Highly active metallic nickel sites confined in N-doped carbon nanotubes toward significantly enhanced activity of CO2 electroreduction

Abstract

Carbon dioxide electroreduction (CO2ER) still faces the challenges of low product selectivity, high overpotential, and high cost of electrocatalysts. Herein, we develop a low-cost and highly efficient precious-metal-free CO2ER electrocatalyst, composed of Ni nanoparticles (NPs) with the size range of 50–100 nm, confined within N-doped carbon nanotubes (NCNTs) with the diameter of 100–200 nm (Ni@NCNTs). Benefitting from the confinement effect, the resulting 1D Ni@NCNTs hybrid exhibits an exceptional electrocatalytic activity and selectivity for CO production with a relatively positive onset potential of −0.3 V, low Tafel slope of 97 mV dec−1, and high Faradaic efficiency of 99.1%. The high selectivity of Ni@NCNTs for CO production during the CO2ER is almost the best among all previously reported N-doped carbon based CO2ER electrocatalysts. Experimental observations demonstrate that the confined Ni NPs inside NCNTs is a key step to promote the conversion of CO2 to CO. Density functional theory calculations reveal that the confinement effect of NCNTs can weaken the binding strengths between Ni NPs and *CO intermediates, thus improving the rate-limiting step of *CO desorption during the CO2ER process. Further integration of 1D Ni@NCNTs electrocatalyst with a solar panel or two alkaline batteries enable highly active and sustainable CO2ER and water splitting.