Hole-Doping Control of Nanomagnetism in Ni-Doped Co3O4 Nanoplates for Spin Catalysis

Abstract

Oxygen 2p holes can be induced through self-doping in bulk transition metal oxides to enable beneficial properties that result in a variety of fascinating and useful behaviors like half- metallicity and metal-insulator transitions─properties used for many different applications. O 2p holes also affect catalytic reactions by modifying surface adsorption energies and driving reaction kinetics at the active sites. This makes Ni-doped Co3O4 an excellent candidate for spintro-catalysis (or spin catalysis), which shows enhanced efficiency in various catalytic reactions, such as the oxygen evolution reaction, CO2 conversion, and the synthesis of ammonia. We find that hole-doping control of nanoscale transition metal oxides provides a simple, useful mechanism to tune the electronic and magnetic properties. O 2p hole doping’s impact is explored using density functional theory calculations on pure and transition metal-doped bulk and nanoscale Co3O4 with and without vacancies, and further investigated via a range of spectroscopies and nanomagnetism on Co3O4 and Ni-doped Co3O4 nanoplates. We find that doping nano-Co3O4 with Ni induces holes on the surrounding ligands, inducing changes to the electronic and magnetic structure. Hole doping increases the strength of the exchange interactions, which induces large changes to the nanomagnetism, introducing unique short-range magnetic order while retaining the persistent long-range antiferromagnetic order typical of Co3O4. Ligand holes are only present with the introduction of Ni into the octahedral sites.