The fundamental and distinguishing feature of GDY as a catalytic platform is its ability to engage in noninteger charge transfer with anchored metal atoms^[108]. This capability arises directly from GDY’s intrinsic electronic heterogeneity of the periodic alternation of electron-rich alkyne linkages (–C≡C-C≡C–) and electron-deficient aromatic rings, which creates a spatially varying electrostatic potential that facilitates bidirectional electron exchange with anchored atoms. The alkyne domains of GDY actively participate in electronic communication with metal species^{[106,109-111]}. The electron-rich sp-hybridized carbon atoms donate electron density to incoming metal atoms while accepting back-donation from the metal’s d-orbitals. This synergistic charge transfer stabilizes metal atoms in unconventional zero-valent states, a configuration that maximizes d-electron availability for catalytic turnover while preventing aggregation into larger clusters or nanoparticles^[112-114].

Through efficient charge transfer, the d-band center of anchored metal atoms can be precisely modulated to achieve optimal binding strength for nitrogenous intermediates, thereby facilitating N₂/NO₃^- activation and the release of NH₃. Such electronic tunability is unattainable on electronically homogeneous sp²-carbon surfaces.

This electronic modulation principle has been demonstrated across a wide range of metal species. Theoretical screening has identified numerous transition metal atom catalysts (TM@GDY) with tailored d-band centers for nitrogen reduction. Experimentally, zero-valent metal atoms of Pd^[72], Pt^[115], Ru^[74], Rh^[73], Os^[116], Mo^[71], Fe^[117], Co^[118], and Ni^[117] have all been successfully stabilized on GDY through noninteger charge transfer. The extent of charge transfer can be further tuned by varying the metal identity, GDY thickness, or the introduction of substituent groups, providing a versatile platform for optimizing catalytic activity and selectivity across different nitrogen-fixation reactions. Beyond single atoms, unique noninteger charge transfer also extends to dual-atom catalysts (DACs), QD catalysts, and heterostructured catalysts. These reported catalysts all exhibit enhanced catalytic performance through cooperative electron transfer.

GDY possesses natural triangular pores with a radius of approximately 0.45 nm^{[101,119,120]}. These nanopores can also serve as geometrically matched cages that impose spatial confinement on deposited metal species and simultaneously modulate their local electronic environment. For example, triangular pores are ideally sized to accommodate isolated metal atoms, preventing their migration and coalescence even under harsh electrochemical conditions^[121-123]. This restricts the free movement and volume change of the anchored species, ensuring high active-site stability and maximizing the atom-utilization efficiency, which are the critical requirements for efficient catalysis^[101]. Owing to these advantages, the extended 2D surface of GDY can direct the growth of QDs, clusters, and heterostructures with controlled size, crystallinity, and dispersion.

Importantly, the spatial confinement effect is not merely passive but also synergistically coupled with electronic modulation. Density functional theory (DFT) calculations show that transition metal atoms and clusters anchored within the triangular pores of GDY exhibit high adsorption energies, indicating the stability of these catalytic systems^[124]. Experimentally, researchers have achieved controlled growth of active sites on GDY by exploiting the confinement effect. Such spatial and electronic dual confinement of GDY creates a unique catalytic microenvironment that cannot be replicated on open surfaces or in larger pores^[55,103]. For nitrogen fixation applications, this capability enables rational catalyst design with precisely defined active-site architectures, from isolated single atoms to closely spaced dual atoms and clusters, for selective N₂ or NO₃^- activation and NH₃ formation.

Another important design principle extends beyond the GDY itself to the interfaces formed between the GDY and metal nanostructures. The chemical addressability of GDY, enabled by its sp-hybridized carbon atoms, allows for seamless integration with a diverse range of materials, from transition metal dichalcogenides (TMDs) to metal oxides, nitrides, and metal-organic frameworks (MOFs)^[97,125]. The resulting heterointerfaces exhibit synergistic effects that are unavailable in single-component systems, including heterointerface charge redistribution that drives electron transfer across the interface, creating an internal electric field that facilitates charge separation and enhances catalytic kinetics^[68]. For nitrogen fixation, interfacial charge transfer can optimize the adsorption energetics of nitrogenous intermediates on the active sites. For example, the GDY/Co₂N^[83] interface has been shown to facilitate preferential N₂ adsorption at coordinatively unsaturated Co sites, whereas alkyne C-sites redistribute H-species to suppress the competing HER. In addition, the lattice strain effect at GDY heterointerfaces can continuously tune the electronic structure of the active sites, shifting d-band centers and modifying adsorption energetics. The magnitude of strain can be systematically controlled by varying the GDY layer thickness or the heterostructure partner, providing a tunable parameter for optimizing catalytic performance. Strain engineering offers an additional lever for fine-tuning the binding strength of N₂, NO₃^-, and reaction intermediates to achieve the optimal balance between activation and product release during the nitrogen fixation process.

