Influence Of Annealing Temperature On The Electrochemical Performances Of Hydrogenated TiO₂ Nanotube Arrays For PEC Water Splitting And Lithium Ion Battery

TiO₂ nanotube arrays?TNTAs?fabricated by electrochemical anodization have widely potential applications such as photoelectrochemical?PEC?water splitting,lithium-ion battery,supercapacitor and so on.Hydrogenation has been demonstrated to be a quite effective strategy for improving the PEC and electrochemical performances of TNTAs.In this work,well-separated TNTAs with large specific surface area were fabricated by electrochemical anodization.Subsequently,hydrogenated TNTAs?H-TNTAs?were conducted using electrochemical hydrogenation technique to enhance the PEC water splitting and electrochemical lithium ion storage performance.The relationship between the phase structure and composition of TNTAs and their PEC water splitting and electrochemical lithium-ion storage performances was established through systematic characterization and performance testing.The mechanism of phase-dependent improvement in PEC water splitting and electrochemical lithium-ion storage performances of H-TNTAs electrodes was fully explored.The main research results are as follows:?1?Electrochemical hydrogenation significantly improved the PEC and electrochemical performances of H-TNTAs.The resulting H-TNTAs obtained with optimized parameters of 4 V and 20 min and using 0.1 M Na₂SO₄ as the electrolyte deliver the best PEC and electrochemical performances.?2?PEC water splitting performance of H-TNTAs was well tuned by designing and adjusting the phase structure and composition of TNTAs.The results from systematic characterization and PEC performance measurement indicated that with increase of annealing temperature from 300?to 700?,amorphous TiO₂ crystalized into anatase phase,and transformed from anatase to rutile phase at 600?,and finally tube-structures were destroyed at 700?.Electrochemical hydrogenation could significantly improve the PEC performance of H-TNTAs,yet the PEC performance improvement of various H-TNTAs electrodes were different from each other.Prior to electrochemical hydrogenation,well-crystallized single anatase phase TNTAs-400 photoanode shows the best PEC performance.After electrochemical hydrogenation,anatase-rutile mixed phase H-TNTAs-600 photoanode exhibits the highest PEC performance,and under simulated solar illumination,H-TNTAs-600 achieves the best photoconversion efficiency of up to 1.52%and maximum H₂ generation rate of 40.4?mol h^-1 cm^-2.The significantly enhanced PEC performance for A-R mixed phase H-TNTAs-600photoanode could be attributed to the synergy of A-R mixed phase and intentionally introduced Ti³⁺?oxygen vacancies?which enhances the photoactivity over both UV and visible-light regions,and boosts both charge separation and transfer efficiencies.?3?Electrochemical lithium-ion storage performance of H-TNTAs was well tuned by designing and adjusting the phase structure and composition of TNTAs.The results from systematic characterization and electrochemical performance testing reveal that with the increase of annealing temperature,the discharge capacity of various TNTAs electrodes gradually decreased,while the discharge capacities and rate performances of various H-TNTAs electrodes were greatly improved to different degrees after hydrogenation treatment,depending on the annealing temperatures,which was ascribed to the different concentration and stability of intentionally introduced Ti³⁺in different TiO₂ phase structures during hydrogenation process.Among various H-TNTAs electrodes,the discharge capacities and rate performances of single anatase-phase and well-crystallized H-TNTAs-500 was enhanced more significantly.