Phyto-mechanochemical synthesis of an Ag@GO/CNT catalyst: enhanced hydrogen production via a continuous flow system

Abstract

Due to its high energy density and minimal emissions, hydrogen is a promising alternative energy source. For sustainable development, hydrogen production from non-fossil sources is essential. The hydrolysis of sodium borohydride enables rapid hydrogen production on demand, particularly with the aid of a catalyst. Thus, developing efficient and cost-effective catalysts for this process is essential. Herein, a phyto-mechanochemical approach is employed to obtain a material containing silver (Ag), reduced graphene oxide (rGO), and multi-walled carbon nanotubes (MWCNTs) for use as a high-performance H₂ production catalyst at room temperature via the water displacement method. All the samples (Ag NPs, Ag@rGO, and Ag@rGO/CNT) were characterized by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The morphological analysis confirmed the presence of mechanochemical Ag NPs uniformly dispersed on the rGO and CNTs. The results revealed that Ag@rGO/CNT exhibited superior particle distribution and porosity characteristics, achieving a high hydrogen generation rate of 4243 mL min⁻¹ g_cat⁻¹. The activation energy for the sodium borohydride hydrolysis reaction on the Ag@rGO/CNT catalyst was determined to be 7.08 kJ mol⁻¹, as calculated using the Arrhenius equation and the zero-order reaction model. The catalyst's superior performance is confirmed by its low activation energy compared to Ag NPs and Ag@rGO catalysts. The results of the recycling experiments also showed that, after four repetitive cycles, the catalyst's performance gradually declined with each subsequent cycle. The Ag@rGO/CNT catalyst's previously listed characteristics make it an effective catalyst for the hydrolysis of NaBH₄, resulting in the production of hydrogen.