Atomic catalysts (ACs) represent a new frontier in catalysis and are defined as catalysts consisting of zero-valent metal atoms that are atomically dispersed and anchored on supporting materials^[126-128]. This architectural paradigm maximizes metal atom utilization efficiency, approaching the theoretical limit of 100%, while offering unique electronic and geometric properties that are unattainable with conventional nanoparticles or clusters^[129-131]. However, traditional single-atom catalysts face persistent challenges in terms of the migration and aggregation of metal atoms, and conventional synthesis methods lack precision in controlling the chemical structure and charge distribution of individual metal atoms. These limitations seriously impede the understanding of structure-activity relationships and catalytic mechanisms at the atomic level^[35,132-134]. The unique sp/sp²-carbon framework and the confinement effects resulting from the uniform acetylenic cavities and strong noninteger charge transfer between metal atoms and GDY enable effective and precise single-metal-atom stabilization^[135-137]. Unlike N-doped carbon substrates, the neutral C≡C bonds in GDY tend to stabilize zero-valent or low-valence transition metals^[138]. This electronic regulation simultaneously activates the N≡N triple bond via M-to-N₂ π-backdonation and optimizes p-d orbital coupling while restraining competitive HER, thus increasing both selectivity and catalytic activity in electrochemical NRR.

In 2019, Hui et al. reported the first zero-valent molybdenum-atom catalyst (Mo⁰/GDY) with a high metal loading of 7.5 wt% for ammonia synthesis from the reduction of nitrogen^[71]. The structural configurations of Mo⁰/GDY at different reaction stages are shown in Figure 1A. High-angle annular dark field imaging in the aberration-corrected scanning transmission electron microscope (HAADF-STEM) and X-ray absorption near edge strucure (XANES) confirm the anchoring of individual Mo⁰ atoms at the alkyne ring corners of GDY [Figure 1B and C]. For example, Mo⁰/GDY achieved a maximum FE exceeding 21% and an ammonia yield rate (Y_NH3) of 145.4 μg·h^-1·mg_cat.^-1 at -1.2 V vs. saturated calomel electrode (SCE) in neutral 0.1 M Na₂SO₄ [Figure 1D]. More recently, Yu et al. reported the spontaneous anchoring of zero-valent single palladium atoms supported on GDY (Pd-GDY) for the electrocatalytic NRR [Figure 1E]^[72]. HAADF-STEM images confirm the atomic dispersion of isolated Pd atoms on GDY [Figure 1F]. In addition, XANES clearly shows that Pd atoms in Pd-GDY are in a zero-valent state [Figure 1G]. This unique property of GDY endows the catalyst with excellent NRR activity and durability. In 0.1 M Na₂SO₄, Pd-GDY achieved an optimal Y_NH3 of 4.45 ± 0.30 mg_NH3 mg_Pd^-1·h^-1 and an FE of 31.62% at -0.16 V vs. reversible hydrogen electrode (RHE) [Figure 1H], as well as durability over consecutive recycling tests. Zou et al. reported a one-pot stereo-confinement strategy to anchor high-loading transition metal atoms (Rh, Ru, and Co) on GDY using C-C cross-coupling and reductive elimination to entrap metal single atoms on GDY [Figure 1I]. HAADF-STEM images confirmed the dense atomic dispersion of the metal atoms [Figure 1J]. Their experimental results revealed that a high partial pressure (55 atm N₂) could significantly increase N₂ solubility and the thermodynamic driving force while effectively retarding the HER for the NRR. Among the synthesized catalysts, Rh single atom anchored on GDY (Rh SA/GDY) achieved an exceptional Y_NH3 of 74.15 μg·h^-1·cm^-2, an FE of 20.36%, an NH₃ partial current density (j_NH3) of 0.35 mA·cm^-2 at -0.20 V vs. RHE [Figure 1K and L], and high cycling stability^[73].

