Nano-socketed nickel particles with enhanced coking resistance grown in situ by redox exsolution

Abstract

Metal particles supported on oxide surfaces are used as catalysts for a wide variety of processes in the chemical and energy conversion industries. For catalytic applications, metal particles are generally formed on an oxide support by physical or chemical deposition, or less commonly by exsolution from it. Although fundamentally different, both methods might be assumed to produce morphologically and functionally similar particles. Here we show that unlike nickel particles deposited on perovskite oxides, exsolved analogues are socketed into the parent perovskite, leading to enhanced stability and a significant decrease in the propensity for hydrocarbon coking, indicative of a stronger metal–oxide interface. In addition, we reveal key surface effects and defect interactions critical for future design of exsolution-based perovskite materials for catalytic and other functionalities. This study provides a new dimension for tailoring particle–substrate interactions in the context of increasing interest for emergent interfacial phenomena.

Evolution of the electrochemical interface in high-temperature fuel cells and electrolysers

“…In spite of this, recent investigations could not establish any clear correlation between the SrO segregation and the surface oxygen exchange rate on RP-type O2-electrodes 15,35 , suggesting that our understanding of the SOC electrode process related to surface reorganisation is still incomplete. Nonetheless, recent reports suggest that surface segregation in perovskites may be minimised by adequate choice of A-site cations and perovskite defect chemistry 31,36,37 .…”

“…Evidence so far suggests that redox exsolution from perovskites is a phase decomposition process driven by reduction and controlled by bulk and surface defects and external conditions 36,87,92 . Initially the lattice is reduced, losing oxygen and gaining electrons until the point where metal nucleation becomes favourable.…”

“…Initially the lattice is reduced, losing oxygen and gaining electrons until the point where metal nucleation becomes favourable. Nucleation is likely to occur primarily on the surface of the host lattice where the nucleation barrier is lowered by crystal defects 36,92 . The surface nucleation process drains exsolvable ions from the nearby perovskite lattice which causes additional reducible ions to diffuse to the surface to balance the compositional gradient and fuel the growth of the metal clusters.…”

“…This not only allows for such attractive structural interplay, but also for combining it with other desirable electrode functionality (see Figure 2a) 84,87,89,91,95 , chromite 86,90,94 or chromite-manganite 93,96 perovskite supports. These have been applied to solid oxide fuel cells 86,90,92,94,97 , electrolysis cells 95,98 and for other catalytic process 36,84,85 .…”

“…The surface nucleation process drains exsolvable ions from the nearby perovskite lattice which causes additional reducible ions to diffuse to the surface to balance the compositional gradient and fuel the growth of the metal clusters. In fact, cation diffusion to the surface plays an essential role for sustaining exsolution given that during this process reducible ions from typically at least 100 nm deep emerge on the surface to form metal particles 36 .…”