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Wheeler, Danika

University of British Columbia

The electrochemical conversion of CO₂ into fuels or commodity chemicals is a means to store renewable energy in fuels and chemical products. A CO₂ electrolyzer is an electrochemical flow cell that uses electricity, carbon dioxide, and water to produce carbonaceous products such as carbon monoxide (CO). For electrolytically generated CO to be cost competitive with CO produced by fossil fuel feedstocks, a CO₂ electrolyzer must simultaneously achieve: high product formation rates (current density > 200 mA cm⁻²); high product selectivity (faradaic efficiency > 90%); and high energy efficiency (cell voltage < 3.0 V). An understanding of reaction conditions and an optimization of cell components are needed to achieve these performance targets. This thesis details a method to rapidly prototype electrolyzer flow plates by electroplating 3D printed composite conductive plastic parts. The rapidly prototyped flow plates have comparable performance to an all-metal flow plate at half of the cost and 1/7 of the weight. The prototyping methods were utilized to develop an “analytical electrolyzer” that directly measures fluid conditions within an operating cell. Proof of concept work was completed using a PEM water electrolysis cell. The measured temperature and pressure in the analytical cell were in agreement with literature results and simulations. These methods were then applied to a gas-phase CO₂ electrolyzer to quantify water concentration throughout the cathode compartment. Water is a reactant and integral to CO₂ electrolyzer performance. Humidity and temperature measurements were used to produce a mass transport and fluid flow model of the cathode compartment. The model quantified the method and magnitude by which water enters the cathode compartment. The molar fraction of water at the cathodic GDE/membrane interface remains constant under a range of operating conditions (current density = 25-200 mA cm⁻², flow rate = 25-200 sccm, CO₂ feed humidity = 0% or 70%). An increased water flux across the membrane occurred while operating with dry CO₂ feedstocks at higher flow rates and current densities. The increased water flux across the membrane negatively affected CO₂ electrolyzer performance and stability. The techniques and results reported in this thesis will empower the more thoughtful design of electrolyzer cells.

Text

2022-10-19

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82934

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/