Recently, researchers have investigated the durability and distinctive characteristics of zero-valent single-atom catalysts. Feng et al. designed a Ru single-atom catalyst supported on a graphdiyne/graphene sandwich architecture (Ru SAs/GDY/G)^[74]. At a low potential of -0.1 V vs. RHE, the catalyst delivered a remarkable NH₃ yield rate of 56.8 μg·h^-1·mg_cat.^-1 (4.7 mg·h^-1·mg_Ru^-1), with a FE of 37.6%. GDY not only suppresses hydrogen coverage at Ru single-atom sites, thereby minimizing the competitive HER, but also generates hydrogen radicals (H·), accelerating the hydrogenation kinetics of the NRR. Notably, this hydrogen radical transfer (H·-transfer) pathway represents a novel mechanistic discovery in the electrocatalytic NRR [Figure 1M-P]. In addition, Mn SA/GDY exhibits efficient NH₃ synthesis under ambient conditions, delivering a production rate of 46.78 μg·h^-1·mg_cat.^-1 and a FE of 39.83%^[77]. Zou et al. reported that the NRR performance of atom catalysts on GDY (M SA/GDY; M = Cr, Mo, W, Mn, and Re) decreased in the order Re > Mo > Cr > W > Mn^[76]. Strong M-to-N₂ pi-backdonation on Re SA/GDY lowers the free-energy input for the potential-determining stage (*N₂ to *NNH) to +0.39 eV, establishing an N₂/H₂O-assisted ligand-exchange mechanism for facile NH₃ desorption with a low energy requirement of +0.83 eV. Xiong et al. demonstrate that GDY-supported uranium single atoms (U/GDY) leverage the unique electronic properties and f-orbital interactions of actinide sites to effectively promote N₂ coordination and N≡N bond activation^[139].

Collectively, these studies reveal that GDY, with a unique sp/sp²-hybridized framework and intrinsic noninteger charge-transfer capability, serves as an exceptional platform for stabilizing zero-valent single atoms across a broad range of transition metals and even actinides. Precise control over metal coordination environments, combined with the electronic modulation enabled by GDY’s alkyne-rich cavities, not only optimizes reactant activation and hydrogenation kinetics but also effectively suppresses the competing HER. This atomic-level catalyst design paradigm offers a versatile, robust strategy for high catalytic performance, paving the way for the rational development of next-generation single-atom catalysts for sustainable ammonia synthesis.

While single-atom catalysts offer maximized atom utilization and well-defined active sites, they are inherently limited by the linear scaling relations (LSRs) that govern the adsorption energies of reaction intermediates on single metal centers^[140,141]. In the context of the NRR, this limitation manifests as competition between N₂ activation/hydrogenation and NH₃ desorption, which demand opposite binding strengths, thereby imposing a thermodynamic ceiling on the achievable activity and selectivity. Multi-atom catalysts provide a compelling strategy to overcome this limitation by introducing proximal metal centers that can cooperatively bind and transform nitrogenous species, effectively decoupling the scaling constraints inherent to single-site catalysis^[142].

A representative demonstration of this cooperative effect comes from Guo et al., who synthesized subnanometer Pd clusters supported on hydrogen-substituted GDY (Pd/HsGDY)^[78] [Figure 2A-E]. Their results showed that the electron-withdrawing diacetylene units in HsGDY shift the d-band center of Pd clusters downward, preventing overbinding of nitrogen reaction intermediates and accelerating N-hydrogenation kinetics, leading to high FE (44.45%) and an NH₃ yield rate (115.93 mg_cat^-1·h^-1).

Extending this concept to heteronuclear dual-atom systems, theoretical studies have demonstrated that GDY can function as a dynamic electron reservoir, shuttling charge through metal bridges to adsorbed N_xH_y intermediates and thereby breaking conventional scaling restrictions between *N₂H and *NH₂ species [Figure 2F]. Systematic DFT screening of vanadium-paired transition metals of the 3d series on GDY (V-TM@GDY) revealed a volcano-type correlation between N₂ charge transfer (Q(N₂)) and the limiting potential. V-Cr@GDY and V-Fe@GDY achieve exceptionally low limiting potentials (-0.36 and -0.42 V) alongside a theoretical FE of nearly 100% for NH3^[143]. Free-energy profile evaluations for Co-Ni@GDY (distal mechanism, U_L = -0.52 V) and Mo₂@GDY (consecutive mechanism, U_L = -0.61 V) further confirm that dual-atom bridging sites provide the coordination flexibility to optimize intermediate binding and lower reaction barriers^[147]. Another pivotal insight emerges from comparative studies on homonuclear (Co₂@GDY^[148], Fe₂@GDY^[145], and Mo₂@GDY^[145]) and heteronuclear (FeCo@GDY and NiCo@GDY^[145], and Rh-Hf@GDY and Rh-Ta@GDY^[144]) dimers [Figure 2G-I], which highlight the decisive role of the metal interatomic distance (~2.4-2.6 Å) in determining the N₂ adsorption geometry. Optimal interatomic spacing promotes side-on N₂ chemisorption, enabling simultaneous two-center electron donation/backdonation to elongate the N≡N bond and lower the initial hydrogenation barrier (ΔG_*N2→*NNH).

