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Meng et al. J. Mater. Inf. 2025, 5, 3 https://dx.doi.org/10.20517/jmi.2024.74 Page 7 of 25

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mechanism . Yang et al. reported that a single Mo atom supported on nitrogen-doped graphene (Mo /Gr -
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N G) has high activity and selectivity with low U (-0.50/-0.75 V) and high selectivity (40%/100%) via a new
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distal-to-alternating hybrid mechanism involving two spectator N molecules .
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Liu et al. demonstrated that defective graphene substrates could act as electron reservoirs during the NRR
process . In a series of single TM atom anchored divacancy 555-777 graphene systems (containing three
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pentagons and three heptagons constructed by removing two neighboring C atoms), MoN @555-777
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graphene sheets showed good catalytic activity with a low U of -0.57 V.
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Niu et al. explored a series of TM atoms (from Sc to Au) supported on graphitic carbon nitride (g-CN)
SACs for NRR . Due to high activity (with low U of -0.42, -0.39, -0.35, -0.29, and -0.39 V, respectively),
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high selectivity (100%, 100%, 100%, 94%, and 69%, respectively), and good kinetic stability, Nb, Mo, Ta, W,
and Re/g-CN were identified as efficient NRR electrocatalysts.
In summary, leveraging the advantages of Mo atom active centers inspired by natural nitrogenase and 2D
substrate materials holds great promise for achieving the catalytic conversion of N to NH under mild
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conditions. This can be realized by precisely tuning the coordination environment of Mo atoms.
Furthermore, a detailed and accurate characterization of the electronic structure of SACs is essential for
gaining a deeper understanding of their NRR activity .
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Non-Mo-based SACs
Fe-based SACs
Apart from Mo, Fe has garnered significant attention as an essential metal in nitrogenase enzymes
responsible for biological nitrogen fixation . For example, Fe-based catalysts have been widely used in the
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industrial Haber-Bosch process for NH synthesis . Li et al. demonstrated that a highly spin-polarized
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FeN active center on graphene with a local magnetic moment, which enhances N adsorption and
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activation, is a promising NRR catalyst at room temperature . Li et al. revealed that Fe(V)-PTC exhibited
[67]
excellent NRR activity among a series of TM-PTC (TM = Fe, Sc, Ti, V, Cr, Mn, Co, Ni, Cu) SACs, attributed
to the donation/back-donation mechanism . Sahoo et al. investigated the NRR mechanism for single Au
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and Fe atoms supported on C N monolayers. Their findings indicated that Fe-C N was a better catalyst than
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Au-C N, with a U of -0.7 V, owing to its stronger N adsorption energy .
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V-based SACs
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Vanadium nitrogenase is another biological nitrogenase system in nature . Therefore, researchers have
extensively studied the NRR performance of V-based SACs.
Among others, Choi et al. examined the NRR performance of single atoms anchored on defective graphene
derivatives by DFT computations . Ti@N and V@N were identified as efficient catalysts with low U and
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high selectivity due to strong back-bonding interactions between the hybridized d-orbital metal atoms and
the π orbital of N . Zhu et al. found that V/β -BM demonstrated good energy efficiency for NRR due to the
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acceptor-donor interaction between the V atom and N .
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Zhen et al. showed that TM@GDY nanomaterials (TM = Ti, V, Fe, Co, Zn, Rh, Hf) are promising SACs for
NRR, surpassing Ru(0001) stepped surfaces in performance. In particular, V@GDY exhibited the lowest U
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of -0.67 V . Most recently, Xu et al. screened V-, Fe-, Co-, and Ru-doped arsenene nanosheets, identifying
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them as efficient, low-cost NRR catalysts. In particular, during the NRR process, the arsenene nanosheet
acts as a medium for accepting and donating electrons, while VAs serves as a charging transmitter between
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