Defense Date

2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Everett E. Carpenter

Abstract

Transition metal phosphide materials have found themselves at the forefront of research revolving around energy applications. Due to the vast range of properties possessed by marginally different phase compositions, binary and ternary metal phosphides are utilized as catalysts, semi-conductors and magnetocaloric materials along with many others. These attractive properties, which are highly phase dependent, call for a versatile and cost effective synthesis route for various phosphide materials without sacrificing properties important at the nanoscale such as particle size and morphology.

The primary focus outlined in the work of this dissertation pertains to a versatile wet chemical synthesis capable of producing multiple phases of binary and ternary phosphides containing one or more of the transition metals cobalt, iron and nickel. These metals were of particular interest due to the proven catalytic activity of iron, cobalt or nickel binary phases and the lack of research conducted on the corresponding ternary phases. The challenge presented by wet chemical synthesis methods is the ability to separate different crystal phases of metal phosphide in a short amount of time, with less toxic and lower cost chemicals, and a simple synthetic process with the ability to produce products on a larger scale. Oleylamine was used as a solvent, capping agent and reducing agent along with trioctylphosphine or triphenylphosphine as a phosphorus source. Many binary phosphide phases were synthesized with the same method and purity of phase was controlled primarily with temperature or phosphorus to metal ratio (P:M). At lower temperatures (290-320°C) or lower P:M (4:1) Ni3P,Ni2P, Fe2P, and Co2P were synthesized while higher temperatures (330-360°C) or higher P:M (22:1) produced Ni5P4, Ni12P5, FeP and CoP. Ternary phosphides FeCoP and CoNiP were also successfully synthesized at temperatures of 300-330°C with small excesses of phosphorus (2-5 molar excess).

Preliminary catalytic studies for the evolution of hydrogen gas were conducted to test the efficacy of phosphide materials produced via the simplistic oleylamine method. Ni2P was found to have the highest activity toward hydrogen evolution with an overpotential of 320 mV which is comparable and in some cases better than other unsupported phosphide catalysts of the same phase. The ability to control phase composition using a simple, cost effective wet chemical synthesis is promising for the future production of active metal phosphide materials.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

8-12-2016

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