Highly Selective CO₂ Electroreduction to C₂H₄ Using a Metal–Organic Framework with Dual Active Sites

Abstract

Conversion from CO 2 to C 2 H 4 is important for the development of energy and the environment, but the high energy barrier of hydrogenation of the *CO intermediate and C−C coupling step tend to result in C 1 compounds as the main product and thus restrict the generation of C 2 H 4 . Here, we report a metal−organic framework (denoted as PcCu-Cu-O), composed of 2,3,9,10,16,17,23,24-octahydroxyphthalo-cyaninato)copper(II) (PcCu-(OH) 8 ) ligands and the square-planar CuO 4 nodes, as the electrocatalyst for CO 2 to C 2 H 4 . Compared with the discrete molecular copper-phthalocyanine (Faradaic efficiency (FE) of C 2 H 4 = 25%), PcCu-Cu-O exhibits much higher performance for electrocatalytic reduction of CO 2 to C 2 H 4 with a FE of 50(1)% and a current density of 7.3 mA cm −2 at the potential of −1.2 V vs RHE in 0.1 M KHCO 3 solution, representing the best performance reported to date. In-situ infrared spectroscopy and control experiments suggested that the enhanced electrochemical performance may be ascribed to the synergistic effect between the CuPc unit and the CuO 4 unit, namely the CO on the CO-producing site (CuO 4 site) can efficiently migrate and dimerize with the *CO intermediate adsorbed on the C 2 H 4 -producing site (CuPc), giving a lower C−C dimerization energy barrier.

Toward High‐Performance CO2‐to‐C2 Electroreduction via Linker Tuning on MOF‐Derived Catalysts

“…Main eCO 2 RR products were identified as CO at low current density and C 2 H 4 at high current density. For the NH 2 -Cu-BDC and OH-Cu-BDC [2,12,[27][28][29][30][31][32][33] (Table S1, Supporting Information). Black square for the results in the literature.…”

“…2F-Cu-BDC ranks high in the comparison with the prior best results in literature. [2,12,[27][28][29][30][31][32][33] It also should be noted that although a few catalysts exhibit high R C2/C1 (such as ref. [ 33 ]), their current densities are impractical (<15 mA cm -2 ).…”

2D π‐conjugated metal–organic frameworks for CO2 electroreduction

“…However, active‐site engineering in multimetal‐site MOFs may be a promising strategy for C−C dimerization from the perspective of chemistry. For example, Liao's group 69 found that the suitable distance between C 2 H 4 ‐producing and CO‐producing sites of MOF was easy for C 2 H 4 generation. In this study, they prepared PcCu‐Cu‐O MOF composed of PcCu‐(OH) 8 ligands and the square‐planar CuO 4 nodes for CO 2 RR.…”

“…However, active-site engineering in multimetal-site MOFs may be a promising strategy for C−C dimerization from the perspective of chemistry. For example, Liao's group 69 found that the suitable distance between…”

Highly‐Exposed Single‐Interlayered Cu Edges Enable High‐Rate CO2‐to‐CH4 Electrosynthesis

“…[ 10 ] In spite of the enhanced CH 4 selectivity, almost all of the reported catalytic activities (assessed by j CH4 ) are <400 mA cm −2 to date, [ 9 ] which can be attributed to the low densities (typically < 10 wt%) of single‐atomic Cu catalytic sites inside the catalysts. Due to the limitation of maintaining the chemical environment of SAC sites, further increase of the Cu loading often results in close proximity of multiple‐atomic sites [ 13,14 ] and even aggregation, [ 15,16 ] and thus shifts the CO 2 RR pathway from CH 4 to C 2+ products due to the enhanced C–C coupling. For instance, it has been reported that when two Cu SAC sites get close enough, the coupling of two *CO intermediates is facilitated to form a *OC–CO dimer, leading to the increase of the C 2 H 4 /CH 4 ratio.…”