Electric vehicles with longer driving mileage and unmanned aerial vehicles with prolonged cruise duration require urgently higher energy density of batteries. (1?4) Lithium–carbon dioxide (Li–CO₂) battery, which demonstrates a high theoretical energy density of 1876 W h·kg–1 and a high discharge plateau (?2.8 V vs Li⁺/Li), has attracted increasing attention as one of the promising next-generation metal-gas batteries. (5?7) Li–CO₂ batteries can simultaneously realize the fixation of greenhouse gas CO₂ and high energy density supply, which show enormous application potentiality in CO2-rich situations such as deep-sea work and Mars exploration (96% of its atmosphere on Mars is CO₂). The main reaction process involved in aprotic Li–CO₂ batteries is as follows: 4Li⁺ + 3CO₂ + 4e^- ? Li₂CO₃ + C. (8?10) However, the sluggish kinetics of the discharged product Li₂CO₃ with stable chemical stability during recharging have greatly restricted the rate performance and cycling stability of Li–CO2 batteries. Meanwhile, the arduous decomposition of insulating Li₂CO₃ during recharging also leads to high overpotential and consequent electrolyte degradation. (11?13) The continuous accumulation of undecomposed Li2CO3 on the cathode occupies the reaction sites and severely blocks the CO₂ diffusion channels, further resulting in large polarization and poor cycling performance of the batteries. Therefore, efficient cathode catalysts are highly imperative to boost the decomposition of Li₂CO₃ and facile reaction kinetics.

In recent years, several kinds of cathode catalysts, including carbon materials, (14?20) noble metals, (10,12,21?26) transition metals and their compounds, (27?36) metal–organic frameworks, (37,38) and covalent organic frameworks, (39,40) have been developed and improved the electrochemical performance of Li–CO₂ batteries. Among them, integrating an efficient metal catalyst into highly conductive carbon have shown significantly facilitated kinetics in Li–CO₂batteries as well as other gas-involved catalytic reactions. (29,32,36) A variety of carbon/metal composite catalysts, such as ultrathin Ir nanosheets on N-doped carbon fibers, (21) RuO₂ on carbon nanotubes (CNTs), (22) ultrafine Ru nanoparticles on activated carbon nanofibers, (23) ZnS quantum dots on N-doped reduced graphene oxide(GO), (27) adjacent Co single atom/GO, (35) Ru–Cu nanoparticles on graphene, (41) Mo2C/CNTs, (42) Ru–Co nanoparticles on carbon nanofibers, (43) etc., have been prepared and showed outstanding catalytic activity and remarkably reduced the voltage gap between CO₂ reduction and evolution process. However, reported carbon/metal composite catalysts have several drawbacks: weak bonding strength between carbon and metal catalysts, uneven distribution of the nanoparticles, and limited catalyst utilization, leading to the formation of large aggregates and high loading but partly inefficient catalytic behavior. Moreover, the loading amount, crystal structure, and catalytic sites of metal catalysts are difficult to precisely regulate to further improve and optimize their catalytic activity.

The emerged graphdiyne (GDY) material is a novel allotrope of carbon (44) which contains both sp and sp2 hybridized carbon atoms in the carbon framework and possesses a large specific surface area, uniform pore structure, and excellent electrochemical stability. Different from traditional carbon materials like graphene and CNTs, it was suggested that the coexistence of sp and sp2 carbon atoms is favorable for chelating metal atoms and facilitating the charge transfer between metal atoms and GDY. (45) These merits make GDY an ideal substrate for anchoring metal catalysts with suppressed aggregation. So, GDY/metal composite catalysts such as GDY-WS2 (46) and MoS₂/N-GDY (47) have shown efficient catalytic activity in hydrogen evolution reaction (HER). In addition, single metal atoms can be stably anchored and evenly dispersed on GDY, such as Ni(Fe)/GDY, (48) Pd/GDY, (49) and Mo/GDY, (50) with highly efficient catalytic activity to the HER and the nitrogen reduction reaction. At the same time, GDY can be synthesized through a copper-catalyzed C–C cross-coupling reaction, which makes it possible to precisely adjust its morphology and chemical properties, including conductivity, pore structure, and affinity for metal atoms, thereby conveniently optimizing the catalytic activity of the GDY/metal catalyst...