Fabrication of Electrode by Electrodeposition of Non-precious Catalyst and Their Applications to Solar-fuel Production

Abstract

The consumption of fossil fuels has adversely affected the environment, thereby resulting in a rapid increase in the global demand for investigating alternative sources of clean energy. One of the promising approaches for solving this issue is to convert solar energy into storable chemical fuels via photoelectrochemical reactions. Photoelectrochemical cell (PEC) is generally composed of several components, such as photoelectrodes, membrane separators, and catalysts

the development of efficient, economic, and robust catalysts is of great significance. Several studies on electrocatalysts have focused on the discovery of new electrocatalytic materials. Although active research for their commercialization is currently underway, development of electrocatalysts for commercialized solar-fuel production system still remains a challenge, attributed to the gap between performance and cost. Stepping back from the issues related to new material, this dissertation describes two examples of designing electrocatalysts using well-known materials by solution-processing methods, which are representative of low cost and scalability.

First, a light-guided electrodeposition technique was developed, which involves a method of directly patterning a catalyst on amorphous Si (a-Si) by exploiting its photoconductive nature. A NiMo pattern, a well-known non-noble catalyst for hydrogen (H2) evolution, was electrodeposited under the patterned illumination generated using a digital micromirror display (DMD) module. This process was completed in a single step without the use of any mask. Such patterned NiMo/SiOx/a-Si photoelectrodes with sufficient catalyst loading exhibited a bare surface, which allows for light transmission, resulting in the intrinsic current density at 0 (V vs. RHE) and photovoltage of a-Si. Moreover, long-distance lateral electron transport between the adjacent NiMo catalyst patterns was observed.

Second, a biomimetic system for the PEC conversion of carbon dioxide (CO2) to formate was developed, which represents one of the promising media H2 storage in the future. The cathode at which the reduction of CO2 occurs was prepared by the single-step electropolymerization of dopamine in the presence of formate dehydrogenase (FDH) as the biocatalyst, nicotinamide adenine dinucleotide (NADH) as the electron mediator between the underlying electrode and the reaction center in FDH. The cathode thus prepared was connected to cobalt phosphate (CoPi)/bismuth vanadate (BiVO4), which oxidizes water for producing oxygen (O2) as the counter reaction to CO2 reduction. Owing to the powerful catalytic activity of FDH, PDA serving as the electronic wire, and, the CoPi/BiVO4 photoanode supplying sufficient photovoltage, the self-biased, prolonged conversion of CO2 to foramte at zero voltage under simulated AM 1.5 illumination was possible.

Keywords: Photoelectrochemical cells, Catalyst, Light-guided electrodeposition, Hydrogen evolution, Carbon dioxide, Polydopamine, Electropolymerization

Student number: 2009-22918