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

The electrochemical conversion of CO into CO represents a promising strategy for mitigating excessive global greenhouse gas emissions. Nevertheless, achieving industrial-scale electrochemical CO-to-CO conversion with enhanced selectivity and reduced energy consumption presents significant challenges. In this study, a borate-enhanced molten salt process for CO 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 electro-reduction (COER) with the anodic oxygen evolution reaction (OER) at an overall current density of 500 mA cm using non-nanostructured transition-metal plate electrodes at 650 °C is coupled. By regulating the electrolyte's oxo-basicity with earth-abundant borax (NaBO), 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 , BO , and BO ) 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, contributing to a lower carbon footprint by establishing a sustainable borate-mediated closed loop.