High-efficiency thermal reduction of CO2 to high-valued carbon nanotubes

Abstract

To reduce the amount of carbon dioxide (CO2) already emitted into the atmosphere, various carbon capture, utilization, and storage (CCUS) technologies have been developed for climate and economic reasons in recent years. However, the state of art CCUS techniques suffer from deficiencies such as high cost, low yield, and harsh and discontinuous production conditions. In this work, we report a new thermal reduction method for continuously conversing CO2 to methane (CH4) by introducing sodium borohydride (NaBH4) as a reductant under catalyst-free conditions. Experimental results show that CO2 can be fully captured and converted to CH4 and carbon monoxide (CO) and the selectivity efficiency of CO2 to CH4 can be achieved to be as high as 90% with the optimization of experimental conditions. Such a result originates from the high activity of NaBH4 and high selectivity of the thermal reduction of CO2. To demonstrate one of the potential usages of the reduction products, we integrated the thermal reduction of CO2 with the production of carbon nanotubes (CNTs). As long as CO2 is supplied at the source end, the reduction products can undergo catalytic decomposition to produce a CNT fiber or film continuously at the final end. The present technique is featured with simple equipment setup, low cost, and continuous thermal reduction, thus providing a new pathway for the large-scale conversion of CO2 into high-valued products for wide applications.