Preparation Of 2D Ni Co/carboxylated Graphene Composites And Their Hydrogen Generation Performances From NaBH₄ Hydrolysis

Sodium borohydride（NaBH₄）has a high hydrogen storage capacity and can produce hydrogen spontaneously.The hydrolysis reaction is environmentally friendly and its hydrolysis by-product NaBO₂ is non-toxic and harmless,but the hydrolysis process is slow and requires catalysts to achieve hydrogen generation on demand.Among many non-precious metal catalysts,cobalt-based catalysts show good catalytic hydrogen generation performance but still have some problems.In order to solve the problems of agglomeration and deactivation of cobalt-based catalysts to obtain better hydrogen generation catalysts,Co/rGC,NiCo/rGC and Co-NiCo/rGC catalysts were prepared on carboxylated graphene carriers in this paper,and their structure,morphology and valence were characterized by XRD,TEM and XPS.Their performance in catalytic hydrogen generation from sodium borohydride was investigated by changing the hydrolysis hydrogen generation conditions.The main studies are as follows:1)Carboxylated graphene（rGC）was obtained by modification with chloroacetic acid.The results showed that when chloroacetic acid was used as the nucleophilic reagent,good carboxylated graphene rGC could be obtained by carboxylation modification of graphene oxide with 2 g chloroacetic acid and 1 g NaOH at 35℃.Its specific surface area was 1.3times higher than before the modification,and an increase in C-O bonding with reduced-COOH functional groups could be clearly observed in its XPS and FTIR characterization,and the carboxylated graphene rGC was determined by methylene blue The concentration of carboxyl groups in carboxylated graphene was 0.13235μM·mg^-1.2)Co/rGC and NiCo/rGC catalysts were prepared on carboxylated graphene carriers by reduction and replacement methods.The results showed that the NiCo/rGC catalysts showed a homogeneous layer structure after 30 min of replacement,which proved that the addition of carboxylated graphene could effectively improve the agglomeration of the catalysts.Both catalysts showed high activity in catalyzing the hydrogen generation from sodium borohydride at p H 10 and hydrolysis temperature of 35℃.The NiCo/rGC catalyst produced hydrogen at a rate of 2926.15 m L·（min·g）^-1 with an activation energy of 27.70k J·mol^-1,which was significantly lower compared to the Co/rGC reaction activation energy(31.49 k J·mol^-1).3)The 2D nanolayer Co-NiCo/rGC catalysts were obtained by reducing the Co²⁺in the replacement solution to reload it onto the catalyst surface using a reduction method.The results showed that the Co-NiCo/rGC catalyst had the most efficient hydrogen generation activity at p H 10 and a hydrolysis temperature of 35℃.The hydrogen generation rate was3586.67 m L·（min·g）^-1 and the activation energy was effectively reduced to 23.77 k J·mol^-1;and the hydrogen generation activity of 95.3%was still maintained in the 5 cycle test.On this basis,the mechanism of hydrogen generation in Co-NiCo/rGC catalysts was also investigated.The use of carboxylated graphene as a carrier allows for better dispersion of the catalyst and fully exposes the Niand Co metal active sites,which better facilitates the electron transfer and intermetallic synergy in the hydrogen generation process and greatly improves the catalytic hydrogen generation rate.