Pushing the boundary toward higher nuclearity, investigations into Mo₃@GDY^[149], Fe₃-GDY^[150] and Ti-Co₃@GDY^[146] catalysts reveal that triatomic hollow sites achieve ultrahigh mass loading while expertly balancing reactant activation and product release, with limiting potentials between -0.26 and -0.32 V [Figure 2J]. Notably, this multinuclear synergy is not confined to metallic systems. In the nonmetallic domain, double boron-doped GDY (GDY-2B^[151]) exemplifies a dual-Lewis-acid “pull-pull” mechanism that traps N₂ lone pairs, achieving an overpotential as low as 0.12 V. Theoretical simulations confirm the stable incorporation of S and N atoms into the GDY monolayer (GDY@SN), yielding structurally robust doped frameworks with tunable electronic properties for NRR^[152]. This multinuclear strategy defines a robust framework for the design of efficient electrocatalytic nitrogen conversion systems.

These studies demonstrate that GDY-based multi-atom catalysts effectively circumvent the intrinsic scaling limitations of single-site catalysis through the synergistic interaction of adjacent metal sites. Continued exploration of GDY-supported multi-atom architectures, through integrated computational screening and precision synthesis, holds great promise for unlocking next-generation catalysts toward sustainable and scalable ammonia production.

In addition to serving as a support for metal-based catalysts, GDY and its derivatives can also be used as metal-free catalysts with high intrinsic activity for NRR. This is particularly attractive from the perspectives of cost, sustainability, and scalability. This section summarizes the strategies for realizing and enhancing metal-free NRRs on GDY-based platforms, including H^[80], N^[153,154], O^[155], B^[156], F^[79], or Cl-doped graphdiyne^[81].

HsGDY features a fully conjugated sp/sp² carbon network^[157]. The localized electron polarization on its inner alkynyl carbon chain lowers the activation barrier for key hydrogenation steps, particularly the NH₂NH₂ formation, while inherently suppressing the competing HER. Xing et al. successfully synthesized crystalline fluorinated GDY (cFGDY) with a 9-fold stacking mode, as confirmed by high resolution transmission electron microscopy (HRTEM) analyses [Figure 3A and B]. The high-quality and unique characteristics of cFGDY enable it to act as an efficient metal-free NRR electrocatalyst [Figure 3C], with 100% selectivity toward NH₃ production under room-temperature conditions. The electron-withdrawing fluorine atoms create electron-deficient carbon sites that facilitate N₂ adsorption while suppressing HER^[79]. Yang et al. presented a scalable protocol in which Zn (instead of traditional Cu) was used as the support for growing planar crystalline HsGDY [Figure 3D and E]. At -0.2 V, the synthesized HsGDY shows outstanding NRR catalytic performance, with an NH₃ yield rate of 103 μg·h^-1·mg_cat.^-1, which is comparable to or even higher than that of noble metal and state-of-the-art single-atom catalysts [Figure 3F and G]^[80].

Zou et al. introduced a corrosion engineering approach using Cl₂ gas to simultaneously etch and dope bulk GDY [Figure 3H and I]^[81]. The electronegative Cl atoms form electron-deficient carbon sites that enhance N₂ chemisorption. In performance testing [Figure 3J], Cl-GDY achieves an NH₃ yield rate of 10.7 μg·h^-1·cm^-2 and a peak FE of 8.7%. Isotopic labeling with ¹⁵N₂ and ¹⁴N₂ gas feeds [Figure 3K] confirms that the detected ammonia originates directly from dissolved N₂ gas. Supporting these experimental observations, DFT studies have mapped the free energy landscape for NRR on various heteroatom-doped GDY systems. Wang et al. investigated four different N-doped GDY models and found that sp-N-2-substituted GDY exhibits the highest activity, with nitrogen doping at sp-hybridized acetylenic sites reducing the energy barrier for the potential-limiting step (N₂(g)→HN-N) to -0.99 V through a hybrid pathway [Figure 3L]^[153]. Computational investigations further validate the efficacy of heteroatom doping in metal-free graphdiyne, as evidenced by DFT calculations on oxygen-doped GDY (O-doped GDY)^[156], single-boron-substituted GDY at acetylenic sites (B(S3)@GDY), and dual-boron-doped GDY frameworks (GDY-2B(S2 S2’))^[157], which collectively demonstrate enhanced N₂ activation and reduced reaction barriers.

The above results are summarized in Figure 3. The conjugated backbone of GDY, upon heteroatom doping or polarization modulation, forms electrondeficient carbon active centers, which strengthen dinitrogen activation and suppress side reactions while eliminating metal dependence, thereby achieving highly selective and efficient nitrogen-to-ammonia conversion.

The abundant sp/sp²-hybridized carbon, delocalized π-electrons, and regular acetylenic pores of GDY render it an ideal substrate for constructing heterostructured electrocatalysts. When combined with transition metal nitrides, oxides, borides, or QDs, GDY modulates interfacial charge redistribution and tunes the electronic states of the active sites. This optimizes light absorption and electrical conductivity while simultaneously restraining the competing HER and facilitating N≡N bond cleavage for the NRR^[158,159].

