Impacts of Graphene Nanoribbon Production Methods on Oxygen-Reduction Electrocatalysis in Different Environments

Graphene-based materials have emerged as highly promising catalysts for enhancing oxygen reduction reaction (ORR), a pivotal process in diverse energy conversion applications and the production of eco-friendly oxidants like hydrogen peroxide (H2O2). To design exceptionally efficient catalysts tailored to specific applications, it is essentially crucial to have a thorough understanding of their electrocatalytic behaviour. This involves ascribing functions to structural characteristics like defects and exploring heteroatom doping in graphene matrices. In this work, we study the synthesis of graphene nanoribbons (GNRs) derived from multi-walled carbon nanotubes (MWCNTs) and their doping with nitrogen (N) and phosphorus (P). We investigate how edge defects and oxygenated groups retained from the MWCNT opening process impact both the doping process and GNR electrocatalytic characteristics, with a focus on their relevance to ORR. Our findings underscore the need to optimize GNR structures and doping strategies for specific reaction conditions. We demonstrate how GNR characteristics are effectively influenced by varying MWCNT opening methods, ultimately affecting ORR performance and H2O2 selectivity. The findings show that when MWCNTs are opened to create GNRs with a broader distribution of oxygen atoms across the basal plane and fewer exposed edges, N-insertion enhances catalytic activity, resulting in improved ORR performance. However, this alteration reduces H2O2 selectivity in both acidic and alkaline media. On the other hand, generating GNRs with abundant edges and widespread oxygen functional groups on both the basal plane and edges yields a high oxygen group concentration. This configuration not only facilitates phosphorus insertion at the edges but also plays a crucial role in enhancing ORR performance, leading to selectivities of over 92 % for H2O2 production in alkaline media. This study not only advances our understanding of graphene-based catalysts but also offers meaningful contributions and insights into the development of more efficient and sustainable electrochemical technologies in the realm of energy conversion. Oxygen-reduction electrocatalysis: The study seeks to unravel the intricate interplay between edge defects, oxygenated groups inherited from the multi-walled carbon nanotubes (MWCNTs) opening process, and their collective influence on the doping process and electrocatalytic properties of graphene nanoribbons (GNRs). We highlight the critical role played by the choice of MWCNT opening methods, which significantly impact GNR characteristics, subsequently influencing ORR performance and H2O2 selectivity.image