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It is a very important but still challenging task to develop bifunctional electrocatalysts for highly efficient CO 2 overall splitting. Herein, we report a stable metal–organic framework (denoted as PcNi-Co – O ), composed of (2,3,9,10,16,17,23,24-octahydroxyphthalocyaninato)nickel(II) (PcNi-(O – ) 8 ) ligands and the planar CoO 4 nodes, for CO 2 overall splitting. When working as both cathode and anode catalysts (i.e., PcNi-Co – O || PcNi-Co – O ), PcNi-Co – O achieved a commercial-scale current density of 123 mA cm –2 (much higher than the reported values (0.2–12 mA cm –2 )) with a Faradic efficiency (CO) of 98% at a low cell voltage of 4.4 V. Mechanism studies suggested the synergistic effects between two active sites, namely, (i) electron transfer from CoO 4 to PcNi sites under electric fields, resulting in the raised oxidizability/reducibility of CoO 4 /PcNi sites, respectively; (ii) the energy-level matching of cathode and anode catalysts can reduce the energy barrier of electron transfer between them and improve the performance of CO 2 overall splitting.
Zhang et al. (Thu,) studied this question.