Preparation Of Nanoporous Iridium-Based Alloys And Their Electrocatalytic Hydrogen Evolution Performance

With the continuous advancement of the construction of ecological civilization and the proposal of the "carbon neutral" goal,hydrogen energy with high-quality energy density,green and pollution-free has won the favor of academia and industry.Among the many methods for producing hydrogen,electrocatalytic water splitting has attracted much attention due to its simple operation,low energy consumption,water as the raw material,abundant sources,and high purity of hydrogen and oxygen.For electrocatalytic water splitting,electrocatalysts play a decisive role in the performance of hydrogen production.Noble metals such as Pt and Ru are currently considered to be the best electrocatalysts for hydrogen evolution,but their rare earth reserves led to increased costs.In addition,these noble metal electrocatalysts also face problems such as slow reaction kinetics and poor stability when working in an alkaline environment,which also makes people continue to think about seeking new electrocatalysts.Alloying can adjust the electronic and geometric characteristics of precious metals,while also optimizing their catalytic active centers.The addition of transition metals can modify the binding strength of intermediates through the ligand effect to improve the catalytic performance of noble metals,but it will inevitably block some surface active sites of noble metals.Therefore,it is very necessary to design and synthesize catalysts for efficient water splitting in a wide pH environment with high efficiency,high-cost performance and long life.In response to the above problems,this research designed and prepared nanoporous iridium-based alloys for efficient electrocatalytic hydrogen evolution.By alloying Ir and Ni,a series of nanoporous noble metal electrocatalysts modified by atomic-grade metals was realized through dealloying and self-activation strategies.By using operando X-ray absorption spectrum and density functional theory(DFT)calculations,related catalytic micro-mechanism was revealed.The main contents are as following:(1)Based on the alloying method,the precursor of Ir3Ni97 alloy was obtained by arc melting and single-roller melt spinning process.Combined with electrochemical dealloying process and self activation strategy,an atomic Ni decorated nanoporous Ir catalyst(Ni/np-Ir)was obtained by adjusting the number of CV cycles.The surface of the obtained Ni/np-Ir contains a lot of defects,including vacancy,concave cavity sites,and atomic steps.The addition of Ni at atomic level can not only accelerate the process of water adsorption and water dissociation,but also can regulate the electronic structure of Ir sites,activate more Ir sites as catalytic active sites,and promote the H-H coupling to produce hydrogen.The synergistic effect between Ni and Ir sites promotes the water adsorption and water dissociation of Ni/np-Ir,which makes Ni/np-Ir an efficient electrocatalyst in a wide pH range.The Ni/np-Ir possesses near zero overpotentials and small Tafel slope in 1.0 M KOH and 0.5 M H2SO4.And only require an extremely low overpotential of 20 mV to achieve a current density of 10 mA cm-2 and its mass activity and price activity are superior than commercial Pt/C and Ir/C.(2)We added Pd that is located in the same main group and has similar physical properties as Pt to reduce the amount of Ir in catalyst.The precursor of Pd0.75Ir2.25Ni97,Pdi.5Iri.5Ni97,and Pd2.25Ir0.75Ni97 were obtained by arc melting and single-roller melt spinning process.And the electrochemical dealloying process and self activation strategy were used to obtain Ni/np-Pd0.75Ir2.25,Ni/np-Pd1.5Ir1.5 and Ni/np-Pd2.25Ir0.75.The obtained atomic Ni decorated nanoporous PdIr catalysts(Ni/np-PdIr)present the morphology of three-dimensional microwires,which allow more interface contact between the catalyst and the electrolyte.The Pd and Ir exhibit the metallic property in Ni/np-PdIr alloys,and there are strong electron coupling effect between Pd and Ir sites.Among them,Ni/np-Pd1.5Ir1.5 have excellent catalytic performance exceeding other catalysts including commercial Pt/C and Ir/C in alkaline environment.