Study On The Photoelectrochemical Water Splitting Performance Of ?-Fe₂O₃ Photoanode Material By Hap Modification

The development of society and the economy is inseparable from the large supply and consumption o f energy.At present,human society has been faced with a shortage of non-renewable energy resources an d environmental pollution.Therefore,it is urgent to research and develop new clean energy technologies.H ydrogen energy has the advantages of high energy density,environmental protection,easy ways to storag e and transport.Thus it is the most ideal clean energy.The technology of Photoelectrochemical?PEC?Hy drogen Production from Water splitting is to convert solar energy into chemical energy?hydrogen energy?by the assistace of light and electricity,which is expected to solve the problem of the energy crisis and e nvironmental pollution.Among semiconductor photoanode materials,hematite??-Fe₂O₃?was chosen as a considerable photoanode due to its abundance,nontoxicity,and bandgap position?2.1 e V?,wh ich allows it to absorb solar lightup to 590 nm.The theoretical solar-to-hydrogen?STH?efficiency and photocurrent are 15.3% and 12.6 m A·cm-2 at 1.23 V vs.RHE under AM 1.5G.Hence,?-Fe₂O₃ as an ideal photoanode material for PEC water oxidation.However,the poor conductivity,excit ed-electron lifetime,extremely short hole migration distance,improper band edgepositions,and slow oxygen evolution reaction?OER?kinetics have limited the performanceof ?-Fe₂O₃.Surface modifi cation with oxygen evolution cocatalyst?OECs?is one of the most effective strategies to improve the interfacial hole extraction kinetics,that is,prolong the lifetime of photogenerated carriers,and simultaneously decrease the overpotential of water oxidation,thus accelerating the surface oxygen e volution kinetics over ?-Fe₂O₃.In this work,the surface modification and metal ion doping were u sed to improve the PEC watersplitting performance of ?-Fe₂O₃ photoanode.The main results of thi s dissertation are summarized as follows:?1?The study for the PEC water splitting performance of ?-Fe₂O₃ photoanode modified by C o doping hydroxyapatite?Co-HAP?cocatalyst: we have fabricated a novel OECs Co-incorporated H AP,which was decorated on the surface of ?-Fe₂O₃ nanoarrays by a successive in-situ deposition,in-situ growth and ionic-exchange process.The resulting Co-HAP/?-Fe₂O₃ exhibited excellent PEC water splitting with a high photocurrent density of 2.25 m A·cm-2 at 1.23 V vs.RHE in neutral el ectrolyte,which is ca.9.78 times that for bare ?-Fe₂O₃.Moreover,the onset potential displayed a 200 m V cathodic shift,indicating an accelerated water oxidation kinetics over ?-Fe₂O₃.PEC charac terizations revealed Co-HAP could not only significantly improve the charge-separation efficiency b ut also could enhance the surface charge-separation efficiency in the bulk and on the surface of ?-Fe₂O₃.Comprehensive investigations unveiled the interfacial negative electrostatic field and the incr eased electrical conductivity arising from Co-HAP decoration were of great benefit to improve the charge separation and inhibit surface charge recombination,while the 2D architecture of Co-HAP o ffered high surface area and abundant exposed Co active sites,ultimately boosted PEC water splitti ng over ?-Fe₂O₃.?2?The study for the PEC water splitting performance of ?-Fe₂O₃ photoanode modified by FC o-HAP cocatalyst: In this work,F doping hydroxyapatite?F-HAP?as first constructed on the surfa ce of ?-Fe₂O₃,and then F and Co co-doping HAP decorated ?-Fe₂O₃?FCo-HAP/?-Fe₂O₃?was fabr icated by using ion-exchange and hydrothermal process.The crystalline structure,surface morpholo gy,PEC performance of FCo-HAP/?-Fe₂O₃ were characterized by using X-ray diffraction?XRD?,s canning electron microscopy?SEM?and PEC test and compared with F-HAP/?-Fe₂O₃ and Co-HAP/?-Fe₂O₃.The resulting FCo-HAP/?-Fe₂O₃ exhibited excellent PEC water splitting with a high phot ocurrent density of 2.65 m A·cm-2 at 1.23 V vs.RHE in neutral electrolyte,which is ca.9.46,2.88,2.05 and 1.27 times that for bare ?-Fe₂O₃,HAP/?-Fe₂O₃,F-HAP/?-Fe₂O₃ and Co-HAP/?-Fe₂O₃.Moreover,the onset potential displayed a 210 m V cathodic shift,indicating an accelerated water o xidation kinetics over ?-Fe₂O₃.So it is easy to conclude the higher electronegativity of F-than O H-,F-adjacent the surface of ?-Fe₂O₃ caused much higher internal build-in electric field,which wi ll mediate the chemical environment of Co sites and facilitate OER,thus facilitated the charge tran sfer and separation.?3?The study for the PEC water splitting performance of ?-Fe₂O₃ photoanode modified by Sr Co-HAP cocatalyst: In this work,Sr doping hydroxyapatite?HAP?was first constructed on the sur face of ?-Fe₂O₃,and then Sr and Co co-doping HAP decorated ?-Fe₂O₃?Sr Co-HAP/?-Fe₂O₃?was fabricated by using ion-exchange and hydrothermalprocess.The crystalline structure,surface morpho logy,PEC performance of Sr Co-HAP/?-Fe₂O₃ were characterized by using XRD,SEM and PEC te st and compared with Sr-HAP/?-Fe₂O₃ and Co-HAP/?-Fe₂O₃.The resulting Sr Co-HAP/?-Fe₂O₃ exhi bited excellent PEC water splitting with a high photocurrent density of 2.87 m A·cm-2 at 1.23 V v s.RHE in neutral electrolyte,which is ca.11.04,4.28,2.26 and 1.38 times that for bare ?-Fe₂O₃,HAP/?-Fe₂O₃,Sr-HAP/?-Fe₂O₃ and Co-HAP/?-Fe₂O₃.Moreover,the onset potential displayed a 220 m V cathodic shift,indicating an accelerated water oxidation kinetics over ?-Fe₂O₃.Owing to a p art of Ca2+ replaced by Sr2+ can adjust the acid-base sites and acid-base strength of HAP,and the n improve the strength of adsorption sites on HAP surface to promote the oxidation of water.