been predicted to offer kinetic benefits to sluggish catalytic reactions thanks to their flexibility of reaction environments in each cell. Here we design, assemble, test, and analyze the first complete low-temperature, neutral-pH, cathode precious metal-free tandem CO₂ electrolyzer cell chain. The tandem system couples an Ag-free CO₂-to-CO₂/CO electrolyzer (cell-1) to a CO₂/CO-to-C₂₊ product electrolyzer (cell-2). Cell-1 and cell-2 incorporate selective Ni-N-C-based and Cu-based Gas Diffusion Cathodes, respectively, and operate at sustainable neutral pH conditions. Using our tandem cell system, we report strongly enhanced rates for the production of ethylene (by 50%) and alcohols (by 100%) and a sharply increased C₂₊ energy efficiency (by 100%) at current densities of up to 700 mA cm^-2 compared to the single CO₂-to-C₂₊ electrolyzer cell system approach. This study demonstrates that coupled tandem electrolyzer cell systems can offer kinetic and practical energetic benefits over single-cell designs for the production of value-added C₂₊ chemicals and fuels directly from CO₂ feeds without intermediate separation or purification.