Electrified CO ₂ -to-HCOOH Valorization: A Comparative Technical Analysis on Acidic Flow Cell and Solid-State Electrolyte Cell Reactors

Acidic flow cells and solid-state electrolyte (SSE) cells represent two promising electrolyzer configurations for a practical CO 2 reduction reaction (CO 2 RR), yet their comparative technical metrics remain underexplored. This study systematically investigates the electrolyzer performance, local reaction environment, and technical economic feasibility of acidic flow cells and SSE cells using precise HCOOH electrosynthesis from high-rate CO 2 RR as a model system. High CO 2 utilization efficiency (74.7%) and HCOOH selectivity (96.1%) are achieved in an acidic flow cell aided by a K + -enhanced local electric field that facilitates the *OCHO pathway, as verified by in situ spectroelectrochemistry and numerical simulations. Impedance analysis reveals better CO 2 mass transport kinetics in the acidic flow cell, whereas improved reaction dynamics is observed in the SSE cell. Techno-economic analysis demonstrates a 14.4% lower HCOOH production cost within the SSE system, primarily due to reduced product separation expenses and enhanced energy efficiency. These findings advance the understanding of the CO 2 electrolyzer design and optimization for efficient electrosynthesis.