Correspondent: Wang Chundong *, Xiong Yujie *
SETTING: Huazhong University of Science and Technology and University of Science and Technology of China.
Research background
Article introduction
Recently, the team of Associate Professor Wang Chundong of Huazhong University of Science and Technology and the team of Professor Xiong Yujie of Chinese University of Science and Technology published a research article entitled "Realizing efficient whole urea electrolysis through monoatomic active centers on layered double hydroxides" in the internationally renowned journal Science Bulletin. In this paper, the exact position of single atom (SAC) on layered double hydroxide (LDH) and the influence of different single atom content on catalytic activity were studied in detail, and the interaction between single atom and carrier LDH was systematically expounded from the perspective of combining theory with experiment. This work provides important insights for the design of fully electrolytic multifunctional SAC from the perspective of single atom precise positioning.
Mechanism diagram of electrocatalytic hydrogen evolution and urea oxidation reaction
The main points of this article
Point 1: In this paper, monoatomic Rh was uniformly dispersed on ultrathin NiV-LDH nanosheets (Rh/NiV-LDH) by glycol-assisted hydrothermal method, and was used to catalyze HER and UOR simultaneously. Rh/NiV-LDH has high TOF value and remarkable mass activity, as well as low overpotential and fast HER and UOR reaction kinetics.
Figure 1. Preparation process, structure and micro-morphology of RH/NIV-LDH electrode.
Point 2: Through AC-STEM and HAADF-STEM images, a large number of Rh monads highly dispersed on NiV-LDH carrier were observed. The fitting results of FT-EXAFS show that when Rh/NiV-LDH catalyst (1.55? ), without any metal Rh-Rh bond (2.38? ) or Rh-O-Rh bond (2.65? ), which further confirmed that Rh atoms on NiV-LDH carrier combined with oxygen on the surface of the carrier and existed in monodisperse form. DFT calculation shows that the formation energies of Rh atoms on the surface of NiV-LDH are 0.22eV, 0.37 eV and 0.67 eV, respectively, that is, at the top of the existing Ni, V and O sites, which once again shows that the monodisperse configuration of Rh on the surface of NiV-LDH is more energy feasible than the doping configuration of Ni and V sites of NiV-LDH. In addition, the formation energy of Rh atom is the lowest in the NiV hollow position of NiV-LDH and perpendicular to the oxygen atom configuration, indicating that most Rh atoms are distributed in the Ni-V hollow position (the top of O atom), and a few may be distributed in the top position of Ni atom or V atom.
Figure 2. Spectral characterization of RH/NIV-LDH.
Point 3: The test shows that the HER overpotential of Rh/NiV-LDH cathode catalyst is 64 mV at the current density of100 mA cm-2, and it can work stably for more than 200 h, and the Faraday efficiency of electrocatalytic hydrogen evolution is close to 100%. In addition, Rh/NiV-LDH has high HER mass activity (0.262 mg1) and switching frequency (tof: 2. 125s 1) at the overpotential of 100 mV.
Figure 3. Electrocatalytic hydrogen evolution performance of the prepared catalyst in alkaline electrolyte.
Point 4: Rh/NiV-LDH catalytic electrode Rh/NiV-LDH shows excellent UOR catalytic activity, and it only needs 1.33 V to reach10ma cm 2. A simple Rh/NiV-LDH (+)/RH/NIV-LDH (-) double-electrode urea electrolyzer was assembled with RH/NIV-LDH catalytic electrode as cathode and anode respectively and alkaline urea medium (1 M KOH+ 0.33 M urea) as electrolyte. When the electrolyzer is driven at 100 mAcm-2, it can work stably above 100 h only by applying a voltage of1.34v. When the working current density of the self-assembled RH/NIV LDH (+) | Rh/NiV-LDH (-) electrolyzer reaches100 m. Even after three cycles, the degradation rate of urea can still be kept at about 90%, and H2/RH can be produced stably.
Figure 4. Electrocatalytic Urea Oxidation (UOR) and Performance Test of Urea Complete decomposition of RH/NIV-LDH and its comparative samples in 1 M KOH solution.
Fifth point: Density functional theory (DFT) calculation shows that monodisperse Rh monatomic changed the electronic structure of NiV-LDH, and optimized the adsorption and desorption process of hydrogen adsorption intermediate (H*), thus reducing the reaction barrier of Volmer step and Heyrovsky step in HER process, and furtHER improving her catalytic activity of Rh/NiV-LDH catalyst. At the same time, the monatomic Rh site also optimized the adsorption and activation of Rh/NiV-LDH catalyst for urea molecules, promoted the desorption of its key intermediates (such as CO*/NH*), significantly reduced the reaction energy barrier in the rate-limiting step (RDS) of UOR reaction, accelerated the kinetics of UOR reaction and improved the catalytic activity of UOR.
Figure 5. Density functional theory calculation.
summary
To sum up, the calculation results of AC-STEM, XAS and DFT show that the Rh capsule anchored on NiV-LDH matrix (located in the hollow position of Ni-V) was successfully prepared by one-step hydrothermal synthesis method. The prepared Rh/NiV-LDH showed good bifunctional catalytic activity for HER and UOR in alkaline solution. DFT calculation shows that monodisperse Rh single atom changes the electronic structure of NiV-LDH, and reduces the reaction barrier of HER Volmer step and Heyrovsky step. At the same time, Rh site also optimized the adsorption and/or activation of urea molecules, promoted the desorption of key intermediates (such as CO*/NH*), significantly reduced the reaction energy barrier of UR rate determination step (RDS), and accelerated the UR reaction kinetics. Rh/NiV-LDH catalyst was used as cathode and anode to assemble an integrated urea electrolyzer, which was powered by 1.5 V solar panel, resulting in a large number of H2 and N2 bubbles on both electrodes. This shows that the catalyst has great potential in large-scale energy-saving hydrogen production and purification of urea-rich wastewater. This work has guiding significance for the controlled mass production of capsules with accurate positioning in the future.
Article link
Sun Huachuan, Chen Xiaoqian, Duan Delong, Homayoun, Xia Zhang,,, Pang, Huo Kaifu, Wang Chundong *, Xiong Yujie *. Efficient bulk urea electrolysis through monoatomic active centers on layered double hydroxides. Sci。 Bull. 2022 .
DOI: /~yjxiong/chinese.html
Introduction to the first author
Chuan, Ph.D., Grade 20 19, School of Optics and Electronic Information, Huazhong University of Science and Technology. His research interests are the design and synthesis of highly active metal electrocatalysts and their application in electrolytic water. At present, as the first author and * * * co-first author, he has published 8 SCI papers in J.AM. Chemistry. Socialist, scientific bull, applying Cata. Environment, ACS application materials. Inter Milan. , chemistry. Eng.J and J. Power Sources, two of which were selected as highly cited papers of ESI.
E-mail :huachuansun@hust.edu.cn
Li is a 2020 graduate student of School of Optics and Electronic Information, Huazhong University of Science and Technology. His research interests include monoatomic catalysts and their applications in synthesis electrocatalysis, and computational materials science in electrocatalysis.
E-mail :linfengli@hust.edu.cn
Chen Xiaoqian: 20 1 1 He graduated from Chang Gung University with a doctorate in chemistry and materials engineering, and is now an assistant professor at the Center for Reliability Science and Technology of Chang Gung University. At present, the research direction includes the development and transformation of in-situ characterization technology of electrocatalyst in electrochemical energy.
E-mail :hc_chen@mail.cgu.edu.tw