Efficient CO2 electroreduction coupled with semi-dehydrogenation of tetrahydroisoquinoline by MOFs modified electrodes

Electroreduction of CO2 into formate catalyzed by metal–organic frameworks (MOFs) is a promising avenue to promote the carbon cycle, but the oxygen evolution reaction (OER) process in anode usually limited the reaction efficiency. Here, a new framework {(Me2NH2)[Bi(L)]·4DMF·2H2O}n (V12) was constructed and structurally characterized (L = 5,5′-(1,3,6,8-tetraoxo-1,3,6,8-tetrahydrobenzo[lmn][3,8]phenanthroline-2,7-diyl) dibenzene-1,3-dicarboxylic acid; DMF = N,N-dimethylformamide). V12 possesses large one-dimensional channels with the size of 1.5 × 0.7 nm and exhibits good stability in common solvents. After V12 was modified on electrode via electrodeposition, as-synthesized sample exhibits impressive catalytic performance for the transformation of CO2 into formate with Faraday efficiency of 93.2% and current density of 11.78 mA cm−2 at −0.9 V (vs. RHE). Control experiments revealed that the MOFs electrodeposition strategy significantly improves the charge transfer rate and introduces more structural defects, which promotes the reaction activity. Moreover, tetrahydroisoquinoline is added as an accelerant in the anode to achieve the simultaneous generation of formate and dihydroisoquinoline. More importantly, the cell voltage is reduced from 2.79 to 2.52 V at 10 mA cm−2 in a two-electrode system due to more positive reaction kinetics. This work provides an enlightening strategy for using MOFs to establish an effective system to achieve CO2 reduction while obtaining high value-added oxidation products.