Compositional and Morphology Optimization to Boost the Bifunctionality of Perovskite Oxygen Electrocatalysts

Abstract

Oxygen electrocatalysts are crucial for the development of renewable and sustainable energy conversion/storage (ECS) systems, but a shortage of efficient and low-cost oxygen electrocatalysts is impeding their widespread applications. In this work, to investigate the bifunctionality of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), Ni-substituted LaMnO3 perovskite oxides (LaNi x Mn1–x O3, x = 0.1, 0.3, 0.5, 0.7, and 0.9) and pristine LaNiO3 and LaMnO3 were synthesized using a sol–gel process. After the compositional optimization and electrochemical characterizations, we identified that LaNi0.3Mn0.7O3 (SG LNM-3) within the compositions exhibited balanced intrinsic activity for bifunctional ORR and OER. To further improve the apparent activity of the optimized SG LNM-3, electrospinning was used to prepare one-dimensional nanostructured LaNi0.3Mn0.7O3 (ES LNM-3). ES LNM-3 had a higher specific surface area and continuous electron-transfer pathways, resulting in much improved bifunctional activity in comparison to SG LNM-3. In addition to the morphological effect, we ascribed the high electrochemical performance of ES LNM-3 to the high-spin Mn3+ and low-spin Ni3+ with electron configurations of t2g 3eg 1 and t2g 6eg 1 (a well-recognized design descriptor), as well as the high degree of Jahn–Teller distortion. After assembling ES LNM-3 within Zn–air batteries, promising electrochemical performances such as high power density and rate capability were obtained. Our findings will advance the development of high-performance and inexpensive oxygen electrocatalysts and associated ECS devices.

One-Dimensional Self-Assembled Heterostructured Perovskite Hybrid for Oxygen Reduction and Zn–Air Batteries

“…The significantly improved specific surface area of 1D-HPH in comparison to P-HPH is related to the one-dimensional rod structure with plenty of mesopores, as confirmed by the hysteresis loop in isotherms . The significantly increased adsorbed quantity at a relatively high pressure indicates the presence of macropores . The insets in Figure a,b correspond to the pore-size distribution of P-HPH and 1D-HPH, which further reveals a larger amount of mesopores in 1D-HPH in comparison to P-HPH.…”

“…In light of the similar e g occupancy within P-HPH and 1D-HPH, the difference in electrochemical performance may originate from morphology differences. 18 These above results indicate that highly crystalline 1D porous heterostructured perovskite hybrids are effectively created and that the electron configuration of Mn cations is within the optimal range; thus, we further assessed the electrocatalytic performance. To compare the intrinsic activity of these hybrids, we first evaluated the electrochemical performance without adding carbon species.…”

“…19 The significantly increased adsorbed quantity at a relatively high pressure indicates the presence of macropores. 18 The insets in Figure 4a,b correspond to the pore-size distribution of P-HPH and 1D-HPH, which further reveals a larger amount of mesopores in 1D-HPH in comparison to P-HPH. These observations agree well with the microstructures recorded by other characterizations such as SEM and TEM.…”

“…Therefore, to construct efficient rechargeable ZABs, the bifunctionality of both OER and ORR should be reinforced in future work. 18…”

“…Among the alternative non-precious oxide electrocatalysts, perovskite oxides (ABO 3 ) are recognized as the superior ones. ,− In addition to low cost, perovskite oxides have other apparent benefits, such as their structure and composition flexibility. A significant number of investigations have recently demonstrated that perovskite oxides have prominent activity and good stability. − Particularly, the intrinsic activity has been associated with the orbital electron filling (e g ) and the covalency between B and O of ABO 3 . Among perovskites, LaMnO 3 has shown to be a superb electrocatalyst for ORR as its e g is very close to 1.…”