Motivation for our research - Renewable energy is intermittent and needs to be stored
Renewable energy acquired from either solar or wind energy is intermittent - simply put, the sun does not always shine and the wind does not always blow. Hence, we need to find ways to store the energy harnessed during the day, which is typically wasted, and then make it available for use at night, when the demand is high. We can do this is in two primary ways - by investing in batteries or electrolyzer technology.
Using Electrolyzers to create an Artificial Carbon cycle
Carbon Dioxide (CO2) and electricity can be chemically combined to generate useful chemicals such as methane (natural gas). This methane can then be burnt to heat our homes or even run a car, and in the process it produces more CO2. This forms a sustainable carbon cycle (green solid arrows), where CO2 can be constantly recycled to produce fuels such as methane. In comparison, out existing non-sustainable methods (red dashed arrow) relies on extracting fuels such as methane continuously from the ground or crude oil.
Engineering the nano-, mirco- and macro-porous structure of catalysts to direct product selectivity
The distribution of products formed from this reaction of CO2 with protons and electrons depends significantly on the structure of the catalyst. The performance of a smooth copper electrode is very different than that of a porous copper electrode - These differences are attributed to high surface roughness, hierarchical porosity, and confinement of reactive species. (ACS Catalysis, 2014, 4, 3091 -3095). We are investigating new structures at the micro-, macro- and nano-level to see how they might affect product distribution.
Characterization of Catalysts in Flow-type reactors
Testing a catalyst deposited on a GDL substrate is done using lab-scale flow cells. The figure above shows a 3D computer-aided design rendering of the gas–liquid flow reactor. Reactant gases (CO2 and H2) are moved in and out of the cell via the (1) gas diffusers. To ensure a gas-tight seal, (2) O-rings are compressed between the diffusers and the (3) graphite current collector/flow fields.
Gas diffusion electrodes (4) coated with catalyst are sealed against the current collectors by (5) planar gaskets. Each half cell is assembled identically aside from the GDE catalyst. The (6) electrolyte flow channel with a reference electrode (Ag/AgCl) is placed between the two half-cells, and the planar gaskets provide a liquid-tight seal. Liquid flowed from the bottom to the top of the flow channel. The reactor is compressed by stainless steel bolts and nuts. (Journal of Applied Electrochemistry, 2019, 49, 917 – 928)
Electrodeposition of nano-sized catalysts
The reaction of CO2 and electricity (or electrons) is rather slow and needs catalysts to speed up. We deposit these catalysts on substrates called Gas-Diffusion Layers (GDL). A GDL consists of three layers: (i) Teflon-treated fibrous backing layer (CFS or carbon fiber substrate), (ii) a microporous layer (MPL), which consists of a mixture of carbon nanoparticles and Teflon, and (iii) catalyst-ionomer layer, which interfaces with a liquid (e.g. aqueous) electrolyte.
Using a GDL enhances mass transport of CO2 but also requires intimate contact between the catalyst particles, the ionomer matrix (e.g. nafion) and the carbon in the MPL.
Conventional methods of depositon end up with regions of catalyst with no ionic access (green circles) and no electronic access (red circles), whereas electro-deposition allows simultaneous electronic and ionic access (brown circle), necessary for this proton-coupled electron transfer (PCET) reaction
Research Funding
