Preparation Of Bismuth-based Catalysts And Their Performance In Electrocatalytic Nitrogen Reduction For Ammonia Synthesis

Electrocatalytic nitrogen reduction reaction（NRR）has attracted much attention in recent years as it can achieve eco-friendly ammonia synthesis under mild conditions.However,the ammonia yield and Faraday efficiency（FE）of electrocatalytic NRR are extremely low due to the large bond energy of the N≡N bond in N₂,the extremely low solubility of N₂ in water,and the violent hydrogen precipitation side reactions（HER）in the aqueous phase.Therefore,the core of electrocatalytic nitrogen reduction is the preparation of high-performance electrocatalysts.Transition metal materials have high intrinsic NRR activity,but they cannot effectively inhibit HER.main group metal bismuth（Bi）,which has semiconductor properties,is a promising NRR electrocatalyst with catalytic activity for NRR and catalytic inertness for HER.Inspired by the dual catalytic activity center in nitrogen fixation enzymes,two compounds of bismuth molybdate and bismuth ferrate,which are both transition metal and main group metal bismuth,were selected as NRR electrocatalysts in this paper,and high performance Bi-based electrocatalysts were prepared by modulating their morphology,structure and chemical composition,and their electrocatalytic NRR performance was investigated.The main contents and conclusions are as follows:1.bismuth molybdate nanocatalysts with abundant oxygen vacancies and high bismuth content were prepared by hydrothermal reaction and alkali etching.The morphology,structure and oxygen vacancies of Bi Mo O-OVs were systematically characterized by scanning electron microscopy（SEM）,X-ray diffractometry（XRD）,X-ray photoelectron spectroscopy（XPS）and electron paramagnetic resonance spectroscopy（EPR）.Electrochemical tests showed an ammonia yield of 3.65μg h^-1cm^-2 and an FE of 16.38%in 0.1 M Na₂SO₄ at-0.40 V vs.RHE potential.The excellent electrocatalytic NRR activity was attributed to the promotion of NRR by the dual catalytic active centers of bismuth and molybdenum,the inhibition of HER by the high content of Bi active sites,and the promotion of N₂ adsorption and activation by the abundant oxygen vacancies.2.self-supported electrocatalyst Bi Fe O/FCC was obtained by hydrothermal growth of bismuth ferrate nanomaterials on the surface of functionalized carbon cloth.the morphology and structure of Bi Fe O/FCC were systematically characterized by SEM,XRD and XPS characterization.Electrochemical tests showed an ammonia yield of 3.88μg h^-1 cm^-2 at-0.45 V vs.RHE potential in 0.1 M Na₂SO₄ and an FE of 12.71%at-0.40 V vs.RHE potential.The excellent ammonia production activity of electrocatalytic NRR is attributed to the synergistic interaction between bismuth and iron that effectively promotes the adsorption and activation of N₂ on the electrocatalyst surface.In addition,the in situ growth of Bi Fe O on functionalized carbon cloth helps to accelerate the electron transport and promote the process of electrocatalytic NRR.