In perovskites, exsolution of transition metals has been proposed as a smart catalyst design for energy applications. Although there exist transition metals with superior catalytic activity, they are limited by their ability to exsolve under a reducing environment. When a doping element is present in the perovskite, it is often observed that the surface segregation of the doping element is changed by oxygen vacancies. However, the mechanism of co-segregation of doping element with oxygen vacancies is still an open question. Here we report trends in the exsolution of transition metal (Mn, Co, Ni and Fe) on the PrBaMn₂O_5+δ layered perovskite oxide related to the co-segregation energy. Transmission electron microscopic observations show that easily reducible cations (Mn, Co and Ni) are exsolved from the perovskite depending on the transition metal-perovskite reducibility. In addition, using density functional calculations we reveal that co-segregation of B-site dopant and oxygen vacancies plays a central role in the exsolution.

Electrocatalysis undeniably offers noteworthy improvements to future energy conversion and storage technologies, such as fuel cells, water electrolyzers, and metal–air batteries. The molecular interaction between catalytic surfaces and chemical reactants produces a trade-off between catalyst activity and effectiveness, and hence requires optimization. When enhancing electrocatalysis, atomic surface structure tuning is of primary importance in simultaneously meeting demands for electrocatalytic activity and stability. The impact of lattice strain on catalytic activity tuning is experimentally revealed in de-alloyed bimetallic nanoparticles, in which surface distortion makes essential contributions to the activities of state-of-the-art electrocatalysts that vary over distinct sizes, surface defect concentrations, shapes, and atomic compositions under the studied environments. Further, metal-rich shells show compressive strain in core–shell catalyst nanoparticles, yielding shifts in metal electronic band structure features, weakened chemisorption of oxygenated species, and changes in the mechanisms governing catalyst activity. Our study evaluates the practical and fundamental effects of surface distortion and defects on interfacial electrocatalysis, namely in the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). This is accomplished via an understanding of strain from theory, establishing reactivity–strain relationships that inform the tuning and enhancement of electrocatalytic activity and stability.

Exsolution has been intensively studied in the fields of energy conversion and storage as a method for the preparation of catalytically active and durable metal nanoparticles. Under typical conditions, however, only a limited number of nanoparticles can be exsolved from the host oxides. Herein, we report the preparation of catalytic nanoparticles by selective exsolution through topotactic ion exchange, where deposited Fe guest cations can be exchanged with Co host cations in PrBaMn_1.7Co_0.3O_5+δ. Interestingly, this phenomenon spontaneously yields the host PrBaMn_1.7Fe_0.3O_5+δ, liberating all the Co cations from the host owing to the favorable incorporation energy of Fe into the lattice of the parent host (ΔE_{incorporation} = −0.41 eV) and the cation exchange energy (ΔE_exchange = −0.34 eV). Remarkably, the increase in the number of exsolved nanoparticles leads to their improved catalytic activity as a solid oxide fuel cell electrode and in the dry reforming of methane.

With the need for more stable and active metal catalysts for dry reforming of methane, in situ grown nanoparticles using exsolution are a promising approach. However, in conventional exsolution, most nanoparticles remain underneath the surface because of the sluggish diffusion rate of cations. Here, we report the atomic layer deposition (ALD)–combined topotactic exsolution on La_0.6Sr_0.2Ti_0.85Ni_0.15O_3-δ toward developing active and durable catalysts. The uniform and quantitatively controlled layer of Fe via ALD facilitates the topotactic exsolution, increasing finely dispersed nanoparticles. The introduction of Fe₂O₃ yields the formation of Ni-Fe alloy owing to the spontaneous alloy formation energy of −0.43 eV, leading to an enhancement of the catalytic activity for dry methane reforming with a prolonged stability of 410 hours. Overall, the abundant alloy nanocatalysts via ALD mark an important step forward in the evolution of exsolution and its application to the field of energy utilization.