On the Role of Boron-Engineered MWCNTs as Bifunctional Oxygen Evolution/Reduction Electrocatalysts

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) represent key processes underpinning fuel cell and water-splitting technologies, respectively. In this scenario, boron-doped carbon nanomaterials have emerged as promising and metal-free bifunctional systems to promote both electrochemical processes while offering a sustainable alternative to the use of critical raw materials in electrocatalysts of the state-of-the-art. Herein, we describe the surface engineering of pristine multiwalled carbon nanotubes (MWCNTs) through the covalent grafting of precise boronic acid [R-B(OH)2] or boronic ester [R-B(OR′)2] functionalities, using an aryl-diazonium salt method. Materials were then evaluated as ORR and OER electrocatalysts under alkaline conditions uncovering clear-cut structure–activity relationships commonly overlooked in the literature. DFT simulations on modeled boron-functionalized graphene systems unveiled the role of structural energetics linked to the dynamic evolution of B-active sites [R-B(OH)2 vs R-B(OR′)2] under both electrochemical processes.