Preparation And Hydrogen Storage Performance Of Pt Decorated Nitrogen-doped Carbon Nanosheets

Hydrogen is recognized as the cleanest fuel and known as the"ultimate energy source of the 21st century",which is expected to alleviate the increasingly severe energy crisis and environmental pollution problems.The key of hydrogen energy utilization is the safe storage of hydrogen,so it is very important to develop safe and efficient hydrogen storage materials at ambient temperature.Carbon-based materials have been widely used in the field of hydrogen storage because of their high specific surface area,controllable morphology and tunable pore structure.However,the hydrogen storage capacity of carbon-based materials is very low at room temperature,which limits its application.It has been proved that the hydrogen storage capacity of carbon-based materials at room temperature can be significantly improved by loading noble-metal nanoparticles on the surface,and the dispersion and particle size of nanoparticles can affect the hydrogen absorption efficiency.In order to improve the hydrogen storage performance of carbon-based materials at room temperature by hydrogen spillover,three types of nitrogen-rich precursors were selected as carbon sources to construct Pt-decorated nitrogen-doped carbon composites by carbonization at high temperature and reduction in alcohol.Through physical characterization and performance test,the influence of specific surface area and precious-metals loading on hydrogen storage performance was investigated,and the hydrogen storage mechanism of such composite system was clarified.The main contents are as follows:1)The Pt@ZIF-8-CNS composites with Pt NPs decorated on ZIF-8 derived carbon nanosheets were prepared and studied as hydrogen storage materials.The two-dimensional lamellar ZIF-8 was selected as carbon source,which was directly carbonized to form nitrogen-doped carbon nanosheet（ZIF-8-CNS）,and then the Pt@ZIF-8-CNS composite materials was obtained by the ethylene glycol reduction strategy.The composite exhibited a typical sheet-like structure,and Pt NPs were uniformly dispersed on the surface of carbon nanosheets.Studies proved that the ZIF-8-CNS had a high specific surface area and pore volume of 1598 m² g^-1 and 1.0cm³ g^-1.The hydrogen storage capacity of ZIF-8-CNS was only 0.93 wt%at 77 K,while the hydrogen storage capacity of Pt@ZIF-8-CNS doped with different amounts of Pt was increased by 1.6-8.0 times,mainly due to the large specific surface area of the composite material and hydrogen spillover effect.2)The Pt@NPCNS composites with Pt NPs decorated on silk-derived carbon nanosheets were prepared and studied as hydrogen storage materials.Natural biomass silk cocoons were selected as carbon source precursor,and the hydrophobic and hydrophilic segments in silk fibroin molecular chain self-assembled into a two-dimensional layered structure in solution,and then activated and carbonized treatment methods were used to successfully prepare nitrogen-doped porous carbon nanosheets（NPCNS）.The Pt@NPCNS composites were finally obtained using the ethylene glycol reduction strategy.The porous carbon material prepared by this method had a sheet-like structure with a large specific surface area of 2100 m² g^-1 and a pore volume of 1.68 cm³ g^-1.The NPCNS substrate with a high specific surface area showed a hydrogen storage capacity of 2.19 wt%at 77 K and 1 bar,while Pt@NPCNS displayed an improved hydrogen storage capacity at 298 K,10-20 times higher than that of NPCNS,due to hydrogen spillover effect of the composite at room temperature.3)The Pt@NCNS composites with Pt-decorated on layered carbon nanosheets derived from metal-organic-framework were prepared and studied as hydrogen storage materials.Fe Cl₃ was selected as the metal salt,and dopamine hydrochloride was the organic precursor to form a layered metal-organic hybrid material at room temperature,which predetermined the structure of the final carbon material,and produced highly porous and N-doped ultra-thin carbon nanosheets through carbonization at high temperature.This strategy did not use polluting activators to obtain a carbon support with high specific surface area and porosity.In the glycol system,Pt NPs were successfully loaded onto NCNS nanosheets,and the Pt@NCNS composites were obtained.The study found that NCNS had an ultra-thin nanosheet morphology,and its hydrogen storage capacity at 77 K was 1.46 wt%.The hydrogen storage capacity of NCNS at room temperature was 0.015 wt%.After Pt loading,the hydrogen storage capacity of the composite reached up to 0.25 wt%.The high specific surface area of nitrogen-doped carbon nanosheets provided a large number of hydrogen adsorption sites,increased the utilization of noble metal,and improved hydrogen storage performance of composites at room temperature.