Design of Ruddlesden–Popper Oxides with Optimal Surface Oxygen Exchange Properties for Oxygen Reduction and Evolution

5 years ago

Design of Ruddlesden–Popper Oxides with Optimal Surface Oxygen Exchange Properties for Oxygen Reduction and Evolution

Xiang-Kui Gu, Eranda Nikolla

Electrochemical high-temperature oxygen reduction and evolution play an important role in energy conversion and generation using solid oxide electrochemical cells. First-series Ruddlesden–Popper (R-P) oxides (A₂BO₄) have emerged as promising electrocatalysts for these reactions due to their suitable mixed ionic and electronic conductivities. However, a detailed understanding of the factors that govern their performance is still elusive, making their optimization challenging. In the present work, a systematic theoretical study is used to investigate the underlying factors that control the process of surface oxygen exchange, which governs oxygen reduction and evolution on these oxides. The effects of A- and B-site composition and surface termination of these oxides on their activities are elucidated. Among the different compositions, Co-based, B-site-terminated R-P oxides are predicted to exhibit the highest activity due to providing the best compromise between the energetics associated with oxygen dissociation and surface oxygen vacancy formation. A “volcano”-type relation between the calculated rates for surface oxygen exchange and O₂ binding energy on a surface oxygen vacancy is found, suggesting the O₂ binding energy might be used as an activity descriptor to identify R-P oxides with optimized performance. These findings shed light on the factors that govern the reported experimental behaviors of these oxides and lay the groundwork for the development of predictive models to design optimal mixed ionic and electronic conducting oxides for high-temperature oxygen reduction and evolution.

Publisher URL: http://dx.doi.org/10.1021/acscatal.7b01483

DOI: 10.1021/acscatal.7b01483