Efficient capture, catalytic reduction, and energy utilization of CO2 via Mg0.50Mn1.75Fe0.75O4 nanoparticles

Abstract

Spinel Mn_1.75Fe_1.25O₄ nanoparticles (MFO NPs) have proven to be promising ferrites for low-temperature catalytic reduction of CO₂ to carbon. However, enhancement of CO₂ reduction capacity, ordering transformation of carbon, and rational application of carbon-deposited products remain challenging. This work explored the effect of Mg²⁺ doping (0.0–1.0 mol/mol) on the CO₂ reduction efficiency of MFO NPs, investigated the kinetics and mechanisms of CO₂ conversion to highly graphitized nanocarbon (HGC), and evaluated the potential of Mg_XMFO NPs@HGC as lithium-ion batterie anodes. Results showed that moderate Mg²⁺ doping neither destroyed the Fd-3m space group of MFO NPs but rather induced abundant Mn⁴⁺, Mn³⁺ (B-site) ions production with high H₂ reduction activity, which promoted the generation of substantial oxygen vacancies, thereby achieving efficient CO₂ capture and reduction. Mg_0.5MFO NPs exhibited superior CO₂ adsorption (129.13 ml/g) and reduction (151.87 ml/g) performance, and CO₂ followed an adsorption-stretching-polarization-reduction mechanism at the (111) plane. During the reduction of CO₂ by Mg_0.5MFO NPs, the controllable synthesis of HGC (5–50 nm, 82 % graphitization) was realized by increasing the temperature (300 °C→650–660 °C) and extending the time (1 min→30 min). Massive Mn²⁺ generated along with oxygen vacancies played a crucial catalytic role in the graphitization of carbon. Mg_0.5MFO NPs with 619.29 mg/g HGC from 100 cycles of CO₂ reduction maintained an outstanding reversible capacity of 749.46mA h after 400 cycles at a current density of 0.2 A g⁻¹. Dense HGC on Mg_0.5MFO NPs as buffer coating enhanced lithium-ion extraction/insertion stability. This Mg²⁺-doped manganese ferrite provides a novel route for energy utilization of greenhouse gas CO₂.