Effect Of Oxygen Vacancy And Phosphorus Doping On Electrolytic Performance Of Iron/Cobalt-based Materials

In recent years,the depletion of fossil fuels has increased exponentially,which is a huge obstacle to global sustainable development.For the longer-term survival and development of mankind,we need to aggressively seek an alternative energy option.In the past decades,noble metal based catalysts such as platinum,iridium and ruthenium have been used to improve the oxidation/reduction rate of water,making it possible to produce hydrogen by electrolyzing water.Nevertheless,the scarcity of these precious-metals largely precludes the possibility of large-scale industrial production.Nowadays,the development of non-precious metal electrocatalytic materials with high activity and strong stability is very important to realize economic hydrogen production.Based on oxygen vacancy and phosphorus atom doping,through the exploration of preparation process and different materials,this paper selects nanostructured electrocatalysts with high intrinsic activity and long-term stability as the goal,and the designed materials include the following.（1）The precursor was synthesized by one-step electrodeposition with stainless steel mesh（SS）as carrier.And then cobalt trioxide nanoflowers containing oxygen vacancies（Ov-Co₃O₄/SS）were obtained by vacuum treatment.After further phosphating,Co₃O₄ nanoflower（P-Ov-Co₃O₄/SS）catalysts with coordinated regulation of oxygen vacancy and phosphorus（P）doping were synthesized.The role of oxygen vacancy and P doping was enormously explored through various material characterization and electrochemical tests.The results show that P-Ov-Co₃O₄/SS had excellent hydrogen evolution and oxygen evolution reaction（HER and OER）performance under higher current.The overpotential is 242 m V at-200 m A cm^-2,and 370 m V at 200 m A cm^-2.Also,P-Ov-Co₃O₄/SS//P-Ov-Co₃O₄/SS forms a total hydrolysis tank,the overpotential is 1.681 V at 20 m A cm^-2.Among them,the morphology of pores and small particles formed by vacuum and phosphating is helpful to increase its surface area and expose more active sites.The synergistic regulation of P doping and oxygen vacancy promotes the performance of HER and OER.（2）Iron Foam（IF）was chosen as the substrate,and needle-shaped flake Fe OOH/IF was grown on IF in a simple soaking way.Fe₃O₄ containing oxygen vacancies（Ov-Fe₃O₄/IF）was admirably prepared by vacuum treatment.After further phosphating,the ferric oxide（P-Ov-Fe₃O₄/IF）nanoneedles were prepared synergistically regulated by oxygen vacancies and P doping.This chapter explores the effects of oxygen vacancy and P doping on the morphology,hydrogen evolution performance and stability of Fe₃O₄.The results show that P-Ov-Fe₃O₄/IF has excellent hydrogen evolution performance.At-10 m A cm^-2,the overpotential is only 40.96m V,showing the performance like Pt,and the Tafel slope is 70.93 m V dec^-1.In addition,P-Ov-Fe₃O₄/IF operates continuously for 96 hours under different currents,the voltage change is basically ignored,and the stability is excellent.Among them,compared with the precursor of direct phosphorylation（P-Fe OOH/IF）,the morphology of Fe₃O₄（P-Ov-Fe₃O₄/IF）containing oxygen vacancy and P doping is more perfect,and its morphology is not completely corroded.What’s more,oxygen vacancy and P doping form double active sites to promote the performance of hydrogen evolution.（3）Previous studies have shown that iron-based materials doped with oxygen vacancy and phosphorus have better hydrogen evolution performance,while cobalt-based materials have better oxygen evolution performance.Therefore,this chapter mainly studies the effects of oxygen vacancy and phosphorus doping on the electrocatalytic performance of iron cobalt bimetallic materials.The precursor was obtained by in-situ immersion,and then calcined in vacuum and phosphated to obtain the Co Fe₂O₄（P-Ov-C_MFO/IF）nanoflowers,which were synergistically regulated by oxygen vacancies and P doping.The results show that the performance of P-Ov-C_MFO/IF is better than Pt/C,at-100 m A cm^-2,the over potential of P-Ov-C_MFO/IF is only 119 m V.Besides,P-Ov-C_MFO/IF material is continuously tested for hydrogen evolution stability of 100 hours under different currents,and the voltage change is basically ignored,so the stability is excellent.At 100 m A cm^-2,the overpotential of P-Ov-C_MFO/IF is only 295 m V,compared with Ru O₂,which has excellent OER performance.In addition,when P-Ov-C_MFO/IF//P-Ov-C_MFO/IF is a bifunctional catalyst,the overpotential is only 1.734 V at 50 m A cm^-2,and the stability is good for 48 h.This work proves that the coordinated regulation of oxygen vacancy and P doping is also applicable to bimetallic oxides,which provides a new way to improve the total hydrolysis performance.