Co-electrolysis of carbon dioxide and ferrous oxide in Ca-based molten salt to iron-encapsulated carbon nanotubes with enhanced microwave absorption

Abstract

Direct utilization of co-existed ferrous oxide (FeO) dust in CO₂ flue gas from the steel industry to product value-added materials is yet to be established. Inspired by the form of CaO-CaCO₃ as natural carbon cycle and the high oxide dissolution capacity of molten salts, CaO is herein introduced into the affordable molten NaCl-CaCl₂-FeO salt to generate CO₃²⁻ through an efficient capture of CO₂. The subsequent co-electrolysis of FeO and CO₃²⁻ successfully produces cathodic Fe-encapsulated carbon nanotubes (Fe@CNT) with enhanced energy efficiency (current efficiency of 83.1% for CO₂ reduction and energy consumption of 22.49 kWh kg⁻¹ for Fe@CNT generation). The in-situ capture of CO₂ by O²⁻ generated from the electro-deoxidation of FeO bridges the electrolysis of CO₂ and FeO, rendering the enhanced current efficiency of the co-electrolysis and template-free generation of Fe@CNT. When evaluated as functional materials for electromagnetic wave absorption, the Fe@CNT integrates dielectric loss of CNT and electromagnetic loss from Fe. The Fe well-defined in CNT induces the synergistic loss and further improves the impedance matching, resulting in excellent electromagnetic wave absorption performance. The co-electrolysis establishes a promising strategy for converting CO₂ into highly functional materials directly from CO₂-containing flue gas from steel industrial without dust removal.