Oxygen Reduction/Evolution Activity of a Mechanochemically Synthesized Multilayer Graphene

Abstract

Multilayer graphenes were synthesized by a mechanochemical treatment of commercial graphite powder and studied as an air electrode for metal-air batteries. The mechanochemical treatment of the commercial graphite powder was performed for 2h using a planetary ball mill apparatus with large stainless steel balls (10 mm diameter) that did not require the aid of solvents. As a result, multilayer graphenes were successfully obtained when the rotational speed of the planetary ball mill was 500 rpm or more. Raman spectroscopy revealed that the resulting multilayer graphenes contains many defects, while electrochemical measurements revealed that this multilayer graphene has high stability against anodic corrosion. Moreover, a higher bifunctional ORR/OER activity was observed for this material than other bifunctional ORR/OER materials, such as LaNiO3 and multilayer graphene synthesized by a modified Hummer’s method. This excellent electrochemical performance implies that the mechanochemically synthesized multilayer graphenes with high stability and high bifunctional ORR/OER activity obtained in this study can be an excellent alternative to carbon black, which is conventionally used for air electrode materials.

Mechanochemical Synthesis of Nitrogen-Doped and Sulfur-Doped Multilayer Graphene for Use in Bifunctional Oxygen Electrodes

“…Materials synthesis.-The undoped MSMG was synthesized as follows. 25 First, 0.3 g of commercial graphite powder (FUJIFILM Wako Pure Chemical Corp., Japan) and five stainless-steel balls (10 mm diameter) were sealed in a stainless steel pot (12 ml volume) in an argon atmosphere. Then, the graphite powder in the stainless steel pot was mechanochemically treated without solvents using a planetary ball-mill apparatus (P-7, Fritsch GmbH, Germany) at a rotational speed of 700 rpm for 2 h to obtain the undoped MSMG.…”

“…Electrochemical measurements.-The ORR/OER properties of the samples were evaluated using an RRDE that consisted of a Au disk (4 mm diameter) and Au ring (5 mm inner diameter and 7 mm outer diameter). 25 First, 10 mg of the sample and 20 μl of 5% quaternary ammonium anion exchange resin in 2-propanol (AS-4, Tokuyama Corp., Japan) were added to 0.5 ml of ethanol under ultrasonication (45 kHz) to obtain the sample dispersion. Then, 10 μl of the sample dispersion was added dropwise onto the disk electrode and dried at 60 °C for 12 h or more to achieve a sample load of 1.53 mg cm −2 .…”

“…Recently, we investigated mechanochemically synthesized multilayer graphene (MSMG) as an electrode material for ORR/OER bifunctional GDEs. 25 The MSMG was synthesized by the mechanochemical treatment of commercial graphite powder using a planetary ball-mill apparatus with a stainless steel pot (12 ml volume) and five stainless steel balls (10 mm diameter) at a rotational speed of 500 rpm or more. As a result, the MSMG showed high stability against anodic corrosion during the OER and higher ORR/OER bifunctional activity than rGO.…”

Understanding hydrazine oxidation electrocatalysis on undoped carbon

“…This suggests that the layer stacking is not interrupted by the ball-milling, meaning few new basal planes are exposed. 51,53,69 To characterize the surface chemistry of the carbons, X-ray photoelectron spectroscopy (XPS) was measured in the C 1s region and the spectra were deconvoluted (Fig. 2c and Table S1, ESI ‡).…”

“…Rather, it is assumed to be limited to the crucial roles of supporting catalytic sites, conducting electricity, and enabling flow of reactants and products. 47 Yet undoped carbon (and in particular, defected graphene) can electrocatalyze several reactions, 48 including CO 2 reduction, 49 O 2 evolution, 50,51 and O 2 reduction in alkali [50][51][52][53][54][55] and acid, 56 though to a lesser extent than metal-doped carbons. To date, only two undoped carbons have been reported as HzOR electrocatalysts, and their active sites were not identified.…”