Preparation And Properties Of Self-supported Ampere-current-bearing Electrocatalysts

With the continuous development of human society,the reserves of non-renewable resources such as oil and natural gas are declining,causing the world to face two major problems,energy crisis and environmental pollution.The development of green,environmentally friendly new energy and the use of renewable energy to replace the old,energy dissipation,high pollution industry is urgent.At present,electrocatalysis technology is promising to solve the above problems.Among electrochemical reactions,oxygen evolution reaction（OER）and nitrate reduction reaction（NO₃RR）are the most probable catalytic technologies,which can solve the problems of the preparation of hydrogen（H₂）and ammonia（NH₃）,two of the most important compounds in the field of energy in the future,hence they are highly expected.The core of catalyst design lies in high yield,low cost,high activity,low energy consumption and well durability.For a long time,due to the effect of sluggish reaction kinetics,most electrocatalysts prepared in laboratory can only bear a small current density(10-100 m A cm^-2),which is far from meeting the actual production demand(≥500 m A cm^-2).We need to find a stable support combined with the catalyst to build an efficient,stable and cheap electrode.The key to solve the problem is to observe the working state of catalyst at micro scale and understand the dynamic evolution process of catalyst interface.Synchrotron radiation X-ray absorption fine structure（XAFS）spectroscopy is highly sensitive and can be used to detect the source of active sites by observing local coordination structures in the dynamic voltage range.In this work,a series of catalysts which can bear ampere-current-density were successfully prepared by using a simple method to support the active component of nickel or copper foams,including bimetallic active center design,solid-liquid reaction,electrochemical growth and pyrolysis.The relationship between the structure and the intrinsic activity of the electrocatalyst was revealed through the representative characterization of microstructure,electrochemical activity and electronic structure.The specific research content of this thesis is as follows:1.Preparation and performance of high value manganese modified spinel selenide as high current OER catalyst.Industrial water electrolysis requires highly-active and ampere-current-bearing OER catalysts,but achieving such a large operating current density at low overpotentials in available OER catalysts still remains a grand challenge.Herein,we present a new type of high-valence metal modified selenospinels（Mn-CuCo₂Se₄）as large-current-density OER catalysts.The optimal Mn-CuCo₂Se₄ exhibits excellent OER activity with overpotentials of 293 and 345 m V to achieve current density of 500 and 1000 m A cm^-2,respectively,and displays large mass activity,high turnover frequency and robust stability in alkaline media.Using in situ X-ray absorption spectroscopies,we observe that a surface active layer of oxyhydroxide-like phase with contracted Co-Co distance was evolved during the OER,which is responsible for the highly-active large-current-density activity.This work provides an effective reference for the screening of OER catalysts with high current density based on a variety of spinel compounds.2.Preparation and performance of copper foam supported Ru as highly efficient NO₃RR catalyst.Ammonia is an important raw material for industrial production,direct synthesis of ammonia without high-energy N≡N bond is an important way for energy storage.Here,we designed a simple synthesis method of NO₃RR catalyst.Through the modification of copper foam and organically combined with Ru,Ru doped Cu foam nanowires（Ru@Cu ONWs）was obtained.It exhibits the excellent catalytic activity and achieves electrochemical reaction of high current density with low potential.The optimal Ru@Cu ONWs-10 exhibits a maximum Faraday efficiency（FE）of 90.8%,a prominent activity with the potential of-0.07 V（vs.RHE）to achieve ampere-level current density and a yield of up to 118 mg h^-1 cm^-2 at a potential of-0.2 V.