Nanohybrid graphene oxide membranes functionalized using 3-mercaptopropyl trimethoxysilane for proton exchange membrane fuel cells

The high proton conductivity of graphene oxide (GO) under humidified conditions has attracted exceptional attention in many applications including fuel cells. However, the proton conductivity of GO membrane (GOM) is much lower than that of high-performance polymer electrolyte such as Nafion®, and in contact with hydrogen gas in fuel cells, the loss of surface functional groups due to reduction by hydrogen is accompanied by an increase in electronic conductivity. In this study, (3-mercaptopropyl) trimethoxysilane (MPTS) was reacted with the GO nanosheets to form MPTS-modified GO, and it was followed by incorporating excess MPTS as a binding agent for the composite electrolyte (MGC). By oxidation of the sulfhydryl groups of MPTS into sulfonic acid groups (-SO3H), a high-speed two-dimensional surface conduction path was formed on the GO surfaces, thereby dramatically improving the proton conductivity of GOM. In addition, a further increase in proton conductivity was achieved by incorporating excess MPTS. The optimal addition amount was investigated by controlling the amount of MPTS from 1 to 70 wt%, increasing this ratio in the GOM matrix, the amorphous siloxane network was increased, simultaneously the 2D GOM lamellar structure was gradually transformed into a dense, composite structure with high-density polymers, and the interlayer space of GO layers increased. The excellent membrane properties of 50 wt% of MPTS hold the proton conductivity of (σin) 42.10 mS/cm at 80 °C and wet conditions, the gas permeability of 1.36 Barrer, a high open circuit voltage of 1.04 V, and the power density of 55.45 mW/cm2, respectively. The MPTS-derived siloxane network has improved the physicochemical properties, negligible fuel crossover, and optimized water uptake with dimensional stability without sacrificing the proton conductivity of MGCs. The assessment of the ion exchange capacity (IEC) showed that MGCs can exchange protons. The physico-chemical properties, proton conductivity, gas crossover, mechanical and thermal stability of MGCs as an electrolyte were investigated and compared with conventional GOM and Nafion®. As an application to a hydrogen fuel cell, the Pd-deposited MGCs were prepared and applied to room-temperature HMFCs for the first time, and their fuel cell performances were reported.