Construction Of Pd-based Micro/nano Array Films For Direct Alcohol Fuels Electrooxidation

In recent years,with the rapid development of the global economy,energy demand has increased dramatically,leading to the depletion of non-renewable fossil fuels and environmental pollution.Therefore,developing renewable,environmental protection,and low-budget new energy is an important research topic for sustainable development.Direct alcohol fuel cells（DAFCs）have great potential to replace fossil fuels as renewable energy because of their potential high energy density,abundant natural content,no pollution,simple equipment,and other advantages.However,applying it directly to real-life remains a considerable challenge.On the one hand,the dynamic process of spontaneous oxidation of alcohol fuel is slow and highly dependent on the role of the catalyst.Currently,the commonly used catalyst is precious metal material,which has high costs and small reserves and cannot be produced on a large scale.On the other hand,in the process of oxidative dehydrogenation of methanol or ethanol,CO-like intermediates will be generated due to an incomplete reaction.These substances will be adsorbed on the electrode surface,resulting in catalyst poisoning and eventual activity loss.Therefore,it is urgent to study catalysts that can reduce the content of precious metals while improving catalytic activity and durability.The structure type and surface chemical properties of electrode materials significantly affect the electrocatalytic performance in the oxidation reaction of alcohol fuel.In this paper,a monolayer colloidal crystal template was constructed by the gas-liquid interface assembly method,and a Ni bowl-like micro/nanoarray was prepared by electrodeposition.On this basis,according to the difficulties faced by direct methanol fuel cells,different layered micro-nano arrays were designed,and catalytic electrodes were synthesized,which can effectively solve a series of problems.SEM,XRD,XPS,and TEM were used to analyze the structure,morphology,and composition of the catalyst.The electrochemical performance of the catalyst in methanol/ethanol solution was tested by electrochemical workstation.The specific research contents are as follows:（1）Construction of Pd/Zn O/Ni micro/nano array with enhanced electrocatalytic activity for methanol oxidation:In order to overcome the problem of anode catalyst poisoning caused by the adsorption of CO-like intermediates during the electrooxidation of methanol,a new composite layered structure was designed to promote the conversion of intermediate products.Based on the colloidal crystal template,Pd/Zn O/Ni porous array catalysts were synthesized by electrodeposition and magnetron sputtering.The catalyst showed excellent electrocatalytic activity for methanol oxidation in alkaline solution.The corresponding mass activity(812.7 m A/mg _Pd)is 6 times that of commercial Pd/C catalyst(134.8 m A/mg _Pd),and the stability is much better than that of commercial Pd/C catalyst.These excellent electrochemical properties can be attributed to its unique layered porous structure（which provides a high specific surface area for methanol reactions）and the Zn O intermediate layer（which effectively removes toxic substances at Pd sites through strong oxidizing hydroxyl radicals）.（2）Construction of Pd Co catalysts on Ni bowl-like micro/nano array films for efficient alcohol electrooxidation:The combination of noble metals with other transition metals to form alloy compounds can effectively reduce the catalyst cost and promote the electrooxidation of methanol/ethanol through the synergistic effect between metals.Pd Co alloy was synthesized by electrodeposition control on the same Ni bowl array template.The effect of stirring rate and concentration of electrolyte on material growth were studied and the optimal experimental conditions were found.The Pd₈Co₁/Ni array film catalyst synthesized at a stirring speed of 200 Revolutions Per Minute（RPM）exhibited the highest electrochemical active surface area（ECSA,95.65 cm2/mg）and specific and mass activities in methanol(173.2 m A/cm² and 2032.9 m A/mg _Pd,respectively)and ethanol(240.1 m A/cm² and 2846.1 m A/mg _Pd,respectively)oxidation in alkaline media.（3）Construction of Pd Ce oxides/Ni array for efficient alcohol electrooxidation:In the past,most of the elements that form composites with precious metals are transitional metals.In this experiment,rare earth group metals were tried and some research results were obtained.Ce element is one of the most widely used rare earth metals,with large reserves and low price.It is often used in catalysis,sensing and fuel cell fields.Due to its strong oxidation ability,the lattice oxygen contained in the reaction itself is converted into a large number of hydroxyl functional groups,which is crucial for removing the intermediate adsorbents on the electrode surface during the oxidation of methanol or ethanol.Pd Ce oxides with different atomic proportions were prepared and the morphology,structure,crystallinity and surface chemical states were characterized in detail.After a series of analysis such as morphology and electrochemical test,the catalyst with atomic ratio of Pd₇₃Ce₂₇ exhibited the highest specific and mass activities in methanol(112.4 m A/cm² and 1584.8 m A/mg _Pd,respectively)and ethanol(156.4 m A/cm²and 2191.8 m A/mg _Pd,respectively)oxidation in alkaline media.In summary,the three experiments designed to address the difficulties faced by direct alcohol fuel cells have achieved certain research results,providing a certain opportunity for the development of direct alcohol fuel cells.