Abstract

In the development of renewable energy technologies, electrocatalysis plays a central role in energy conversion processes, such as fuel cells and electrochemical fuel synthesis. Development of such technologies relies on the rational design of electrocatalysts as well as understanding their interaction with the working environment. Here we focus on gas-involving electrocatalytic reactions, particularly nitrogen electroreduction to ammonia and formic acid electrooxidation to carbon dioxide. First, to understand the structure-activity relationships for nitrogen electroreduction on Ru, we prepared a series of size-controlled Ru nanoparticles using atomic layer deposition. Both catalytic activity and selectivity for ammonia production on Ru catalysts strongly depend on the particle size, while surface-area-normalized activity reached a highest value at ~4 nm Ru particles. Density function theory revealed the D5 step site as the active surface site for nitrogen reduction to ammonia on Ru. Second, to reveal the effect of Fe oxidation state on the nitrogen reduction catalysis, we developed Fe/Fe3O4 catalyst by annealing a metallic Fe foil in flowing O2 at 300 °C and succeeding electrochemical reduction. The Fe/Fe3O4 catalyst showed an enhancement of the Faradaic efficiency by 120 times as compared to that of an Fe catalyst, which was attributed to the increased intrinsic activity and an effective suppression of the competing hydrogen evolution reaction. Finally, we investigated the effect of a hydrophobic microenvironment on the formic acid electrooxidation reaction that generates CO2 gas. After tuning the microenvironment by adding hydrophobic nanoparticles or using hydrophobic electrode support, the CO2 bubble nucleation and detachment from the electrode surface was enhanced, leading to an improved availability of the catalyst surfaces for formic acid adsorption and reaction with a higher activity. Overall, our studies can provide new mechanistic insights for designing metal catalysts and tuning their microenvironment for gas-involving electrocatalytic reactions that are important for renewable energy conversion.

Graduation Date

2020

Semester

Fall

Advisor

Feng, Xiaofeng

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Materials Science and Engineering

Degree Program

Materials Science and Engineering

Format

application/pdf

Identifier

CFE0008335

Language

English

Release Date

12-15-2021

Length of Campus-only Access

1 year

Access Status

Doctoral Dissertation (Campus-only Access)

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