Majee Rahul, Islam Quazi Arif, Mondal Surajit, Bhattacharyya Sayan
Department of Chemical Sciences and Centre for Advanced Functional Materials, Indian Institute of Science Education and Research (IISER) Kolkata Mohanpur - 741246 India
Chem Sci. 2020 Sep 7;11(37):10180-10189. doi: 10.1039/d0sc01323d.
The catalyst surface undergoes reversible structural changes while influencing the rate of redox reactions, the atomistic structural details of which are often overlooked when the key focus is to enhance the catalytic activity and reaction yield. We achieve chemical synthesis of ∼5 unit cell thick double perovskite oxide nanosheets (NSs) and demonstrate their precise structural reversibility while catalyzing the successive oxygen evolution and reduction reactions (OER/ORR). 4.1 nm thick A-site ordered BaPrMnCoO ( = 0.06-0.17) NSs with oxygen deficient PrO terminated layers have flexible oxygen coordination of Pr ions, which promotes the redox processes. When subjected to systematic oxidation and reduction cycles by cyclic voltammetry under small electrochemical bias, the PrO phase appears and disappears alternately at the NS surface, due to the intake and release of oxygen, respectively. The structural reversibility is attributed to the two-dimensional morphology and the A-site terminated surface with flexible anion stoichiometry. Although the underlying B-site cations are well-known active sites, this is the first demonstration of A(Pr)-site cations influencing the activity by reversibly altering their oxygen coordination. Higher Co-doping thwarts the NS formation, affecting the catalytic performance. The facile OER/ORR activity of the thickness-tunable NSs has larger implications as a bifunctional air-electrode material for metal-air batteries and fuel cells.
催化剂表面在影响氧化还原反应速率的同时会发生可逆的结构变化，而当重点是提高催化活性和反应产率时，其原子结构细节往往被忽视。我们实现了约5个晶胞厚的双钙钛矿氧化物纳米片（NSs）的化学合成，并展示了它们在催化连续析氧和氧还原反应（OER/ORR）时精确的结构可逆性。4.1纳米厚的A位有序BaPrMnCoO（ = 0.06 - 0.17）纳米片，其具有缺氧的PrO 端基层，Pr离子具有灵活的氧配位，这促进了氧化还原过程。当在小的电化学偏压下通过循环伏安法进行系统的氧化和还原循环时，由于分别摄入和释放氧气，PrO相在纳米片表面交替出现和消失。这种结构可逆性归因于二维形态和具有灵活阴离子化学计量的A位端基表面。尽管潜在的B位阳离子是众所周知的活性位点，但这是首次证明A（Pr）位阳离子通过可逆地改变其氧配位来影响活性。更高的Co掺杂阻碍了纳米片的形成，影响了催化性能。厚度可调的纳米片易于实现的OER/ORR活性作为金属空气电池和燃料电池的双功能空气电极材料具有更大的意义。
