Tuning Multimetallic Phosphide Nanorods and Hetero-Nanostructures for Electrocatalysis

In the nanoscale regime, materials possess unique properties that enable great potential for various applications. The large surface area to volume ratio of nanomaterials is especially beneficial for heterogeneous catalysis of energy-relevant reactions by exposing plentiful active sites. For further enhancing the efficiency of nanoscale catalysts, increasing their intrinsic activity via alloying or building heterostructures has also been proved effective by modulating ensemble, ligand, and strain effects. To systematically study the synergistic effects, 1-dimensional (1-D) metal phosphide nanomaterials are promising platforms due to their stability in different media, high electroconductivity, and multiple synthesis methods. However, it is difficult to obtain multicomponent 1-D metal phosphides via conventional methods.
This thesis demonstrates a novel and robust strategy to produce multicomponent 1-D metal phosphides with well-defined physical dimensions and broad-range chemical compositions. It starts with an introduction of nanoscience, 1-dimensional nanomaterials, and metal phosphides (Chapter 1) and nanosynthesis (Chapter 2). Then Chapter 3 and 4 summarizes electrocatalytic reactions and characterization techniques applied in my studies.
Next, Chapter 5 focused on a novel strategy to attain a group of 1-dimensional transition metal phosphides Co2P/MPx (M= Fe, Ni, Cu, Mn) with control over morphology and composition with seed-mediated synthesis. The thermal treatment assisted the conversion from core/shell structure to alloyed CoMPx nanorods on various supports. The formation of bimetallic active sites allows synergistic electrocatalysis for oxygen evolution. Chapter 6 discusses a way to synthesize Co2P/Pd (single atoms/clusters decorated or core/shell) NRs with a similar seed-mediated method. Such heterostructure demonstrates core/shell metal phosphide/metal interfaces to utilize precious metal performance and emphasize interfacial effects in hydrogen evolution. Finally, a combination of both methods was applied to obtain alloyed CoPdPx nanorods and compare core/shell and alloy nanomaterials in Chapter 7 in hydrogen evolution and glycerol oxidation. In brief, modulation of ensemble, ligand, strain, and synergy effects play a vital role in promoting catalytic multicomponent nanomaterials activity by tuning their compositions and heterostructures.