CO2 Reduction to Formic Acid/Formate by Intermittent Electricity at Bismuth Gas Diffusion Electrodes.

To avoid the waste of renewable energy resources beyond demand and grid capacity, innovative gas diffusion electrodes (GDE) for operation at intermittent electricity are presented. They are based on Bi as affordable and nontoxic electrocatalyst, to facilitate decentralized and cost-efficient reduction of CO₂ to formic acid. To develop flexible GDE materials, their catalyst composition is optimized by studying systematically inexpensive Bi/Bi₂O₃ mixtures. During initial evaluation at technically relevant current density (150 mA cm^-2, 21 h), the best composition achieve high Faradaic efficiency (FE) (≈90%) and the loss of catalyst is minor. In three demonstrative examples of realistic current patterns based on intermittent electricity, the performance and resilience of the optimized GDE is consistently very good in terms of high FE (≈90%) and stable synthesis rates of formate. However, loss of catalyst is partially increased, especially when GDEs are depolarized between electrolysis phases. Nonetheless, the GDE materials already show robust performances despite swift adjustments of current density (60 s) without any optimization of operational parameters so far. Based on these results, flexible operation of these GDE can be optimized to minimize cathodic corrosion of catalyst at long-term operation, and thus, ultimately evaluate their implementation to valorize intermittent electricity.