2020同步年報

Chemical Science 023 Fig. 1 : (a) Normalized XANES spectra and (b) Fourier transform of k 2 -weighted EXAFS spectra at the Rh K-edge of Rh powder, Rh 2 O 3 powder , Rh 2 Sb RNR/C and Rh 2 Sb SNR. [Reproduced from Ref. 1] The Rougher the Better The yield of ammonia is improved by controlling the surface shape of the electrocatalyst. T he Haber-Bosch process is still the main method for mass produc- tion of industrial ammonia (NH 3 ). This chemical reaction involves hydrogena- tion of nitrogen under high tempera- ture and high pressure, for which the raw materials are hydrogen (H 2 ) and nitrogen (N 2 ). In the process of obtain- ing hydrogen, much carbon dioxide is produced, thereby causing serious environmental issues. An important issue is hence to find another method for NH 3 synthesis. Electrochemical N 2 reduction reaction (NRR) is an efficient and sustainable route to convert N 2 to NH 3 . The NRR performance is restrict- ed mainly by the poor adsorption and activation of N 2 on catalysts because of the strong N ≡ N bond and low proton affinity of N 2 . There are several ways to improve the efficiency of the electrochemical NRR of electrocata- lysts such as size control, composition regulation, defect engineering and ion incorporation, but the effect of surface shape of the electrocatalysts plays an important role in the NRR efficiency. So far, there is no evidence that the surface shape of an electro- catalyst is an important factor affect- ing the efficiency of NRR. Xiaoqing Huang’s group fromWuhan University in China has synthesized surface-rough Rh 2 Sb nanorods (RNR) with high-index facets and surface- smooth Rh 2 Sb nanorods (SNR) through hydrothermal synthesis for electrochemical NRR. The NH 3 yield rates of RNR and SNR are 222.85 ± 12.96 and 63.07 ± 4.45 µgh -1 mg -1 Rh at -0.45 V RHE , respectively, which indicate the effectiveness of surface regulation. These workers also recorded X-ray- absorption fine-structure spectra at TPS 44A1 of NSRRC to investigate the local structure of RNR and SNR on an atomic scale. The Rh K-edge X-ray-absorption near-edge-structure (XANES) ( Fig. 1(a) ) spectra show the coexistence of Rh atoms as metal and in oxidation states; the oxidized Rh is dominant. Moreover, the energy shifts of the white-line absorption edge at the Rh K-edge between the RNR and SNR indicates that the valence state for Rh in RNR is lower than in SNR. The Rh K-edge extended X-ray-absorption fine-structure (EXAFS) spectra ( Fig. 1(b) ) reveal the coordination number around Rh atoms in the RNR sample to be much smaller than in the SNR sample. These results indicate that Rh with unsaturated coordination would be more conducive to activation of small molecules resulting in an en- hanced adsorption and activation of N 2 on RNS samples. In summary, in this work has been syn- thesized unique Rh 2 Sb nanorods with surface-rough and surface-smooth for the first time. The yield rate of electrocatalytic NRR indicate that the surface shape of the electrocatalyst is an important factor affecting the ef- ficiency of NRR. This finding provides a new strategy for creating efficient NRR electrocatalysts. (Reported by Chih-Wen Pao) This report features the work of Xiao- qing Huang and his collaborators published in Angew. Chem. Int. Edit. 59 , 8066 (2020). TPS 44A Quick-scanning X-ray Absorption Spectroscopy • XANES, EXAFS, In-situ/Operando • Materials Science, Chemistry, Phys- ics, Environmental Science Reference 1. N. Zhang, L. Li, J. Wang, Z. Hu, Q. Shao, X. Xiao, X. Huang, Angew. Chem. Int. Edit. 59 , 8066 (2020).