Preparation And Performance Investigation Of The Pd-Based Catalysts For Derict Ethanol Fuel Cells

The lack of resources,environmental degradation is a serious problem facing the world today.Developing clean and renewable energy has become an urgent problem for human.Direct ethanol fuel cells are devices to convert directly chemical energy into electrical energy efficiently and producing low CO2 emissions.The main application of the direct ethanol fuel cells are electronic portable devices,portable auxiliary chargers and transport.Direct ethanol fuel cells has attracted ever-increasing attention due to some outstanding advantages,due to its high energy density,easy storage and transportation,and renewability of ethanol.Despite its great potential in commercialization,the current development of direct ethanol fuel cells is still impeded owing to ethanol's sluggish kinetics.Therefore,the development of direct ethanol fuel cells faces enormous challenges.Crucial to enabling highly efficient and reliable conversion of chemical energy into electric energy is the development of high active,ability and cost-effective electrocatalysts for ethanol oxidation reaction(EOR)in alkaline solution.Currently,platinum(Pt)and Palladium(Pd)are well-known as benchmark catalysts for their excellent performance in ethanol oxidation reaction(EOR).However,their potential is severely limited by their low activity,poor durability arising upon rapid poisoning by the carbonaceous intermediates,and low selectivity toward C-C bond cleavage,as well as high material cost.In an effort to alleviate these problems,several strategies have been developed and implemented to synthesize multicomponent and/or nanocomposite catalysts.Alloying Pt or Pd with 3d transition metals provides a straightforward way to alter the electronic structure and optimize the binding energies of adsorbates on the catalyst surface.Creating synergistic catalysts via a combination of noble metals with oxophilic metal oxides/hydroxides proved a promising approach for improving the durability.According to the literature reports,both approaches are effective in enhancing the activity and durability of Pt-and Pd-based catalysts.Therefore,in order to develop high active,ability and cost-effective electrocatalysts,we employed a combination of concerted catalysis and nanoengineering strategies to simultaneously address the issues of intrinsic activity and utilization efficiency of Pd.In this paper,we designed and prepared some Pd-based catalysts with different compositions and structures for ethanol oxide reaction,and structure and electrochemical properties of the catalysts were further studied.The work of this paper includes the following sections:Firstly,by using a facile glucose-assisted hydrothermal method followed by an electrodeposition process,we synthesized a self-supported hybrid electrocatalyst Pd/Ni(OH)2@C/NF with the size of Pd particles was about 3.5 nm,and they were uniformly distributed on the surface of the catalyst.The results showed that the incorporation of Ni(OH)2 can readily facilitate water dissociation to form-OHads species,which work in concert with the adjacent Pd atoms to improve catalytic performance of Pd/Ni(OH)2@C/NF.Inaddition,our study highlights the important role of morphology control of hydroxide in the EOR electrocatalysis.After a continuous 2000 cycle stability measurement,the catalytic activity of Pd/Ni(OH)2@C/NF hybrid catalyst still maintained of 89.6% of its initial current density.The current density of Pd/Ni(OH)2@C/NF was still maintained of 5% of its initial current density after 5000 s long-term stability measurement.The FE-SEM observation of the post-used Pd/Ni(OH)2@C/NF found that morphological feature was preserved after 5000 s long-term stability measurement.Secondly,highly dispersed Pd/Co3N-Ni3N/CFC nanostructured electrocatalyst was synthesized by a simple three-step method with the size of Pd particles was about 3 nm,and they were uniformly distributed on the surface of the catalyst.The results concluded that the incorporation of Co3N–Ni3N could effectively improve the catalytic activity and durability of Pd/Co3N-Ni3N/CFC towards the EOR in alkaline condition.This is because that the incorporation of Co3N–Ni3N ensures the exposure of abundant accessible active sites,and improves the electrical conductivity of the electrocatalyst.Inaddation,Co3N–Ni3N can readily facilitate water dissociation to form-OHads species,which can work in concert with the adjacent Pd atoms to improve catalytic performance of Pd/Co3N-Ni3N/CFC.After a continuous 2500 cycle stability measurement,the catalytic activity of Pd/Co3N-Ni3N/CFC hybrid catalyst still maintained of 80.4% of its initial current density.The current density of Pd/Co3N-Ni3N/CFC was still maintained of 6.7% of its initial current density after 10000 s long-term stability measurement.The FE-SEM observations and XRD analysis of the post-used catalyst found that morphological feature and phase structure were well preserved after long-term operation.Thirdly,the 3D hierarchically Pd/Ni Fe P/NF microflowers catalyst with a porous morphology was synthesized by a three-step procedure.Our study found that the incorporation of 3D porous microflower-like structure Ni Fe P could increase accessible active sites,enhance mass transfer kinetics and improve the electrical conductivity of the electrocatalyst.Inaddition,the electronic states of Pd were changed by the electronic interactions between Pd and Ni Fe P,which will improve the catalytic performance of Pd/Ni Fe P/NF catalyst.Furthermore,the introduction of Fe in catalyst is essential for the formation of the unique 3D microflower-like morphology,and it also improved electrical conductivity of catalyst and promoted the formation of Pd nanocrystals.The electrochemical tests concluded that the Pd/Ni Fe P/NF catalyst showed a larger electrochemical specific surface area,good electrical conductivity and strong resistance to CO poisoning.After a continuous 2500 cycle stability measurement,the catalytic activity of Pd/Ni Fe P/NF catalyst still maintained of 81.7% of its initial current density.The current density of Pd/Ni Fe P/NF was still maintained of 27.2% of its initial current density after 20000 s long-term stability measurement.The FE-SEM observations of the post-used catalyst found that morphological feature was well preserved after long-term operation.