Defect and interface engineering of GDY-based heterostructured electrocatalysts has shown great potential for enhancing ambient nitrogen reduction. Fang et al. designed an Fe-vacancy-rich Fe₃O₄/graphdiyne heterostructure (IVR-FO/GDY) through coprecipitation and a cross-coupling sequence [Figure 4A and B]. Owing to the synergistic interaction between GDY and Fe₃O₄, many Fe vacancies were introduced in IVR-FO/GDY, and the valence state of Fe was precisely regulated, thus improving the catalytic performance^[82]. In neutral 0.1 M Na₂SO₄, IVR-FO/GDY achieves a peak NH₃ yield (Y_NH3) of 127.92 ± 9.11 μg·h^-1·mg_cat.^-1 and a FE of 59.48% ± 2.57% at 0.255 V vs. RHE [Figure 4C], vastly outperforming pristine Fe₃O₄ and bare GDY. Interfacial regulation can also effectively mitigate competitive HER. Fang et al. constructed a self-standing 3D GDY/Co₂N composite by nitriding cobalt layered double hydroxide (CoLDH) nanowires, followed by in situ growth of GDY films [Figure 4D]. Transmission electron microscope (TEM) imaging [Figure 4E] illustrates the core-shell nanowire morphology when an ultrathin GDY coats the Co₂N core. The rich acetylenic bonds in GDY draw electrons from Co₂N, creating electron-deficient Co sites that favor N₂ adsorption while increasing the kinetic barrier for H chemisorption. In neutral media, GDY/Co₂N maintains stable performance across multiple cycles, delivering a high NH₃ yield rate and FE [Figure 4F]^[83].

Photocatalytic nitrogen fixation represents another promising direction for GDY heterostructures, wherein GDY acts as an electron acceptor to accelerate photogenerated carrier separation and lower activation barriers^[162,163]. Liu et al. reported porous GDY loaded with cobalt oxide quantum dots (GDY@CoO_xQD) [Figure 4G]^[160]. HRTEM [Figure 4H] shows ultrasmall CoO_xQDs (~3.75 nm) uniformly anchored across the porous GDY nanosheets. Under light irradiation in water, the mixed Co²⁺/Co³⁺ valence states and surface plasmon resonance (SPR)-like behavior drive directional electron flow to GDY. In aqueous testing [Figure 4I], GDY@CoO_xQD yields an extraordinary average NH₃ formation rate of 19,583 μmol_NH3·g_cat^-1·h^-1, whereas nonprotonic solvents or control catalysts yield negligible amounts of ammonia, confirming that water is the proton donor^[160]. Fang et al. developed a Janus magnetite/GDY nanorod heterostructure (GDY@Fe-B). Rod-shaped GDY@Fe₃O₄ (GDY@Fe-B) was controllably synthesized [Figure 4J]. HRTEM [Figure 4K] displays distinct lattice fringes of GDY (0.365 nm) and Fe-B (0.246 nm), with nanorod lengths distributed approximately 15-25 nm (inset). Under light and magnetic field assistance, the Janus interface exhibits enhanced charge separation. Consequently, compared with the GDY, Fe-B, and non-Janus GDY@Fe-A controls, GDY@Fe-B maintains superior photocatalytic stability over 8 cycles [Figure 4L], achieving markedly higher NH₃ yields. This study fully exploits the structural and intrinsic properties of GDY and pioneers a new avenue for photocatalysis^[161]. In a single-molybdenum-atom-decorated hydrogen-substituted graphdiyne photocathode system (Mo₁/HsGDY@Cu₂O)^[84], Cu₂O generates photogenerated electrons, while the alkynyl-rich network of HsGDY serves not only as a charge transport channel but also efficiently dissociates water to supply active H·. Concurrently, the adjacent Mo1 single-atom sites function as robust centers for N₂ adsorption and activation, markedly lowering the hydrogenation activation barrier. Under standard simulated sunlight irradiation [Air mass (AM) 1.5G, 100 mW·cm^-2, 0 V vs. RHE], this system delivers an NH₃ yield rate of 15.8 μg·h^-1·cm^-2 with an FE of 42.8%. Remarkably, under 10-sun concentrated solar illumination, the NH₃ yield rate surges to a record 78.9 μg·h^-1·cm^-2 alongside a FE of 38.9%, retaining 86% of its initial catalytic activity after continuous operation for 240 h. This breakthrough further substantiates the universal utility of GDY-based materials in stabilizing single-atom sites, mediating in situ active hydrogen supply, and modulating interfacial charge dynamics.

