Fuel cells offer a promising alternative to industries reliant on non-renewable energy sources such as petroleum and natural gas. The cathodic oxygen reduction reaction (ORR), a crucial aspect of fuel cell technology, tends to be slow under standard conditions. Hence, catalysts are essential to facilitate efficient fuel cell operations. Traditionally, platinum (Pt) catalysts have been widely employed due to their highly efficient ORR with low overpotential values. However, the costliness of Pt, being a precious metal, poses challenges for commercialization. This research elves into the progress made in graphene-based catalysts for their utilization in ORRs, leveraging their abundance and cost-effective synthesis methods. Various synthetic approaches sourced from renewable materials are outlined, with a comparative analysis of their catalytic properties. Additionally, the impact of heteroatom and non-precious metal doping, surface area, and porosity on their performance is explored. This research aims to provide an overview of the synthesis methods, structure, and characteristics of graphene-based materials for electrochemical applications.
In recent years, graphene and its variants (GO, rGO, QDGs, QDGO) have become key research materials due to their exceptional properties like customizable functionalities, efficient electron transport, high thermal conductivity, and mechanical strength. The production methods include "bottom-up" (small molecular precursors) and "top-down" (breaking down larger carbon sources). In this research, acetylacetone and Hummers' method were used for the bottom-up and top-down processes, respectively. The synthesized QDGOs and GO were anlyzed for morphological characteristics using TEM, and their oxygen functional groups were identified through FT-IR and XPS analysis.
Materials derived from graphene exhibit outstanding qualities in diverse applications owing to their electrical properties, expansive surface areas, and robust tolerance for chemical modifications. The adoption of a wet-process presents a promising avenue for their large-scale production. Heteroatom doping stands out as a common approach to enhance their electrical, physical, and electrochemical attributes. In this study, we introduce a novel method for producing boron-doped graphene-based materials through a low-temperature wet-process. This involves the reaction between suspensions of graphene oxide and a BH₃ adduct in tetrahydrofuran under reflux conditions. Elemental mapping images demonstrate well-dispersed boron atoms throughout the materials. Various spectroscopic analyses affirm the reduction of graphene oxide and the integration of boron atoms into the carbon network as levels as high as ~2 atomic percent. The materials exhibited electrocatalytic activity for ORR.
Single-atom-based catalysts are intriguing electrocatalytic platforms that combine the advantages of molecular catalysts and conductive carbon-based materials. In this work, hybrids (Co-NrGO-1 and Co-NrGO-2) were generated by wet-reactions between organometallic complexes (Co(CH₃COO)₂ and Co[CH₃(CH2)3CH(C2H5)COO]2, respectively) and N-doped reduced graphene oxide (NrGO) at 25 ℃. Various characterizations revealed the formation of atomically dispersed Co(O)₄(N) species in Co-NrGO-2. Density functional theory (DFT) calculations explained the effect of the aliphatic C7 group in Co2 on the formation processes. The Co-NrGO-2 hybrid showed excellent catalytic performance, such as onset (0.94 V) and half-wave (0.83 V) potentials, for electrochemical oxygen reduction reaction (ORR). Co-NrGO-2 outperformed Co-NrGO-1, which was explained by more back donation to the antibonding orbitals of O₂ from electron-rich aliphatic groups. DFT calculations support this feature, with mechanistic investigations showing favored ORR reactions and facile breakage of double bonds in O₂.