Preparations And Hydrogen Evolution Electrocatalytic Performances Of Ir-based Metal Alloy Materials

Global consumption of non-renewable energy and the consequent environmental problems have triggered the development and utilization of green sustainable clean energy that has been widely concerned.Among various secondary energy sources,hydrogen is expected to become a substitute of traditional fossil fuels due to its high energy storage density,wide range of sources and low pollution characteristics.At present,most of the hydrogen is derived from oil and natural gas.The traditional hydrogen production method not only causes a large amount of fossil energy consumption,but also causes environmental pollution.Hydrogen production from electrocatalytic water splitting has attracted much attention due to its high-purity and energy efficiency.Currently,precious metals are still considered as the best catalysts for electrocatalytic hydrogen evolution due to their ultra-low overpotential and high current density.However,the high cost and low reserves of precious metals limit the pratical application of the hydrogen energy economy.Although transition metal compounds have been extensively considered as potential alternatives to precious metals catalysts due to their low-cost and earth-abundant characteristics,the electrocataytic performances of the catalysts is far inferior to those of the noble metal catalysts.Alloying noble metals and transition metals may be an effective way to reduce cost and their catalytic properties;at the same time,combining with carbon materials is an effective strategy to improve electrocatalytic performance.In this thesis,noble-transition alloy materials(IrCo/NC and Ir-NiCo/N,S-C)were rationally desingned and prepared by using the hydrotalcite-like materials as precursors with a carbonization process,and their electrocatalytic performances for the HER were also investigated.1.Ir-NiCo/N,S-C electrocatalyst.The Ir-NiCo/N,S-C composite was prepared by annealing metanlic-interclated Ir-NiCo(OH)2 precursor.The Ir-NiCo(OH)2 host provides Ir-NiCo ternary metallic alloys source,and the metanlic guest serves as sources of N,S-doped carbon.Electrocatalytic tests showed that the Ir-NiCo/N,S-C electrode demonstrated an outstanding performance both in acidic and alkaline electrolytes with 77 mV overpotential to achieve the 10 mA cm-2 current density in 1 M KOH solution and 96 mV in 0.5 M H2SO4 solution.Ir-NiCo/N,S-C composite has the following advantages:(i)Doping Ir into transition metallic alloys could change the electronic structure so as to improve catalytic activity;(ii)Ir-NiCo ternary metallic alloys nanoparticles well-dispersed on 3D carbon skeleton,the appropriate specific surface area and mesopore size distribution resulted in the exposure of active sites and the sufficient electrode/electrolyte contact,thus booating the electrocatalytic performances for the HER.2.IrCo/NC electrocatalyst.The IrCo/NC composite was prepared by annealing a Ir-doped Co(OH)2 precursor on g-C3N4(Ir-Co(OH)2/g-C3N4).Electrocatalytic tests showed that the IrCo/NC electrode exhibited excellent electrochemical performances both in acidic and alkaline electrolytes,which achieved 10 mA cm-2 at a low overpotential of 32 mV in 0.5 M H2SO4 and 33 mV in 1 M KOH.The electrocatalytic performances of the IrCo/NC composite were significantly better than those of Co/NC composite and pure IrCo alloy.The IrCo/NC composite has the following advantages:(i)Alloying noble metal and transition metal could change the electronic structure so as to regulate hydrogen evolution reaction behavior;(ii)The dispersion of IrCo bimetallic alloy nanoparticles,and the good distribution of Ir within the Ir doping into the Co(OH)2 layer,both facilitate improving the electrocatalytic performances;(iii)The appropriate specific surface area and the combined meso-/macro-porous textual structure allow for the exposure of enough active sites and the sufficient electrode/electrolyte contact,thereby enhancing the electrocatalytic performances.