Electrochemical synthesis of high-value organonitrogen compounds using low-cost carbon-based and nitrogen-based precursors offers an economical and environmentally friendly alternative to traditional thermal catalytic methods. However, the complex electrochemical reactions occurring at the electrode surface present challenges in controlling selectivity and activity, especially in the production of complex substances such as N,N-dimethylformamide (DMF).
Recently, Professor Miao Zhong’s group from Nanjing University addresses this challenge through a new pathway of asymmetric adsorption and relay catalysis for C–N coupling, based on previous studies on electrochemical asymmetric coupling (Nature 2020, 581, 178–183; Nat. Commun. 2023, 14, 1298). They developed a composite WO2–NiOOH/Ni catalyst that exhibits different adsorption energies for carbon (C) and nitrogen (N) species, enabling efficient production of DMF. WO2 selectively promotes the electrooxidation of dimethylamine (DMA) to produce strongly surface-bound (CH3)2N*, while NiOOH facilitates the electrooxidation of methanol to generate more weakly bound *CHO. The difference in binding energies of the C and N intermediates accelerates the C–N coupling at the WO2–NiOOH interface. In situ infrared spectroscopy, isotope labeling experiments, quasi-in situ electron paramagnetic resonance trapping experiments, and electrochemical operation experiments reveal the C–N coupling mechanism and the enhanced selectivity and activity of DMF synthesis. In situ X-ray absorption spectroscopy and post-reaction transmission electron microscopy studies validate the stability of WO2–NiOOH/Ni during prolonged electrochemical operation. Over an 80-hour DMF production cycle at an industrial current density of 100 mA cm−2, approximately 50% DMF Faradaic efficiency and a DMF yield rate of ~0.44 mmol cm−2 h−1 were achieved.
Figure 1: Current industrial route and proposed relay catalytic pathway for the synthesis of DMF
DMF plays a pivotal role as a chemical feedstock and is widely used to manufacture synthetic fibers, pharmaceuticals, polyurethane, and electronic devices. Traditional industrial DMF-synthesis processes (Figure 1a) rely on energy-intensive thermo-catalytic methods that use fossil-fuel-derived carbon monoxide and DMA as reactants at elevated pressures (2–10 MPa) and temperatures (80–100 °C). This study presents, for the first time, an economically feasible method for the electrosynthesis of DMF using methanol and DMA as raw materials and proposes a relay catalytic method for the electrocatalytic C–N coupling production of DMF (Figure 1b).
Figure 2: Structural and compositional characterization of the WO2–NiOOH/Ni catalyst
Electron microscopy characterization confirmed the presence of distinctly mixed NiOOH/WO2 nanoparticles on the metal Ni surface, with a clear observation of the NiOOH/WO2 interface. X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) were utilized to monitor the changes in the oxidation states of metals within the WO2–NiOOH/Ni catalyst during the electrooxidation process, elucidating the formation of NiOOH and WO2 during the electrosynthesis of DMF.
Figure 3: Electrochemical operational experiments and in situ spectroscopic characterization to validate the mechanism
Quasi-in situ electron paramagnetic resonance spectroscopy, in situ infrared spectroscopy, and electrochemical operational experiments were employed to confirm the formation of C- and N-intermediates during the electrooxidation process, as well as the subsequent relay catalytic process of thermochemical C–N coupling to synthesize DMF.
Figure 4: Performance of the WO2–NiOOH/Ni catalyst in the electrosynthesis of DMF and N,N-dimethylacetamide
The synthesized WO2–NiOOH/Ni catalyst achieved ~50% DMF Faradaic efficiency at a current density of 100 mA cm−2, maintaining stability over five consecutive 16-hour cycles. A 15 cm2 electrode produced 1.4 g of DMF in three hours. The feasibility of C–N coupling for the synthesis of other amides was validated through the electrosynthesis of N,N-dimethylacetamide using ethanol and DMA.
This study, titled “Sustainable Electrosynthesis of N,N-Dimethylformamide via Relay Catalysis on Synergistic Active Sites,” was published online in the Journal of the American Chemical Society on July 25, 2024 (doi: 10.1021/jacs.4c07142). Prof. Miao Zhong and Prof. Haoshen Zhou are the corresponding authors. Weihang Li is the first author. The authors thank the National Natural Science Foundation of China, the National Key R&D Program of China, the Frontiers Science Center for Critical Earth Material Cycling, and the Jiangsu Province Innovation and Entrepreneurship Talent Program, etc for the support.
