New type of unloaded mobile phase electrocatalytic system realizes high efficiency electrocatalytic synthesis of ammonia
Recently, the Center for Environmental and Energy Nanomaterials and the Liquid Phase Laser Processing and Preparation Laboratory of the Institute of Solid State Physics, Hefei Institute of Material Science, Chinese Academy of Sciences have made new progress in the study of electrocatalytic nitrogen reduction at room temperature and pressure. Related research results were published on Communications Chemistry with the title Efficient electrocatalytic nitrogen reduction to ammonia with aqueous silver nanodots. In this study, silver nanodots (AgNDs) catalysts were dispersed in the electrolyte, and titanium mesh was used as the current collector to construct a new type of unloaded mobile phase electrocatalytic system for efficient electroreduction of ammonia. Ammonia is an important chemical raw material and energy carrier, and it occupies an important position in the global economy. In recent years, the electrocatalytic nitrogen reduction (NRR) ammonia synthesis technology at room temperature and pressure has the advantages of green economy and low energy consumption, so it has received widespread attention and is expected to replace the traditional high energy consumption and high investment industrial Haber-Bosch (Haber-Bosch). )law. However, a major challenge currently facing NRR is the lower ammonia yield and selectivity. Therefore, it is of great significance to develop and construct highly efficient electrocatalysts for the synthesis of ammonia and rationally design electrocatalytic systems. In the early stage, the research group of the Center for Environmental and Energy Nanomaterials used a variety of strategies to improve the electrochemical ammonia synthesis activity of catalysts and catalytic systems. For example, they developed phosphorus-rich vacancy Cu3P nanosheets using defect engineering (J.Mater.Chem.A, 2020, 8, 5936-5942), oxygen-rich vacancy Nb2O5 nano-film (Chin.Chem.Lett. 2021) catalyst, and its large number of exposed vacancy defects provide abundant active sites for NRR; graphene-supported disulfide has been developed by size control Molybdenum quantum dots (MoS2 NDs/RGO) (ACS Sustainable Chem. Eng. 2020, 8, 2320-2326), carbonized corn gel supported copper nanocrystals (Cu NCs/CCG) (Inorg. Chem. Front. 2020, 7, 3555-3560) catalyst, small size quantum dots and nanocrystals are beneficial to expose more active sites; the use of liquid phase laser irradiation technology to fully release the single-atom active sites in the Co-SAs/NC catalyst to improve its NRR activity (ACS Appl.Energy Mater. 2020, 3, 6079-6086); the use of single-atom-nitrogen anchoring strategy (single-atom Co/Mo-Nx bond) can effectively inhibit the nitrogen-doped porous carbon catalyst in the NRR reaction process The decomposition of atoms causes false positives and provides reactive sites for NRR (Inorg. Chem. Front. 2021). In addition to regulating the activity of the catalyst, the corresponding catalytic system is also constructed to improve the ammonia yield and Faraday efficiency, such as the construction of a photoelectric NRR system. SAC) on the NRR reaction (Chin. Chem. Lett. 2021). Based on the above research foundation, the research group cooperated with the liquid phase laser processing and preparation laboratory to use the liquid phase laser ablation (LAL) method to prepare small-sized silver nanodots (~2.3 nm) catalysts and construct a new type Unloaded mobile phase electrocatalytic system. The construction of this reaction system is conducive to overcoming the disadvantages of supported catalysts in catalytic reactions. For example, (1) the loading of the catalyst is limited, which means that the active sites of the catalytic reaction are limited, which is not conducive to increasing the ammonia output; (2) the modification is The catalyst on the electrode surface is easy to deactivate, fall off or agglomerate during the reaction process, resulting in the reduction of active sites per unit mass; (3) The adsorption of N2 and the desorption of NH3 occur on the electrode surface, and the presence of an electric field may cause its reaction power Learning slows down. In this unloaded mobile phase electrocatalytic system, AgNDs prepared by laser rapid quenching have high reactivity, and small-sized nanodots can provide a large number of active sites (faces, edges, and corners). Taking advantage of the feature that AgNDs can be highly dispersed in an aqueous solution, the prepared AgNDs catalyst is dispersed in an electrolyte solution, and AgNDs with a large number of catalytic active sites can effectively adsorb N2 molecules dissolved in the electrolyte. In the NRR reaction, the AgNDs adsorbing N2 molecules will collide with the titanium mesh current collector and accept the attack of H+/e- to form NH3. Finally, with the desorption of NH3 molecules, AgNDs regenerate in the solution. This unloaded mobile phase electrocatalytic system can increase the utilization of the catalytic active sites of AgNDs, and avoid the reduction of catalytic active sites caused by the aggregation of AgNDs on the supported electrode. In addition, the adsorption of N2 and the desorption of NH3 occur in the solution, and the reaction kinetics is not affected by the electric field. The results of electrochemical experiments showed that the ammonia yield and Faraday efficiency of AgNDs catalyst in the unloaded mobile phase electrocatalytic system reached 600.4±23.0 μg h-1 mgAg-1 and 10.1±0.7%, respectively. The yield was compared with the traditional supported system. Increased by 7.5 times. In order to further improve the Faraday efficiency of the unloaded mobile phase electrocatalytic system, the oxygen-rich vacancy titanium oxide layer (Ov-TiO2/Ti) was modified on the surface of the Ti net current collector. The surface Ov-TiO2 not only reduces the cathode current, but also acts as an NRR reaction. Provides additional catalytically active sites. The experimental results show that using Ov-TiO2/Ti as the current collector, the Faraday efficiency is increased by 2 times. In addition, the researchers also developed an "S-shaped" titanium plate two-electrode reactor to realize the two-electrode mobile phase NRR reaction. This research provides new ideas for the design and development of high-efficiency electrocatalysts and electrocatalytic systems. The research work was funded by the National Natural Science Foundation of China and the International Cooperation Project of the Innovation Research Team of the Chinese Academy of Sciences. (A) Schematic diagram of AgNDs prepared by liquid phase laser ablation method; (b) TEM image and HRTEM image of AgNDs (the inset is FFT mode); (c) Schematic diagram of NRR reaction in unloaded mobile phase electrocatalytic system; (d) Ov-TiO2 /Ti SEM image; (e) schematic diagram of a two-electrode system flow reactor; (f) DFT calculation of the best path of AgNDs in the NRR reaction (light blue ball, white ball and dark blue ball represent Ag, H and N respectively Atom); (g) Ammonia production rate and Faraday efficiency of AgNDs at each reaction potential in an unloaded mobile phase electrocatalytic system; (h) Ammonia production by AgNDs at each reaction potential with Ov-TiO2/Ti as the current collector Rate and Faraday efficiency; (i) Ammonia production rate and Faraday efficiency of AgNDs corresponding to each reaction potential in a two-electrode flow system Carbon Steel Caps,Carbon Steel End Caps,Carbon Steel Pipe Caps,Carbon Steel Weld Caps Cangzhou Youlong Pipe Fitting Manufacturing Co., LTD , https://www.youlongpipe.com