An international research team coordinated by the University of Trieste's Department of Physics has synthesised a potential bifunctional catalyst, mimicking the functionality of vitamin B12, i.e. one capable of promoting two distinct chemical reactions, each supported by a different oxidation state of the metal. Also known as cobalamin, a molecule to the centre of which is bound a single cobalt atom, vitamin B12 is in fact capable of catalysing different reactions depending on the context. The results of the study, with important application implications in the field of energy storage and transport, have been published in the scientific journal Advanced Functional Materials.

The study involved the collaboration of the Materials Laboratory Institute of the National Research Council (CNR-IOM), Elettra Sincrotrone Trieste and the Laboratory for Surface Nanostructures of EPFL in Switzerland. The activities were funded in the context of the PRIN 2022 and PRIN NRRP projects.

'Energy storage and transport are today's most strategic applications; however, from the point of view of available technologies, they are still far from optimal. Think, for example, of rechargeable batteries and the need to use two separate catalytic agents to support the opposing reactions of oxidation and reduction in reversible charge and discharge processes', explains Erik Vesselli, professor of experimental matter physics at the Department of Physics, University of Trieste. ‘The result we have obtained shows, however, how we can be inspired by nature to create new materials of extreme applicative interest in the field of green energy, i.e. bifunctional catalysts, capable by themselves of promoting different chemical reactions.’

Cobalt is one of the strategic metals in the periodic table, already particularly used in catalysis. Its functionality can be controlled by defining the way it coordinates and calibrating its oxidation state. In nature, vitamin B12 - also known as cobalamin, as it is characterised by a single cobalt atom - in its various forms and through complex mechanisms, is itself able to regulate the oxidation state of this single cobalt atom, thus changing its reactivity and stability.

‘We did the same’, Vesselli continues: ‘That is, we synthesised a matrix of two-dimensional molecules and single cobalt atoms, using a single sheet of graphene as a worktable. By controlling the co-ordination, we were able to modulate the oxidation states of cobalt just as occurs in vitamin B12, and were also able to obtain phases in which several oxidation states are co-present in the material.’

In conclusion, the researchers succeeded in synthesising and characterising a new material whose properties are determined by long-range electronic and magnetic interactions between different reaction centres, i.e. individual cobalt atoms. This was achieved by combining state-of-the-art experimental techniques using laser sources, synchrotron light and microscopy techniques, combined with numerical simulations.

Full study published in Advanced Functional Materials 

Co(III), Co(II), Co(I): Tuning Single Cobalt Metal Atom Oxidation States in a 2D Coordination Network