GDY-based catalysts exhibit exceptional catalytic activity in photocatalytic nitrogen fixation, primarily due to GDY’s unique framework structure and strong electronic coupling with active centers^[164,165]. First, the intrinsic uniform microporous structure and the enyne-rich backbone (sp/sp²-hybridized carbon) endow GDY with a highly heterogeneous surface charge distribution and strong reducibility, providing ideal anchoring sites for active metal species and effectively preventing their aggregation and deactivation during the reaction. Second, pronounced interfacial charge transfer and orbital hybridization occur between GDY and the supported metals, which, under light irradiation, accelerate the dynamic valence-state transitions of the metals and facilitate efficient electron transfer to the π* antibonding orbitals of adsorbed N₂, thereby substantially reducing the N≡N bond strength and decreasing the protonation energy barrier. Moreover, GDY not only significantly enhances the localized SPR effect but also serves as a fast electron-transport channel, effectively suppressing photogenerated charge-carrier recombination and improving the apparent quantum efficiency.

Integrating low-dimensional metals, from QDs^[171] and subnanometer clusters^[172] to single-atom sites^[173], onto GDY offers an effective platform for the electrochemical reduction of nitrogenous species. Catalytic design and interface engineering play a central role in driving nitrate electroreduction^[167]. A prime example is the Cu/Cu_xO/GDY catalyst engineered by Feng et al. [Figure 5A]^[85]. The proposed reaction scheme exploits spatial catalytic coupling, in which the Cu/Cu_xO interface promotes the initial conversion of NO₃^- to NO₂^-, after which the surrounding GDY matrix captures the released NO₂^- to drive subsequent hydrogenation to NH₃. HRTEM [Figure 5B] reveals intimate phase boundaries between the Cu_xO(110) (0.286 nm) and Cu(111) (0.209 nm) domains on GDY. This cooperative pathway yields an NH₃ production rate (Y_NH3) exceeding 34,000 μg·h^-1·mg_cat^-1 and a FE close to 100% at -0.9 V vs. RHE [Figure 5C]. Extending this concept to bimetallic QDs, Wu et al. synthesized amorphous/crystalline PtCu_x QDs on GDY (PtCu_x/GDY) via microwave-assisted anchoring and thermal annealing [Figure 5D]. Characterization revealed “incomplete charge transfer” across the QD-GDY heterojunction interface [Figure 5E], where localized electronic redistribution stabilized mixed valence states (Pt⁰/Pt²⁺ and Cu⁰/Cu²⁺) to prevent intermediate overbinding. Consequently, PtCu_x/GDY achieves a Y_NH3 of 345.3 ± 38.9 μmol·h^-1·cm^-2 and an FE of 96.5 ± 5.1% at -0.5 V vs. RHE [Figure 5F]^[86]. Ligand-mediated electronic tuning allows precise control over the local coordination sphere. Wang et al. introduced fluorine modifications to single Pd atoms on GDY (Pd/GDY-F). The chemical structure [Figure 5G] shows how electron-withdrawing F atoms on the aromatic ring alter the conjugated backbone, increasing the oxidation state of the central Pd site. Aberration-corrected HAADF-STEM [Figure 5H] verifies the atomic dispersion of Pd. For NtRR, Pd/GDY-F delivers an NH₃ yield exceeding 5,000 μg·h^-1·mg_Pd^-1 at -1.1 V vs. RHE [Figure 5I], significantly outperforming the other catalysts [Figure 5J]. This is because F-induced electron withdrawal increases the activation barrier for H* formation, mitigating the competitive HER^[87].

Zero-valent metal atom arrays offer an alternative approach to single-site catalysis. Zheng et al. constructed a zero-valent copper single-atom array on GDY (Cu⁰/GDYNA) through in situ coordination and self-reduction of Cu²⁺ on 3D GDY nanoarrays [Figure 5K and L]. HAADF-STEM [Figure 5M] confirms the presence of dense, monodisperse Cu⁰ single atoms anchored within acetylenic cavities. At -2.0 V vs. SCE, Cu⁰/GDYNA delivers a maximum FE of 81.25% [Figure 5N]. The synthesis and application of Cu⁰/GDYNA catalysts open up a new field of GDY-based ACs^[88]. Complementing these experimental efforts, theoretical calculations provide mechanistic insight into overcoming linear scaling relationships across single-atom, dual-atom, and multi-atom configurations. DFT modeling of single-atom Os/GDY^[174] indicated that it is an effective NtRR catalyst with a limiting potential as low as -0.37 V and pronounced suppression of competing reactions. In dual-atom configurations such as TiCu@GDY, calculations demonstrate a site-coupling effect: electrophilic Ti promotes nitrate activation, whereas adjacent Cu lowers the water dissociation barrier (ΔG_act = 0.64 eV) to supply H, yielding a theoretical limiting potential of -0.20 V^[175]. Extending this to multicenter clusters, N-doped carbon-supported trimers (Co₂Ni, Co₂Cu, and Fe₂Ni) show a theoretical limiting potential of 0.00 V vs. RHE without a distinct potential-determining step in NtRR^[176]. Moreover, Mn₃-GDY clusters induce spin polarization, which triggers a pathway separation mechanism (NO₃H → NO₂* + OH*), reducing the limiting potential to 0.23 V and lowering the NH₃ desorption barrier to 0.18 eV^[177]. These studies demonstrate that integrating the sp-hybridized carbon network of GDY with low-dimensional metal centers effectively optimizes intermediate adsorption, reduces rate-limiting energy barriers, and suppresses competing HER during electrocatalytic nitrogenous transformations.

