Tunable Electrochemical\nHydrogen Uptake and Release\nof Nitrogen-Doped Reduced Graphene Oxide Nanosheets Decorated with\nPd Nanoparticles

Abstract

Strategic surface modification and doping of reduced\ngraphene oxide\n(rGO) support materials via heteroatom functionalization and metal\ndecoration have been shown to improve hydrogen storage performance.\nBy utilizing a microwave-assisted hydrothermal method, a series of\nnitrogen-doped rGO (NrGO) nanomaterials were fabricated with tuned\nnitrogen contents up to 7.0 at. %. The NrGO nanomaterials were then\ndecorated with palladium nanoparticles (Pd NPs) via a facile chemical\nreduction method to form Pd/NrGO nanocomposites. The incorporation\nof an appropriate nitrogen content in rGO significantly improved the\nhydrogen uptake and release activity. The optimized Pd/NrGO nanocomposite\nwith ∼5 at. % of nitrogen exhibited over sixfold enhancement\nof hydrogen storage capacity compared to Pd/rGO. Pair distribution\nfunction analysis by high-energy X-ray diffraction showed the formation\nof PdH_<i>x</i> NPs only in NrGO materials, suggesting\nthat the nitrogen doping enhances the hydrogen affinity of the Pd\nNPs. Systematic structural characterization and electrochemical studies\nreveal that the optimized Pd/NrGO exhibited a uniform distribution\nof Pd NPs on the NrGO nanosheets and low electron-transfer resistance.\nThese results suggest that nitrogen doping leads to a strong metal-carbon\nsupport interaction, higher specific surface area, and larger accessibility\nfor surface diffusion-controlled hydrogen uptake and release processes.\nCompared to Pd/rGO, the optimized Pd/NrGO nanocomposite attained a\nconsistent hydrogen release charge after 3000 cycles, demonstrating\nan excellent stability under acidic conditions. This work opens a\nnew avenue for designing advanced and cost-effective hydrogen storage\nmaterials by tuning the dopant content to maximize their performance\ntoward a hydrogen economy.