UC Santa Cruz

The intense research interest in nanomaterials is largely fueled by the unique properties of nanoscale materials. Because of this, fuel cell technology can benefit from the optimization of nanomaterials. However, since Platinum is the leading state-of-the-art electrocatalyst for ORR, developing a catalyst that is cost efficient is under investigation. Developing electrocatalyst that are abundant earth metals is critical for a large-scale application of fuel cell technology. Among the non-precious metals explored in recent decades; Iron, Cobalt, and Nickel catalyst are regarded to be the most suitable candidate for the oxygen binding intermediates of ORR. Therefore, by introducing an additional non-noble metal, a bimetallic system, can have a further influence on the activity for ORR. Because of this, my dissertation will focus on a bimetallic system where they will be deposited onto two 3D nitrogen-doped carbon skeleton structures.In chapter 1, fuel cell reaction mechanism is introduced. A systemic overview of designing Metal Nitrogen Centers (MNC’S) using various techniques. Additionally, the design of nitrogen centers in carbon materials is crucial for ORR. Upon the deposition of metals on nitrogen doped carbon, the M-N coordination site has shown to be the active site. Therefore, optimization of M-N site is done by using delicate selection of precursors, a process where is largely based on test and trial method. Chapter 2 describes the design of CHS-FeCo(X) carbon cages using SiO2 as a sacrificial template. A series of CHS-FeCo-X metal to metal mole feed ratio was used. The deposition of both Fe and Co resulted in single atoms decorated on the carbon skeleton as seen by the TEM. Furthermore, the chemical composition of CHS-FeCo(X) is in agreement with TEM, suggesting an oxidized state. Additionally, all dual-metal samples showed a significant enhancement of the catalytic performance towards ORR in alkaline media, compared to its single metal dopants. Chapter 3 is an extension of chapter 2. In this chapter, cobalt complexes were used instead of cobalt chloride salt. Electron microscopy also confirmed hollow carbon cages. However, due to the higher uptake of metals, nanoparticles occur. Additionally, FeCo-NC-Na3[Co(NO2)6] and FeCo-NC- [Co(im)4](NO3)2 exhibited metallic phases as seen by both them and XPS with an obvious M-N interaction. Moreover, XPS, a charge transfer from Fe to Co was seen. Such an interaction resulted in a highly active electrocatalyst. In chapter 4, a soft template synthesis was used to engineer 3D- hierarchical bimetallic (Fe,Ni) carbon nanoflowers. Transmission electron microscopy studies show that FeNi-NCF samples had a consisted flower-like morphology over various pyrolysis temperature. The FeN-NCF(3) sample had three times the uptake of iron compared to nickel. Additionally, XPS showed that it had the largest Ni to Fe electron transfer. Because of this, it exhibited an active electrocatalyst in alkaline conditions.