Ammonia (NH3) is a vital nitrogen feedstock for producing fertilizers, pharmaceuticals, dyes, high-energy materials, and resins, and it is also a promising hydrogen storage medium due to its high hydrogen content [1,2]. The Haber-Bosch process (N2 + 3H2 → 2NH3) has been the primary industrial method for NH3 synthesis since World War II, but it requires harsh conditions (400–500 °C and 150–250 atm) and emits substantial greenhouse gases, especially CO2 [[3], [4], [5], [6]]. Inspired by biological nitrogen fixation, the electrocatalytic nitrogen reduction reaction (N2RR) under ambient conditions offers a green, sustainable alternative for NH3 production when powered by renewable energy [7,8]. However, the major challenge remains in developing stable, efficient, and cost-effective catalysts [9]. Single-atom catalysts (SACs) have emerged as promising candidates due to their highly under-coordinated active sites, which provide superior catalytic activity over bulk materials [10]. Their intrinsic catalytic properties can be further tuned by coordination with various substrates [[11], [12], [13]]. SACs have demonstrated efficiency in multiple electrocatalytic reactions including CO2 reduction (CO2RR) [[14], [15], [16], [17]], oxygen evolution (OER) [18], oxygen reduction (ORR) [19], hydrogen evolution (HER) [[20], [21], [22]], and N2RR [[23], [24], [25], [26]]. Two-dimensional materials such as graphene-like molybdenum disulfide (MoS2) have been extensively studied as SAC substrates due to their large surface area and unique electronic properties [[27], [28], [29], [30], [31]]. For example, Fe@MoS2 shows excellent N2RR catalytic activity with a 1.02 V activation barrier [32], and Co-doped MoS2-x nanosheets exhibit over 10 % faradaic efficiency and high NH3 yield at low overpotentials [33]. Despite these successes, the basal plane of MoS2 is relatively inert with catalytic activity largely limited to edge sites, restricting its HER and N2RR performance [[34], [35], [36], [37]].

Beyond direct catalytic mechanisms, understanding broader catalyst performance, including poisoning resistance and mass transport, is vital. Recent work on chlorinated volatile organic compound oxidation offers insights into deactivation mechanisms, informing the design of more robust NRR catalysts [38]. Furthermore, continuous advancements in materials for various catalytic processes provide significant lessons for NRR catalyst design. The progress of metal-organic framework (MOF) materials in selective catalytic reduction highlights their tunable properties and potential as versatile platforms for active site engineering [39]. The evolving field of 2D materials also presents new avenues. Studies on assembling lamellar g-C3N4 on hydrophobic films to create flexible film photocatalysts demonstrate innovative functionalization and performance enhancement applicable to diverse electrochemical systems [40]. Finally, the catalyst-electrolyte interface microenvironment significantly impacts reaction efficiency. Molecular dynamics simulations of competitive transport and adsorption, like CO2 and H2O in graphene nano-slit pores, underscore the importance of mass transfer effects in optimizing catalytic processes [41].

Electrocatalytic NH3 synthesis at ambient conditions is an environmentally friendly process powered by renewable electricity and conducted at room temperature and atmospheric pressure [42]. Since the initial report by Pickett et al. on ambient electrosynthesis of NH3 using a molecular catalyst [43], various heterogeneous electrocatalysts have been developed [[44], [45], [46]], including Bi4V2O11/CeO2 hybrids, Au/CeOx-RGO, 7b and Li+/poly (N-ethyl benzene-1,2,4,5-tetracarboxylic diimide) systems, which efficiently convert N2 in aqueous solutions. Theoretical predictions also suggest promising activity from single Mo atoms on defective boron nitride [9] FeN3-embedded graphene [47], and metal nitride surfaces [[47], [48], [49]]. A significant barrier to scalable ambient NH3 production is the difficulty of cleaving the strong N ≡ N triple bond (940.95 kJ/mol) and the complex, multistep N2RR mechanism. Additionally, understanding this mechanism is critical for catalyst design. Nitrogen-doped carbon materials have attracted attention for their low cost, high efficiency, and stability in N2RR [50]. Pyridinic and pyrrolic nitrogen species are especially important for electrocatalytic activity [51,52]. Co-doping with secondary heteroatoms such as B, S, or P can further enhance catalytic performance by modulating electronic properties and surface polarity [52,53]. However, the roles and mechanisms of co-doping in N-doped carbons for N2RR are not fully understood. Unlike graphene and graphdiyne, graphyne (GY) features a mixed sp–sp2 hybridization, forming a porous and π-conjugated structure that enables stronger binding with single metal atoms and richer electronic tunability [54]. These features make GY a distinct and promising platform for single-atom catalysis, especially for reactions like N2RR that benefit from enhanced charge transfer and molecular activation. In this study, we conduct a comprehensive first-principles investigation to evaluate the potential of single-atom transition metals (Fe, Mo, Ru, and W) anchored on graphyne (GY) as electrocatalysts for the nitrogen reduction reaction (N2RR). By analysing their structural stability, electronic properties, adsorption behaviour, and catalytic performance, we aim to identify active configurations capable of overcoming the limitations of pristine GY and conventional N2RR catalysts. Special attention is given to the competition between N2RR and the hydrogen evolution reaction (HER), a key challenge in aqueous media. Our findings provide deep insights into the structure–activity relationships of TM-GY systems and establish design guidelines for the rational development of efficient and selective electrocatalysts for sustainable ammonia synthesis.