Using elastin protein to develop one-dimensional nanomaterials for energy storage
Date of Issue2017
School of Materials Science and Engineering
In this thesis, elastin-like protein (ELP) GPG-AG3-Histidine tag (His tag), is designed for control synthesis of nanomaterials. The hydrophobic domain (GPG domain) is responsible for self-assembling and the hydrophilic domains (AG3 and His tag) are capable of mineralizing inorganic materials. It is hypothesized that by combining these components into a fusion protein, control synthesis of one-dimensional (1D) inorganic materials can be realized in an effective and efficient way. 1D noble metals and transition metal-nitrogen-carbon (M-N/C) catalysts are effective in improving the electrochemical kinetics of lithium-O2 battery (LOBs) cathodes to increase the battery efficiencies as well as cycle life. 1D structure with rich and uniformly distributed active catalytic centers can confine the size of generated Li2O2 during the discharge by facilitating rapid electron transport and surface electrochemical reactions. By using these 1D structures as catalysts for LOBs cathodes, the over-potential phenomena are to be suppressed by tuning the deposition and distribution behavior of Li2O2 on the catalyst surface. Transition metal phosphides (TMPs) are very competitive high-capacity candidates for lithium and sodium storage yet they suffer the low electric conductivities and the drastic volume change during the conversion reaction process. The construction of TMPs into nanoscale materials, especially into 1D structures such as nanotubes or nanorods is most promising strategy to address these issues. The self-assembling behaviors of the GPG-AG3-His tag proteins are revealed and nanobeads or nanofibers are obtained. In inorganic materials synthesis, mineralization capability of AG3 in the fusion protein is firstly investigated. 1D Pt or Pd composed of the platinum nanoparticle and palladium nanoparticle decorated on the protein fibers are obtained through hydrothermal treatment at 80 ℃. Next, the mineralization behavior of His tag is investigated. 1D metal-nitrogen/carbon (M-N/C, M=Fe, Co) catalysts are synthesized by mixing the protein nanobeads, metal salt precursors and carbon nanotubes (CNTs) in aqueous solution followed by annealing and acid leaching processes. The mineralization capability of His tag in oil-phase synthesis is then explored and 1D CoP and FeP4 are obtained. All these results demonstrate that the strategy proposed in this dissertation is effective and the fusion protein designed is versatile for application in 1D inorganic materials synthesis. To consolidate the studies, these 1D nanomaterials are applied in secondary batteries. The catalytic performance of 1D Pt and 1D Pd in LOBs are investigated. The results show that the 1D Pt catalysts-based cathodes have typical charge potentials at 3.8 V at 100 mA /g. The discharge capacities maintain at the capacity cut-off at 1000 mAh/g for 15 cycles and the energy efficiency is 65%. The charge voltages of the Pd nanotube catalyst maximize at about 4.2 V with an average of 3.9 V. An energy efficiency of 63% with a capacity of 800 mAh/g is obtained at 50 mA/g. The obtained M-N/C (M=Fe, Co) catalysts are also used as cathode materials in LOBs. It is discovered that during discharge, Li2O2 nanoparticles first nucleate and grow around the bead-decorated CNTs regions (M-N/C centers) and coat on the catalysts at high degree of discharge. The Fe-N/C catalysts based cathode delivers a capacity of 12441 mAh/g at 100 mA/g. When cycled at a limited capacity of 800 mAh/g at 200 or 400 mA/g, these cathodes show stable charge voltages of ~3.65 or 3.90 V, corresponding to energy efficiencies of ~ 71.2% or 65.1%, respectively. Finally, 1D CoP nanostructure is applied as anode material in lithium ion batteries (LIBs) and sodium ion batteries (SIBs). For lithium storage, the anode delivers a specific capacity as high as ~ 350 mAh/g at 3.0 C over 200 cycles and shows good capacity retention. In sodium storage, when tested at 0.1 C, the delivered capacities are stable at ~ 520 mAh/g for 100 cycles. At 1.0, 2.0, and 5.0 C, the specific capacities are stable at ~ 400, 360, and 300 mAh/g over 250, 250, and 1000 cycles, respectively. It is of significance to study the mineralization capabilities of each functional sequence in the GPG-AG3-His tag fusion protein simultaneously since they are aligned together. Besides, further discussions of constructing novel functional fusion proteins for constructing hierarchical structure and their applications in energy storage are also presented.