Rational Design And Activity Regulation Of Hydrogen Energy Conversion Nanocatalysts

Hydrogen energy is one of the most important renewable energy sources in the 21 st century,which is a new approach to support the sustainable development of the national economy in the future.The key points of the development of hydrogen energy lie in how to achieve large-scale production and storage-transportation,and the low-cost utilization of hydrogen energy.In the prior art,small organic molecules such as formic acid,act as a chemical carrier for high density hydrogen storage,possess prominent advantages in hydrogen energy storage and transportation.It is an international research hotspot to realize the catalytic decomposition of formic acid at room temperature and thus to seek an efficient way for hydrogen production.In regards to the utilization of hydrogen energy,fuel cells are efficient energy conversion devices.The main obstacle to the development of fuel cells is the slow kinetics of cathodic oxygen reduction reaction（ORR）,which leads to the high cost of noble metal catalyst Pt.The complexity and the low speed of the above-me ntioned hydrogen energy conversion result in the necessity of administration of highly effective catalysis to meet the practical requirements.The inefficiency of the conventional catalysts for hydrogen energy conversion has become a bottleneck for the application of hydrogen energy.The present paper focused on figuring out solutions against the bottleneck for improving the efficiency of hydrogen energy conversion catalysts.Through systematic and rational design,the dependence between composition-structure-performance was explored,and the corresponding precise control means for the preparation of low/non-noble metal catalysts were developed,which provided a new way to realize low cost and high efficiency conversion of hydrogen energy.This thesis mainly contains the following four parts:1.According to the design idea of lattice expansion,a series of Au@Pd/C catalysts towards the formic acid decomposition reaction at room temperature were synthesized incorporating the modified co-reduction precipitation method by introducing element Au to increase the bond length of Pd-Pd and producing tensile strain effect,and then changing the proportion of the key active substance Pd O dispersed on the surface of the supports,resulting in a substantial improvement of the catalytic activity.After the relationship between the chemical active components and the catalytic activity was studied,and the reasonable rational design regulation of the core-shell structure was further carried out,the TOF of optimized Au@Pd（1:1）/C catalyst achieved a TOF of 5189 h^-1 for the decomposition reaction of formic acid.2.After an in-depth study of the effect of Au in Pd Au alloy on the catalytic activity of Pd based catalysts for decomposition of formic acid,it is found that the introduction of Au has a double-sided effect:On the one hand,the strain effect caused by Au leads to the increase of the propotion of Pd O,which is the key active substance on the surface of catalyst nanoparticles,which in turn brings about the enhancement of the catalytic activities.On the other hand,as the proportion of Au further increased the ligand effect of Au would block the generation of Pd O,and led to theactivity decline of the catalysts.Therefore,the activity of the catalyst varies volcanically as the the content of gold increases.Based on the precise regulation of Au optimal ratio content,a series of Pd Au/C alloy catalysts were synthesized by modified co-reduction precipitation method,wherein the conversion frequency of Pd0.69Au0.31/C nano-catalyst for decomposition of formic acid at room temperature was 6634 h^-1,the value of which is higher than that of any other nano-catalysts have been reported by the current literatures.3.Based on the design idea of enhancing catalytic performance by element doping,N and P dual-doped porous carbon nanosheet-like ORR catalysts were synthesized by template-assisted polymer pyrolysis derivative method（TAPPD）.It was found that the dual-doped catalysts had better ORR activities than single doped catalysts due to the synergy effect of N and P.In addition,the introduction of C₃N₄ template had a multiplier effect on the specific surface area structures of N and P dual-doped porous carbon nanosheets.Combined with the optimization of temperature,components and other conditions,the ORR catalysts with excellent intrinsic activity and selectivity in electrocatalysiswere successfully synthesised.The ORR half-wave potential could reach up to 0.85 V,which is comparable to the commercial Pt/C catalysts（0.84 V,under the same measurement conditions）.4.The number of active sites of the N,S and O tridoped porous carbon nanosheet-like ORR catalysts were increased by the increase of the specific surface area and the reinforcement of the oxygen-rich effect caused by employing SiO₂ as hard template.Through the study on how the size of the SiO₂ templates influence the structures of the template-assisted polymer pyrolysis derivative ORR catalysts,it is found that the smaller the size of the SiO₂ templates,the larger the specific surface area of doped porous carbon nanosheets,thereby doping more O elements.Meanwhile controllable doping of element O could be realized by regulating the content of SiO₂ templates of selected dimensions.After optimizing the conditions,N,S and O tridoped catalysts comparable to the commercial Pt/C catalysts were obtained,and the ORR half-wave potential of which was 0.86 V,rivals to the commercial Pt/C catalysts（0.84 V,under the same measurement conditions）.