Green synthesis of Si-GQD nanocomposites as cost-effective catalysts for oxygen reduction reaction

Hybrid silicon nanosheets (NSs)-graphene quantum dot nanocomposites (Si-GQD NCs) were prepared from a mixture of GQDs and Si NSs in ethanol at 25 °C for 2 h and used as a catalyst for oxygen reduction reactions (ORR) in direct methanol fuel cells (DMFCs). GQDs were prepared from fenugreek seed extracts (300 °C, 8 h) and wrinkled Si NSs were obtained from pyrolysis of rice husks (700 °C, 2 h). The Si-GQD NCs fabricated glassy carbon electrode (GCE) has greater electrocatalytic activity for ORR in comparison to Si NSs and GQDs modified GCEs, showing the synergistic effect provided by Si NSs and GQDs. The GQDs enhance O₂ adsorption and ORR activity, while Si NSs function as a support to increase charge transfer. Additionally, high surface area and the wrinkled structure of Si NSs allow efficient mass transfer, leading to greater ORR activity. The onset potential of the Si-GQD NC electrode is -0.33 V (versus Ag/AgCl) with a current density of 2.61 ± 0.27 mA cm^-2, showing greater electrocatalytic activity. Furthermore, the Si-GQD NC electrode exhibits greater tolerance against methanol and carbon monoxide poisoning than the Pt/C electrode. The environmentally-friendly, active, stable and inexpensive Si-GQD NCs hold great potential for DMFCs.