Study On Electrochemical Reaction Mechanism Of Energy Devices Under Operando Conditions

Electrochemical in-situ characterization techniques have been fundamentally studied and applied in this study.Specifically,the electrochemical in-situ two-dimensional（2D）X-ray diffraction（XRD）has been explored and studied firstly,which gives a depth understanding towards the materials temporal properties responding to different electrochemical states,such as the crystal structure transformation,electronic structure changes and even interface properties.In light of these instrumental understandings,the enhanced electrochemical performance and behind mechanism of single nanowire/nanosheet devices have been explored and achieved.Furthermore,its interesting behavior under multi-physical fields have also been fundamentally studied in my work.The following interesting results are achieved:（1）Electrochemical in-situ 2D XRD techniquesThe conformation of free-oxygen has been effectively captured during electrochemical reaction in the battery where Na_0.76V₆O₁₅ as anode by exploring and using high time resolution in-situ XRD techniques equipped with high/low temperature testing environment.On this base,by controlling the potential range,the cycle performance of Na_0.76V₆O₁₅ anode has been improved by three times.Besides,when the same techniques applied in LiFePO₄ batteries,the structural dynamics and reaction routes of LiFePO₄ have been detected.It found that the intermediate phases between LiFePO₄ and FePO₄,driven by the overpotential and limited ion transfer rate along the b direction at low temperature are the fundamental reason for its unsatisfactory low temperature performance.（2）Single nanowire/nanosheet electrochemical storage devicesThe electrochemical performance of the single MnO₂ electrochemical storage device has been studied on nano-meter scale and it novel behavior under additional electronic field has further been explored using micro-nano device fabrication techniques.It found that the capacitance of the storage can be improved by increasing the additional voltage value.Specifically,the capacitance achieves around 4.7 times higher than original ones when the voltage comes to 3 V and levels off when voltages increases further.It demonstrates that the reason for this improvement is the enhancement of ions concentration in the region near the materials surface and the ions diffuse speed,improving the dynamic process.Also,this conclusion was verified in other materials,such as MoS₂ nanosheet and K_0.51V₂O₅ nanowire.（3）Single nanowire/nanosheet electrochemical catalysis devicesThe electrochemical behavior under additional electronic field was explored wildly into electrcatalyst field.It shows that the double layer properties near the surface of the materials can be tuned under additional voltages,such as the ions concentration and distribution.On base of this founding,the performance of catalyst was largely enhanced through wisely controlling the additional field.For example,the VSe₂ sheet,in this work,its onset potential was reduced from^-175 mV to^-95mV,and its electronic transfer resistance R_ct,decreasing from 1.03 M?to 0.15 M?.Besides,how carrier concentration on the MoS₂ nanosheets influences its photocatalyst behavior was studied,as well as the oxygen influence for the Ni/graphene nanosheet electrcatalyst behavior.