In situ oxidation and reduction of triangular nickel nanoplates via environmental transmission electron microscopy

TY - JOUR

T1 - In situ oxidation and reduction of triangular nickel nanoplates via environmental transmission electron microscopy

AU - Lagrow, Alec P.

AU - Boyes, Edward

AU - Gai, Pratibha L

AU - Lloyd, David Carlos

AU - Alyami, N

AU - Bakr, O M

N1 - Funding Information: P.L.G. and E.D.B. thank the EPSRC (UK) for a critical mass Grant EP/J0118058/1, a postdoctoral research assistantship (PDRA) for A.P.L., and a PhD CASE studentship in association with Johnson Matthey plc, for D.C.L. We thank Ian Wright for expert technical assistance. Publisher Copyright: © 2017 The Authors Journal of Microscopy © 2017 Royal Microscopical Society

PY - 2018/2

Y1 - 2018/2

N2 - Understanding the oxidation and reduction mechanisms of transition metals, such as nickel (Ni), is important for their use in industrial applications of catalysis. A powerful technique for investigating the redox reactive species is in situ environmental transmission electron microscopy (ETEM), where oxidation and reduction can be tracked in real time. One particular difficulty in understanding the underlying reactions is understanding the underlying morphology of the starting structure in a reaction, in particular the defects contained in the material, and the exposed surface facets. Here-in, we use a colloidal nanoparticle synthesis in a continuous flow reactor to form nanoplates of nickel coated with oleylamine as a capping agent. We utilise an in situ heating procedure at 300 °C in vacuum to remove the oleylamine ligands, and then oxidise the Ni nanoparticles at 25 °C with 2 Pa oxygen, and follow the nanoparticles initial oxidation. After that, the nanoparticles are oxidised at 200 and 300 °C, making the size of the oxide shell increase to ∼4 nm. The oxide shell could be reduced under 2 Pa hydrogen at 500 °C to its initial size of ∼1 nm. High temperature oxidation encouraged the nanoparticles to form pure NiO nanoparticles, which occurred via the Kirkendall effect leading to hollowing and void formation.

AB - Understanding the oxidation and reduction mechanisms of transition metals, such as nickel (Ni), is important for their use in industrial applications of catalysis. A powerful technique for investigating the redox reactive species is in situ environmental transmission electron microscopy (ETEM), where oxidation and reduction can be tracked in real time. One particular difficulty in understanding the underlying reactions is understanding the underlying morphology of the starting structure in a reaction, in particular the defects contained in the material, and the exposed surface facets. Here-in, we use a colloidal nanoparticle synthesis in a continuous flow reactor to form nanoplates of nickel coated with oleylamine as a capping agent. We utilise an in situ heating procedure at 300 °C in vacuum to remove the oleylamine ligands, and then oxidise the Ni nanoparticles at 25 °C with 2 Pa oxygen, and follow the nanoparticles initial oxidation. After that, the nanoparticles are oxidised at 200 and 300 °C, making the size of the oxide shell increase to ∼4 nm. The oxide shell could be reduced under 2 Pa hydrogen at 500 °C to its initial size of ∼1 nm. High temperature oxidation encouraged the nanoparticles to form pure NiO nanoparticles, which occurred via the Kirkendall effect leading to hollowing and void formation.

KW - In-situ, Triangular nickel nanoplates, environmental transmission electron microscopy

KW - shape controlled nanomaterials

KW - Electron microscopy

KW - flow chemistry

UR - http://www.scopus.com/inward/record.url?scp=85040778309&partnerID=8YFLogxK

U2 - 10.1111/jmi.12621

DO - 10.1111/jmi.12621

M3 - Article

SN - 0022-2720

VL - 269

SP - 161

EP - 167

JO - Journal of Microscopy

JF - Journal of Microscopy

IS - 2

ER -