Beyond single-component metal/metal compound catalysts, GDY-based heterojunctions offer a particularly powerful platform for NtRR by exploiting synergistic interfacial effects. The sp- and sp²-hybridized carbon network and alkynyl bonds of GDY modulate inorganic phase growth while inducing local strain and defects. This creates efficient interfacial charge-transport pathways that optimize intermediate adsorption and suppress the HER^[89,90,92].

Zhang et al. synthesized a Cu₃N/GDY catalyst with a nitride/GDY interface that operates via an in situ vacancy generation mechanism [Figure 6A and B]^[89]. Under an applied potential, GDY accelerates water dissociation to generate reactive hydrogen radicals, which attack the lattice nitrogen of Cu₃N to form nitrogen vacancies. The resulting nitrogen-vacancy sites and GDY matrix modulate the local electron density of adjacent Cu atoms, thus promoting NO₃^- adsorption and hydrogenation, achieving an ammonia yield rate (Y_NH3) of 35,280 μg·h^-1·mg_cat.^-1 and a FE of 98.1% at -0.9 V vs. RHE [Figure 6C and D]. Figure 6E and F show the synthesis of the Cu₂O/GDY composite using electron beam irradiation. Optimizing the Cu loading prevented nanoparticle aggregation while maintaining a high active-site density, enabling the catalyst to achieve an FE of 94% and an NH₃ yield of 26,997 μg·h^-1·mg_cat.^-1 at -1.7 V vs. Hg/HgO [Figure 6G and H]^[90]. Furthermore, Cu_xO grown on pyridine-nitrogen-dominated nitrogen-doped GDY^[91] utilizes the synergistic effect of pyridine nitrogen and Cu_xO to accelerate H* formation, achieving an 89% FE in a fluidized bed.

Introducing planar defects into one-dimensional structures can accelerate reaction kinetics. Luan et al. synthesized grain boundary-rich one-dimensional CuCo₂O_x/GDY nanowires, where the coordination of sp carbon with metal sites induces high-angle grain boundaries and localized strain in the nanowires [Figure 6I and J]. When used for NtRR, CuCo₂O_x/GDY achieved ~100% FE and a yield rate of 3,332 μg·cm^-2·h^-1 in 1.0 M KOH + 0.1 M NO₃^- aqueous solution at a potential of -0.132 V vs. RHE [Figure 6K]. Mechanistic analysis shows that interfacial defects on CuCo₂O_x/GDY could effectively reduce the energy barrier of the deoxygenation step (*NO₂ → *NO → *N) from 3.23 to 1.63 eV [Figure 6L]^[92]. Similarly, Co₃O₄/GDY nanowires^[93] achieved 92.45% FE by utilizing sp-C–Co bonds and incomplete charge transfer to facilitate continuous electron transfer at -1.05 V vs. RHE. GDY heterojunctions can also be extended to manganese-based systems [GDY-MnO_x; Figure 6M]. HRTEM [Figure 6N] confirmed that the interplanar spacing of MnO_x was 0.49 nm. The charge transfer from sp carbon to Mn reduced the average oxidation state of Mn from 3.74 to 3.52, increasing the proportion of Mn³⁺ sites. GDY-MnO_x achieved 95.4% FE and 463.4 μmol·h^-1·cm^-2 at -0.891 V vs. RHE [Figure 6O]. Isotope labeling experiments [Figure 6P] confirmed that the ammonia was entirely derived from nitrate reduction^[95].

