Tailoring Borate Mediator Species Enables Industrial COProduction with Improved Overall Energy Efficiency by Sustainable Molten Salt CO 2 Electrolysis.

The electrochemical conversion of CO ₂ into CO represents a promising strategy for mitigating excessive global greenhouse gas emissions. Nevertheless, achieving industrial-scale electrochemical CO ₂ -to-CO conversion with enhanced selectivity and reduced energy consumption presents significant challenges. In this study, a borate-enhanced molten salt process for CO ₂ capture and electrochemical transformation is employed, achieving over 98% selectivity for CO and over 55% energy efficiency without the necessity for complex and costly electrocatalysts. Cathodic CO ₂ electro-reduction (CO ₂ ER) with the anodic oxygen evolution reaction (OER) at an overall current density of 500 mA cm ^-2 using non-nanostructured transition-metal plate electrodes at 650 °C is coupled. By regulating the electrolyte's oxo-basicity with earth-abundant borax (Na ₂ B ₄ O ₇ ), a borate-enhanced electrolyte is established that accelerates the overall electrochemical reaction efficiently. This system involved a series of well-designed target borate species (BO ₃ ^3- , BO ₂ ^- , and B ₄ O ₇ ^2- ) that acted as mediators shuttling between the cathode and anode, favoring CO as the primary cathodic product. Manipulating the atmosphere above the anode facilitated a spontaneous transformation of borates, further enhancing OER performance with long-term operational stability over a cumulative period of 50 h, while also reducing overall energy consumption. This work presents a cost-effective strategy for the industrial-scale production of CO derived from CO ₂ , contributing to a lower carbon footprint by establishing a sustainable borate-mediated closed loop.
(© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)