| Nowadays,the problems and pressures caused by energy shortage and environmental pollution are increasing severe.Development of noble-metal-free catalysts with high catalytic performance to improve the efficiency of hydrogen evolution reaction(HER)and synthesis of energy storage device with high power and energy density are expected to be the effective ways to solve the problem.Transition metal oxides(Nb2O5,MnO2,etc)and nitrides(Nb2N,TiNxOy,etc)have good electrochemical properties due to their special d-band structures and was considered as the promising electrocatalytic materials.Besides,it is an effective way to enhance the electrochemical performance by increasing the active site and improving the conductivity of the materials.As is well known,anodization is the most frequently nano-fabrication method to form ordered one-dimensional porous or tubular array structures.However,only a few electrolytes for anodization of Nb have been reported and most of them are achieved in harsh conditions or accompanied by the shallow oxide layer,poor structure,etc.Moreover,to the best of our knowledge,most of the reported TiNxOy nanoarrays only exhibit the short length and the long TiO2 nanoarrays is easy to peel off from the Ti substrate,which is ascribed to the poor adhesion between TiO2 nanoarrays and Ti substrate.In addition,it remains a challenge to find a material that can maximize the property of the active materials MnO2 while preserving its own morphology.The main contents of this thesis are as follows.(1)In this study,we successfully explore a new anodization electrolyte of oxalic acid/HF to obtain the highly self-organized nanoporous Nb2O5 at room temperature.The optimum anodizing conditions for the preparation of nanoporous Nb2O5 were featured by the morphology characterization,which was 20 min of 80 V oxidation in 1 M oxalic acid and 0.5 wt%HF mixed electrolyte.Furthermore,the results of the LSV and Tafel electrocatalytic performance tests showed that the nanoporous Nb2O5 has a high current density and superior stability,but the electrocatalytic performance of Nb2O5 has yet to be further improved.(2)The nanoporous Nb2O5 were converted into Nb2N by annealing in the ammonia atmosphere at different temperatures(400 ?-700 ?)for 4 h in order to improve the electrocatalytic performance of Nb2O5.The optimal annealing temperature(700 ?)was then determined through the XRD characterization.Besides,the Nb2N exhibits more excellent HER performance than Nb2O5,the current density of the Nb2N is 3.9 times higher than the Nb2O5 at the same applied potential and the onset overpotential of the Nb2N is 4.2 times lower than that of Nb2O5.Moreover,the Nb2N possesses a lower Tafel slope and the excellent stability.(3)The anodization was carried out in an electrolyte of glycol containing 0.3 wt%NH4F and 2 vol%ultrapure water at a voltage of 60 V under various anodization durations(0.5-3 h)for synthesizing the TiO2 nanoarrays with different lengths.Subsequently,the nitridation process of obtained TiO2 nanoarrays was performed i under ammonia flow at 800 ?C for 3 h.After cooling down to room temperature,the TiNxOy nanoarrays were obtained.TiNxOy/MnO2 nanoarrays were synthesized at various potentials(1.0-1.5 V)for 120 s using an aqueous electrolyte containing MnSO4(10-40 mM)and(NH4)2SO4(40 mM).Besides,we explored the influence of different TiNxOy tube length,deposition voltage and the deposit amount of MnO2 deposition on electrode performance.The loaded thin MnO2 layer presents a superior specific capacitance of 1404.4 F g-1 at 0.5 A g-1.Moreover,two identical symmetric films of TiNxOy/MnO2 nanoarrays were directly used as electrodes for flexible SCs and can offer energy and power densities of 1.24 ?Wh cm-2 and 9.14 mW cm-2 at 30 mA cm-2,respectively.Remarkably,the assembled TiNxOy/MnO2 flexible supercapacitor achieves excellent cyclic stability with a retention of 93.88%over 10000 cycles. |
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