Leveraging the inherent properties of GDY, diverse GDY-based heterojunction catalysts (e.g., h-FeCoNiPBA@GDY and Fe₃C@GDY) have been rationally fabricated and deployed for electrocatalytic nitrogen fixation toward ammonia synthesis^[99]. The integration of GDY with metal coordination nanostructures offers a complementary strategy for constructing high-performance NtRR catalysts. The well-defined porous architecture and abundant coordination sites of metal-organic coordination compounds, when coupled with GDY’s exceptional conductivity and electronic tunability, create interfaces that enhance nitrate-to-ammonia conversion. Zhao et al. developed a hybrid architecture by growing a conformal GDY layer directly on zeolitic imidazolate framework nanocubes (ZIFNC@GDY)^[96]. As shown in Figure 7A-C, Co²⁺ and 2-methylimidazole self-assemble into ZIF-67 nanocubes (ZIFNC) nanocubes, which then serve as a template to catalyze the growth of a GDY shell. ZIFNC and GDY function as the electron acceptor and donor, respectively, linked through covalent sp-C–Co and sp-C–N bonds to establish an efficient charge-transfer channel. This configuration increases the electron density on the GDY surface and enhances nitrate electroreduction activity. High-magnification TEM images [Figure 7D and E] verify the well-defined architecture, showing a crystalline ZIFNC core encapsulated by a uniform GDY layer. The high-resolution image reveals 0.251 nm lattice fringes for the ZIFNC core and a 0.335 nm interlayer spacing for the outer GDY layer [Figure 7E]. In neutral aqueous media, ZIFNC@GDY outperforms bare ZIFNC across the entire potential range [Figure 7F and G], reaching a peak FE_NH3 of 98.51% ± 0.75% with an ammonia yield rate of 0.40 ± 0.02 mmol·h^-1·cm^-2 at -1.4 V vs. SCE (-0.745 V vs. RHE).

To address intermediate adsorption mismatches during nitrate reduction, Wang et al. designed a dual-interface tandem catalyst (NiBDC@HsGDY@Cu) by linking ultrathin Ni-BDC MOF nanosheets with HsGDY carrying Cu single atoms and clusters^[97]. As illustrated in Figure 7H, ultrathin NiBDC nanosheets are conformally wrapped with a thin HsGDY layer via the Glaser coupling of 1,3,5-triethynylbenzene, followed by the electrodeposition of Cu single atoms/clusters onto the HsGDY framework. Within this 0-3.6 nm interface, HsGDY acts as a conductive bridge. Unsaturated Ni²⁺ sites promote H₂O cleavage to generate active *H species that spill over via HsGDY to Cu sites, while NO₂^- released from Cu sites diffuses to Ni²⁺ sites to complete the cascade conversion of NO₃^- to NH₃. In 1 M KOH + 0.1 M KNO₃, NiBDC@HsGDY@Cu retained high selectivity (FE_NH3 > 90%) across a broad window from -0.01 to -0.51 V vs. RHE [Figure 7I], markedly exceeding the performance of individual HsGDY@Cu and NiBDC. At a low overpotential of -0.11 V vs. RHE, the catalyst achieves an FE_NH3 of 95.5% and a Y_NH3 of 0.321 mmol·h^-1·cm^-2.

For bimetallic coordination systems, Ma et al. synthesized a self-supported NiCoBDC@HsGDY nanowire array on carbon paper^[98]. As depicted in Figure 7J, NiCo carbonate hydroxide (NiCoHC) nanowires serve as initial templates. A protective HsGDY layer is polymerized on their surface via Glaser coupling, followed by a solvothermal anion-exchange reaction with 1,4-benzenedicarboxylic acid (BDC). The outer HsGDY shell acts as a physical cage that confines the in situ transformation, yielding well-aligned NiCoBDC@HsGDY core-shell nanowires, as shown by the SEM image in Figure 7K. Electronic coupling between Ni²⁺ and Co²⁺ drives partial charge transfer from Ni²⁺ to coordinatively unsaturated Co²⁺ sites through bridging O₂^- ligands, simultaneously optimizing NO₃^- deoxygenation at Co²⁺ and H₂O activation at Ni²⁺. Consequently, NiCoBDC@HsGDY outperforms its monometallic counterparts (CoBDC@HsGDY and NiBDC@HsGDY) as well as pristine NiCoBDC in terms of geometric yield [Figure 7L], delivering a Y_NH3 of 0.56 mmol·h^-1·cm^-2 with an FE_NH3 of 99.1% at -0.34 V vs. RHE in alkaline media.

These breakthroughs underscore that graphdiyne is a uniquely powerful and versatile platform for engineering advanced NtRR electrocatalysts. By integrating various active domains onto the sp/sp² carbon matrix of GDY, researchers can trigger synergistic phenomena such as incomplete charge transfer, interfacial strain, and tuned coordination environments. These modifications fundamentally bypass the scaling limitations of single-site catalysts, lower energy barriers for rate-limiting deoxygenation and hydrogenation steps, and effectively eliminate the competitive HER. As a result, GDY-based heterostructured architectures provide a clear roadmap for achieving ultrahigh-rate, selective, and durable nitrate-to-ammonia electrosynthesis, bridging the gap between fundamental catalyst design and practical industrial water treatment/energy conversion applications.