Virus-enabled design of high-performing, three-dimensional nanomaterials for electrochemical energy applications

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, May, 2020Cataloged from student-submitted PDF of thesis.Includes bibliographical references (pages 171-185).The accelerating pace of anthropogenic climate change has galvanized intensive interest in electrochemical energy storage and conversion. Developing electrode materials for electrochemical devices requires precision and synthetic control over a number of factors, including surface morphology, nanostructure, and distribution of active materials. To this end, my thesis work investigated strategies to implement the M13 bacteriophage as a programmable, lightweight scaffold in the synthesis of three-dimensional, nanoporous foams. Virus-templated nanofoams were incorporated into several relevant energy applications spanning water electrolysis, microbatteries, and electrolytic urea decomposition. The virus-mediated synthesis toolkit yielded clear enhancements in electrochemical performance, as well as design insights into improving nanostructured electrodes in diverse contexts.Virus-templated, platinum-nickel hydroxide nanofoams were first designed and optimized, displaying strong performance as electrocatalysts for the hydrogen evolution reaction in alkaline conditions (ca. -200 mA cm⁻² [subscript geo] and -4.9 A mg⁻¹ [subscript Pt] at -70 mV versus the reversible hydrogen electrode). Mass-normalized activity was definitively linked to the platinum dispersion within the virus-templated matrix, providing a guideline for future electrocatalyst development. Next, virus-templated metal phosphides were engineered with orthogonal control over nanoscale features, phase, and composition. Synthetic versatility was developed across monometallic nickel and copper, as well as bimetallic nickel-cobalt, material systems.When applied as Li-ion microbattery anodes, virus-templated Ni₅P₄ demonstrated a discharge capacity of 677 mAh g⁻¹ (677 mAh cm⁻³) and an 80% capacity retention over more than 100 cycles, outperforming analogous reported Ni₅P₄ materials. The strong performance was attributed to the virus-templated nanostructure, which remains electronically conductive throughout cycling and obviates the need for conductive additives. In the final application, a fundamental exploration into Ni-based catalysts for the electrooxidation of urea was undertaken, highlighting the need for revised benchmarks to facilitate accurate comparisons across the literature and developing an empirical hypothesis for catalyst instability under constant-current electrolysis. Virus-templated, Ni[subscript x]P[subscript y] nanofoams were again applied as electrocatalysts, displaying strong activity relative to the field and enhanced resistance to deactivation.Finally, several directions for scaling methodologies were presented with a future outlook for virus-templating as a material synthesis platform in electrochemical energy storage and conversion.by William Christopher Records.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Chemical Engineerin

Virus‐Templated Nickel Phosphide Nanofoams as Additive‐Free, Thin‐Film Li‐Ion Microbattery Anodes

Transition metal phosphides are a new class of materials generating interest as alternative negative electrodes in lithium-ion batteries. However, metal phosphide syntheses remain underdeveloped in terms of simultaneous control over phase composition and 3D nanostructure. Herein, M13 bacteriophage is employed as a biological scaffold to develop 3D nickel phosphide nanofoams with control over a range of phase compositions and structural elements. Virus-templated Ni5P4 nanofoams are then integrated as thin-film negative electrodes in lithium-ion microbatteries, demonstrating a discharge capacity of 677 mAh g⁻¹ (677 mAh cm⁻³) and an 80% capacity retention over more than 100 cycles. This strong electrochemical performance is attributed to the virus-templated, nanostructured morphology, which remains electronically conductive throughout cycling, thereby sidestepping the need for conductive additives. When accounting for the mass of additional binder materials, virus-templated Ni₅P₄ nanofoams demonstrate the highest practical capacity reported thus far for Ni₅P₄ electrodes. Looking forward, this synthesis method is generalizable and can enable precise control over the 3D nanostructure and phase composition in other metal phosphides, such as cobalt and copper. Keywords: 3D nanostructure; transition metal phosphide; biotemplating; M13 bacteriophage; Li-ion microbatteryUnited States. Defense Advanced Research Projects Agency (Grant HR0011835402)National Science Foundation (Grant DMR‐1419807)Shell International Exploration and Production B.V. (Grant 4550155123

Virus-templated Pt–Ni(OH)₂ nanonetworks for enhanced electrocatalytic reduction of water

Clean hydrogen production via water electrolysis is incumbent upon the development of high-performing hydrogen evolution reaction electrocatalysts. Despite decades of commercial maturity, however, alkaline water electrolyzers continue to suffer from limitations in electrocatalytic activity and stability, even with noble metal catalysts. In recent years, combining platinum with oxophilic materials, such as metal hydroxides, has shown great promise for improving performance potentially by enabling stronger water dissociation at the surface of electrocatalysts. In this work, we leveraged the nanoscopic proportions and surface programmability of the filamentous M13 bacteriophage in the design, synthesis, and exceptional performance of 3D nanostructured biotemplated electrocatalysts for alkaline hydrogen evolution. We developed a facile synthesis method for phage-templated, Pt–Ni(OH)₂ nanonetworks, relying on scalable techniques like electroless deposition. After optimization of the platinum content, our materials display –4.9 A mg⁻¹Pt at −70 mV versus the reversible hydrogen electrode, the highest reported mass activity in 1 M KOH to date, and undergo minimal changes in overpotential under galvanostatic operation at −10 mA cm⁻²[subscript geo]. Looking forward, the performance of these catalysts suggests that biotemplating nanostructures with M13 bacteriophage offers an interesting new route for developing high-performing electrocatalysts. Keywords: Hydrogen evolution reaction; Electrocatalysis; M13 bacteriophage; 3D nanostructure; BiotemplatingUnited States. Defense Advanced Research Projects Agency (Award HR0011835402)Shell International Exploration and Production B.V. (Award 4550155123

Highly adjustable 3D nano-architectures and chemistries

Porous metal nanofoams have made significant contributions to a diverse set of technologies from separation and filtration to aerospace. Nonetheless, finer control over nano and microscale features must be gained to reach the full potential of these materials in energy storage, catalytic, and sensing applications. As biologics naturally occur and assemble into nano and micro architectures, templating on assembled biological materials enables nanoscale architectural control without the limited chemical scope or specialized equipment inherent to alternative synthetic techniques. Here, we rationally assemble 1D biological templates into scalable, 3D structures to fabricate metal nanofoams with a variety of genetically programmable architectures and material chemistries. We demonstrate that nanofoam architecture can be modulated by manipulating viral assembly, specifically by editing the viral surface coat protein, as well as altering templating density. These architectures were retained over a broad range of compositions including monometallic and bi-metallic combinations of noble and transition metals of copper, nickel, cobalt, and gold. Phosphorous and boron incorporation was also explored. In addition to increasing the surface area over a factor of 50, as compared to the nanofoam's geometric footprint, this process also resulted in a decreased average crystal size and altered phase composition as compared to non-templated controls. Finally, templated hydrogels were deposited on the centimeter scale into an array of substrates as well as free standing foams, demonstrating the scalability and flexibility of this synthetic method towards device integration. As such, we anticipate that this method will provide a platform to better study the synergistic and de-coupled effects between nano-structure and composition for a variety of applications including energy storage, catalysis, and sensing.United States. Army Research Office (Grant W911NF-09-0001)National Science Foundation (U.S.) (Grant DMR-0819762)National Science Foundation (U.S.). Graduate Research Fellowship (NSFGRFP