Synthetic nitrogen (N) fertilizers, especially urea (CO(NH2)2) with the highest nitrogen content, nourish crop production to underpin human life. The conventional urea synthesis relies on harsh industrial processes, which consumes approximately 2% of annual global energy. Instead, electrocatalysis is an emerging sustainable technology to produce urea at ambient conditions. Herein, by directly coupling nitrate (NO3 − ) with carbon dioxide (CO2) on an indium hydroxide catalyst, we realize highly selective urea electro-synthesis at ambient conditions. We derive that CO2 can suppress adverse hydrogen evolution reaction by transforming the surface semiconducting behaviour of the model catalyst in our work.The key step of C-N coupling initiates at an early stage through the reaction of *NO2 with *CO2 intermediates owing to the low energy barrier on {100} facets, hence the subsequent urea is synthesized with high Faradaic efficiency, nitrogen selectivity, and carbon selectivity, which reach 53.4%, 82.9% and ~100%, respectively. This work offers a desirable urea synthesis route and provides deep insights into the fundamental origin of C-N coupling for guiding other sustainable synthesis of indispensable chemicals.

Synthesizing urea from nitrate and carbon dioxide through an electrocatalysis approach under ambient conditions is extraordinarily sustainable. However, this approach still lacks electrocatalysts developed with high catalytic efficiencies, which is a key challenge. Here, we report the high-efficiency electrocatalytic synthesis of urea using indium oxyhydroxide with oxygen vacancy defects, which enables selective C–N coupling toward standout electrocatalytic urea synthesis activity. Analysis by operando synchrotron radiation–Fourier transform infrared spectroscopy showcases that *CO2NH2 protonation is the potential-determining step for the overall urea formation process. As such, defect engineering is employed to lower the energy barrier for the protonation of the *CO2NH2 intermediate to accelerate urea synthesis. Consequently, the defect-engineered catalyst delivers a high Faradaic efficiency of 51.0%. In conjunction with an in-depth study on the catalytic mechanism, this design strategy may facilitate the exploration of advanced catalysts for electrochemical urea synthesis and other sustainable applications.

Interfacing epitaxial dinickel phosphide to 2D nickel thiophosphate nanosheets for boosting electrocatalytic water splitting

The electrochemical oxygen reduction reaction (ORR) mechanism was generally considered to be O2 → OOH* → O* → OH* → H2O (O* mechanism). This O* mechanism predicted reasonable ORR half-wave potential (E 1/2) of Co/N/C but abnormally underestimated the one of Fe/N/C. Herein, we highlight an unconventional 2OH* ORR mechanism (O2 → OOH* → 2OH* → OH* → H2O), which was often ignored because the free energies (ΔG) of 2OH* and O* are equal, according to the famous scaling relation: 2ΔG(OH*) = ΔG(O*). This scaling relation is true for traditional catalysts with near-continuous active sites. We find a different scaling relation: ΔG(2OH*) = ΔG(O*) + 1.5 eV on single-atom catalysts (Me/N/C, Me = Fe, Co, etc.) and suggest that the 2OH* mechanism should not be overlooked. In consideration of both O* and 2OH* mechanisms, the ORR E 1/2 values of Co/N/C and Fe/N/C are in good agreement with experimental results. This work reveals the structure dependence of ORR reaction mechanisms and scaling relations in single-atom catalysis, and it is also heuristic for other reactions, such as O2 evolution and N2 reduction on single-atom catalysts.

With the maximum atom-utilization efficiency, single atom catalysts (SACs) have attracted great research interest in catalysis science recently. To address the following key challenges for the further development of SACs: i) how to stabilize and avoid the aggregation of SACs, ii) how to enhance the specific surface area and conductivity of supports, and iii) how to achieve scalable mass production with low cost, a SAC consisting of single Pd atoms anchored on well-designed graphdiyne/graphene (GDY/G) heterostructure (Pd 1 /GDY/G) is synthesized. Pd 1 /GDY/G exhibits high catalytic performance, as demonstrated by the reduction reaction of 4-nitrophenol. Furthermore, density functional theory calculation indicates that graphene in the GDY/G heterostructure plays a key role in the enhancement of catalytic efficiency owing to the electron transfer process, deriving from the gap between the Fermi level of graphene and the conduction band minimum of GDY. The GDY/G heterostructure is a promising support for the preparation of extremely efficient and stable SACs, which can be used in a broad range of future industrial reactions.