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Performance and Stability Optimization of Solar Fuel Devices


Zhou, Xinghao (2018) Performance and Stability Optimization of Solar Fuel Devices. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/SSNP-XW29.


Fossil fuels enabled the Industrial Revolution, and have been the most important power for promoting the world's economic growth ever since. However, burning fossil fuels have also been causing severe air pollution, and global warming is also related to excessive use of fossil fuels. Solar energy is considered to be the largest renewable clean energy resource. The principal problems of solar energy are low energy concentration and intermittency. Storing solar energy in chemical bonds, similar to photosynthesis in nature, is a possible way to overcome these two problems. Carbon-free chemicals, like hydrogen gas produced by solar-driven water splitting, or carbon-neutral chemicals, like methane, ethylene, formic acid, carbon monoxide, etc. produced from solar-driven CO2 reduction, are all promising clean fuels for solar storage, as they feature high energy/power intensity, are easy and cheap to store and transport, and have direct interface with existing infrastructures.

In this thesis, we focus on improving the efficiency and stability of the solar-driven fuel generation devices, which consist of (photo-)anode and (photo-)cathode. For the anode part, cobalt oxide Co3O4 ultrathin (2 nm) films by atomic layer deposition (ALD) were deposited onto silicon photoanode prior to deposition of thick nickel oxide (NiOx) layers. The photovoltage of the photoanode increased from 200 mV to 580 mV after including the interfacial Co3O4 layer, and the anode was stable in 1.0 M KOH(aq) for 1700 hours, which was equivalent to one year of operation in the field at a maximum photocurrent density of 30 mA/cm2 assuming a 20% solar capacity factor. Furthermore, the non-uniform sputtered (NiOx) layer of the n-Si/SiOx/Co3O4/NiOx photoanode was removed, and the 2 nm Co3O4 film was thickened to 50 nm, and the stability of n-Si/SiOx/50 nm-Co3O4 was improved to 2500 hours with lower efficiency decay rate. For the cathode part, an optimized Pd/C nanoparticle coated Ti mesh cathode exhibited < 100 mV overpotential at 8.5 mA/cm2 current density, and > 94% Faradaic efficiency for the reduction of 1 atm of CO2(g) to formate in 2.8 M KHCO3. A solar-driven CO2 reduction (CO2R) cell was constructed with this cathode, showing 10% solar-to-fuels conversion efficiency.

This thesis can be divided into three parts. The first part discusses importance of solar fuels, as well as gives an introduction of solar-fuel generators. The second part includes Chapter II and Chapter III, which deal with performance improvement of silicon photoanode with ALD Co3O4 thin films. The third part is Chapter IV, in which we study the cathode for CO2 reduction to formate, and demonstrate a 10% efficiency solar-driven CO2 reduction cell with the cathode.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Solar fuel device; photoanode; CO2 reduction; water oxidation
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Minor Option:Computer Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Lewis, Nathan Saul
Thesis Committee:
  • Lewis, Nathan Saul (chair)
  • Faber, Katherine T.
  • Goddard, William A., III
  • Johnson, William Lewis
Defense Date:23 April 2018
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
Gordon and Betty Moore FoundationGBMF1225
Record Number:CaltechTHESIS:05062018-164727269
Persistent URL:
Related URLs:
URLURL TypeDescription for Chapter II for Chapter III for Chapter IV
Zhou, Xinghao0000-0001-9229-7670
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10851
Deposited By: Xinghao Zhou
Deposited On:21 May 2018 22:22
Last Modified:08 Nov 2023 18:46

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