In situ encapsulated Co3O4 nanoparticles into self-catalyzed grown CNTs for efficient CO2 conversion

Co 3 O 4 -based catalysts emerged as promising candidates for electrocatalytic CO 2 reduction reaction (eCO 2 RR), while the unclear active sites and poor stability are challenging for the application of Co 3 O 4 as an electrocatalyst. Here, we developed a feasible method to in situ encapsulate Co 3 O 4 nanoparticles (NPs) into self-grown CNTs . Co 3 O 4 NPs were elaborately controlled to terminate with the occupation Co 2+ Th /Co 3+ Oh sites (with Co 2+ and Co 3+ in the center of tetrahedral/octahedral cells). The well-dispersed Co atoms derived from ZIF-67 catalyzed the in situ assembly of CNTs, allowing controlled oxidation and growth into Co 3 O 4 nanoparticles spatially confined by CNTs, resulting in Co 3 O 4 highly-dispersed into hollow CNTs and well-protected. The enhanced electrocatalytic performance of Co 2+ Th was revealed with an onset potential of −0.24 V, and the CO production rate (131 μmol/s·g·cm 2 , −0.85 V vs. RHE) on Th-Co 3 O 4 /CNTs (exposed with Co 2+ Th sites) is 3.1 times of that on Oh-Co 3 O 4 /CNTs (exposed with Co 3+ Oh sites). DFT calculations demonstrated a significant reduction in the rate-limiting activation barrier of CO 2 , and Co 2+ Th was proved to be more active than Co 3+ Oh with elongated *CO-OH bonds. In situ ATR-SEIRAS confirmed that the enhanced CO 2 adsorption and rapid formation of *COOH on Th-Co 3 O 4 /CNTs were key factors leading to efficient CO production. This work introduced a clear understanding of the eCO 2 RR performance of Co 2+ Th /Co 3+ Oh sites, along with a feasible approach for catalyst construction and protection.