Electrochemical reduction of CO2 (CO2RR) provides an attractive pathway to achieve a carbon-neutral energy cycle. Single-atom catalysts (SAC) have shown unique potential in heterogeneous catalysis, but their structural simplicity prevents them from breaking linear scaling relationships. In this study, we develop a feasible strategy to precisely construct a series of electrocatalysts featuring well-defined single-atom and dual-site iron anchored on nitrogen-doped carbon matrix (Fe1–N–C and Fe2–N–C). The Fe2–N–C dual-atom electrocatalyst (DAC) achieves enhanced CO Faradaic efficiency above 80% in wider applied potential ranges along with higher turnover frequency (26,637 h–1) and better durability compared to SAC counterparts. Furthermore, based on in-depth experimental and theoretical analysis, the orbital coupling between the iron dual sites decreases the energy gap between antibonding and bonding states in *CO adsorption. This research presents new insights into the structure–performance relationship on CO2RR electrocatalysts at the atomic scale and extends the application of DACs for heterogeneous electrocatalysis and beyond.

In this work, we report a series of crystalline viologen-based porous ionic polymers (denoted VIP-X, X ¼ Cl or Br), that have in situ formed dicationic viologens paired with halogen anions and intrinsic hydrogenbonded water molecules, towards metal-free heterogeneous catalytic conversion of carbon dioxide (CO 2 ) under mild conditions. The targeted VIP-X materials were facilely constructed via the Menshutkin reaction of 4,4 0 -bipyridine with 4,4 0 -bis(bromomethyl)biphenyl (BCBMP) or 4,4 0 -bis(chloromethyl) biphenyl (BBMBP) monomers. Their crystalline and porous structures, morphological features and chemical structures and compositions were fully characterized by various advanced techniques. The optimal catalyst VIP-Br afforded a high yield of 99% in the synthesis of cyclic carbonate by CO 2 cycloaddition with epichlorohydrin under atmospheric pressure (1 bar) and a low temperature (40 C), while other various epoxides could be also converted into cyclic carbonates under mild conditions. Moreover, the catalyst VIP-Br could be separated easily and reused with good stability. The remarkable catalytic performance could be attributed to the synergistic effect of the enriched Br À anions and available hydrogen bond donors -OH groups coming from H-bonded water molecules.Scheme 1 Synthetic route to crystalline viologen-based porous ionic polymers VIP-X (X ¼ Cl or Br) with intrinsic H-bonded water molecules via the Menschutkin reaction of 4,4 0 -bipyridine with (a) BCMBP and (b) BBMBP under solvothermal conditions (i.e., CH 3 CN, 100 C, 48 h). This journal isScheme 2 A proposed catalytic reaction mechanism for the cycloaddition of CO 2 with epoxides over the catalyst VIP-Br with Br À anions and H-bonded water molecules.This journal is

POSS and viologen-linked porous cationic frameworks (V-PCIF-X, X = Cl, Br) are constructed via the Zincke reaction between octa(aminophenyl)silsesquioxane and viologen linkers. The typical V-PCIF-Br has a high surface area with abundant ionic sites, micro-/mesopores and Si-OH groups, serving as an efficient porous adsorbent and metal-free catalyst for simultaneous CO2 capture and conversion.