M13 virus-enabled assembly of 3D nanostructured composites : synthesis and applications in solar energy conversion and electrochemical energy storage devices

Abstract

We live in an age where our society faces the great challenge of generating, storing and transporting energy in responsible ways that minimize impact to the environment. Significant effort has been spent to develop new technologies capable of (1) efficiently converting renewable energy into usable electricity, (2) storing energy into high performance energy storage devices, and (3) fabricating advanced energy conversion and storage devices using environmentally benign technologies. One of the approaches is to genetically engineer M13 bacteriophage (M13 virus) to display proteins with specific functionalities, which allow the synthesis and organization of hybrid materials in environmentally friendly manners. The primary goal of my Ph.D. thesis has been to develop M13 virus-enabled processes for building the electrodes of advanced energy conversion and energy storage devices, including dye-sensitized solar cells (DSCs), electrochemical capacitors, and perovskite hybrid solar cells (PSCs). In order to fabricate nanostructures for the DSC photoanodes, the M13 viruses were crosslinked into a virus hydrogel that served as a multifunctional 3D scaffold capable of binding gold nanoparticles (AuNPs) to the virus proteins. The AuNP-virus hydrogel was encapsulated in titanium dioxide (TiO₂) to produce a plasmon-enhanced nanowire (NW)-based DSC photoanode that enabled a power conversion efficiency (PCE) of 8.46%. A theoretical model was developed that predicted the experimentally observed trends of plasmon-enhancement. Furthermore, to optimize the surface-to-volume ratio of the photoanodes to maximize PCE, a tunable fabrication process used individual free-floating M13 virus as the template for TiO₂ NWs, and the assynthesized NWs were blended with sacrificial polymer to control the film porosity. The optimized semiconducting mesoporous networks were used as photoanodes in both DSCs and PSCs, and the effects of surface morphology on the photovoltaic properties was experimentally investigated. In order to construct the electrodes of electrochemical capacitors, M13 viruses were genetically programmed to bind single-walled carbon nanotubes (SWNTs) in a controlled fashion by aligning SWNTs along the length of the phage without aggregation. The SWNTs-virus complexes were used as the basis for the formation of crosslinked virus hydrogel scaffolds for the fabrication of porous 3D polyaniline (PANI) nanostructures. The PANI-coated SWNT nanocomposites further improved the electrical conductivity and electrochemical activity of thin films. In addition, by using a fog generator to deliver the crosslinker solution, larger-area virusbased hydrogels were fabricated for versatile material coatings, including PANI, MnOx, Ni, and Ni-MnOx. Lastly, an environmentally-responsible process to fabricate efficient PSCs was developed that recycled lead content from discarded car batteries. Perovskite films, assembled using materials sourced from either recycled battery materials or high-purity commercial reagents, showed the same material characterizations and the identical photovoltaic performance, indicating the practical feasibility of recycling car batteries for lead-based PSCs.