Ultra-High-Rate Pseudocapacitive Charge Storage in the 3D Nanoporous Metal Scaffold-Supported Silver Oxide and Kinetics Analysis
Currently, I am working with Professor Detsi’s research group where I study Ultra-High-Rate Pseudocapacitive Charge Storage in the 3D Nanoporous Metal Scaffold-Supported Silver Oxide and Kinetics Analysis.
Pseudocapacitors stand apart from batteries for their unique capability to quickly store and release energy by taking advantage of rapid oxidation and reduction (i.e. Faradaic) reactions at material interfaces. In many pseudocapacitors, the ion which participates in the reaction (the working ion) is a “foreign” element not found in the actual electrode material. The Detsi Group demonstrated a pseudocapacitive charge storage approach where the working ion is part of the material. In their system, Ag+ acts as the working ion in a non-aqueous electrolyte, where silver (I) oxide grown on a three-dimensional nanoporous gold (NP-Au) scaffold acts as the storage medium. Charge storage appears to occur through the electrochemical oxidation/reduction of silver (I) oxide to silver (III) oxide, however, this hypothesis is based primarily on theoretical redox potentials of silver (I) oxide and silver (III) oxide.
Before the COVID-19 pandemic, I created multiple cells using three-dimensional NP-Au as the working electrode and silver foil as the counter/reference electrode in ACN-AgNO3 electrolyte. The cells were charged to different potentials (0.01 - 0.7 V, 0 - 0.85 V, 0 - 0.925 V) in order to change the oxidation state of Ag on the NP-Au surface, and eventually removed for analysis. The redox peaks were recorded using a cyclic voltammogram (CV) and the peaks indicate the fast charge storage capability of the NP-Au/oxide composite (working electrode) vs. Ag (counter/reference electrodes) at sweep rates of up to 1000 mV/s.
Now, I am working on the Kinetics Analysis where I analyze and find the percent capacitive of the coin cell. There are two different types of current: capacitive current (Ic) and faradaic current (If) and the total current is expressed by the equation: I = Ic+If. For capacitive current, during the reaction, charge transfer occurs at the electrode surfaces, not inside the electrode and it is also known as “fast kinetics.” There’s no diffusion of ions inside the electrode for capacitive current. Yet for faradaic current, charge transfer occurs inside of the electrode during the reaction and it is known as “slow kinetics.” For faradaic current, the whole process of the charge transfer is diffusion-limited.
The total current can be expressed through the equation: I (V,v) = k1V + k2V1/2, where capacitive current (Ic) equals to k1V and faradaic current (If) equals to k2V1/2. The goal of the Kinetics Analysis is to find the percent capacitive by integrating and dividing capacitive current by the total current.
Through this research, I learned a lot about Kinetics Analysis which can be very helpful in my future since I would like to focus on renewable energy research.