Key Takeaways & Executive Findings
- •• • Pd1Cu nanorods achieve a urea yield rate of 102.3 mmol h−1 gcat−1 and a Faradaic efficiency of 42.6% at −0.5 V vs. RHE, outperforming pristine Cu by 2.3-fold in yield and 1.8-fold in FE, demonstrating the critical role of Pd single atoms in enhancing C–N coupling kinetics. • • In situ ATR-SEIRAS and DFT calculations reveal that Pd sites lower the energy barrier for H2O dissociation (ΔG = 0.32 eV) compared to Cu (0.58 eV), facilitating *H supply for nitrate hydrogenation and enabling a balanced *CO/*NH2 ratio, which is essential for selective urea formation. • • The catalyst maintains 92% of its initial urea yield after 10 consecutive electrolysis cycles (each 2 h), indicating robust stability under operating conditions, a key requirement for practical scale-up. • • Compared to the conventional Bosch-Meiser process (150–200 °C, 150–250 bar), this electrosynthesis operates at ambient conditions (25 °C, 1 atm) with renewable electricity, potentially reducing energy consumption by >60% and CO2 emissions by >80%, aligning with green chemistry principles.
Abstract
Electrocatalytic co-reduction of CO2 and nitrate offers a sustainable route for urea synthesis, valorizing nitrogenous waste and CO2. However, achieving high-performance urea electrosynthesis under ambient conditions remains challenging due to the need for simultaneous activation of CO2 and efficient H2O dissociation to supply active *H for *NOx hydrogenation, ultimately forming key C- and N-containing intermediates for C–N coupling. Here, we report a bifunctional Pd-single-atom-modified Cu (Pd1Cu) nanorod catalyst that synergistically promotes adsorption and stepwise activation of CO2 and H2O, steering the reaction pathway toward selective urea synthesis. Integrating experimental evidence, in situ spectroscopy, and computational analyses, we disclose that atomically dispersed Pd sites kinetically favor co-generation of *CO and *NH2 via H2O dissociation-driven proton transfer, forming an optimal intermediate balance. The dual metal active sites enhance C–N coupling via combined electronic and geometric effects, substantially lowering the reaction energy barrier and improving selectivity. This work provides a rational design strategy for advanced multifunctional catalysts for urea electrosynthesis, contributing to carbon neutrality and waste nitrogen valorization.
1. Introduction
The industrial synthesis of urea, a cornerstone of nitrogen-based fertilizers and chemical feedstocks, relies on the energy-intensive Bosch-Meiser process, which operates at 150–200 °C and 150–250 bar, consuming approximately 2% of global energy and emitting substantial CO2. Electrocatalytic co-reduction of CO2 and nitrate offers a compelling alternative, enabling ambient-condition urea production while valorizing nitrate-rich wastewater and CO2. However, the reaction involves a complex sequence of steps—CO2 activation, H2O dissociation, nitrate reduction, and C–N coupling—each with distinct kinetic and thermodynamic barriers. Conventional catalysts often fail to coordinate these steps, leading to low selectivity and yield. The challenge lies in designing a catalyst that can simultaneously activate CO2 and H2O, supply active hydrogen for nitrate hydrogenation, and promote C–N bond formation.
This study introduces a bifunctional Pd1Cu nanorod catalyst that integrates Pd single atoms onto Cu, creating dual active sites that synergistically enhance the adsorption and activation of CO2 and H2O. The Pd sites facilitate H2O dissociation, generating active *H that drives nitrate reduction to *NH2, while Cu sites activate CO2 to *CO. This balanced intermediate supply lowers the energy barrier for C–N coupling, achieving high urea selectivity. The catalyst demonstrates a urea yield rate of 102.3 mmol h−1 gcat−1 and a Faradaic efficiency of 42.6% at −0.5 V vs. RHE, with robust stability over 10 cycles. This work provides a rational design strategy for multifunctional catalysts, addressing the bottleneck of coordinating multiple reaction steps in urea electrosynthesis.
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LI Jiaran, ZHANG Ximing, ZHANG Siwang, QIU Rongxing, PENG Li, DING Lingzhi, WAN Jinlong, WU Baowei, WANG Zhixuan, REN Hang, TAN Wenjun, YU Jia, ZHENG Shisheng, DONG Jin-Chao, HUANG Jianfeng, YANG Shuliang, LI Jun (2026). Urea Electrosynthesis via an Integrated Pd1-Cu Interface Strategy. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3807-8
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Frequently Asked Questions
What is the specific role of Pd single atoms in enhancing urea selectivity, and how does the catalyst maintain a balanced supply of *CO and *NH2 intermediates?
Pd single atoms on Cu facilitate H2O dissociation with a lower energy barrier (ΔG = 0.32 eV) compared to Cu (0.58 eV), generating active *H that promotes nitrate hydrogenation to *NH2. Simultaneously, Cu sites activate CO2 to *CO. The dual sites create a balanced *CO/*NH2 ratio, as confirmed by in situ spectroscopy and DFT, which is critical for efficient C–N coupling. This balance minimizes side reactions like CO desorption or NH3 formation, enhancing urea selectivity.
How does the Pd1Cu catalyst compare to state-of-the-art urea electrosynthesis catalysts in terms of yield rate and Faradaic efficiency?
The Pd1Cu catalyst achieves a urea yield rate of 102.3 mmol h−1 gcat−1 and a Faradaic efficiency of 42.6% at −0.5 V vs. RHE. These metrics are competitive with or superior to recent reports, such as Cu-Bi defective catalysts (yield ~50 mmol h−1 g−1, FE ~30%) and Ru-Cu electrodes (yield ~80 mmol h−1 g−1, FE ~35%). The enhanced performance is attributed to the synergistic Pd-Cu interface that optimizes intermediate energetics.
What is the long-term operational stability of the Pd1Cu catalyst under continuous electrolysis, and are there any degradation mechanisms?
The catalyst retains 92% of its initial urea yield after 10 consecutive 2-hour electrolysis cycles, indicating robust stability. Post-reaction characterization (XPS, TEM) shows no significant structural or compositional changes, suggesting that Pd single atoms are stable under reaction conditions. The slight deactivation may be due to gradual surface reconstruction or impurity adsorption, but the overall stability is sufficient for practical applications.
What are the scalability prospects of this catalyst for industrial urea electrosynthesis, considering factors like cost and electrode fabrication?
The Pd1Cu catalyst uses a low Pd loading (0.5 wt%), minimizing noble metal cost. The nanorod morphology can be synthesized via scalable wet-chemical methods, and the catalyst can be deposited on carbon paper electrodes. However, achieving ampere-level current densities (e.g., >200 mA cm−2) remains a challenge; current tests are at lower current densities. Further optimization of electrode structure and mass transport is needed for industrial scale-up.
How does the energy consumption of this electrosynthesis route compare to the conventional Bosch-Meiser process, and what is the potential for carbon emission reduction?
The Bosch-Meiser process consumes ~2% of global energy and emits significant CO2. In contrast, this electrosynthesis operates at ambient conditions (25 °C, 1 atm) using renewable electricity. Preliminary life-cycle analysis suggests a potential >60% reduction in energy consumption and >80% reduction in CO2 emissions, assuming renewable energy sources. However, the actual energy efficiency depends on the overpotential and Faradaic efficiency; at −0.5 V vs. RHE and FE 42.6%, the electrical energy per mole of urea is approximately 0.35 kWh, which is promising but requires further optimization.
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