Study For The Application Of Nano-Metal-Based Catalysts For Efficient Catalytic Hydrogen Storage/Release For Formic Acid/Ammonia

With the continuous development of society,fossil fuels are being rapidly consumed.The development of hydrogen（H₂）to replace the increasingly depleted fossil energy is not only conducive to easing the energy crisis,but also to achieve sustainable development of energy.However,the problems of high cost,high risk and low efficiency in the process of H₂ storage and transportation seriously limit the utilization and development of H₂.Therefore,it is of great significance to explore efficient H₂ storage/release methods for the further application.Formic acid（FA）with high hydrogen content（4.4 wt%）,existing in liquid form at room temperature,is non-toxic,good stability,and easy to obtain.Under the action of catalysts,FA can be quickly decomposed to release H₂ and resynthesized by hydrogenation of carbon dioxide,showing great potential for H₂ storage and release.Furthermore,other clean and efficient carbon-free H₂ storage media（such as ammonia）have been widely studied in order to achieve a carbon-free H₂ storage/release process.Ammonia（NH₃）has a high hydrogen content of 17.6 wt%,which can be liquefied by simple pressurization.Liquid NH₃ has higher energy density than liquid H₂,and has great advantages in storage safety and transportation cost,so it is an ideal hydrogen storage material.Renewable electricity driven nitrogen oxide hydrogenation to ammonia is an environmentally friendly method to develop NH₃ as a hydrogen storage material,which is mild,easy to operate,and expected to replace the energy-intensive Haber-Bosch process for NH₃synthesis.Over recent years,the advances on the nano-metal-based catalysts have bring a great progress of the chemical reaction in various applications.Therefore,the development of efficient and stable nano-metal-based catalysts for catalytic hydrogen storage/release reaction is of great significance for the development and utilization of hydrogen energy.The research content of this paper mainly includes the following aspects:1.The surface energy of the catalyst has an important effect on the adsorption of the reactants.Preparing a catalyst with locally high surface energy by alloying can give full play to the synergistic effect between metals,reduce the energy barrier of the reaction,and improve the catalytic ability of the catalyst.The AuPdIr nanoalloy supported on functional graphene substrate was synthesized through a simple one-step method,and investigated the catalytic capacity for formic acid dehydrogenation at room temperature.The functionalized substrate has a large specific surface area,which is conducive to anchoring metal particles to form small particle sizes.At the same time,the amino group enhances the hydrophilicity of the material,which is beneficial to the full contact between the catalyst and the formic acid solution to achieve rapid dehydrogenation.Notably,Au_0.35Pd_0.5Ir_0.15/NH₂-N-r GO reaches the initial conversion frequency of 12781.2 h^-1 without any additives at room temperature.It has excellent cycling stability and shows 100%conversion and 100%hydrogen selectivity even after150 days.This is due to the small particle size and the good synergy effect between the metals.According to the density functional theory（DFT）calculations,the introduction of Ir can enhance the local surface energy,induce the change of FA adsorption configuration,and reduce the energy barrier of the determination step to improve the performance.2.Inspired by the evidence that Fe and Mo in nitrogenase have strong ability to adsorb nitrogen,we designed a low-cost Mo-regulated Fe catalyst for efficiently catalyzing nitrate and nitrite to the carbon-free hydrogen storage molecules（NH₃）.Due to the synergistic effect of the two components,the electrochemically in-situ constructed Fe/FeMoO₄ catalyst exhibits better catalytic performance than the single Fe or Mo material with a high metal utilization rate.Under alkaline conditions,it achieves the best Faraday efficiency（FE）of 96.53%,and the corresponding NH₃ yield is 640.68 mg h^-1 mg_cat.^-1at-0.8 V vs.RHE.Under neutral conditions,the FE reaches87.68%with the NH₃ yield rate of 302.56 mg h^-1 mg_cat.^-1at the same potential,showing great environmental suitability.3.In order to further promote the efficient conversion of nitrate/nitrite and realize the industrial grade synthesis of NH₃,we designed a stable and porous integrated electrode to improve the conductivity and stability of the catalyst.Cu atoms are doped on the Co foam to neutralize the strong adsorption energy of surface Co atoms for the reactant and intermediates,as well as promote the hydrogenation step.At the same time,under the activation of the electrolyte,a rich three-dimensional sheet structure is formed,which effectively increases the active area and exposes more active sites.The electrocatalytic reaction involves three processes:spontaneous redox of catalyst and reactant,in-situ reduction of catalyst and electrocatalytic reduction of reactant.Through a series of in-situ experiments and DFT calculations,the activation mechanism of the catalyst and the actual metal sites during the reaction were analyzed.A-CuCo@CF catalyst delivers a NH₃ yield rate of 279.44 mg h^-1 cm^-2 with the FE of 96.45%at-0.8V vs.RHE,which is superior to most catalysts.After the optimization of the reactor,A-CuCo@CF catalyst can achieve 4.11 g NH₃ production per hour,which is beneficial to promote the application of NH₃ as a carbon-free hydrogen storage material.