Graphite Intercalation Compounds Derived by Green Chemistry as Oxygen Reduction Reaction Catalysts

Abstract

Precious group metal (PGM) catalysts such as Pt supported on carbon supports are expensive catalysts utilized for the oxygen reduction reaction (ORR) due to their unmatched catalytic activity and durability. As an alternative, PGM-free ORR electrocatalysts that offer respectable catalytic activity are being pursued. Most of the notable PGM-free catalysts are obtained either from a bottom-up approach synthesis utilizing nitrogen-rich polymers as building blocks, or from a top down approach, where nitrogen and metal moieties are incorporated to carbonaceous matrixes. The systematic understanding of the origin of catalytic activity for either case is speculative and currently employed synthesis techniques typically generate large amounts of hazardous waste such as acids, oxidizing agents, and solvents. Herein, for the first time, we investigate the catalytic activity of graphite-based materials obtained via intercalation strategies that minimally perturb the graphitic backbone. Our outlined approaches demonstrate initial efforts to not only elucidate the role of each element but also significantly reduce the use of hazardous chemicals, which remains a pressing challenge. Graphite intercalation compounds (GIC) were obtained using fewer steps and solvent-free processes. X-ray diffraction and Raman results confirm the successful intercalation of FeCl3 between graphite layers. Electrochemical data shows that the ORR performance of FeCl3-intercalated GIC displays slight improvement where the onset potential reaches 0.77 V vs RHE in alkaline environments. However, expansion of the graphite and solvent-free incorporation of iron and nitrogen moieties resulted in a significant increase in ORR activity with onset potential to 0.89 V vs RHE, a maximum half-wave of 0.72 V vs RHE, and a limiting current of about 2.5 mA cm–2. We anticipate that the use of near solvent-free processes that result in a high yield of catalysts along with the fundamental insight into the origin of electrochemical activity will tremendously impact the methodologies for developing next-generation ORR catalysts.

Effect of Process Parameters on the Graphite Expansion Produced by a Green Modification of the Hummers Method

“…It can be noticed a position shift of the G peak towards a higher wavenumber between samples ( Figure 5 b) can be related to distribution differences between inserted oxygenated functional groups (hetero-atoms) in the material [ 42 ]. Intercalated species also cause graphitic structural defects, inducing the appearance of a shoulder next to the G band; this signal is called the D’ band (located at 1610 cm −1 ); it was related to changes in the Fermi level [ 43 ]. The intensity of the 2D band is also lower for the intercalated sample, which can be attributed to defects in the graphitic layer arrangement due to the breaking of the stacking order in the c-axis derived from the chemical reaction and more graphene-like structure by the presence of the sp 2 bonds [ 44 ].…”

“…The dry IG was expanded using an alternative heating route based on a domestic microwave oven (Frigidaire, model FMDL17S4GLW) operated at 700 W using heating cycles of 10, 30, and 50 s (10 s heating/10 s resting). This method was chosen because, under microwave radiation, IG particles are rapidly expanded, and the solid reaches hundreds of grades in s, giving uniform heating [ 21 ]; this causes rapid evaporation of intercalated species, resulting in fuming and lightening obtaining highly porous worm-like structures [ 10 , 43 , 48 , 49 ].…”

Synergistic Modulation of Carbon-Based, Precious-Metal-Free Electrocatalysts for Oxygen Reduction Reaction

“…By introducing heteroatom dopants into the carbon nanostructures, the charge density, as well as the spin density of the carbon base, will be changed, accelerating the electron transfer during the electrocatalysis process. For example, the nitrogen-doped carbon nanostructures (e.g., graphene, nanotube, graphene aerogel, and so on) have widely studied since Dai’s group proposed the idea of nitrogen-containing carbon nanotubes as ORR catalysts in the year 2009, some of which present even comparable ORR catalytic performance to the Pt/C catalysts in both acid and alkaline solutions as well as long lifetime. , Pyrolyzing N-containing precursors, − taking the annealing process in ammonia , or N-containing gas plasma, , can easily produce N-doped carbon nanostructures, which is due to the favorable lattice match endowed by nitrogen atom to carbon atom’s similar radius. For example, a N-doped carbon nanotubes (N-CNTs) aerogel has been designed with oxidized CNTs and N-containing pyrrole molecules as precursors as shown in Figure a,b.…”

Selective recovery of critical materials in supercritical water desalination

“…The XRD spectra were obtained at 2θ angle range from 5 • to 60 • with a scanning speed of 0.4 • / min. The detailed experimental procedure was also presented in the previous report by Zhao et al [37]. The measured spectra were analyzed by comparing them with theoretical spectra calculated from the unit cell structures.…”