Design of Single-Layer Graphene over Cobalt Nanoparticles and Insight into Active Sites for Efficient Oxygen Evolution

Controllable synthesis of graphene-coated metal nanoparticles (NPs) presents a major challenge when considering the practical application of these catalysts. Herein, we demonstrate systematic and effective synthesis of single-layer graphene-coated Co NPs with and without N doping (Co@N-SG and Co@SG) for the first time with the help of SiO₂ as a radical sieve to tactfully control CH* radical diffusion generated by 800 ^oC chemical vapor deposition. Complementary physical and electrochemical analyses prove the predominant development of single-layer graphene shell over the metal core and the presence of carbon defects such as N species and carbon vacancies present in the graphene shell.<br/><br/>As-prepared single-layer graphene-coated cobalt NPs with and without N doping (Co@N-SG and Co@SG) exhibit noticeable oxygen evolution reaction (OER) activity. Furthermore, a magnet-assisted binder-free Co@N-SG electrode illustrates much improved OER activity and stability over conventional binder-assisted counterparts, suggesting this as an effective way to overcome the recognized issues of high electron transfer resistance and poor adhesion of binder-based electrodes in practical OER applications. Interestingly, the graphene shell possesses varying defects, and OER active sites are found around said defects in the shell, while separately isolated Co@SG with a defect-free shell, despite exhibiting a slightly lower initial activity, illustrates a much-improved durable OER performance. The underlying Co affects the electron density of the graphene shell through interface dipole interaction and the electron density is optimized for adsorption of reaction intermediates, hence accelerating OER performance. This work will provide new clues to design efficient and durable electrocatalysts for further enhanced OER/HER and other electrochemical reactions.