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Page 2 of 12 Chi et al. J. Mater. Inf. 2025, 5, 11 https://dx.doi.org/10.20517/jmi.2024.49

INTRODUCTION
With a notable high nitrogen content of 46%, urea [i.e., CO(NH ) ] is widely used worldwide as a nitrogen
2 2
[1]
fertilizer, whose annual synthesis has exceeded 100 million tons . In addition, urea has various applications,
such as cosmetic formulations, synthesis of engineered wood products, and monosodium glutamate . As a
[2]
consequence, sustainable and efficient urea synthesis is of great importance. In the present industry, the first
[3,4]
step of urea synthesis relies predominantly on the Haber-Bosch process for ammonia (NH ) synthesis ,
3
which requires a high temperature (~700 K) and an elevated pressure (~100 bar). Here as well, as a second
step, the energy-intensive Bosch–Meiser process that combines NH with CO to synthesize urea
[5]
3
2
necessitates elevated temperature (~423-473 K) and pressure (~150-200 bar) . Annually, the entire
[6]
[7]
synthesis process not only accounts for approximately 1% to 2% of total energy consumption , but also
consumes 80% of global NH synthesis . Therefore, it is imperative to develop a strategy for urea synthesis
[8]
3
with clean, environmentally friendly, energy-efficient, and resource-conserving features.
Electrocatalysis is recognized as a promising alternative since it directly converts N to urea under milder
[9]
2
conditions, thereby bypassing the need for NH synthesis and significantly conserving energy and resources.
3
The electrocatalytic strategy involves the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms
[Figure 1A]. The difference between them is that N and CO are co-adsorbed or not on the catalyst.
2
Following the adsorption process, a key intermediate NCON is formed through the C-N coupling. Then,
*
hydrogenation of NCON occurs gradually to form urea by the distal or the alternate mechanism. We note
*
that the intermediate NCON has been formed by Chen et al. through the LH mechanism and
*
experimentally identified by analyzing the infrared spectrum vibration signal . Over there, the energy
[10]
barrier (E ) of the C-N coupling and the maximum free energy change in the whole reaction pathway
b
(ΔG ) serve as the critical indicators for evaluating the catalyst performance. The key C-N coupling
max
process calls for the challenging destruction of the N≡N, the transfer of CO from its adsorption site to N
atoms, and the creation of a C–N bond. However, the cleavage of the N≡N is highly challenging due to its
great activation energy of ~941 kJ/mol . To effectively catalyze this step, the catalyst should strongly bind
[11]
with N , aiming to fully activate the corresponding N . In this context, triatomic catalysts are able to act as
2
2
excellent choices, where two of the constituent atoms can be designed to work in tandem to activate N
2
while the third one is optimized to weaken CO adsorption. To achieve the above goal, transition metals
(TMs) can be selected due to their unfilled d-orbitals, which participate in a “donor-acceptor” mechanism
[12]
with the adsorbate . As an ideal substrate, the two-dimensional (2D) γ-graphdiyne (γ-GDY) can be used to
support TMs, because it, as the most stable graphdiyne isomer [13,14] , provides large pores to accommodate
three TM atoms and the excellent stability and electrical conductivity [15-17] .
Based on the considerations mentioned above, the selection of elements that compose TMs@γ-GDY is
crucial. In conventional electrocatalyst design, researchers often use the volcano plot to select elements and
design catalysts, where the adsorption energy is taken as the variant. However, this method usually
considers the first and last steps of the catalytic reaction, neglecting the overall intermediate processes. With
the development of electrocatalysis, we have gradually realized that the active sites in the catalytic reaction
process are not fixed to one location but change during the reaction progress. Therefore, considering the
intermediate steps in catalyst design is particularly important. Since intermediates in the reaction process
always move towards the sites with the highest adsorption energy, we calculate the adsorption energy of the
catalyst for intermediates in all the reaction steps, thereby optimizing each reaction step to promote the
transfer of active sites, break the scaling relationship, and improve catalytic performance.

In this work, using density functional theory (DFT) calculations, we designed the Fe Mo@γ-GDY catalyst
2
through the aforementioned design strategy. The catalyst exhibits a favorable limiting potential (U =
L