Preparation And Electrocatalytic Performance Of Palladium-Nickel Composite Catalysts Of Different Dimensions

In recent years,environmental pollution is becoming more and more serious and energy demand is increasing,so it becomes urgent to explore clean energy to replace the depleting fossil fuels.Combining renewable energy sources such as solar and wind power with electrolytic water technology to produce clean energy-hydrogen energy-is one of the key technologies to realize the transformation of traditional energy structure and the sustainable development of new renewable energy sources.Zinc-air batteries（ZABs）have a broad application prospect and important research value due to their intrinsic safety and environmental friendliness.In addition,direct alcohol fuel cells（DAFCs）have also attracted much attention due to their high energy efficiency,simple design and easy fueling.The most critical part in these new cells is the electrocatalyst,which makes electrocatalysis a hot topic of research.There are many types of catalyst materials,and it is well known that precious metal catalysts such as Ru O₂ and Pt-based catalysts are most widely used in the oxygen evolution reaction（OER）,hydrogen precipitation reaction（HER）and oxygen reduction reaction（ORR）.However,these noble metal catalysts are severely limited in their potential due to their low activity,resistance to toxicity,poor durability,and high cost of noble metals.Pd,as a metal in the same group as Pt,has a similar external electronic structure and chemical properties.By introducing 3d transition metals（e.g.Ni,Fe）into Pd catalytic materials,the lattice shrinkage of Pd can be induced,weakening the binding energy of Pd to oxygen species and improving the catalytic activity.This makes Pd-based catalysts one of the most promising electrocatalytic candidates to replace Pt.In addition,improving the utilization of noble metals and optimizing the catalytic performance of noble metal catalysts are also hot topics of current research.How to take advantage of the different dimensional structure of the carrier itself to improve the catalytic activity while reducing the amount of precious metals has become a major challenge.In this thesis,three different dimensional PdNi-based nanomaterial catalysts were synthesized by hydrothermal and water bath methods,namely one-dimensional Pd_0.05Ni Fe_0.2O_0.35 nanowires,two-dimensional Pd Ni O/Ni nan sheets and three-dimensional dendritic Pd Ni DNTs/NF.They were applied to alcohol oxidation,total hydrolysis and the assembly of zinc vacancy cells.The specific studies are as follows:1.We develop an efficient and stable trifunctional electro catalyst of self-supportive Pd_0.2Ni₅₈Fe₃₀O_11.8 nanowires for Zn-air batteries and overall seawater splitting,which connect with photovoltaic cells to assemble a solar-driven self-powered electro catalytic water splitting system.It is noticed that the obtained self-supportive Pd_0.2Ni₅₈Fe₃₀O_11.8nanowires show a special 3D network structure connected by nanowires with a hierarchical structure,improving the charge and mass transfer.Furthermore,the self-supportive Pd_0.2Ni₅₈Fe₃₀O_11.8 nanowires displayed low over potentials of 39 and 143 m V to deliver current densities of 1600 cm^-2and 1200 m A cm^-2,which is at the top level of great prospects for industrialization.The output voltage of Zn-air battery is 1.88 V with a constant and stable current density of 10 m A cm^-2,successfully creating an efficient and stable 24 h overall water-splitting system.The solar-powered uninterrupted overall water-splitting systems open up exciting opportunities for fully renewable and sustainable energy applications.2.We report the synthesis of PdNiO/Ni seashell-like nanostructures with trace Pd through a novel one-step wet chemical method for the first time.The optimized Pd Ni O/Ni seashell-like nanostructures with an ultra-thin nan sheets（0.5 nm）are connected self-assembly to form a network structure,which exhibits a large surface area and unprecedented ORR/OER with a positive half-wave potential of 0.894 V vs.RHE and an over potential of 180 m V at 10 m A cm^-2 in alkaline solution,outperforming most of Pd Ni catalysts.When the Pd Ni O/Ni seashell-like nanostructures are applied as electrodes for zinc-air batteries,it delivers a high power density of 170.1 m W cm^-2 and an impressive energy density of 817.3 m A h g^-1.This work opens up a new strategy for generating superior oxygen electro catalysis and provides new insight into the correlation of trace Pd and Ni in the improvement of alkaline oxygen electro catalysis.3.This work reports the preparation of self-supported PdNi dendrites on Ni foam（self-supported Pd Ni DNTs/NF）with a large specific surface area by a simple self-sacrificing template and hydrothermal method.The presence of NF with enrichment of nucleation sites is crucial for the generation of self-supported Pd Ni DNTs.The as-obtained self-supported Pd Ni DNTs/NF exhibits an excellent property for ethanol and glycerol electrooxidation with the mass activity of 2375.7 m A mg_cat^-1 and 2451.6 m A mg_cat^-1,the specific activity of 10.07 m A cm^-2 and 10.84 m A cm^-2,respectively,in alkaline media,which should attribute to abundant high-index facets and low-coordinated atoms on the edge of branches.Furthermore,the Pd Ni DNTs/NF exhibits outstanding long-term durability in the current–time test for 7200 s with superior anti-CO poisoning performance,possessing a potential application in DAFCs.