Fig. 4: Catalytic performance of the paired CO₂RR//FOR system.

a Schematic illustrations of the CO₂RR//FOR and CO₂RR//OER systems with half-cell equilibrium potentials (E⁰)^28,38. b Comparison of LSV curves for the CO₂RR//FOR and CO₂RR//OER systems at a scan rate of 20 mV s^–1. Voltages are non-iR corrected. c, d HCOO^– FEs (c) and HCOO^– formation rates (d) for the CO₂RR//FOR system at various cell voltages without iR compensation. Data are presented as mean ± s.d. Error bars represent s.d. from three independent measurements. e Performance comparison of paired CO₂RR and representative anodic reaction systems for the bipolar HCOO^– formation based on performance metrics as j_total, HCOO^– FE, and cell voltage in a flow-type or MEA electrolyzer. Details are given in Supplementary Table 5. f Plant-gate levelized cost per tonne of HCOOH and the corresponding quantity of H₂ produced on the CO₂RR//FOR and CO₂RR//OER systems at a j_total of 500 mA cm^–2. The total reference price of HCOOH and H₂ is marked by the dashed line. Source data are provided as a Source Data file.