Preparation Of Pt-MoP Composite Catalyst And Its Application In Hydrogen Production By Methanol Electrolysis

The research area of electrolysis of water to produce high-purity hydrogen from renewable intermittent energy sources is currently one of the most promising in terms of carbon peaking and carbon neutrality objectives.The efficiency of water splitting reaction is severely hindered by the relatively sluggish kinetic process of anodic oxygen evolution reaction(OER),which is a component of electrocatalytic water splitting,alongside cathodic hydrogen evolution reaction(HER).At present,the precious metal platinum(Pt)is considered as the best electrocatalyst for HER,but its high cost,scarcity and susceptibility to poisoning by carbonaceous intermediates(e.g.CO)limit its large-scale application.Therefore,in order to reduce the energy consumption and cost required in the electrolysis of water,this thesis selects methanol oxidation reaction(MOR)with lower theoretical potential to replace OER,and constructs efficient and stable bifunctional Pt-MoP based composite electrocatalysts,which has been successfully applied to the methanol-assisted water splitting for hydrogen generation system.Interfacing engineering design was employed to create a variety of Pt-MoP-based composites,and their morphology,structure,and electrochemical properties were thoroughly examined in this research.The following are the primary research topics.1.Spatially confined growth of carbon nanosphere-supported molybdenum phosphide coupled platinum(Pt-MoP/C)composite catalysts were selectively synthesized by hydrothermal reaction,thermal annealing treatment and liquid phase reduction.Scanning and transmission electron microscopy results indicated that Pt-MoP/C is composed of ultrafine Pt-MoP nanoparticles in an interconnected three-dimensional carbon nanosphere structure.Electrochemical test results showed that the obtained Pt-MoP/C catalysts exhibited extremely efficient bifunctional catalytic activity of HER and MOR under acidic conditions,even better than commercial Pt/C.The Pt-MoP/C‖Pt-MoP/C water-methanol electrolyzer assembled using Pt-MoP/C as both cathode and anode only required 0.68 V at a current density of 10 mA cm-2.Compared with the conventional water electrolysis using only water as the electrolyte,this methanol-assisted water electrolysis system with Pt-MoP/C as the symmetric electrode has a lower voltage of 1.03 V,resulting in higher efficiency in hydrogen production.2.An ultrafine Pt nanoparticle composite catalyst(Pt/MoP-NC)supported by molybdenum phosphide-nitrogen-doped carbon hybridized carrier was prepared by simple molecular polymerization,phosphorization and liquid phase reduction method.Physical characterization results showed that ultrafine Pt nanoparticles with an average size of 2.53 nm were anchored on MoP-NC nanospheres assembled by nanosheets;the layered porous spherical structure conferred a strong synergistic interfacial effect between Pt and MoP.Electrochemical tests showed that the catalytic activity and stability of Pt/MoP-NC electrode in HER and MOR were significantly enhanced,which was superior to that of commercial Pt/C catalysts.The water-methanol electrolyzer assembled by the bifunctional Pt/MoP-NC catalyst electrode is capable of driving a current density of 10 mA cm-2 at a voltage of only 0.67 V,which is much lower than the voltage required for water electrolysis,thus greatly reducing the energy consumption.3.A strategy of combining metal organic framework(MOF)materials with polyoxometalates was adopted to prepare Zn/Mo MOF with a nanoblock structure,and then through further high-temperature phosphating and liquid phase reduction reactions,Zn/Mo MOF was in-situ converted into a nitrogen doped carbon coated molybdenum phosphide coupled platinum nanoparticles(Pt-MoP@NC)composite catalyst.The scanning electron microscopy results showed that Pt-MoP@NC exhibited a structure of Pt nanoparticles uniformly grown on nanoblocks with a size of about 70 nm.The electrochemical test results confirmed that the composite exhibited excellent bifunctional electrocatalytic activity for MOR and HER,and the performance of the electrolyzer assembled with Pt-MoP@NC as the cathode was significantly improved,with a current density of 10 mA cm-2 at 0.65 V,which was 1.04 V lower than that of the overall water splitting system,which greatly reducing the total energy consumption for hydrogen production.