One-Step Synthesis of a Binder-Free, Stable, and High-Performance Electrode; Cu-O|Cu3P Heterostructure for the Electrocatalytic Methanol Oxidation Reaction (MOR)

Although direct methanol fuel cells (DMFCs) have been spotlighted in the past decade, their commercialization has been hampered by the poor efficiency of the methanol oxidation reaction (MOR) due to the unsatisfactory performance of currently available electrocatalysts. Herein, we developed a binder-free, copper-based, self-supported electrode consisting of a heterostructure of Cu₃P and mixed copper oxides, i.e., cuprous-cupric oxide (Cu-O), as a high-performance catalyst for the electro-oxidation of methanol. We synthesized a self-supported electrode composed of Cu-O|Cu₃P using a two-furnace atmospheric pressure-chemical vapor deposition (AP-CVD) process. High-resolution transmission electron microscopy analysis revealed the formation of 3D nanocrystals with defects and pores. Cu-O|Cu₃P outperformed the MOR activity of individual Cu₃P and Cu-O owing to the synergistic interaction between them. Cu₃P|Cu-O exhibited a highest anodic current density of 232.5 mAcm^-2 at the low potential of 0.65 V vs. Hg/HgO, which is impressive and superior to the electrocatalytic activity of its individual counterparts. The formation of defects, 3D morphology, and the synergistic effect between Cu₃P and Cu-O play a crucial role in facilitating the electron transport between electrode and electrolyte to obtain the optimal MOR activity. Cu-O|Cu₃P shows outstanding MOR stability for about 3600 s with 100% retention of the current density, which proves its robustness alongside CO intermediate.

Graphene Oxide and Reduced Graphene Oxide Nanoflakes Coated with Glycol Chitosan, Propylene Glycol Alginate, and Polydopamine: Characterization and Cytotoxicity in Human Chondrocytes

Recently, graphene and its derivatives have been extensively investigated for their interesting properties in many biomedical fields, including tissue engineering and regenerative medicine. Nonetheless, graphene oxide (GO) and reduced GO (rGO) are still under investigation for improving their dispersibility in aqueous solutions and their safety in different cell types. This work explores the interaction of GO and rGO with different polymeric dispersants, such as glycol chitosan (GC), propylene glycol alginate (PGA), and polydopamine (PDA), and their effects on human chondrocytes. GO was synthesized using Hummer's method, followed by a sonication-assisted liquid-phase exfoliation (LPE) process, drying, and thermal reduction to obtain rGO. The flakes of GO and rGO exhibited an average lateral size of 8.8 ± 4.6 and 18.3 ± 8.5 µm, respectively. Their dispersibility and colloidal stability were investigated in the presence of the polymeric surfactants, resulting in an improvement in the suspension stability in terms of average size and polydispersity index over 1 h, in particular for PDA. Furthermore, cytotoxic effects induced by coated and uncoated GO and rGO on human chondrocytes at different concentrations (12.5, 25, 50 and 100 µg/mL) were assessed through LDH assay. Results showed a concentration-dependent response, and the presence of PGA contributed to statistically decreasing the difference in the LDH activity with respect to the control. These results open the way to a potentially safer use of these nanomaterials in the fields of cartilage tissue engineering and regenerative medicine.