Coupling CO2 reduction and energy storage by electrolytic zinc

Scalable and efficient CO2-to-CO reduction, driven by renewable energy, is a promising way for decarbonization. However, solar and wind energy are characterized by intermittent fluctuations and high uncertainty. Here, we couple CO2 reduction with cost-effective energy storage by utilizing electrolytic Zn, allowing the long-term storage of electrical energy as metallic Zn instead of batteries. First, ZnO is electrodeposited to Zn and O2 in a KOH solution using an inert anode, achieving a high Faradaic efficiency of 99.2 %. Second, CO2 is reduced to CO by the electrolytic Zn in a closed reactor (500 degrees C), achieving a high CO2-to-CO conversion efficiency of 98.3 %. The addition of metal catalysts also facilitates the conversion of CO2 into a C-metal composite. The two-step approach is a closed-loop process that indirectly reduces CO2 into CO and O2 with an estimated voltage efficiency of 68.8 %. DFT calculations reveal that adsorbed CO* on the Zn surface can easily desorb with only 0.04 eV, leading to a high CO production. Beyond its role as a reducing agent, Zn also serves as an energy carrier that can achieve both energy storage and decoupling of the CO2 splitting reactions to embrace the intermittency of renewable energies.