Colloidal Nanochemistry Applied to the Discovery and Characterization of Earth-abundant Nanoparticles as Catalysts for the Hydrogen Evolution Reaction and Co2 Photoreduction

Open Access
Author:
Mcenaney, Joshua M
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 21, 2015
Committee Members:
  • Raymond Edward Schaak, Dissertation Advisor
  • Raymond Edward Schaak, Committee Chair
  • Thomas E Mallouk, Committee Member
  • Benjamin James Lear, Committee Member
  • Michael Anthony Hickner, Committee Member
  • Barbara Jane Garrison, Special Member
Keywords:
  • Nanosynthesis
  • Water Electrolysis
  • Hydrogen Evolution Reaction
  • CO2 Photoreduction
  • Electrocatalyst
  • Metal Phosphide
Abstract:
Colloidal nanosynthesis has become a powerful fundamental and practical science with increasing methodologies available for the formation of highly controllable, high surface area nanoparticles. By expanding these methodologies to targeted nanomaterials, we have been able to synthesize and characterize new catalytic nanoparticle systems, primarily for the catalysis of the hydrogen evolution reaction (HER) but also for CO2 photoreduction to carbonaceous fuels. Both of these reactions offer exciting potential routes toward a clean energy future if they can be produced and perform with enough cost efficiency. We begin with a discussion of the capabilities of colloidal nanosynthesis, followed by the intricacies of the HER and CO2 photoreduction. For the HER, replacing highly active noble metals with Earth-abundant, active, and stable materials is a major goal. The majority of this dissertation will focus on the discovery, characterization, and evaluation of new materials to satisfy this goal. For this, we will start by reporting on the synthesis and evaluation of new amorphous molybdenum phosphide and amorphous tungsten phosphide nanoparticles as HER catalysts. Each of the full HER evaluations will include linear scan voltammetry for testing the activity of each material, comparison versus a platinum standard electrode and a bare Ti foil substrate as controls, then sustained cyclic voltammetry as well as a galvanostatic hold for stability testing. We will then discuss the discovery of hollow nanospheres of FeP as an exceptionally active HER catalyst. This will be followed by the establishment of a synthetic route to colloidal transition metal silicide nanoparticles. Ni2Si, Pd2Si, and Cu3Si nanoparticles were all synthesized preliminarily tested for their ability to catalyze the HER. Next, we discuss phase control of cobalt sulfide nanomaterials and establish parameters in a non-polar synthesis to make each of three crystalline phases, and begin to compare them for the HER. After this, we will show specific colloidally controlled manipulations of TiO2 truncated bipyramidal nanoparticles, including size control of Ag domains grown on TiO2 and multilayered assemblies of TiO¬2 nanoparticles. Finally, we delve into the challenges and opportunities of CO2 photoreduction before concluding. Briefly, for CO2 reduction, activity has typically been low compared to the HER, product selectivity remains a major hurdle, and there is a lack of standardization in testing methods, though the infrastructures of first world countries are already built for carbon based fuels, and CO2 itself provides an excellent feedstock from a growing pollutant. We highlight colloidally synthesized SnO nanosheets with primarily exposed (001) facets as selective for ethanol production from CO2 and water, then directly compare CuPt alloy nanospheres against Pt nanospheres on a TiO2 substrate for CO2 photoreduction to methane. Each of the chapters included will illustrate the powerful capabilities of colloidal nanosynthesis, as they can be applied to learn about and discover solutions to real world problems such as the development clean energy technologies.