Design Of Pd-based Nanomaterials And Performance Study In Electrocatalytic Alcohol Oxidation

Increasing environmental pollution and excessive consumption of traditional fossil fuels make it urgent to develop new eco-friendly energy sources and efficient energy conversion devices.Direct alcohol fuel cells（DAFC）,which use alcohols as fuel to convert chemical energy into electrical energy,have been applied to alleviate the energy crisis and reduce environmental pollution because of their advantages of abundant sources,high energy storage capacity and low toxicity.In recent years,polyhydric alcohols（ethylene glycol,glycerol,etc.）have received increasing attention due to their high theoretical energy density,low toxicity,non-volatility,and bio-renewability.However,the application of catalysts in alkaline alcohol fuel cells still faces numerous challenges and challenges.Numerous studies have shown that some noble metal catalysts,especially Pd and Pd-based nanomaterials,have excellent catalytic ability for alcohol oxidation（AOR）.However,the complicated preparation process,low catalytic activity and poor stability are still the main obstacles limiting the large-scale application of electrocatalysts.Considering the above factors,more research is devoted to the rational design of Pd-based nanomaterials and their use in fuel cells as well as other sustainable energy devices.A generally effective strategy is to introduce another metal or metals into monometallic Pd to form bimetallic or polymetallic Pd-based alloy nanostructures.By this approach,the utilization of the precious metal Pd is improved,while the formation of the alloy phase helps to tune the electronic structure.In addition,the synergistic and electronic effects between different metals contribute to the improvement of intrinsic activity and resistance to toxicization.Since catalytic reactions all occur on the surface of the catalyst,catalysts with more available active sites will provide higher catalytic activity.For the design of Pd-based catalysts for alkaline alcohol oxidation,the main work is as follows:1.complete oxidation to CO₂ by achieving ozone-assisted electrocatalytic ethanol C-C bond cleavage.in alkaline solution,the ethanol oxidation reaction（EOR）activity of the ozone-assisted Pd-Mn O₂/Ti catalyst is greatly improved with a high EOR area activity(14.66 m A cm^-2),which is 2.7 times higher than that without the addition of ozone,and also higher than that of the Pd-Mn/Ti catalyst after ozone assisted,4.3 times higher than that of the Pd-Ti catalyst and 6.1 times higher than that of the Pd-Ti catalyst.The high activity of the Pd-Mn O₂/Ti catalyst EOR after ozone assisted action was attributed to the activation of ozone on Mn O₂ as a highly oxidatively active intermediate（·OH）,while the characteristic·OH signal was also observed in the EPR spectra.Further H-NMR product analysis showed that for the electrolyte after ozone-assisted ethanol,the intermediate acetic acid reported in the literature was not detected.Long-term stability was demonstrated by2000 CV cycle stability test and chronoamperometric（CA）test.Combined with electrochemical tests reveals that ethanol acts directly on the cleavage of C-C bonds under the strong oxidation of ozone without producing CO intermediates,solving the problem of CO poisoning to Pd.2.Porous tetrametallenes were rationally designed and successfully prepared by combining OH adsorption effect,electron effect and C-C bond cleavage site strategy for improving EOR performance.The porous Pd₅₉W₈Rh₁₉Bi₁₄ metallene showed the highest electrocatalytic activity for EOR in alkaline solution with a mass activity of 16.70 A mg_Pd^-1,which was better than Pt/C(1.54 A mg _Pd^-1)and Pd/C(1.83 A mg _Pd^-1).The stability of Pd₅₉W₈Rh₁₉Bi₁₄ remained 85.3%of its initial activity after 5000 CV cycles of testing,while the catalyst maintained 32%of its initial activity after 20,000 s CA testing.While the structure of the introduced porous metallene is stable,the synthesized Pd₅₉W₈Rh₁₉Bi₁₄ has a larger ECSA(107.4 m² g^-1),indicating that its structure can expose more active sites.Further product analysis showed that the C1 selectivity of Pd₅₉W₈Rh₁₉Bi₁₄ reached 65.41%.Electrochemical tests and in situ FTIR further demonstrated that Pd₅₉W₈Rh₁₉Bi₁₄ has a strong C-C bond cleavage ability,and the Rh site can promote the C-C bond cleavage of ethanol to C1 intermediates,while the introduced Bi can provide a large amount of adsorbed OH_ad for the oxidation of intermediates such as CO_ad,thus improving the performance of the catalyst.The porous Pd₅₉W₈Rh₁₉Bi₁₄ metallene has excellent EOR activity and stability,and can also effectively convert ethanol to CO₂,improving the efficiency of clean energy ethanol utilization.3.Rapid synthesis of Pd Pt Au Cu Ni high-entropy alloy aerogel（HEA）by a simple one-step method.In alkaline medium,the EOR mass activity of Pd Pt Au Cu Ni is 6.09 A mg _Pd^-1,which is 2.6 times higher than that of Pd Black mass activity(2.33 A mg _Pd^-1),while Pd Pt Au Cu Ni has good resistance to toxicization,as well as good electrocatalytic kinetics,and shows excellent oxidation of other alcohols including methanol,glycerol and ethylene glycol electrocatalytic performance.The excellent electrocatalytic performance is mainly attributed to the high porosity of Pd Pt Au Cu Ni HEA,the abundance of active sites,and the synergistic interaction between multiple metals.In addition,the interconnected porous structure of the aerogel resulted in good long-term stability of the prepared Pd Pt Au Cu Ni HEA,with a mass activity of about 5.2 A mg _Pd^-1 for Pd Pt Au Cu Ni after 3000 CV cycle stability tests,which was much higher than that of Pd Black(0.81 A mg _Pd^-1).In contrast to the reported HEA,this work achieves the synthesis of high-entropy alloy aerogels by a simple one-step method.This synthetic strategy can be extended to prepare more HEA electrocatalysts with various compositions（six or more elements）in the future.