Highly Selective Pressure-Driven Electrochemical Conversion of CO2 into CO over Nickel-Encapsulated Nitrogen-Doped Carbon Nanotubes

Abstract

The selective electroreduction of CO2 to CO is an attractive avenue for storing intermittent renewable energy. Although designing a precise confining microenvironment for active sites is challenging, most CO2-to-CO catalysts are developed by considering the potential of structural reconstruction. Herein, we report encapsulating Ni within nitrogen-doped carbon nanotubes (NCNTs) as an effective strategy for improving CO2 adsorption and catalytic activity. The Ni/NCNT catalyst exhibited a faradaic efficiency exceeding 99.4% for the conversion of CO2 into CO, with a current density of −27.73 mA cm–2 at −3.0 V under high-pressure conditions (8.0 MPa). The high CO selectivity (>99.2%) and low potential (−3.0 V) were maintained during long-term operation (12 h) at 6.0 MPa. Two strategies were used to produce CO in a highly selective manner: the first involved designing Ni/NCNTs that maintain good CO selectivity, while the second involved developing a high-pressure CO2RR system that delivers a superior local CO2 concentration and suppresses the competing hydrogen-evolution reaction. The synergy between these two strategies led to the production of CO via stable and efficient CO2 reduction. The Ni/NCNT catalyst promotes the linear adsorption of CO while suppressing the bridged-adsorption mode on the catalyst surface.