NSRRC Activity Report 2022

064 NSRRC ACTIVITY REPORT 2022 Fig. 5 : (a) Operando Fe K-edge XANES spectra of CoFeO x H y  (Fe 30%) at various potentials compared to reference samples such as Fe foil, FeO, Fe 3 O 4 , and Fe 2 O 3 . (b) Correlation of edge energy with the Fe oxidation state. [Reproduced from Ref. 3] Xile Hu (École Polytechnique Fédérale de Lausanne, Switzerland) and his coworkers utilized operando XAS at TLS 01C1 3 to investigate the nature of Fe and Co ions in CoFeO x H y during OER. They discovered that the catalytic activity scales with the concentration of Fe 4+ species at the surface, rather than with the concentration of Co 4+ in bulk. Figure 5 shows that, upon immersion in the electrolyte, the Fe sites were slightly oxidized by the OH − electrolyte, and during OER with the increase in the applied potential, the Fe 4+ species were detected. Therefore, the Fe species not only promoted the oxidation of Co 3+ to Co 4+ , but also created a new active site on the surface with higher activity. The analysis indicated that, rather than bulk Co 4+ species, surface Fe 4+ species were the active sites for OER on CoFeO x H y . This study improves our understanding of the mechanism of a benchmark OER catalyst. In summary, the three studies presented provide a valuable example of the reconstruction of atomic and electronic structures at the interface for the water-splitting reaction. This knowledge could advance fundamental research of catalyst design via interface engineering with the aim of developing more effective catalysts. (Reported by Yan-Gu Lin) This report features the work of Hao Ming Chen and his collaborators published in Adv. Energy Mater. 12 , 2200079 (2022) and J. Am. Chem. Soc. 144 , 1174 (2022); as well as the work of Xile Hu and his collaborators published in Energ. Environ. Sci. 15 , 206 (2022). TLS 01C1 EXAFS TLS 16A1 Tender X-ray Absorption, Diffraction TLS 17C1 EXAFS SP 12B1 Materials X-ray Study • XANES, EXAFS • Materials Science, Chemistry, Condensed-matter Physics, Environmental and Earth Sciences References 1. C.-W. Tung, T.-R. Kuo, Y.-P. Huang, Y.-C. Chu, C.-H. Hou, Y. Li, N.-T. Suen, J. Han, H. M. Chen, Adv. Energy Mater. 12 , 2200079 (2022). 2. H. Sun, C.-W. Tung, Y. Qiu, W. Zhang, Q. Wang, Z. Li, J. Tang, H.-C. Chen, C. Wang, H. M. Chen, J. Am. Chem. Soc. 144 , 1174 (2022). 3. S. Lee, A. Moysiadou, Y.-C. Chu, H. M. Chen, X. Hu, Energ. Environ. Sci. 15 , 206 (2022).